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Red Sea - Dead Sea Water Conveyance Study Program Additional Studies Red Sea Study Best Available Data Report December 22 th , 2010 Thetis SpA The Interuniversity Institute For Marine Sciences In Eilat Marine Science Station Uni. of Jordan/Yarmouk Uni. Aqaba Israel Oceanographic & Limnological Research Ltd.

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Red Sea - Dead Sea Water Conveyance Study Program

Additional Studies

Red Sea Study

Best Available Data Report

December 22th, 2010

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TABLE OF CONTENTS

Table of abbreviations……………………………………………………………………...…………............4

1 Introduction ................................................................................................................................. 5

2 Description of the existing and predicted future environmental conditions in the no action case.................................................................................................................................. 6

2.1 Present environmental conditions of the Gulf................................................................... 6

2.1.1 Climatic conditions and weather patterns............................................................ 6

2.1.2 Topography and bathymetry................................................................................ 6

2.1.3 Currents and circulation....................................................................................... 6

2.1.4 Water quality and ecological conditions of water body........................................ 6

2.1.5 Bottom sediments ................................................................................................ 6

2.1.6 Coral reefs ........................................................................................................... 6

2.1.7 Coral reefs larvae (fish and invertebrate larvae) ................................................. 6

2.1.8 Seagrass.............................................................................................................. 6

2.1.9 Macroalgae .......................................................................................................... 6

2.1.10 Benthic macrofauna............................................................................................. 6

2.1.11 Fish ...................................................................................................................... 6

2.1.12 Zooplankton ......................................................................................................... 6

2.1.13 Marine Turtles ...................................................................................................... 6

2.2 Pollution loads entering the Gulf....................................................................................... 6

2.2.1 Distribution and characteristics of main pollution sources................................... 6

2.2.2 Pollution loads estimate....................................................................................... 6

2.3 Trends of environmental conditions (no abstraction scenario) and their effects on marine environment ......................................................................................... 6

3 Preliminary description of the effects of the RDC project ........................................................... 6

3.1 Effects of abstraction on water circulation ........................................................................ 6

3.1.1 Modelling scenarios to be considered to address the evaluation of the effects of RDC project.................................................................................... 6

3.2 Effects of abstraction on water quality.............................................................................. 6

3.3 Effects of abstraction on marine ecosystems................................................................... 6

3.4 Effects of construction and operation on the coastal zone and shoreline ........................ 6

3.4.1 Description of the impacts ................................................................................... 6

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3.5 Indication of how climate change may affect the above analysis..................................... 6

3.6 Cumulative impacts of other future abstractions planned in the area .............................. 6

4 Preliminary description of water quality supply to the intake in different scenarios.................... 6

5 References.................................................................................................................................. 6

Appendix 1 - Papers describing driving forces and mechanisms determining the dynamics of the coral reefs in the northern Gulf of Aqaba (GoA) and the surrounding deep waters

Appendix 2- Marine habitats: biology, ecology, biodiversity

Revisions of the document

Best Avaiable Data Report, 3rd revision – RSS-REL-T102.2 - December 23th, 2010

Best Avaiable Data Report, 2nd revision – RSS-REL-T102.1 - November 12th, 2010

Best Avaiable Data Report, 1st revision – RSS-REL-T102.0 - July 15th, 2010

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TABLE OF ABBREVIATIONS

MOCNESS Multiple Opening–Closing Net and Environmental Sensing System

RDC Red Sea – Dead Sea Water Conveyance Project

GOAE Gulf of Aqaba-Eilat

ADCP Acoustic Doppler Current Profiler

HF High Frequency

NMP National Monitoring Program

INMP Israeli National Monitoring Program

JNMP Jordanian Nationa Monitoring Program

mpn Most probable number

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1 Introduction

The goal of the proposed Red Sea – Dead Sea Water Conveyance Project (RDC) is to abstract seawater from the northern end of the Gulf of Aqaba and transfer it to the Dead Sea where it will be used for multiple purposes including desalination, generation of electricity, and stabilization and restoration of the water level of the Dead Sea. In some scenarios up to 2 billion cubic meters of water would be pumped from the gulf every year. It is quite likely that removing this amount of water from the northern gulf will have an effect on various aspects of the marine environment. Clearly the most noticeable impact will occur in the immediate vicinity of the intake; however there may also be cumulative effects resulting in slower, long term changes that may be felt at much larger distances. The proposed study aims to critically examine (go-no-go assessments) potential impacts of the RDC project on the marine environment of the northern Gulf of Aqaba/Eilat (GOAE) specifically, as well as the overall, long-term, large-scale impacts. Possible environmental impacts on the Gulf include changes in the circulation, modification of animal distribution and habitats, and possible effects on the dynamics of natural and anthropogenic chemical elements.

Potential changes in the circulation, especially in the nearshore zone, are expected to be a major driving force of all other impacts. There is no doubt that the circulation in the immediate vicinity of the intake will be directly affected in the short-term by the construction activities and over the long-term by the abstraction of large amounts of water during the operational phase. Depending upon the location of the intake, one could expect a synergetic interaction between various effects. For example, for a proposed intake site in the north beach area, internal waves associated with the reflection of the internal tide near the head of the gulf could produce a significant and interesting additional impact on the local flow. The general approach to addressing these issues will consist of a combination of analysis of exiting data, collection of new data as necessary to fill in gaps, and the application of a suite of numerical models designed to simulate the circulation on multiple spatial and temporal scales.

Of greatest concern are the potentially detrimental impacts of the RDC project on the biological connectivity among the coral reefs in Aqaba and Eilat. The lifecycles of most coral reef species involve a larval stage, during which dispersal is achieved and which ultimately defines the demographic and genetic structures of adult populations and communities. Disruption of larval transport by anthropogenic activities has been proven to be an important factor in adversely affecting marine ecosystems in other locations. In the gulf, it is expected that changes that adversely constrain larval transport would quickly cascade to the state of the whole reef. At present very little is known about the pathways of the coral reef species larvae in the northern gulf. In order to assess the potential risk of entrainment of nearshore larvae into the intake, it will be crucial to investigate and understand the present transport patterns through coordinated field measurements.

If approved, construction of the Red Sea – Dead Sea Water Conveyance will take several years and when completed it is expected to operate for many decades. Therefore in addition to the immediate impacts of the construction and pumping it will be necessary to consider the potential effects of anthropogenic climate change as well as anticipated changes in the pollution load and distribution into the northern gulf. These aspects will also be addressed in the proposed study through the combined use of model simulations and the analysis of the best information available concerning these anticipated changes.

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The present report represents the Best Available Data of the project. In this report we provide an overview of the substantial body of scientific and monitoring literature that describes in detail the morphology, climate and salient chemical and biological conditions of the GOAE. This overview (chapter 2) provides a point of reference by which we will be able in the further development of the project to assess how anticipated changes in climate and the impact of the RDC on local and general circulation patterns in the GOAE will affect its existing ecosystems. Qualitative provisional assessment of the effects of the RDC project is given (chapter 3), under the constraints and limitations due to: limited information available at the stage of the project, considering that the collection of relevant field data is still in progress; lack of any results from detailed modelling tools, presently under development; lack of understanding of relevant processes such as details of the three dimensional structure of water circulation or the distribution of coral-reefs larvae.

The assessments will be based primarily on analysis of the available historical data collected in the Gulf during the past several decades (e.g. Klinker et al., 1978; Reiss and Hottinger, 1984; Krumgalz and Erez, 1984; Krumgalz et al., 1990; Gordon et al., 1994; Badran and Foster, 1998; Plahn et al., 2002; Manasrah et al., 2004; Lazar and Erez, 2004; Herut and Cohen, 2004; Badran and Zibdah, 2005; Rasheed et al. 2005; Silverman et al., 2007 (a; b); Lazar et al., 2009) and from the data collected by the on-going monitoring activities, especially the joint Israeli-Jordanian National Monitoring Program.

Monitoring and modelling activities very relevant for the scope of the assessment are on-gong in the framework of the Red Sea Study. Among additional monitoring activities, investigations are being carried out to support the evaluation of potential impacts of the project on biological connectivity among the coral reefs in the Gulf of Aqaba/Eilat. First available results on monitoring and modelling activities will be presented in the Mid Term report. Additional results will be included in the Final Report of the Study.

Qualitative provisional assessment provided within this report is going to be reviewed and integrated by the support of quantitative results from monitoring and modelling activities during the next phases of the Study. Particularly, information on the intake alternative locations provided by the Feasibility Study Consultant will be considered and analyzed in better detail. A first advancement in this direction will be presented in the Mid Term report; the assessment will be further reviewed and completed in the Final Report.

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2 Description of the existing and predicted future environmental conditions in the no action case

The Gulf of Aqaba/Eilat (GOAE), which is part of the Syrian-African rift valley, is a long (180 km), narrow (5-25 km), and deep (average 800 m, maximum 1800 m) northward extension of the Red Sea. It is connected to the Red Sea through the Straits of Tiran where the sill depth is approximately 250 m. The Gulf is located in an arid region with annual rainfall of less than 30 mm and the surface runoff is practically zero. The best estimate for the annual mean evaporation from the surface is 1.6-1.8 m (Ben-Sasson et al., 2009).

The Gulf is a concentration basin in which less saline water enters through the straits in the upper layer and the more saline water, formed in the gulf due to excessive evaporation, flows out near the sill depth (Murray et al., 1984). Estimates of the water exchange through the straits, based on the observed thermohaline structure, vary between 30,000 – 70,000 m3/s. The volume of surface water loss through evaporation is much smaller than the volume of water exchange through the Straits as in other concentration basins such as the Mediterranean Sea. While this loss is compensated by inflow through the Straits, it is this small imbalance that drives the overall subtidal circulation.

The surface temperature varies between 21°C in winter and 27°C in summer. Since the deep water is formed locally (in the gulf), the deep water temperature remains at just below 21°C throughout the year (NMP reports 2003-2010). The salinity is among the highest in the world ocean and is around 40.68 ± 0.2 psu. The variations are due mainly to the high surface salinity in summer and the inflowing, less saline Red Sea water which appears as a subsurface salinity minimum in spring and summer.

The seasonal dynamics of the GOAE is unique for a warm, sub-tropical water body, as water column stability changes from stably stratified conditions in the summer to unusually deep (350->850 m) mixing in the winter. Consequently, the concentrations of nutrients in the upper water column change from extreme depletion during the summer, to nutrient-replete conditions and phytoplankton bloom during winter-spring. Nearly all year a sharp nutricline exists, with relatively high nutrient concentrations in the deep water (e.g. reaching 6-7 μM NO3 at 500-700 m depth).

The water quality of the Gulf changes naturally over an annual cycle due to changes in the density structure of the water column. During the winter cooling at the surface causes convective mixing which can deepen the mixed layer down to >850 m (Genin et al., 1995) transporting nutrient rich deep water to the surface, which supports increased levels of productivity both in the open water and in benthic habitats along the coasts. During the summer warming at the surface causes stratification of the water column (6ºC thermocline from the surface to 250 m depth) leading to nutrient depletion in the surface water and substantially reduced rates of productivity both in the open sea water column and shallow benthic habitats. These changes in density structure influence and are influenced by the general circulation of the Gulf both vertically and horizontally.

The unique morphological characteristics and climate of the Gulf set the stage for a delicate balance between the physical/chemical environment and the species rich ecosystems characteristic of oligotrophic oceanic regions, which have managed to develop and thrive within its boundaries.

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Previous studies have shown that ecosystem in the GOAE is strongly dependent on physical and chemical conditions, which have been shown to be perturbed both by short term changes in climate (Genin et al., 1995), naturally occurring extreme phenomenon such as extreme low tides (Loya, 2004) as well as man made perturbations.

A very important component of Gulf ecosystem is represented by coral reefs.

Fringing coral reefs are the overwhelmingly dominant form along the shores of the GOAE. At greater depths, down to at least 65-70 meters, coral carpets covering marginal slopes are abundant. Growth of these deep reefs is facilitated by the clarity of the water that allows light penetration to a depth of ~100m.

The presence of a shallow sill at Bab-el-Mandeb greatly affects the extent and diversity of the coral reefs in the Red Sea, especially those at higher latitudes in the Gulfs of Aqaba and Suez. Unlike “normal” open oceans, where the deep and intermediate water found in the tropics and subtropics is cold, the shallow sill at Bab-el-Mandeb effectively separates the deep waters in the semi-enclosed Red Sea from those in of the Indian Ocean. For example, the water at 1500 m depth in the Gulf of Aden, (the water body connecting the Red Sea to the Indian Ocean), is <10ºC, whereas the deep waters at this and greater depths in the Red Sea including its deepest zone, is always warmer than 20ºC. This characteristic determines the lowest temperature the shallow water can be cooled down to during winter. The ensuing year-round occurrence of warm waters allows coral reef to flourish as far north as the northernmost end of the GOAE.

On the other hand, the occurrence of warm water at depth substantially weakens vertical stratification. For example, below ~300 m, the vertical gradient in temperature in the Gulf of Aqaba is ~0.09ºC / 100 m, compared with more than an order of magnitude steeper gradient in “normal” oceans at a similar latitudes (e.g., 1.07ºC/100 m south of Bermuda, 1.67ºC/100 m at the Central North Pacific).

The weak stratification in the Gulf of Aqaba, together with low air temperature during winter, drives an extraordinarily deep vertical mixing, reaching exceeding >600 m depth, in cold winters. The most striking phenomenon driven by this is the recurrence of immense spring blooms of benthic algae that cover wide sections of the local reefs, sometime causing substantial coral death (Genin et al., 1995). This “intermediate” disturbance, occurring once every 5-20 years, can be one of the processes responsible for the maintenance of the high coral diversity in the Gulf (Connel 1978). Note, however, that the occurrence of deep mixing is limited to the Gulf of Aqaba, at the northern end higher-latitude part of the Red Sea. Air temperature at lower latitudes, south of the Straits of Tiran, is too high to induce deep mixing, even during the winter (Paldor and Anati, 1979; Reiss and Hottinger, 1984).

While its connection with the Indian Ocean places the biogeographic origin of Red Sea fauna and flora within the Indo-Pacific domain, it's setting and geological history make for unique conditions that have direct bearing on the development of reefs along the coasts of this elongated narrow sea. The reefs are dominated by stony, hermatypic corals, consisting of a diverse mixture of branching, foliose and massive species. Most abundant are corals belonging to the genera Acropora, Stylophora, Montipora, Pocillopora, Porites, Platygyra, Pavona, Echinopora, and Favia (Loya and Slobodkin 1971). The hydrozoan Millepora is very abundant in the shallow, sub-tidal zone. Soft corals are also

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abundant throughout the Red Sea, dominated by Sinularia, Sarcophyton, Lobophyton, and Xeniids, with magnificent thickets of nephtheids (mostly Dendronephthya) found on elevated substrates and vertical walls exposed to strong currents (Benayahu and Loya 1977(a) and (b)). Due to the clear water in the northern Red Sea, zooxanthellate corals reach at least 145 m in depth (Fricke et al. 1987).

The number of coral species found in the Red Sea is approximately 190, belonging to 70 genera (Head, 1987). While the total number of species is generally higher in other tropical Indo Pacific reefs (e.g., ~360 species in the Great Barrier Reef- Veron 1986), the local, within-habitat diversity in the Red Sea is higher than in GBR (Loya 1972). However, almost any biological-ecological parameter studied at that northern Gulf reefs represents the property of high level of variation on a small geographic scale (reviewd in Rinkevich 2005). These geographically small scale variations were reflected in studies revealing rates of coral recruitment, population genetics of corals, interactions of algae and herbivorous organisms, natural catastrophe, substrate type, structure and topography, light intensity and sedimentation and more.

The fishes in the Red Sea coral reefs, like corals, share an Indo-Pacific origin. Especially abundant and diverse are the guilds of site-attached and mobile zooplanktivorous species, schooling and individual herbivorous fish, including acanthurids, siganids, and scarids, and many benthic predators, including serranids and balistids. Of the 462 reef-associated species (belonging to the ten richest families) that inhabit the Arabian Sea, 69% have crossed successfully into the Red Sea; of these, 55% have crossed into the Gulf of Aqaba. Present-day differences in the species richness of reef associated species among the Arabian Sea, Red Sea and Gulf of Aqaba appear to be the product of external, non-selective constraints on colonization (Kiflawi et al. 2006).

The Red Sea coral reefs are among the most studied reefs in the world. Detailed accounts of their structure and biological composition can be found in numerous publications. Useful references include Loya and Slobodkin (1971), Mergner (1971), Scheer (1971), Fishelson (1971), Benayahu and Loya (1977a; 1977b), and Edwards and Head (1987).

During the last four decades, the coral reefs of Aqaba and Eilat have undergone major changes resulting from increasing impacts due to human activities, coupled with those from natural disasters (e.g., Genin et al., 1995; Meir et al., 2005, Rinkevich, 2005).

Rapid developments in the cities of Eilat and Aqaba intensified the pressure on the coral reefs of the Gulf, including phosphate loading, touristic projects and other anthropogenic activities. The increased diving industry also results in coral damages. Fortunately, stricter rules are being applied on the coastal human activities in both cities to reduce the negative impacts on the neighbouring marine environment.

Moreover, the restoration and rehabilitation efforts on the damaged coral reefs have increased in the past years, such as the development of Artificial Reefs on both sides, as well as the establishment of coral nurseries to produce corals for transplantation in damaged reef areas (Rinkevich 2006; Shafir et al. 2006).

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2.1 Present environmental conditions of the Gulf

2.1.1 Climatic conditions and weather patterns

Changes in the density structure of the water column in the GOAE over an annual cycle arising from naturally varying seasonal climatic conditions have a strong effect on the water quality of the Gulf primarily in terms of nutrients. This aspect is of primary concern because of the potential impact of increased nutrient load on shallow water benthic ecosystems, primarily coral reefs that line the shores of the Gulf (e.g. Genin et al., 1995; Silverman et al., 2007a). Therefore, a good and clear understanding of the Gulf’s climate is necessary in order to consider the potential impact of water abstraction on this ecosystem due to its possible effect on the density structure of the water column in the GOAE. Unfortunately, most of the available climatic data both in terms of water column hydrograph and atmospheric conditions were measured at the northern end of the Gulf and are very scarce in other areas.

Long term records of temperature proxies from coral cores in the GOAE as well as the Red Sea indicate that this region is influenced by the strength of the South Asian Monsoon (Klein et al., 1997; Eshel et al., 2000; Felis et al., 2004), which in turn has been shown to be influenced by the North Atlantic Oscillation (NAO, Gupta et al., 2003). Where, a high NAO index during winter (cold winter in Canada and Greenland) leads to warmer than usual conditions in the Eurasian continent and a weakening of the NE Monsoon (Hurrell, 1995, 1996). This has an apparent effect on the flux of Indian Ocean sea water through the Bab-El-Mandab Strait and rates of evaporation over the Red Sea. In general the climate of the GOAE is extremely arid. The yearly precipitation in the northern GOAE averages only around 20mm (Figure 2-1). The air temperature during the summer can reach as much as 45°C during the summer and during the winter can fall below 10ºC but usually no less than 7ºC (Figure 2-2). The prevailing winds blow over 90% of the time with a principal velocity component along the axis of the Gulf from north to south (Genin and Paldor, 1998; Figure 2-3 and Figure 2-4).

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Figure 2-1 Annual precipitation rates measured in the northern Gulf of Eilat for the period 1981 to 2002. The multi annual average precipitation rate for this period was 22 mm/year. Data was derived from annual reports of the Israeli hydrological Institute.

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Figure 2-2 Daily average (blue line), minimum and maximum (red lines) air temperature measured at IUI pier 10 m above the water surface during 2009.

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Figure 2-3 Polar histogram of wind direction (A) and histogram of wind speed (B) measured at IUI pier 10 m above the water surface at 10 min intervals during 2009. During this year the wind blew 96% of the time from the north along the longitudinal axis of the GOAE.

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Figure 2-4 Quiver plots of wind speed (m/sec) and direction measured at the IUI pier 10 m above the surface of the water at 10 min intervals from January 2009 (top) to December 2009 (bottom).

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No rivers flow into the Gulf, and fresh water, other than rain, reaches it only occasionally during winter floods. Low relative humidity (Figure 2-5), relatively warm water temperature (Figure 2-6), strong winds (Figure 2-7) and unstable boundary layer (cold air over warm water during winter, Figure 2-8) combine to produce very high evaporation rates. According to early estimates (evaporation pan measurements) the evaporation rates from the GOAE can reach about 1cm day-1 (Assaf and Kessler, 1976), a value Monismith et al (2006) found was required to match observed changes in mixed layer heat content over several weeks of their observations. More recent estimates of evaporation based on several state-of-the-art parametrizations of latent heat loss based on wind speed, relative humidity, air pressure, seawater and air temperature are somewhat more conservative at ca. 5 mm/day (Ben Sasson et al., 2009). Notably, this revised estimate of the evaporation means that the inferred heat flow due to advection through the Strait of Tiran, 40 w/m2, is substantially less than the 125 w/m2 estimated by Assaf and Kessler (1976). This is important because it implies a factor of 3 differences in the implied exchange rate between the Gulf and the main Red Sea. Indeed, were the exchange rate known, the evaporation rate could be computed from overall heat and salt balances for the Gulf as was done for the Red Sea by Sofianos et al (2002), whose estimated evaporation rate is quite similar to what Ben Sasson et al (2008) estimate.

Strong solar insolation (Figure 2-9) results in surface warming and stratification of the open water column with a 6-7ºC thermocline (Figure 2-10) whose base reaches by the end of summer down to 250 m. Surface cooling during the winter, high evaporation rates, warming and stratification during the summer, and a shallow sill at the Tiran Strait that allows only warm surface water to enter the Gulf, combine to drive an annually varying thermohaline circulation in the Gulf. This has been postulated by a number of authors in the past that have shown based on considerations of heat, salt and water budgets for the entire Gulf that fresh Red Sea water flux through the Tiran Strait should be substantially higher during the winter than during the summer (see reviews in Silverman and Gildor, 2008; Ben-Sasson et al, 2009). Additionally, since only warm Red Sea surface water enters the Gulf, deep water is formed in-situ and therefore it is quite warm (20.7ºC) even at depths of >1000 m.

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0

10

20

30

40

50

60

70

80

90

100

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

RH

(%)

Figure 2-5 Daily average relative humidity measured of the IUI pier 10 m above the sea surface during 2009.

20

21

22

23

24

25

26

27

28

29

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonth

T S (°

C)

Figure 2-6 Multi annual monthly average sea water temperature that was measured at the IUI pier from 1997 – 2001. Measurements were made automatically with a thermistore and recorded every 10 minutes. The error bars indicate the standard deviation of monthly averages and the dashed line indicates the annual average temperature for all monthly averages, which is 23.8ºC.

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0

1

2

3

4

5

6

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonth

Ws

(m·s

ec-1

)

Figure 2-7 Multi annual monthly averages of wind velocities measured at IUI pier 10 m above the water surface during the period 1993 to 1999. The error bars indicate the standard deviation of the monthly averages measured during this period.

0

5

10

15

20

25

30

35

40

45

Dec Jan Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Tem

pera

ture

(ºC

)

Figure 2-8 Daily average (blue), minimum and maximum (red) air temperature measured at the IUI pier 10 m above the water surface, and daily average sea surface temperature (pink) measured at the IUI pier during 2008.

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0

50

100

150

200

250

300

350

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GR

(wat

t·m-2

)

Figure 2-9 Multi annual monthly averages of global radiation measured at IUI during the period 1993 to 2001. The error bars indicate the standard deviation of the monthly averages measured during this period.

Figure 2-10 Evolution of the vertical temperature profile at station A throughout 2005. Station A is located 10 km south of the north end of the GOAE along its longitudinal bisecting axis. Note that deep water temperatures do not go below 20.5ºC.

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Figure 2-11 Evolution of the vertical salinity profile at station A throughout 2005. Station A is located 10 km south of the north end of the GOAE along its longitudinal bisecting axis. Note the development of a salinity minimum during the summer months from April through September.

Reflecting the general thermohaline circulation of the Gulf, as water flows northward from the Tiran Strait during the summer months, it undergoes evaporation resulting in the formation of a salinity minimum at ~100 m depth (Figure 2-11). This is a salient feature of the summertime salinity profile in the northern end of the Gulf that also bares witness to the continuous northward flow of Red Sea water (Wolf-Vecht et al., 1992). In the deep water (>200 m) salinity is homogenous at ca. 40.6 PSU and in the surface layer (<200 m) salinity varies annually between a high of 40.8 PSU and 40.5 PSU.

During the winter, low nighttime temperature results in surface cooling along the margins of the Gulf. Excessive cooling of the shallow water column relative to the adjacent deeper open sea water has been shown to result in deep dense plume formation (Niemann et al 2004; Monismith et al 2006), which can potentially penetrate the deep water reservoir of the Gulf (Biton et al, 2008). This is considered to be a mechanism which contributes substantially to the convective mixing of Gulf water during the winter in addition to open water convection. The convective mixing depth varies from one winter to the next between as little as 250 m and as much as all the way down to the bottom of the Gulf (Lazar et al., 2009). This variation appears to reflect the severity of the winter, i.e. cold air temperatures, cloudiness, wind velocities and duration of cooling. However, it has also been suggested that significant decrease in SST (~1ºC) of northern Red Sea water entering the GOAE during the winter related to changes in the south Asian Monsoon cycle could also cause very deep mixing events (Silverman & Gildor, 2008).

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Finally, given the key role played by the main Red Sea in the heat and salt balances of the Gulf, it is important to note the paucity of data concerning conditions existing in the adjacent northern Red Sea, where few hydrographic measurements have ever been made (Siddell et al 2002).

In this report we have described briefly the salient features of atmospheric and oceanographic climate in the GOAE. In the final report of the study we shall provide a much more detailed description, which will also address issues of mass balance between the Red Sea and the GOAE including nutrients and total alkalinity, both of which play important roles in the development of coral reefs. We will be basing this study on the accumulated knowledge appearing in the scientific literature since the 1970’s and data bases detailed in Table 2-1 below.

Table 2-1 Available data bases for the climate analysis of the present report.

Data type Source/Location Period of measurement

Parameters measured

Meteorological data IUI/Eilat west coast 1993-2001 Ws, Wd, Ta, Pa,

GR, RH, Ts

IUI/Eilat west coast 2007-2009 Ws, Wd, Ta, Pa, GR, RH, Ts

MSS/Aqaba east coast 2007-2009 Wd, Ws, RH, Ta

NOAA/Sharm El Sheikh south GOAE 2006-2009 Wd, Ws, Ta, Tw

Hydrographic Data

IUI-DCPE/station A time series, transect data from Tiran to northern GOAE

1975 - 1977 T, S, P

IUI-REEFLUX/station A time series 1989-1991 T, S, P

IUI-RSP/station A time series 1996 - 1998 T, S, P

IUI-RSMPP/station A time series 1999-2002 T, S, P

IUI-NMP/station A time series 2004-2010 T, S, P

IOLR-IUI/GOAE transect cruise 1981 T, S, P

RV-METEOR/GOAE transect cruise 1998 T, S, P

NATO project 2007-2010 T, S, currents

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2.1.2 Topography and bathymetry

2.1.2.1 Gulf topography and bathymetry

The Gulf of Eilat/Aqaba (~180 km long and 20 km wide) is situated at the southern extent of the Dead Sea Transform. The Gulf started to evolve with the initiation of the Red Sea Rift in the late Oligocene to early Miocene (Garfunkel and Ben-Avraham, 1996). It is comprised of three elongated, coalescing, en-echelon, actively subsiding pull-apart basins that are expressed in the seafloor as a series of distinct deeps: the Tiran and Dakar deeps in the southern basin, the Arnona and Aragonese deeps in the central basin, and the Elat Deep in the northern basin (Ben Avraham et al. 1979, Ben Avraham 1985).

The bathymetry and bottom morphology of the northern part of the Gulf of Eilat/Aqaba (“Gulf head”) represent the transition from the Eilat Deep (~ 900 m WD) to the Arava Valley and the influence of active tectonic processes.

Previous bathymetric and geophysical surveys

Several geophysical and bathymetric surveys in the Gulf of Eilat/Aqaba where done in the past, the first systematic survey was that of the Pola in 1895–1896, an Austrian transport, which more than 740 km of track between 50 deep wire soundings outlined the gulf’s deep basins. The earliest surveys with modern echo-sounding, magnetics, and gravimetry were conducted by the Lamont Doherty Earth Observatory on board the Vema in June 1958 followed by the NATO ship Aragonese, which obtained the deepest sounding of 1830 m in what is now the Aragonese Deep (Hall and Ben-Avraham, 1978). In 1970 an extensive Israeli survey of the Straits of Tiran (Hall, 1975; Israel Ministry of Transport, 1975) resulted in the first detailed 50-m contour charts in the gulf. The first seismic profiling was the extensive Israeli survey by the Ramona in 1976 (Ben-Avraham et al., 1979). The Ramona survey was followed in May 1977 by four days of seismic profiling and geophysical measurements by the Atlantis II (Cruise 93). The data from the Vema, Aragonese, Ramona, and Atlantis II cruises, as well as the Tiran survey, were used in the compilation of the first coloured bathymetric map (Hall and Ben-Avraham, 1978; Figure 2-12).

The first multibeam work in the gulf was carried out in 1999 during Cruise 44 Leg 2 of the F/S Meteor with coverage ~ 40% of the gulf and only in Egyptian, Israeli, and Jordanian waters. Shortly after this cruise, in August 1999, the U.S. Naval Oceanographic Office’s survey vessel USNS Littlehales (T-AGS-52) carried out a detailed survey of the Jordanian coastline, producing two charts at scales of 1:5,000 and 1:10,000 of the Port of Aqaba (van Norden and Kren, 2001). The resolution of the survey was different from site to site, reaching 50m in the northern gulf area, where both the proposed intake locations (north and east) are located (Figure 2-13).

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Figure 2-12 The Gulf of Eilat, after Hall and Ben-Avraham (1978) .The map has been overlain by the swath data from the DS-2 Hydrosweep multibeam sonar system used aboard the German research vessel F/S METEOR during her cruise 44 Leg 2 (12 March–7 April 1999) in the gulf. The METEOR swath grid is 30 m. slightly modified by Sade et al., 2008.

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34.8 34.82 34.84 34.86 34.88 34.9 34.92 34.94 34.96 34.98 35Longitude (°E)

29.35

29.37

29.39

29.41

29.43

29.45

29.47

29.49

29.51

29.53

29.55

Latit

ude

(°N

)

East Intake

Figure 2-13 General bathymetry map of the Jordanian waters of the Gulf of Aqaba. (ASEZA, 2000: Jordan-US Navy bathymetric survey in Jordanian waters during 1999).

The Gulf Head

In 1987 Reches et al., carried out a study of the shallow north-western part of the Gulf head (up to WD ~200 m) with a small submarine. Ben-Avraham and Tibor (1993) carried out a bathymetric and shallow geophysical survey in the northwester part of the Gulf head. In 2004, CHIRP and bathymetric data were collected on the shelf of the western and north-western part of the Gulf head (Makovsky et al., 2008).

The most extensive study of the Gulf head was done in 2006 by Tibor et al., (2010). During this study a marine geophysical survey was carried out at water depths of 10–700 m onboard the Israel Oceanographic and Limnologic Research vessel R/V Etziona. More than 280 multibeam lines were collected with a total length of 400 km. The multibeam data were gathered by means of a hull-mounted Simrad EM 1002 multibeam sonar system that operates at a frequency of 95 kHz and generates 111 2° beams spread over an arc of up to 150°. The spatial coverage of the survey area

X North Intake

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gave a 60% overlap of the multibeam swaths, resulting in a spatial resolution of approx. 1–2 m. A poster showing the new bathymetric data together with the topography (Figure 2-14) was produced and distributed to the scientific community and relevant Ministries and organizations (Sade et al., 2008). Unfortunately the digital data from this survey are restricted and not currently available for this study.

Figure 2-14 Multibeam shaded color bathymetry of the northern Gulf of Eilat/Aqaba.

2.1.2.2 Bathymetry in the areas affected by the intakes

Bathymetry of the North Intake site

The bathymetry of the proposed intake site (North Intake) in the northern of the Gulf of Aqaba characterizes by a smooth gradient and relatively homogenous geometry (Figure 2-15). The bottom slope within 0-20 m depth range is ~0.094; i.e. depth to horizontal distance ratio is about 1:11. No significant hills or valleys exist at the bottom of the study area. The slope decreases generally with increasing depth, and becomes ~0.054 (1:18.5) within the 20-60 m segment.

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Bathymetry of the East Intake site

The general bathymetry map of the Jordanian waters (Figure 2-16) shows a general description of the bottom topography at the East Intake Site. The bathymetry map in the East Intake site shows three features of topography in that area. The steep bathymetry appears between 0-50 m depth, smooth slope between 50-80 m depth, and again steep slope below 80 m depth.

A more detailed survey at the East intake site was carried out by CoB, showing fine resolution transects (Figure 2-17) within a ~130 m square around the proposed intake location. The bottom slope within 0-4 m depth range is ~0.15; i.e. depth to horizontal distance ratio is about 1:6.7. The slope decreases generally with increasing depth, and becomes ~0.55 (1:1.8) within the 4-60 m segment, which is considered as very steep slope.

Areas covered by the bathymetric surveys described above are shown in Figure 2-18. Some additional bathymetric data in shallow areas were generously provided by Prof. Amotz Agnon from the Hebrew University. These data together with the data shown in Figures 2-13, 2-15 and 2-16 will be used to create a gridded data set for the models.

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302000 302250 302500 302750 303000 303250 303500 303750 304000 304250 304500 304750 305000 305250 305500x-JTM (m)

268000

268250

268500

268750

269000

269250

269500

269750

270000

270250

270500

270750

271000

271250

271500

271750

272000

y-JT

M (m

)

Jordan

International boarder

Gulf of Aqaba

0 500 1000 1500 2000

Figure 2-15 Detailed bathymetry map in the proposed intake area (North Intake) in the northern of the Gulf of Aqaba (ASEZA, 2000. Jordan-US Navy bathymetric survey in Jordanian waters during 1999).

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34.976 34.978 34.98 34.982 34.984 34.986 34.988

Longitude (°E)

29.482

29.484

29.486

29.488

29.49

29.492

29.494

29.496

Long

itude

(°E

)

Figure 2-16 General bathymetry map in the proposed intake area (East Intake) in the northern of the Gulf of Aqaba (ASEZA, 2000. Jordan-US Navy bathymetric survey in Jordanian waters during 1999).

X Eastern Intake

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Figure 2-17 Results of bathymetric surveys carried out by CoB in the proposed Eastern Intake.

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Figure 2-18 Location of the areas covered by the main bathymetric surveys relevant to the aims of this study. Violet identifies the Jordan-US Navy bathymetric survey in Jordanian waters of year 1999; striped light green identifies the 2006 multibeam survey carried out by Tibor et al.; red identifies the extension of the detailed map reported above for the northern intake area. The two proposed intake locations are identified by yellow x marks. Note that violet and light green overlap in the north-eastern area of the north tip (see pink area).

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IIssrraaeell OOcceeaannooggrraapphhiicc && LLiimmnnoollooggiiccaall RReesseeaarrcchh LLttdd..

2.1.3 Currents and circulation

2.1.3.1 Overview

The large-scale circulation of the Gulf appears to be affected by three distinct processes: (1) the large-scale thermohaline circulation associated with warmer, fresher water from the main body of the Red Sea entering the Gulf through the Strait of Tiran and the formation of colder, saltier water by evaporation and surface cooling; (2) the wind-driven circulation and associated upwelling and downwelling; (3) internal tides generated at the Strait of Tiran that propagate northward along the Gulf and possibly reflect from the steep slope of the northern end of the Gulf. Overall, because of limits to observational efforts, direct examination of these processes has been limited. It should also be noted that the thermohaline circulation has an important small-scale manifestation: convective exchange between the nearshore waters where the reefs are found with deeper offshore waters.

2.1.3.2 In–situ current observations

Limited direct current measurements have been reported in the northern GOAE (Hulings, 1979; Brenner et al., 1988, 1989, 1990, 1991; Genin and Paldor, 1998; Niemann et al., 2004; Manasrah et al., 2004; Biton et al., 2008; Gildor et al., 2009). The observations of Genin and Paldor (1998), made over a several year period (1987-91) with a small set of electromagnetic current meters typify what has been found to date. A southward current along the west coast was observed most of the year, with a short period (November-January) of northward flow and an abrupt reversal in early February, behavior they attributed to changes in the position of hypothesized wind-generated gyres. Their measurements also show dramatic annual variability in the semi-diurnal “tidal” currents, as well as significant offshore flows near the bottom in 40 m of water.

The first reported direct current measurements near the north intake site were conducted by Brenner et al. (1988, 1989, 1991), Goodman et al. (1990) over a four year period (1988-1991) as part of the preliminary monitoring of the environmental impacts of the fish cages (which were completely removed from the sea at the end of 2008). A single mooring with two current meters (5 m and 17 m below the surface) was located at a point about 500 m south of the north beach, adjacent to the international border, at a bottom depth of 30 m. The statistical summary of the distribution of the current speed and direction for the two current meters for the final year of the measurements is shown in Table 2-2 and Table 2-3.

Table 2-2 Percent occurrence of currents in the various speed (cm/s) and direction bins near the north beach at 5 m below the surface for the period Oct 1990 – Sep 1991.

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Table 2-3 Percent occurrence of currents in the various speed (cm/s) and direction bins near the north beach at 17 m below the surface for the period Oct 1990 – Sep 1991.

At both depths, the dominant direction of flow was shore parallel with roughly equal amounts of flow directed towards Aqaba and towards Eilat.

The most comprehensive study of water movement near the North Intake site in the northernmost Gulf of Aqaba was made during summer, autumn, winter and spring seasons of 2004-2005 by Manasrah et al. (2007). These measurements illustrate the complexity of flows in the northern Gulf. Two current regimes were observed during the summer at depths between 6-34 m in the nearshore. At depths of 6 to 12 m there was a south-southwestward current of (∼200°) That was nearly parallel to the prevailing winds with relatively strong averaged speeds of 30 cms-1 at 6 m and 12 cms-1 at 12 m. Accordingly, the daily displacement of water particles was 20 km day-1 at 6 m and 6 km day-1 at 12 m (Figure 2-19; Table 2-4). Below 12 m (18, 24, 30 and 34 m depth layers). weak currents with vertically anticlockwise rotation were observed flowing northwestward (∼320°) at 18 m depth and westward (∼280°) at 34 m (Figure 2-19; Table 2-1). The average values of current speed and the daily displacements of water particles below 12 m depth were about 3 cms-1 and 1.5 km day-1, respectively. During autumn, at which time significant mixed layer deepening had begun (see above), at 6 m the current flowed south-southwestward (∼210°) at 7 cms-1 (3 km day-1) and was parallel to the foremost wind direction (Figure 2-20; Table 2-4). Below 6 m (12, 18, 24 and 26 m), the current direction rotated in the anticlockwise direction from northwestward (∼340°) at 12 m depth to westward (∼280°) at 26 m (Figure 2-19; Table 2-4). Below 12 m the current direction alternated direction between southeastward and northwestward, i.e. parallel to the shoreline of the study area (Figure 2-19) with values of ca. 4 cms-1 (1 km day-1- Table 2-4). During the winter deep mixing period, current structure was similar to that of the summer and autumn, except that the current direction changed gradually from north-northwestward (∼340°) at 6 m to west-southwestward (∼250°) at 34 m (Figure 2-21). Moreover, a fluctuation in current direction was observed at each depth with larger time scale compared to that observed during autumn (Figure 2-20). The average value of current speed for all depths were about 5 cms-1 (2 km day-1 - Table 2-4). Finally, currents during the spring showed abrupt changes in current direction from southeast to northwest with depth except that at 24 m where the change in direction was from southeast to west (Figure 2-22). The average values of current speed, current direction and displacement rate of water movement for all depths were about 5 cms-1at 300° (1 km day-1 - Table 2-4).

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IIssrraaeell OOcceeaannooggrraapphhiicc && LLiimmnnoollooggiiccaall RReesseeaarrcchh LLttdd..

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Figure 2-19 Partial raw data set of current speed (cms-1) and direction (°) and progressive vector diagram at selected depth levels during summer season in the North Intake site in the northernmost Gulf of Aqaba.

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Table 2-4 Statistical summary of current speed (cms-1), current direction (°) and displacement rate (km day-1) of water movement at selected depth levels during the four seasons in the North Intake site in the northernmost Gulf of Aqaba.

August 4th-11th, 2004 (summer)

Speed (cms-1) Direction (°)

Depth Mean SD Mean SD

count Dis. rate (km day-1)

6 28.1 13.01 199 38.7 961 20.5

12 12.9 11.33 204 39.6 961 6.2

18 3.2 1.94 321 52.9 961 1.4

24 3.1 1.91 325 53.7 961 1.6

30 3.2 1.82 310 50.2 961 1.5

34 3.5 1.86 277 45.9 961 1.2

September 30th-October 22nd, 2004 (autumn)

6 7.0 3.69 210 36.4 3227 3.0

12 3.8 2.51 338 62.4 3227 1.1

18 4.1 2.60 322 60.0 3227 1.2

24 3.7 2.43 291 60.1 3227 1.2

26 3.6 2.19 279 60.4 3227 1.1

January 11th-28th, 2005 (winter)

6 5.6 3.06 340 59.1 2400 1.1

12 6.2 3.67 317 62.1 2400 2.4

18 5.6 3.41 306 62.7 2400 2.2

24 5.1 3.33 289 61.9 2400 2.1

30 4.8 2.91 265 60.9 2400 2.4

34 5.1 2.66 244 57.2 2400 3.0

March 6th-April 4th, 2005 (spring)

6 5.2 3.94 321 66.0 4135 0.6

12 5.1 3.90 336 67.6 4135 1.0

18 4.6 3.87 310 67.8 4135 0.8

24 4.2 3.41 241 63.1 4135 1.1

SD – standard deviation, Dis. rate – displacement rate

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Figure 2-20 Partial raw data set of current speed (cms-1) and direction (°) and progressive vector diagram at selected depth levels during autumn season in the North Intake site in the northernmost Gulf of Aqaba.

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Figure 2-21 Partial raw data set of current speed (cms-1) and direction (°) and progressive vector diagram at selected depth levels during winter season in the North Intake site in the northernmost Gulf of Aqaba.

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Figure 2-22 Partial raw data set of current speed (cms-1) and direction (°) and progressive vector diagram at selected depth levels during spring season in the North Intake site in the northernmost Gulf of Aqaba.

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The current at the northern Gulf of Aqaba although quite variable in direction, do have some consistence seasonal trends. Southward current along the western coast is observed most of the year, with a short period (November-January) of northward flow and a reversal in early February, when the water column is vertically mixed, a clear onshore (westward) current is observed near the surface and a return (offshore) current over the bottom. This cross-shore pattern is consistent with a wind-driven Ekman circulation.

The spatial structure of flows in the Gulf, at least as seen by current meters (see radar section below) has been best revealed in observations made along the entire Gulf of Aqaba, during February-March 1999 using a 150 KHz ADCP on the RV Meteor (Manasrah et al., 2004). These unique observations reveal a sequence of flow changes with time and space (Figure 2-24). These changes do not match the basic tidal motion, and represent in some parts a phase difference in the horizontal current components of about 90°. These appear to be a chain of cyclonic and anti-cyclonic eddies positioned along the Gulf axis and occupying at least the upper 300m of the water column (Manasrah et al 2002; Manasrah 2002). The diameter of the eddies ranged from 5 to 8 km with velocities ranging from 0 to 0.30 ms-1. Some of this spatial variability is seen in Figure 2-23, a plot of spatial variability in the northern Gulf taken from Manasrah (2002). This spring-time data shows that the current in the upper 200 m in the western and eastern parts of the northern Gulf of Aqaba was dominantly directed to the NE, while in the center the current is mainly SE. Consequently, an anti-cyclonic circulation was observed in the upper 150 m between the western and central parts. Between 200 m to 300 m the NE current still dominated in the western part, while a transition from NE to SE can clearly be seen in the east. Obviously, the two opposite currents are parts of a larger anti-cyclonic circulation between eastern and western parts.

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Figure 2-23 Distribution of the horizontal current vectors in the Northern Gulf of Aqaba at selected depth levels during March 5th 01:40-March 6th 16:00 1999.

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Figure 2-24 Time-latitude distribution of the current vectors along the axis of the Gulf of Aqaba at 105 m depth on repeated tracks during February 21st-March 6th 1999.

The current pattern in front of the East Intake site in the northern Gulf of Aqaba was studied during summer 2007 (from Figure 2-24 to Figure 2-24; Table 2-5). Currents at 3-5 m depth were southward (∼150°-180°) with average speeds of about 15 cms-1 at 3 m depth and about 7 cms-1 at 5 m. The current at 7 m was weak (∼ 3 cms-1) with unstable direction. Below this depth, the current started to change its direction to northeastward, which could be assumed as a transition layer between two opposite layers direction. The current between 9-25 m remained northtward with average speed of 4 cms-1. Thus, in general, the current in the 3-27 m can be divided into three different patterns. The first pattern was southwestward in the upper layers (3-5 m). The second pattern was unstable in direction with weak speed in 7 m depth. The third pattern was southeastward and southwestward in the depth layers of 9-27 m.

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Table 2-5 Statistical summary of current speed and direction at different depth levels in the study area during the period of study.

Speed Direction

Depth (m) Average std. dev. Average std. dev. Displacement rate (km/day)

3 14.61 13.40 147 18.8 13.24

5 7.26 5.14 181 32.9 8.54

7 3.07 4.31 108 22.8 0.12

9 4.50 4.04 38 16.7 0.94

11 4.26 3.99 35 17.1 1.07

13 4.02 3.94 33 17.3 1.13

15 3.78 3.78 32 17.5 1.13

17 4.34 4.39 37 16.5 1.06

19 3.27 3.29 28 18.2 0.91

21 2.96 2.95 22 19.3 0.68

23 2.78 2.70 18 21.8 0.54

25 2.68 2.43 6 24.9 0.42

27 2.65 2.21 337 29.5 0.37

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Figure 2-25 Distribution of mean current speed (cms-1) at different depth levels in the East Intake Site during the study period.

Figure 2-26 Distribution of mean current direction (°) at different depth levels in the East Intake Site during the study period.

0

45

90

135

180

225

270

315

360

3 5 7 9 11 13 15 17 19 21 23 25 27

Depth (m)

Ave

rage

dir

ectio

n (°

)

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20.00

30.00

40.00

50.00

3 5 7 9 11 13 15 17 19 21 23 25 27

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Ave

rage

spe

ed (°

)

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‐400

‐300

‐200

‐100

0

100

200

‐100 0 100 200

N-S

dist

ance

(Km

)

E-W distance (Km)

3m

‐300

‐250

‐200

‐150

‐100

‐50

0

‐10 0 10 20 30

N-S

dist

ance

(Km

)E-W distance (Km)

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‐6

‐4

‐2

0

2

4

6

8

‐1 0 1 2 3 4

N-S

dist

ance

(Km

)

E-W distance (Km)

7m

Figure 2-27 Progressive vector diagram of current at different depth levels in the East Intake Site during the study period.

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Making measurements on the western shore of the Gulf, Reidenbach et al (2006) and Monismith et al (2006) focused on smaller scale processes operant in shallow water. Reidenbach et al (2006) showed that the tidal flows over the Eilat reef were well described by the law of the wall for rough surfaces. These measurements showed the flows likely to be important for a shallow intake – turbulent tidal flows in the longshore direction and buoyancy-driven flows in the cross-shore direction. Using ADCP and temperature data from a series of deployments carried out at all time of year from 1999 to 2002, Monismith et al (2006), observed during periods of cooling an exchange flow characterized by a fixed vertical structure (flow offshore at the bottom and onshore at the surface) with a strength that depended on the strength of the cooling and on the turbulent mixing associated with the tides. In summer, this “thermal siphon” operated in both directions: offshore at the surface during heating and offshore at the bottom during cooling. Typical exchange rates implied a residence time for water on the shallow reef of a few hours, suggesting that these flows were important to supplying phytoplankton to the reef and thus to the rate of net heterotrophy by the reef (Genin et al 2009).

These convective flows were later examined by Biton et al. 2008 using in situ observations and a high resolution, nonhydrostatic general circulation model. They showed that dense water forms over the shallow shelf at the northern tip of the Gulf during winter and cascades down-slope in daily pulses following the buoyancy loss. Similar pulses have been observed in a small canyon descending from the eastern shore of the Gulf of Eilat [Niemann et al., 2004]. Field studies were conducted during winter 2007 near the northern shore of the Gulf. This region is characterized by a relatively gentler slope (~0.1 m/m) of the continental shelf in comparison to the much steeper shelves along the western and eastern shores of the northern Gulf (0.2–0.4 m/m). During these field campaigns, vertical profiles of temperature and salinity were measured with a Sea Bird Electronics SBE-19 CTD profiler. Vertical profile stations were situated along a transect extending out from the northern shore (bearing 220~) at 10, 20, 30, 50, 75,100, 150 and 200 m bottom depth. An upward looking 600 kHz RDI Workhorse Sentinel Acoustic Doppler Current Profiler (ADCP) was deployed at 45 m bottom depth (for the exact location and time of the CTD casts and ADCP, see Figure 2-28). Finally, six Vemco Minilog 12 bit temperature data loggers were distributed along the ADCP mooring line between the bottom and the surface. Four of these loggers were deployed in the lower 18 m above the ADCP in order to successfully capture the cold water anomalies associated with the density current (DCs) signal.

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Figure 2-28 Meridional velocity component profile (top) and temperature at constant depths of 3, 8, 13, 18, 27, and 42 m above the bottom (bottom) measured in the north shore region of the Gulf of Eilat during 6–8 March 2007. The arrows indicate two succeeding cold water pulses (separated by one day), characterized by high down-slope velocities (up to 15 cm s-1 (negative values)) in the bottom layer (up 15 m above the bottom). From Biton et al., 2008.

The ADCP and temperature data show pulses of anomalous high density water confined to the bottom with a diurnal frequency. The meridional velocity component profile during the 7–8 of March 2007 is characterized by high southward velocities up to 15 cm s-1 in a layer 15 m above the bottom, which begins to develop at 0500 and disappears at 1500 (Figure 2-28 top). During the same time period, the temperature at 3, 8 and 13 m above the bottom begins to drop, while temperature in the upper layer increases due to daytime heating (Figure 2-28 bottom). Finally, the density profiles indicate the increasingly deepening penetration over time of high density water along the slope from the north shore. These observations clearly indicate that the northern shore of the Gulf is the source of cold bottom water anomalies. During the night, maximal buoyancy flux loss from the surface leads to the formation of relatively denser water over the shallow shelves at the northern end of the Gulf, when compared to the adjacent deeper open water. The dense plume then cascades down-slope and gains buoyancy by entraining the lighter ambient water, until reaching a depth of 200 m (the maximal measured depth), approximately 2.5 km from its formation site. Similar pulses were observed during all winter months of 2007 (not shown) suggesting that these pulsating DCs are common.

The observed DCs were compared to two 5-day, high resolution simulation using the Massachusetts Institute of Technology Ocean General Circulation Model (MITgcm) [Marshall et al., 1997a, 1997b], which solves the Navier Stokes equations including the non-hydrostatic terms. The model domain included the entire Gulf of Eilat and part of the northern Red Sea with a bathymetry that is adapted

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from Hall and Ben-Avraham [1973], while partial cell method was used to give smooth bottom topography [Adcroft et al., 1997]. At the southern end of the domain, they used a ‘sponge-layer’ in which temperature and salinity were relaxed at all levels to the monthly mean hydrographic climatology from present-day Red Sea model simulations of Biton et al. [2008]. The horizontal resolution was 75 m and the water column was divided into 38 levels in the vertical. The time step for all simulations was 60 sec. At the surface they used climatological wind stress and thermohaline fluxes to drive the model.

Figure 2-29 Modeled down-slope (top) and along-slope (bottom) flux distribution associated with the high density signal in the northern Gulf of Eilat (m3 s-1) at different times during the diurnal cycle. The black contours indicate the 0, 100, 200, 300, and 400 isobaths. The results indicate that the northern shore is a major source for the deeply penetrating DC signal and that the flux distribution is highly dependent on topography and rotation. The dense plume is channeled into two canyons that descend from the north beach. Six hours after it forms, the dense plume veers westward in response to the Coriolis force and converges on the western side of the Gulf at a depth of 300–400 m. At this depth the dense current continues to flow southward isobathically as a narrow stream in almost perfect quasigeostrophic balance. From Biton et al., 2008.

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The results, which show a formation of dense water over the shelf during the nighttime and cascading down-slope during the daytime, nicely captured the main characteristics of the measured DC signal. These reproduced characteristics include: 1) arrival and departure times of the pulse to and from the 50 m depth mark, 2) downward velocities up to 15 cm s-1, 3) plume thickness of 15 m. Both the model results and the observations have, 4) completely mixed open water at least down to 200 m in the background density and, 5) dilution of plume water by entrainment of ambient water. According to the model, the dense plumes that form along the north shore are channeled into two canyons that descend southwards leaving the area in between these two canyons almost free from DC flux (Figure 2-29 top). During its decent the modeled dense plume increases its flux due to entrainment and convergence. At a depth of 170 m, the dense plume veers westward in response to the Coriolis force and the along slope fluxes start to increase (Figure 2-29 bottom). The model DC flux converges on the western side of the Gulf, while descending down to 300–400 m depth. At this depth the DC continues to flow southward isobathically as a narrow stream in almost perfect geostrophic balance (balancing the buoyancy and Coriolis forces). Based on the model results, almost all of the DC signal originates at the north shore of the Gulf, where the coast has a relatively moderate slope, while along the much steeper eastern and western side boundaries, density pulses hardly exist, suggesting that narrow and steep shelves are not able to support the formation of Dcs. Because the northern beach is a preffered site for shelf convection, further studies are required to asses the potential effect of a northern intake on the rate of deep water formation in the gulf.

A mooring line equipped with current meter and set of thermistors that was deployed in front of the IUI over water depth of 300 m during winter 2008 as part of the NATO project confirm the model results (Figure 2-30). As long as the gulf was well mixed as demonstrated by the temperature measurements (lower left panel), density currents formed and flow southward along the coast as seen by the progressive vector diagram. Once the water column began to restratified, the density currents disappear and the net current at depth is nearly zero.

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Figure 2-30. Current meter and set of termistiors were deployed in from of the IUI (red X, upper-left panel). The water were well mixed during the early stage of the deployment (lower left, each color represents the temperature at different depth) and later the water column restratified. The progressive vector diagram indicates southward currents when the water column is well mixed and we expect the formation of density currents and near zero velocity once stratification begins.

2.1.3.2 Radar data analysis

As outlined above, the surface circulation in the GOAE has wind-driven, tidal, and thermohaline components. Although measurements of surface circulation are crucial for our understanding of larvae transport and of other passive tracers, until recently, very few direct measurements of surface currents were conducted in the GOAE, and most of them were point measurements.

Since August 2005, Two 42 MHz SeaSonde HF radar systems have been operational in the northern gulf near the city of Eilat. This network is used to measure the complex surface circulation structure of the northern GOAE with very high spatial (300 m) and temporal resolution (30 min) (Gildor et al., 2009). Each of these stations measures the radial velocity of the surface currents. To reconstruct the velocity at a certain patch of water, at least two radar sites should measure the radial velocity there from two different angles (ideally with at least 15o difference). Strictly speaking, the radar measures the currents at the top few tens of cm of the water column. However, comparison to measurements by an Acoustic Doppler Current Profiler (ADCP) demonstrate that the shear in the top few meters is usually small, and most of the time the surface currents represent the upper 10-20 m. As with any remote-sensing observation system, there are gaps and outliers in the HF radar data that require post-processing. The open boundary modal analysis (OMA) of Lekien et al. (2004) is applied to raw

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HF radar data to yield the spatially interpolated and filtered velocity on a regularly spaced grid (300 m resolution) with a time step of 30 min, as detailed in Lekien and Gildor (2009).

Using the HF radar dataset of surface currents we have been investigating the horizontal mixing on the scale of a few km. The observed flow field is often quite variable and can be rather complex. Our study yielded important, unexpected results and we demonstrated, experimentally, the existence of temporary barriers to mixing. This has important implications for the dispersion of pollutants, nutrients, larvae, etc., and therefore for a wide range of predictions. We were able to also verify the existence of these barriers by aerial-photographs (Figure 2-31). Mixing barriers within the gulf are highly intermittent and variable in spatial structure, and at certain times the whole region is relatively well-mixed. Based on analysis of a few months of HF radar data from different seasons, similar barriers exist somewhere within the domain over 30% of the time. The mechanism behind the barriers is still unknown and further analysis is required to better understand their evolution and their effect on the ecological system.

Figure 2-31 Left: Relative dispersion in the Gulf of Eilat based on 36 hours of virtual particle tracking simulation using the measured HF radar surface velocities on February 3, 2006. The light-colored lines with higher relative dispersion values divide the domain into relatively well mixed regions, but little mixing occurs across these lines that therefore serve as barriers to mixing. Note the high relative dispersion line (between the red arrows) that starts in the western side of the northern coast and ends on the eastern coast. White areas are regions from which particles have moved out of the domain. Right: An aerial-photograph of the Gulf on Feb 5, after a flood washed sediments into the ocean. Note that the sediments do not mix across the same barrier line that was calculated from the currents observed by the HF radar and shown on the left. For orientation, note that the green rectangle both panels marks the same location. From Gildor et al., 2009.

Berman et al. (2000) suggested that the circulation along the gulf is made up of a series of small scale, localized eddies (sometimes called gyres). The observed flow field is most of the time quite variable and not coherent. Nevertheless, the high-resolution radar observations of the surface currents revealed an occasional and perplexing presence of a large (much of the domain) spatially coherent eddy with a lifetime of a day or so. Such coherent eddies are rare and appear only a few times a year, from November to April, when the wind is relatively calm. The associated velocities are relatively high, and can reach 100 cm s-1 near the edge of the eddies, compared to the averaged velocities of 15 cm s-1 observed over most of the year. The rarity and timing have been puzzling and the mechanism behind the formation of such coherent eddies is unclear.

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Figure 2-32 Coherent eddy in the Gulf of Eilat observed on November 29, 2005. From Gildor et al., 2010.

We also studied the temporal correlations of the sea surface currents at the Gulf of Eilat and found long-range temporal correlations, from a timescale of several hours to a timescale of several months (Ashkenazy and Gildor, 2009). This was done using the Fourier transform and the Detrended Fluctuation Analysis methods. We also found weak volatility correlations that indicate nonlinearity of surface currents. We used the time-dependent surface Ekman layer model to test whether the source of these correlations is the wind. It was found that the wind by itself actually leads to stronger temporal correlations than observed, as well as enhanced diurnal periodicity; other nonlinear terms as well as tides, convection, and spatial variability may weaken the temporal correlations imposed by the wind. Our results show significant spatial variability of correlation exponents even in this small region (6 x10 km); in addition, stronger correlations are observed during winter.

The time series of a particular location is highly variable (Figure 2-33; weak seasonal and daily variability is also present with reduced speeds during the winter months. This pattern is a typical pattern.

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Figure 2-33 (a) An example of a time series of surface current speed (in cm/s) as measured by the HF radar. The time series spans one year starting at Oct. 1st 2005 and represents the mean surface current of a grid point of ≈300 m x≈300 m located at 34.969◦E and 29.501◦N. It is noticeable that the speed is weaker during the winter time. (b) An enlargement of the time series presented in (a). The daily and sub-daily variability is visible. From Ashkenazy and Gildor, 2009.

A detailed analysis of the time series shown in Figure 2-33 is depicted in Figure 2-34. We first perform a conventional Fourier transform (Figure 2-34a) from which it is clear that the low frequencies dominant the signal where the daily periodicity is relatively weak. This hints to long-range temporal correlations. To assess this more accurately we plot the power spectrum on a log-log plot (Figure 2-34b), both using linear and logarithmic binning. It is apparent that the scaling curves have similar slope for the different frequency regimes. We estimate the power law scaling exponent by least squares fitting the power spectrum to a power law function and obtain a power law exponent

of 0.7β» , suggesting long-range temporal correlations. We estimated the scaling exponent of 20

shuffled time series of the time series shown in Figure 2-33 and obtain a mean exponent of -0.01 and a standard deviation of 0.05, suggesting that the long-range temporal correlations are highly significant. (The autocorrelation function is related to the Fourier power spectrum; if the autocorrelation function decays as a power law, gtA(t) −~ , the power spectrum also decays as a

power law, βfP(f) −~ where g=β −1 and 0 < g < 1. β = 0 indicates white noise (i.e., all

frequencies are equally important), β = 2 indicates red noise (i.e., the low frequencies are

dominant) while β = -2 indicates blue noise (i.e., the high frequencies are dominant).

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We repeated the calculation of the scaling exponent using the DFA method of order two (Figure 2-34c); that is, linear trends in the time series are excluded. We obtain a DFA exponent of 0.8α» for annual, winter (January to March 2006), and summer (July to September 2006) time series. This value is roughly consistent with the value of the power spectrum scaling exponent 0.7β» , since

theoretically 0.612α ==β − ; the difference of 0.1 may be attributed to the presence of linear

trends in the surface speed time series. Also here the DFA scaling curves do not seem to have crossovers. To estimate the significance of the scaling exponent we generate 20 shuffled time series out of the original one and obtain, as expected, a mean exponent of 0.51 and a standard deviation of 0.015. Thus, the estimated temporal correlations are highly significant and since we use the DFA they, most probably, are not associated with linear trends or seasonal variability as on the scales we consider here (days to months) the mean seasonal cycle appears as linear curves.

Figure 2-34 (a) Frequency power spectrum of the time series shown in Figure 2-33a. (b) Same as in Figure 2-33a but on a log-log plot with linear binning (black curve) and logarithmic binning (red curve). The estimated power law exponent is β ≈ 0.7 β . (c) The DFA scaling curves for the entire year (black, October 2005 to September 2006), winter (red, January to March 2006), and summer (blue, July to September 2006). The estimated DFA exponent is α ≈ 0.8 with no apparent crossover. (d) Fluctuation function curves for the volatility time series (i.e., absolute value of the increment time series). The DFA curves indicate weak volatility correlations of 65.0≈vα . From Ashkenazy and Gildor, 2009.

Finally we estimate the volatility correlations (Figure 2-34d) using the DFA method. Here the temporal correlations are marginal and the scaling exponent is α v »0 . 65 indicating weak nonlinearity of the time series. Usually, such nonlinearity is expressed by clustering of large fluctuations (up or down) followed by clustering of small fluctuations which are arranged in a self-similar pattern. Such behavior may be associated with storm activity followed by days with calm winds. To asses that indeed the volatility correlations are not an artifact of the shape of the

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distribution, we generate 20 surrogate time series out of the original (increment) time series using the surrogate data test proposed by Schreiber and Schmitz [2000]. The mean volatility exponent of the surrogate time series is 0.5 and the standard deviation is 0.02, suggesting that the observed volatility correlations are significant and that the surface current time series is indeed nonlinear.

One may expect that the results shown in Figure 2-34 would be similar to other time series in nearby locations within the domain considered here due to the small basin dimensions and since the atmospheric forces (like temperature and winds), which are the main driving forces of ocean circulation, vary on much longer scales. To check this hypothesis we estimate the different scaling

exponents ( β ,α , and α v ) for each of the available grid points. The results are presented in

Figure 2-35.

Figure 2-35 A summary of the scaling exponents of surface current speed. The x/y-axis denotes the longitude/latitude. The left column summarizes the Fourier transform scaling exponent β, the middle column summarizes the DFA scaling exponent α, and the right column summarizes the volatility scaling exponent αv. The top/middle/bottom panels are the scaling exponents of the annual (Oct. 1st, 2005 to Sep. 30, 2006), winter (Jan. 1st, 2006 to Mar. 31st, 2006), and summer (Jul. 1st, 2006 to Sep. 30, 2006) time period. From Ashkenazy and Gildor, 2009.

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We analyze the time series of an entire year (October 2005 to September 2006), winter (January to March 2006), and summer (July to September 2006). We present (1) the Fourier power spectrum scaling exponent, β, that was estimated based on logarithmic binning curves, (2) the DFA (of order two) scaling exponent, α, and (3) the volatility scaling exponent αv. The surface currents are long-range correlated with Fourier power spectrum exponent β ≈ 0.7 and DFA exponent α ≈ 0.8. The correlations are stronger during the winter and weaker during the summer. To estimate the significance of the exponents we generate 20 shuffled time series for each of the grid points and estimate the exponents. We obtain mean Fourier power spectrum exponent of 0 and standard deviation that is less than 0.12 and for the DFA we obtain mean exponent of 0.5 and standard deviation that is less than 0.03. These values indicate that the measured correlation exponents are highly significant. The similarity between the β and α exponents, both spatially (Figure 2-35) and through the relation β = 2α − 1, indicates that the effect of trends on the estimation of the exponents is small and that the weak daily periodicity does not really affect the estimation of the scaling exponents.

For the volatility scaling exponent the situation is a bit different. While the volatility correlations are moderate and the exponent is αv ≈ 0.65, there are no substantial differences between the summer and winter (Figure 2-35). Still, the volatility correlations, as expressed by the volatility scaling exponent αv, are somehow weaker during the summer, as for the Fourier and DFA scaling exponents, α and β. As mentioned above, volatility correlations may hint for nonlinearity of the underlying process. We validate the observation that indeed the volatility correlations indicate nonlinearity by generating 20 surrogate time series for each of the available grid points, for which the Fourier phases are random but the probability density function and the Fourier power spectrum remain almost unchanged. We apply this for the increment time series of the surface speed current [see, Ashkenazy et al., 2003b]. We then measure the volatility scaling exponent of the surrogate time series using the DFA technique. We find that the mean volatility exponent is 0.494 and that the standard deviation is less than 0.054, significantly lower than the measured volatility exponent of 0.65. The volatility correlations thus represent nonlinearity of the underlying process.

2.1.3.3 Tides and Internal Waves

Tides play a major role in the dynamics of the Gulf. It appears that the primary manifestation of their importance is the presence of internal tides generated at the Strait of Tiran as the stratified water column is forced back and forth over the sill by the barotropic tide. The barotropic tide itself appears to be a co-oscillation of the Gulf with the northern Red Sea (Monismith and Genin 2004).

Tides and sea level in the northern Gulf of Aqaba are measured continuously every 10 minutes at the MSS and readjusted reference to the chart datum. The maximum sea level range during the year 2009 was 145.1 cm. The highest value was 74.5 cm observed on August 20th, and the lowest was -70.6 cm recorded on February 11th (Figure 2-36 and Figure 2-37). The sea level anomalies apparent in these figures depict a clear yearly cycle (Figure 2-38), where the lowest monthly mean anomaly (-14.4 cm) was observed in September. The highest monthly mean anomaly was 22.7 cm that occurred in February.

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Figure 2-36 Tidal records (cm) at the Northern Gulf of Aqaba reference to the Chart datum for the months January-June 2009.

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Figure 2-37 Tidal records (cm) at the Northern Gulf of Aqaba reference to the Chart datum for the months July-December 2009.

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-25

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Figure 2-38 Monthly mean of sea level (cm) records at the Northern Gulf of Aqaba reference to the Chart datum for the year 2009.

The yearly cycle of the sea level anomalies at the northern Gulf of Aqaba follows the corresponding sea level variations in the Red Sea. The sea level changes of the Gulf of Aqaba are determined by the water level in the Red Sea, which varies in response to winds on the Red Sea (Sultan et al. 1995; Sofianos and Johns 2001). In general, during the period December-May, northward winds elevate the water level in at the northern end of Red Sea and thus the Gulf of Aqaba. During the period July-October, southward winds due to the south-west monsoon result in a set down of the northern end of the Red Sea. As shown in Sofianos and Johns (2001), the setup and setdown correspond well with what would be calculated from a simple balance of applied stresses and hydrostatic pressures.

While simple dynamics describe low-frequency sea level variations, tidal currents are more complex. Noting that barotropic tidal currents at the Eilat reef should be ca. 1 mm/s not the observed values of 10 to 20 cm/s, Monismith and Genin (2004) examined correlations of sea level and velocities, finding significant (although weak) correlation between sea level and tidal velocity at a lag of 72 hours. Computing the speeds of the lowest few internal wave modes, they calculated that this was the time required for a first mode internal wave to travel from the Strait of Tiran to Eilat. This hypothesis was based on the observations of flows in the Strait reported in Murray et al (1984), the only known measurements documenting tidal flows through the Strait. Murray et al found evidence for the existence of an internal hydraulic control at the sill in the narrow section of the Strait. This sill essentially regulates the exchange over the sill (Armi and Farmer, 1986); given the unsteady nature of the tides, internal wave generation at the sill seems likely based on current understanding of internal hydraulic controls. It appears that there are several reasons that the correlation between sea level and currents may have been low, e.g. the effects of mixing as the waves propagate northward, interactions of the waves with the gyre field, and the effects of reflections of the waves off the northern boundary of the Gulf. Based on the phase speed of these first-mode waves, ca. 1 m/s, it is also expected that there should be significant cross-Gulf variations due to Coriolis forces since the

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Rossby radius of deformation for these waves is ca. 13 km, a scale that is comparable to the width of the Gulf (see Gill 1982). Finally, Monismith and Genin’s model gives an explanation of the changes in tidal velocities observed by Genin and Paldor (1999): annual variations in stratification give rise to changes in internal wave generation, with weaker internal tides accompanying the deeper mixed layers found in winter.

More recent measurements of the internal tide were made in 2008-09 by several members of the project team who deployed a mooring near the Israeli station A that included an upward looking 600 KHz ADCP to record near-surface currents and a 150 KHz ADCP looking down that measured currents to 250 m (Figure 2-39, Figure 2-40). While analysis of this data is ongoing, what is evident from this data is that the internal tide does persist throughout the year and extends throughout the water column.

Figure 2-39 ADCP data taken near Station A Sept 2008-July 2009. Velocities are given in mm/s (unpublished data from Monismith et al).

The average velocity components of the currents during January 2009 are plotted as a function of depth in Figure 2-40. The speeds are generally quite weak, ranging from +5 cm/s to -5 cm/s, with maxima observed at the shallowest and deepest levels. The magnitude of the surface flow is northwestward and gradually decreases with depth until reaching zero at a depth of approximately 150 m. After 150 m, the flow reverses direction towards the southwest and gradually increases with depth.

The average currents are weaker during June 2009 and the depth profile reveals a more complex flow than observed in January (see Figure 2-41). The east-west component of the flow (U) is negative or nearly zero at all depths. The maximum magnitude of U (-1.5 cm/s) occurs at approximately 50 m. The profile of the north-south component of the flow (V) suggests the presence of a two-layer flow. The upper 100 m appears to flow to the north with a return flow to the south below.

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Figure 2-40 The average east-west (U) and north-south (V) velocity components during the month of January 2009 are plotted with depth.

Figure 2-41 The same as above, but for the month of June 2009.

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Finally, in addition to internal tides, there also appears to be a vigorous internal wave field in the Gulf (as there is in any stratified water body). Using data from a short term deployment also made in summer 2008, Steinbuck et al (in prep.) show how this short period internal wave field can contribute to dispersion at scales of O(km). Figure 2-42 shows an example of temperature records at various depth between the surface and 400 m taken in from of the IUI during September 2008. While it is clear that the dominant waves are tidally driven, with an amplitude of few tens of m, higher frequencies are also clearly seen.

Figure 2-42 Temperature records at various depth between the surface and 400 m.

2.1.3.4 Upwelling and downwelling

In the Gulf of Aqaba, the northeasternmost segment of the Red Sea, phytoplankton blooms are more intense than in other oligotrophic regions (e.g., the Sargasso Sea). Multiyear in situ (1988-2000) and Sea viewing Wide Field of View Sensor (SeaWiFS) (1999-2001) chlorophyll a (Chl a) data were used to describe the dynamics of phytoplankton biomass throughout the Gulf of Aqaba (Labiosa et al. 2003). The temporal pattern of phytoplankton biomass in the Gulf of Aqaba includes a strong spring bloom and a somewhat weaker autumn bloom, the length, intensity, and timing of which vary from year to year. In addition, highly positive west-to-east (W to E) gradients in Chl a were found throughout the Gulf of Aqaba. A corresponding negative gradient in sea surface temperature (SST)

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obtained from MODerate resolution Imaging Spectroradiometer (MODIS) in 2001 indicates that the gradient of chlorophyll a across the Gulf of Aqaba is an outcome of an Ekman-driven upwelling along the eastern side. Calculations of the upwelling and convective fluxes that are based on meteorological data from Eilat, Israel, indicate that upwelling is comparable to or exceeds convection during much of the year. The Authors present a conceptual model demonstrating how upwelling and convection can either support or oppose each other, thereby jointly controlling mixed-layer depth and the development of phytoplankton blooms. Coastal upwelling plays a larger role in controlling phytoplankton dynamics than was previously thought, and it explains much of the observed spatial and temporal variability in phytoplankton distributions.

A cross section of CTD casts in the northern tip of the Gulf of Aqaba was done on March 6th 1999 during R/V Meteor cruise 44/2 at five stations (s1, s2, s3, s4, and s5) distributed on the latitude line 29.41° N between the east and west coasts. Figure 2-43 shows the distribution of the potential temperature (θ) on the cross section in the northern part of the Gulf of Aqaba. The well mixed surface water was separated from the deep-water by a pycnocline in about 450 m depth. Weak horizontal and vertical gradients were observed. The differences of potential temperature were 0.37 °C horizontally and 0.63 °C vertically. The vertically and horizontally difference of salinity was 0.05 PSU (Figure 2-43b). This indicates that the water mass in the northern part of the Gulf of Aqaba was rather homogenous during the period of February 21st to March 7th 1999. The potential density (σθ) in Figure 2-43c shows a value range between 28.75-28.91 kgm-3. The pattern observed in θ and σθ in the pycnocline suggests upwelling at the eastern coast and downwelling at the western coast. Such a pattern would in general be associated with a southward directed geostrophic circulation trapped at the shores. Moreover, Figure 2-43c shows in the eastern part a downward shape of the density, σθ, in the upper 300 m and the upward bent shape near 500 m depth. This suggests a northward current in upper 300 m, and a southward counter current below the surface current. This is consistent with the directly observed current patterns, Figure 2-23, as deep as the ADCP ranges.

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Figure 2-43 Cross section distribution of the potential temperature θ (°C), salinity S (psu) and potential density σθ (kgm-3) in the northern Gulf of Aqaba on March 6th 1999, R/V Meteor cruise 44/2.

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2.1.3.5 Results from numerical modelling

Early three dimensional modelling studies of the GOAE (e.g., Berman et al., 2000; 2003) were designed to isolate and focus on the roles of particular forcing mechanisms such as the wind or tides. Consequently these studies were idealized and did not include the full variability of the various forcing functions. They also used a relatively coarse grid spacing of ~ 1.5 km which is barely sufficient to resolve the larger scale features of the circulation. Through such an approach Berman et al. (2000) were able to show that the large scale circulation of the gulf consists of a series of gyres aligned along the north-south axis of the gulf. The location and size of these gyres are determined primarily by the geometry of the coastline and the bathymetry. The seasonal stratification also influences the diameter of these gyres and thus may explain the observed seasonal reversal of the currents measured near IUI. An example of their results for the spring season is shown in Figure 2-43. This overall structure of the gulf wide circulation was later confirmed by the current measurements (ship mounted ADCP) conducted by Manasrah et al. (2006) as shown above in Figure 2-44.

Figure 2-44 Simulated wind driven free surface height (m) and average currents in the upper 50m for the spring season (from Berman et al., 2000).

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Similarly by adding tidal forcing Berman et al. (2003) were able to explain the winter disappearance of the M2 tidal harmonic in the observed currents near IUI. Nevertheless in both cases the simulated circulation was much steadier than the observed flow since the forcing used in these simulations did not include the full spatial and temporal variability, and the model grid was relatively coarse.

More recently, Brenner and Paldor (2004) increased the spatial resolution of the model used by Berman et al. (2000; 2003), incorporated a more realistic bathymetry, and added a passive tracer advection capability to assess the effects of mariculture on the gulf. These results confirmed the structure of the gulf wide consisting of a series of gyres aligned along the length of the gulf. In addition they showed a clear pattern of simulated upwelling along the eastern edge and downwelling along the western edge of the gulf as shown by the 10 m temperature fields for summer and autumn in Figure 2-45. This upwelling/downwelling pattern was found in the satellite images of sea surface temperature and chlorophyll a analyzed by Labiosa et al. (2003) as noted in the previous section. While these results refined the previous results, the resolution was still too coarse to adequately assess the potential impacts of water abstraction and the forcing still did not contain the full temporal variability.

Figure 2-45 Simulated temperature and currents at 10 m in summer and autumn (from Brenner and Paldor, 2004).

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Finally, Biton et al. (2008) ran a very high resolution (75 m grid) model to study the evolution of density currents in the northern gulf as discussed above. However these simulations focused on a particular process and were limited to a five day period in winter. Thus the results currently available from modelling studies are inadequate to address the potential impact of the proposed water abstraction from the gulf. It is for this reason that we have proposed to apply a series of nested models with progressively increasing resolution for this study.

2.1.3.6 Summary

Existing measurements of currents show the importance of meteorological forcing (winds and evaporation) as well as tides, both interacting with the unique topography of the Gulf, to drive flows in the Gulf. In terms of the evaluating the effects of a proposed RDC, what stands out is the importance of understanding the baseline and dynamical processes, which are currently limited due to the scarcity of data and theoretical models. In addition the forcing must also be known, in particular the forcing at the southern end of the Gulf, both in terms of mean salinity and temperature structure, as these affect the thermohaline circulation and internal tide generation at the sill in the Strait of Tiran. Moreover, given the energetic nature of the internal tides, their interaction with the intake-induced flow is likely to be significant.

2.1.4 Water quality and ecological conditions of water body

The shores of the GOAE are lined with well developed fringing coral reefs, which have grown successfully despite the high latitude of the Gulf relative to where coral reefs are typically found. These reefs are likely one of the most important components of the Gulf’s ecological system. They provide recycled nutrients that support open water productivity (Erez, 1990; Silverman et al., 2007a), provide a food source and together with sea grass habitats, they function as nurseries for many pelagic species. Both coral reefs and sea grass meadows are very susceptible to changes in water quality especially in the GOAE considering that these habitats experience over an annual cycle naturally occurring large variations in environmental conditions such as temperature, light penetration, aragonite saturation and nutrient levels (Silverman et al., 2007b). Seemingly small changes in water column density structure associated with Red Sea water abstraction, external nutrient input, increase in total suspended solids and reduction in light penetration (in the vicinity of the abstraction site) could have detrimental effects on both coral reefs and sea grass meadows. Deterioration of these habitats can conceivably affect the well being of the entire ecological system of the Gulf.

The waters of the GOAE are generally considered to be oligotrophic and have been characterized as mildly productive with an annual average primary production of 80 g C·m-2·yr-1 (Levanon-Spanier et al., 1979). This state reflects the lack of regular supply of nutrients to the surface layer of the GOAE (Lazar et al., 2008). Throughout the annual cycle the supply of nutrients to the surface layer of the GOAE is very low accept during the winter. The shallow sill (~250 m) at the Tiran Strait separating between the GOAE and the northern Red Sea allow only warm nutrient poor surface water to enter the Gulf (Reiss and Hottinger, 1984). Additionally, nutrient supply through terrestrial surface runoff is limited to one or two flood events per year during the winter. More recent studies have shown that the deposition of dust transported from nearby sources and subsequent biological fixation of nitrogen

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acts as a significant nutrient source to the Gulf (Richter and Abu- Hilal, 2006), while others showed no significant N-fixation at the northern part of GOAE (Hadas and Erez, 2004, IET Report).

Most of the available water quality data was obtained from past and ongoing monitoring programs (Table 2-6), while the knowledge base for interpreting this data was obtained from available scientific literature some of which has been cited in the text. Location of monitoring stations is shown in Figure 2-46.

Dissolved inorganic nutrients

Stratification of the water column during the summer months (April-November) prevents recycled nutrients from the deep reservoir (<250 m) to enter the photic zone that accumulate there (Figure 2-47). As a result the surface layer concentrations of inorganic nutrients, particularly nitrogen and phosphate, in the GOAE are especially low during summer (<0.05 and <0.01 µmol/l, respectively) (Al-Qutob et al., 2002; Rasheed et al. 2003; Silverman et al., 2007b). However, during winter, deep convective mixing (>250 m) in the GOAE results in nutrient enrichment (2-3 orders of magnitude) of the open and coastal surface water (Rasheed et al., 2002; Manasrah et al. 2005; Silverman et al., 2007b; Lazar et al., 2008). This enrichment supports phytoplankton and benthic macro-algae blooms, which have a detrimental affect on the coral reefs lining the coast of the GOAE (Figure 2-48, Genin et al., 1995; Silverman et al., 2007a). In addition, high nutrient levels also cause decrease the net CaCO3 deposition rates by corals possibly resulting from an increase in CaCO3 dissolution as a result of increased boring organism activity (Lazar and Loya, 1991; Glynn, 1997; Silverman et al., 2007b) or a decrease in CaCO3 deposition rates in corals (Kinsey and Davies, 1979; Marubini and Davies, 1996).

During summer stratification the upper ~100 m of the water column are almost completely depleted of inorganic nutrients (e.g. Figure 2-47) and below this level a nutricline (Reiss and Hottinger, 1984; Badran et al., 2001; Lazar et al., 2008) develops indicating the threshold between nutrient uptake by primary production in the photic zone and the supply of recycled nutrients from deep water through diapycnal mixing. Above the bottom at station A there is an additional nutricline indicating the flux of recycled nutrients from the sediments (Figure 2-47). This pattern of repletion and depletion during summer stratification below 100 m depth in the GOAE is typical of nitrate, phosphate and silicate. Whole water column (0-725 m) inventories of nutrients show variations which are associated primarily with the winter deep mixing (e.g. Figure 2-49). These parameters have been measured in the open and coastal water by both the Israeli and Jordanian National monitoring programs for the last 10 years on a monthly basis. Prior to this period measurements were made for discontinuous periods of time in the framework of scientific projects (see Table 2-6).

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Table 2-6 Available data bases on water quality for use in this study.

Data type Source/Location Period of

measurement Parameters measured

Water Quality

Eilat coastal sampling stations (/From RSMPP and INMP (1999-2002, 2003-2010)/Only surface water sampled

1999 - 2010 Sal, DO, pH, AT, NO2, NO3, Si(OH)4, PO4, Chl_a, Secchi depth, Temp

Eilat Station A1/From DCP (1975-1977), REEFLUX (1989-1991), RSP (1996-1998), RSMPP (1999-2002) and INMP (2003-2010) data bases/vertical profile measurements

1975-2010

Sal, DO, pH, AT, NO2, NO3, Si(OH)4, PO4, Chl_a, Temp, PAR, fluorescence, Pico-plankton, PP (14C)*

Eilat Stations FF and OS/From RSMPP (1999-2002) and INMP (2003-2010)/vertical profile measurements

1999-2010

Sal, DO, pH, AT, NO2, NO3, Si(OH)4, PO4, Chl_a, Temp, PAR, fluorescence, Pico-plankton, PP (14C)*

INMP/Jordan station B1 2003-2010

Sal, DO, pH, AT, NO2, NO3, Si(OH)4, PO4, Chl_a, Temp, PAR, fluorescence, Pico-plankton, PP (14C)*

JNMP/Jordan Reference Offshore Station 2003-2010

Sal, DO, pH, Temp, Sig T, NO2, NO3, NH4, Si(OH)4, PO4, Chl_a, Entereococcus, HC

JNMP/Jordan Coastal Stations 2003-2010

Sal, DO, pH, Transparency, Temp, Sig T, NO2, NO3, NH4, Si (OH)4, PO4, Chl_a. Entereococcus, HC

J-Industrial Complex Monitoring Program-South Boarder 2003-2010

Sal, DO, pH, Transparency, Temp, Sig T, NO2, NO3, NH4, PO4, SO4, F, TN, TP

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Figure 2-46 Northern GOAE shoreline with sampling stations that are sampled by the Israeli (blue) and Jordanian (green) national monitoring programs at the surface (empty circles) and vertical profiles (filled triangles) on a monthly basis from 1999-2010.

Figure 2-47 Vertical profiles of nitrate (NO3

-1) and density calculated as a function of salinity and potential temperature (θ) in sigma units measured a station A on a monthly basis during 2005.

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Figure 2-48 Benthic macro-algae bloom smothering acropora coral head in the northern GOAE during winter of 2000. Under such conditions corals may suphoccate and die. In 1992 an exceptionally deep mixing event occurred resulting in a benthic macro-algae bloom and large scale mortality of coral in the Eilat reef (Genin et al., 1995). Picture was taken by D. Zakai.

Figure 2-49 Changes in whole water column (0-725 m) NO3 inventories during 2004-2009 at Station A (INMP Report).

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Some recent records of the monthly average total phosphate and organic nitrogen concentrations in the seawater of the Gulf of Aqaba are shown in Figure 2-50. Total phosphorus and organic nitrogen concentrations showed rather irregular month to month variations. Concentrations of these two species are associated with dissolved and particulate material, which can be either living or non-living. Concentrations are difficult to predict because they can be of either biogenic or anthropogenic origin.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

TN  (mg/l)

Total Nitrogen

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

TP  (mg/l)

Total Phosphorus

Figure 2-50 Concentrations of total nitrogen and total phosphorus (mg/l) in the water of the Gulf of Aqaba – southern Jordanian area – in 2009.

Chlorophyll a

Chlorophyll a concentrations and primary productivity have been concurrently studied by Levanon-Spanier et al. (1979). The authors presented an annual cycle of the two parameters during 1976-1977 based on monthly measurements between the surface and 200 m in the north-western section of the Gulf. Phytoplankton succession has been studied by Kimor and Golandsky (1977) and more recently by Lindell and Post (1995) including the pico-fraction. Studies that included chlorophyll a concentrations along the eastern coast of the GOAE were mostly restricted to coastal waters along the Jordanian coast or had temporal resolutions of 2-3 months (Leger and Artiges, 1978; Natour and Nienhuis, 1980; Mahasneh, 1984; Wahbeh and Badran, 1990; Badran and Foster, 1998; Richter et al., 2001; Rasheed et al., 2003; and Niemann et al., 2004). Badran et al. (1999) and Rasheed et al. (2002) reported significantly higher nutrient and chlorophyll a concentrations in coastal coral reef waters as compared to water column waters just 3 Km offshore. This observation was supported by the results of a study conducted by Labiosa et al. (2003) who showed that upwelling of nutrient rich water along the eastern coast of GOAE resulted in an apparent cross-shore gradient in chlorophyll a

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concentrations. This was demonstrated Using SeaWIFS and MODIS imagery, however no direct measurements of upwelling have been made to prove this theory conclusively. From long term records of chlorophyll a concentrations in the open water of the northern GOAE measured by the Israeli National Monitoring Program at station A it is evident that surface water concentrations vary between a low value of 0.03 μg/l during summer and 0.87 μg/l during the onset of stratification at the end of March and beginning of April (Figure 2-51). During the summer months the water column is stratified and a typical deep chlorophyll maximum (DCM) develops at 60 – 100 m depth near the limit of light penetration and close to the deep nutrient reservoir below the base of the thermocline (250 m). Unlike surface concentrations, which are very low during the stratified season (O 0.1 μg/l), the concentration of Chlorophyll a at the DCM is relatively constant at 0.36 ± 0.10 μg/l. Nonetheless, the depth integrated concentration of chlorophyll a is greater by a factor of 2 Dec-Feb than the summer months Jun-Oct (Stambler, 2006).

0.0

0.2

0.4

0.6

0.8

1.0

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Chl

orop

hyll

a ( μ

g/l)

Figure 2-51 Successive annual cycles of chlorophyll a measured in the 0-10 m surface layer from 1999 to 2010 on a monthly basis at station A (see station location in Figure 2-46).

Microbiological parameters: Enterococcus

Enterococcus in the Jordanian water was mostly not detectable except on the northern station at Tourist sites and Port sites (Table 2-7, Figure 2-5). Enterococcus was extraordinary higher in the middle Port and sometimes in the enclosed lagoon. The higher values at different stations might be caused by the livestock ship anchoring usually near Clinker Port or any uncontrolled discharge at different sites.

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Table 2-7 Enterococcus (mpn) in the surface offshore and coastal waters of the Jordanian sector of the Gulf of Aqaba, Red Sea, during 2009. Data from Jordanian National Monitoring Program.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Northern Boarder <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10

Enclosed Lagoon-North <10 <10 <10 <10 <10 20 20 42 42 75 20 75

Middle Port 20 10 10 82 10 10 60 75 <10 80 48 20

Marine Science Station <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10

South Region <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10 <10

Fluoride and sulphate

Records of the monthly average fluoride and sulphate concentrations in the seawater of the Gulf of Aqaba are shown in Figure 2-52. Fluoride and sulphate are two conservative species, their concentrations are not affected by the biological productivity. The values of fluoride and sulphate concentrations were usually in the normal range. Also the concentrations of the two species showed in 2009 only minor variations from one month to another.

2.84

2.88

2.92

2.96

3.00

3.04

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Sulpha

te (g/l)

Sulphate

0.00

0.40

0.80

1.20

1.60

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Fluoride  (m

g/l)

Fluoride

Figure 2-52 Concentrations of sulphate (g/l) and fluoride, total in the water of the Gulf of Aqaba – southern Jordanian area – in 2009.

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Dissolved trace metals and organic pollutants

Concentrations in seawater at representative sites near potential pollution point sources and the coral reef along the Israeli coast of the GOAE were measured in 2002-2004 (Herut and Halicz, 2004). The concentrations of all metals were very low, in the ppt/sub-ppb range, and all below Israeli standard for water quality. The results revealed low levels (below the analytical detection limits) of volatile organic compounds (<0.5 ug/L), PAHs (<0.1 ug/L), PCBs (<0.3 ug/L), and chlorinated pesticides (<0.03 ug/L, measured in 2002 only). However, significant, but low concentrations of tributyltin (TBT) and its degradation products) were detected in the Port of Eilat and marinas on the Israeli side of the GOAE.

Organochlorine pesticide concentrations in water of the Gulf of Aqaba (Table 2-8) were found to be very low ranged from below detection limit to 0.539 ug/kg (Al Masri et al. 2009).

Table 2-8 Organochlorine pesticides concentrations (µg/kg) in the water of the Gulf of Aqaba.

Organochlorine Pesticide

HCB Heptachlor Aldrin p,p’ - DDE p,p’ - DDD p,p’ - DDT β-HCH

Conc. ug/kg <d.l 0.001 <d.l <d.l <d.l 0.539 0.201

Spatial changes were found in the concentration of the total hydrocarbon (THC) in the Gulf of Aqaba (Rasheeed et al. subm.). The concentrations of THC in water were generally low (less than 0.01 mg/l) except in the water of enclosed tourist lagoons that used for yachts and boats parking (average 0.02 mg/l).

Light penetration

The depth of light penetration limits how deep a reef will grow because of the association between endosymbiotic algae also know as zooxanthellae and their coral hosts. Under poor light conditions corals aren’t able to sustain their energetic demands, which are provided for by photosynthates of their algal symbionts. In the GOAE the average depth of maximum light penetration calculated according to equation 1 following Kleypas et al. (1999) and using measurements made over a three year period (1993-1996) in the GOAE of Iluz (1997) is 40 m (Silverman et al., 2007b). The minimum and maximum depths are 10 m and 70 m, respectively. These values are very similar to those reported by Kleypas et al. (1999) for oceanic waters inhabited by coral reefs.

( )1 ln

490

min

KPAR

PAR

Z noonnoon

⎟⎠⎞⎜

⎝⎛

=

Znoon – Depth of maximum light penetration, m

PARmin – minimum PAR necessary for reef growth, 250 μE·m-2·sec-1 (Kleypas et al., 1999).

PARnoon – maximum daily PAR at sea surface, μE·m-2·sec-1.

K490 – diffuse extinction coefficient of light (λ = 490 nm), m-1.

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Light field measurements made at station A during 1996-2000 on a monthly basis indicated that the euphotic zone depths (1% of light at surface) varied between 80 and 115 m (Stambler, 2006). Regular measurements of Secci depth and PAR in the coastal and open waters of the northern GOAE have also being made on a monthly basis the by national monitoring programs of Jordan and Israel since 2000.

Carbonate chemistry

It has been shown that the degree of aragonite saturation (Ωarag) also limits the latitudinal distribution of coral reefs (Kleypas et al., 1999) by limiting the rate of CaCO3 deposition in corals (e.g. Langdon and Atkinson, 2005; Schneider and Erez, 2006). Thus, a coral will calcify at an increasing rate as Ωarag increases and visa-versa. Since [Ca+2] is relatively constant in the oceans it could be said that Ωarag is actually a measure of the carbonate ion concentration ([CO3

-2]) according to equation 2. Where, Ksp-arag is the apparent solubility product for aragonite that is the mineral deposited by corals. The coral reefs in the GOAE are considered to be relatively high latitude reefs, i.e. at the northern latitudinal limit of coral reef distribution globally. However, since the Gulf is a terminal basin with high evaporation rates, the water is relatively saline (average ~40.7 PSU) compared to other oceanic regions inhabited by coral reefs (~35 PSU) resulting in comparatively high total alkalinity (~2500 μmol/kg). Therefore, the carbonate ion concentration is also relatively high. The average Ωarag in GOAE based on two years of measurements (2000-2002) on a monthly basis in the nature reserve reef, Eilat was 4.0 (Silverman et al., 2007a). The minimum and maximum Ωarag values for this period were 3.7 and 4.4, respectively. These values are somewhat higher than the corresponding values for the global distribution of coral reefs (min = 3.3, mean = 3.8, max = 4.1) defined by Kleypas et al. (1999).

[ ] [ ] ( )2 2

32

aragsparag K

COCa

−+ ⋅=Ω

Silverman et al. (2007) also showed that Ωarag varied seasonally with temperature and productivity in the adjacent open sea (Figure 2-53). More importantly this study showed that the rate of net calcification (Gnet) of an entire reef was well correlated with ambient Ωarag demonstrating the importance of this parameter in assessing the water quality in coral reef environments.

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Figure 2-53 Daily average degree of aragonite saturation in the nature reserve reef in Eilat plotted against daily average temperature. Filled data points indicate measurements made during open sea water column stratification (nutrient depletion) and empty markers indicate measurements made during open sea water column mixing depth >250 m (nutrient repletion). Note the positive correlation between Ωarag and temperature for nutrient deplete conditions. Under nutrient replete conditions productivity offsets the expected reduction in Ωarag with temperature due to increased uptake of CO2.

Total alkalinity reflects the concentration of dissolved minerals in seawater and therefore should be conservative with salinity, i.e. as salinity increases total alkalinity should increase linearly and visa-versa (Brewer et al., 1997). In the GOAE total alkalinity is generally lower than the calculated value as a function of salinity using the relations developed by Brewer et al. (1997) indicating that the entire Gulf is a net sink of Alkalinity, i.e. deposition of CaCO3 (Figure 2-54). This is in agreement with the fact that there are many calcifying organisms in the GOAE primarily coral reefs, which reduce total alkalinity below conservation with salinity by precipitating their CaCO3 skeletons. Measurements made at station A from 1989 to 2010 indicate that total alkalinity in the northern GOAE is increasing over time, getting closer to conservation. This could be the result of a number of processes: 1) reduction in calcification due to ocean acidification (e.g. Silverman et al., 2009). 2) Increase in dissolution of CaCO3 in the deep water of the Gulf due to organic loading (see below). 3) Increase in salinity – values are not normalized to constant salinity.

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2.35

2.40

2.45

2.50

2.55

2.60

2.65

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

AT (m

mol

· kg

-1)

Figure 2-54 Total alkalinity measured at station A at discrete depths ≤20 m (red squares) and ≥200 m (blue diamonds) from 1989 to 2010. The dashed line indicates the value of total alkalinity calculated as a function of average salinity in the GOAE (40.7 PSU) using the relation between total alkalinity and salinity developed by Brewer et al., 1997 (AT = 703.7 + 45.785 * 40.7 = 2567 μmol/kg).

2.1.4.1 Coral reefs effects on water quality

Coral reefs on the Jordanian and Israeli side of the GOAE have been shown to recycle particulate organic matter imported from the open sea into biologically available dissolved inorganic nutrients (Richter et al., 2001; Silverman et al., 2007a). Rasheed et al (2003) have also shown rapid recycling in carbonate sediments associated with the coral reef. Badran et al. (2001), Rasheed et al. (2002) reported significantly higher nutrient and chlorophyll a concentrations in coastal coral reef waters as compared to water column waters just 3 Km offshore (order of magnitude during summer). Silverman et al. (2007) showed that the reef is actually a source of dissolved nutrients for open sea productivity during the summer, while during the winter it is a sink (Figure 2-55).

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Figure 2-55 Net production estimated from the diurnal cycle of NO3

-1 (Pn-N) in the fringing reef at the Coral Beach Nature Reserve on the western side of the Gulf plotted against the open sea (1 km offshore) NO3

-1 concentration for all studies conducted between 2000-2002. The black line indicates the calculated linear trend and the dashed lines indicate the boundaries of the 95% confidence interval. Positive values indicate that the reef is a source of dissolved nutrient and negative a source. During winter mixing nitrate levels in the open sea are high. During the stratified summer nitrate levels in the open sea decrease to <0.1 μM.

2.1.4.2 Long term trends in water quality of the northern GOAE

During the 1970’s a significant productivity gradient with increasing oligotrophy towards the north was observed from the Tiran Strait to the north end of the Gulf (Levanon-Spanier et al., 1979; Reiss and Hottinger, 1984). During the early 2000’s an increasing nutrient reservoir in the deep water and decreasing oxygen concentrations observed in both the deep and surface layers of the northern Gulf were thought to be caused by fish cages nutrient loading (Fig. 9, Lazar and Erez, 2004; Lazar et al., 2008), or alternatively have been increasing with time, as part of a natural “cycle” (Figs. 3, 9, 10; Herut and Cohen, 2004; Atkinson et al, 2004, IET Report). Specifically, the frequency of deep mixing events and the interaction between deep convective mixing and the horizontal circulation (Herut and Cohen, 2004; Silverman and Gildor, 2008). The frequency of deep mixing events and the interaction between deep convective mixing and the horizontal circulation may be especially important in this context (Atkinson et al, 2004, IET Report) and have implications on the water quality variations in this area.

Deep water nitrate levels increased from a typical value of 4 μmol/l (early 1990’s) to 7 μmol/l in 2003-2004, while dissolved oxygen decreased from 180 μmol/l to 150 μmol/l. After the deep mixing of the water column during the winter of 2007 oxygen levels in the deep reservoir (Figure 2-56) increased almost to the levels observed in the early 2000’s while nutrient levels decreased. Silverman and Gildor (2008) showed using a box model of the entire Gulf that an increase of nutrient levels in the

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deep northern basin of the Gulf could occur as a result of nutrient loading into surface water at its northern end. Additionally, they also showed that the frequency of deep mixing events or lack thereof can result in deep water nutrient accumulation as well. Thus, while the residence time of water in the Gulf is ca. 9 months in the surface layer and ca. 8 years for deep water (> 250 m), nutrients have a residence time on the order of 10’s of years.

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Figure 2-56 Contour plots of Dissolved Oxygen, NO2, NO3

-1, SiO2, PO4-3, and Chl_a measured

at discrete depths at station A (in the middle of the GOAE, 10 km south of its northern shore) down to a depth of 750 m during the period 1999 – 2009 (including). The measurements were made within the frameworks of the Red Sea Marine Peace Park Monitoring Program (1999 – 2002) and the Israeli National Monitoring Program (2003 – to present). Sampling points are indicated by the black dots overlying the contour plot.

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The decrease in dissolved oxygen in the deep reservoir until 2005 (Figure 2-57) was accompanied by a decrease in pH indicating the production of CO2 due to recycling of organic matter through aerobic processes (data not shown). This decrease in dissolved oxygen also became apparent in the surface layer (Figure 2-58), which could only be explained by the decrease in the deep reservoir concentration since there was no significant warming. Consistent with the decrease in deep water pH and surface dissolved oxygen, surface water pH also decreased significantly until 2005 (Figure 2-59). This decline (ca. 0.1 pH units) is somewhat larger than the expected decline due to ocean acidification (Caldeira and Wicket, 2003) in this short period of time. This decline continues and is not offset by an equivalent increase in total alkalinity by dissolution of deep water carbonates it will causes a significant reduction in the carbonate ion concentration and Ωarag. This will cause a reduction in the ability of coral reefs in the GOAE to calcify and maintain their CaCO3 frameworks as shown by Silverman et al. (2007b, 2008).

Figure 2-57 Oxygen levels at different depths below the water surface at station A (see station location in Figure 2-46) in the GOAE from 2000 to the end of 2009 (INMP annual report, 2009). The trend in the dissolved oxygen concentration is mainly controlled by deep mixing events (~600-700m) occurred in 2000, 2005, 2007, 2008 and horizontal circulation, and not related to fish cages operation in the past.

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190

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89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09

Year

Dis

solv

ed O

xyge

n ( μ

mol

·L-1

)

ΔDO/Δt = -7 mmol · L-1 · 10 years-1

Figure 2-58 Dissolved oxygen concentration at the surface in station A from 1989 to 2009 indicating the long term decreasing trend. Note that the trend stopped around 2005.

8.14

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8.28

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8.32

1996 1996 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Year

pH(2

5°C

)

Figure 2-59 Long term record of pH measured at a constant temperature (25ºC) on samples of surface water from station A from 1996 to 2009. Since the pH was measured at constant temperature the decline reflects an increase in surface water CO2 concentration, which is consistent with the decrease in surface dissolved oxygen concentrations.