LSM3254_Lecture 6 Fundamentals of Oceanography

8/3/2019 LSM3254_Lecture 6 Fundamentals of Oceanography

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LSM3254 Ecology of Aquatic Environments

Introduction to marine biology +

Peter Todd


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aspects of:

ome s ory o mar ne researc .

The geography and geomorphology of the oceans,

formation.

The physical properties of the marine environment


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So whatis Marine

Biology?


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Some history

Pacific Islanders, Phoneicians, Chinese,, , , .


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Challenger: 1872 for 3 yrs. Published results in 50 volumes

.

US NOAA

4,717 new species The first systematic plot of currents and temperatures in the ocean A ma of bottom de osits - much of which still relevant An outline of the main contours of the ocean basins

The discovery of the Mid-Atlantic Ridge


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Geo ra h and eomor holo of theoceans

Sea water covers ~71% of the Earths surface

,Hemisphere).

How many oceans?


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Five! Three major oceans (Pacific, Atlantic, Indian) converge

n e area aroun e n arc c con nen e ou ernOcean). Also the Arctic Ocean smaller and shallower. Allthe oceans are interconnected.


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Continental shelf

Slopes from land to a depth of 100-200m

Makes up only 7-8% of total sea area

u g commerc a va ue:

- over 95% of landings of world fisheries- oil and gas are also exploited here


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Distribution of the worlds continental shelves.The seaward edges of these shelves are at an averagedepth of ~130 m.


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Ab ss Beyond the shelf the average depth is ~4000m

-,

Over half the globe lies below 4000m of sea

Permanently dark


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Submarine ridges

chain that has been found in all oceans, e.g. Mid-Atlanticridge (will explain formation later).

u mar ne pea s may rea e sur ace an orm

islands.

Trenches 7000m to 11,000m deep

Marianas Trench (discovered by Challenger II in 1951)explored by the US Navy in the submersible Triestein1960. They touched bottom at 10,912m (why has no onegone any deeper?).


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ross sect on o an ocean as n, s ow ng t evarious geographic features (not to scale)


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Plate tectonics and zones of


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General

s ruc ure othe earth


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Plate tectonics

Plates are bounded byridge and trenchsystems Seven major plates cover most of the planet

The rigid plates float and move on the underlying mantle

(convection currents) The movement of these plates over geological time is

responsible for the differing positions of the continents

DRIFT


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The plates move because the oceanic ridges are centers

o vo can c ac v y w ere new crus a ma er a s ormeand added to the crust.

A hi h n h l m v l r ll in i

directions, causing SEAFLOOR SPREADING (2-5 cm/yr)

NeMONeMO


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Seafloor spreading was proposedin 1960 by US geologist HarryHess (confirmed by Vine andMatthews in 1963).

the Atlantic Ocean was made upof strips, each being magnetizedeither normally or reversely.

These strips were parallel and

formed identical patterns on both.

The implication was that eachstrip was formed at some stage

magnetic field was polarized in acertain way.

Flips on average every 0.25m yrs, but

not happened since 0.7 m yrs ago!US Geological Survey


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The opposite occurs in the trench systems, where ther v r

adjoining plate, a process called SUBDUCTION.

Ocean crust is more dense (basalt) and so sinks under thecontinental rock (granite).

NeMONeMO


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Loc tion nd bound ries of the E rths l tes


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Rift valley

-Ridge


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Pangea, the ancient supercontinent of 200 million years

ago, was a s ng e an mass


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Zones of the marine environment

2 main divisions pelagic (open water) and benthic (sea bottom)

Divided horizontally into neritic (over the continental shelf)and oceanic (all other open water) zones.

EPIPELAGIC 0-200m (photic zone) EPI- = topPELGOS = sea

MESOPELAGIC 200-1000m (MESO- = middle)

BATHYPELAGIC 1000-4000m (BATHY- or BATHO- = deep) ABYSSOPELAGIC 4000-6000m (A-, without; BUSSOS, bottom.]

=and ruler of the nether world


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Zones of the marine environment


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Benthic

Divided into:

Littoral or intertidal zone (seashores)

Bathybenthic/archibenthic/bathyal zone = 200 to 4000m

=6000m

Hadal zone = >6000m


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Ph i l r r i


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Total amount of salt dissolved in seawater.

Measured in parts per thousand (number of grams of salt.

If 35 gm of salt left after evaporating 1000gm ofseawa er, sa n y s pp . 00

Sometimes, the unit of measurement used is PSU (Practical Salinity

n .


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Narrow ran e in the marine environment ~37C ran e

of about 145C in the terrestrial ecosystems). Varies north to south with changes in latitude and

vertically with depth.

Very important factor governing ocean currents, the

, .

e ept zone o most rap temperaturedecline is the thermocline


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Vertical distribution

of water temperatureand densit in 35salinity seawater. Thethermocline is the depth

temperature and densityrapidly change.


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Thermal stratification

12 14 16 18 20 22 24 26 28 30

)

50

100

EP

TH

(150

200

thermocline

D250

300 Persistent feature of tropical

wa ers350 Temperate waters in summer

months

Absent in polar waters


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Highest salinities at about 25N and S of equator where there is highevaporat on. quator a reg ons rece ve a un ant prec p tat on, so trop casurface waters approach the average salinity of the worlds oceans.


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GasesThe lower the temperature of seawater the greater the

solubility of gases

There is an oxygen minimumzone between 200-1000m in

the tropics).

Due to minimal mixing and

as aerobic bacterialdecomposition).

No photosynthetic activityand contact with theatmosphere to permitrenewal.

North Pacific


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Transparency of seawater Even in clear water

total radiationentering the surfaceis absorbed within

Light fails topenetrate due to:

Angle of light Degree of ruffling of

surface Turbidity of water

Light penetration is

photosynthesis


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1) Very turbidcoas a wa er

2) Moderately

Water

Water

NB The shift to

shorterwavelengths(bluer light) inclearer water.


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Average depth about 30m.

Semi-diurnal tides. Tidal range ~3m.

.

Good mixing throughout water column.

erma s ra ca on near causeway.

Good diversity of marine species and ecosystems.

Sea surface temperature range: 27 310

C.

Salinity range: 28-32ppt.


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Wind generated currents and waves

Major currentpatterns in

during southwestand northeast SWmonsoons.


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Fish palisade trap. Local term kelong

Floating fish farm (Changi)

Floating fish cages (St. Johns)


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Instead one of worldsbusiest harbours and thirdlargest oil-refining centre.

Oil refinery

onta ner port

Oil refiner


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a n mpacts

habitats replaced or eliminated, new livingcommunities develo where ossible.

Nutrient levels elevated promotes growth ofmarine plants and algae.

(marine life affected); smothers benthic.


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Coastal reclamation and modification

east coast reclamationartificial lagoon

dredgingdumping


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SPOT images. a) Singapore in 1973. b) Singapore in 1999., .


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Algal bed at Changi indication of nutrient

.


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Sediment mostly

rom re g ngand land


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Reduced lightenetration


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But, if you look hard enough!

Rocky shore (Labrador) Mangrove (Pulau Tekong)

angrove unge u o a es g t ouse ree

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LSM3254_Lecture 6 Fundamentals of Oceanography