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Page 1 of 2

OCE - CHEMICAL OCEANOGRAPHY

PD 98-1670 02/15/10

996000354

University of Hawaii

0016105000

2530 Dole StreetORS, Sakamaki D-200HONOLULU, HI 96822-2303

Redox dynamics resulting from chemical and physical fluxes in surficial permeable sediments

682,069 36 09/01/10

Oceanography Department

808-956-9225

205 Marine Science Building1000 Pope Rd.Honolulu, HI 96822United States

Brian T Glazer PhD 2004 808-956-6658 glazer@hawaii.edu

Francis J Sansone PhD 1980 808-956-8370 sansone@soest.hawaii.edu

965088057

Redox dynamics resulting from chemical and physical fluxes in surficial permeable sediments

The upper layers of nearshore permeable sediments are dynamic, active sites of intense redox cycling. Previous research and our preliminary results indicate that vertical redox oscillations in these sediments can be driven by biogeochemical or physical variability, or by episodic events such as severe storms and their associated terrestrial runoff. Further, it can be assumed that each of these forcings operate on different and distinctive time and vertical scales. We propose to calculate rigorous estimations of biogeochemical fluxes across the hyperactive sediment-water interface (SWI) of permeable sediments, and within the upper 10cm of the sediment, by coupling porewater velocity modeling with fine-scale real time physical (temperature across the SWI, and sediment ripple topography) and chemical measurements (in situ voltammetry, pH and Eh profiles). The research will couple cutting-edge in situ, fine-scale chemical and physical sensors, cabled observatory infrastructure and data handling, and pioneering numerical models of porewater motion. This highly interdisciplinary approach aims to provide detailed information on the role that permeable sediments play in biogeochemical cycles of nearshore sediments, and to elucidate the processes that modulate permeable sediment functioning. The Intellectual Merit of the proposed research focuses on its central goals of calculating the fluxes of redox-sensitive chemical species in surficial permeable coastal sediments, and understanding the transformations within the highly responsive “zone of reactivity” in the upper centimeters of these sediments. We aim to: (1) improve our understanding of the interaction between these active, carbon recycling sediments and the overlying water column; (2) examine in detail the temporal and spatial variability of key redox-reactive chemical species; (3) quantify the relative contributions of benthic photosynthesis, sand ripple position, currents and waves, and episodic organic loading events to redox oscillations; and 4) integrate fine-scale chemical measurements with porewater velocity modeling to calculate biogeochemical fluxes. Specifically, we hypothesize that: (1) centimeter-scale surficial transport in permeable sediments can be measured and modeled using temperature as a natural tracer; (2) redox-sensitive chemical species (O2, Fe2+, Fe3+

aq, FeSaq,H2S/HS-, Sx2-) important to biogeochemical cycling can be measured by solid-state in

situ voltammetry on spatial and temporal scales relevant to the porewater transport calculations, allowing calculated biogeochemical flux estimates for the upper centimeters of the sediment and across the SWI; and (3) temporal variability of porewater chemical concentrations, rates, and fluxes can be measured, and this variability can be linked to specific forcing mechanisms. The existing Kilo Nalu Nearshore Reef Observatory and its data acquisition and data dissemination systems provide an ideal facility for studying benthic boundary layer biogeochemistry: (1) it provides easily accessible power and high bandwidth communications for in situ instruments; (2) a wide range of physical oceanographic measurements important to this project are already being collected by the observatory; and (3) Oahu’s south shore has a wide and predictable variety of surface wave conditions and land-based inputs that impact the redox-sensitive biogeochemistry of its permeable sediments. The project’s Broader Impacts reflect the interdisciplinary nature of the research. Permeable sediments are important habitats for bottom fish, invertebrates, and other commercially important species, and our proposed research provides information that can be used to support the management of these habitats to help ensure their ecological health. Additionally, the PIs will participate in education and outreach programs to promote the public’s understanding of the key role that permeable reef sediments play in the recycling of carbon and nutrients in reef ecosystems. The project will also support the research of a post-doctoral fellow, an Oceanography graduate student, and a Global Environmental Sciences undergraduate.

1.0 INTRODUCTION 1.1 Importance of benthic boundary layer geochemistry We have selected nearshore permeable (sandy) carbonate sediments as a research site for investigating the coupling between biogeochemical redox cycling and physical-chemical forcing within the upper 20 cm of sediment and across the sediment-water interface (SWI). Traditional views held that sandy sediments were biogeochemically inactive due to low levels of organic carbon (Boudreau et al. 2001). However, interest in sandy sediments in coastal zones has been growing because of the potential sands have for high turnover rates of organic matter and rapid exchange with the overlying water column, driven by advective mass transfer (Viollier et al. 2003). There is growing consensus that sandy-sediment benthic boundary layer (BBL) processes are actually highly dynamic due to their rapid response to physical and biogeochemical forcing.

Sandy sediments act as a biological filter for water-column suspended organic matter that is cycled through the sediments due to pressure gradients established by benthic currents in the water column interacting with sand ripples and other bathymetric features (Shum and Sundby 1996; Huettel et al. 1996). This organic matter may travel several centimeters into the sediment making the organic matter available for rapid oxidation through respiratory activity (Lohse et al. 1996; Jahnke et al. 2000). This same forcing is likely also to flush out remineralized products, thereby enhancing the transport of dissolved oxygen and metabolites across the sediment-water interface (Haberstroh 1994, Falter and Sansone 2000).

Solute transport across the sediment-water interface and within the upper sediment that results from such hydrodynamic processes may be several orders of magnitude greater than that in diffusively controlled muddy sediments (Hebert et al. 2007). Thus, enhanced mixing or displacement of solutes within surficial sediments is important to consider for many reasons. For example, wave-forced nutrient input from the sediments to the otherwise oligotrophic overlying water may stimulate phytoplankton (pelagic and benthic) and/or coral production (Haberstroh 1994; Falter and Sansone 2000a). 1.2 Significance of distribution of redox-reactive biogeochemical species Redox-reactive chemical species are biologically important as nutrients, energy sources, and terminal electron acceptors. Microbes living at and below the sediment-water interface exploit fluxes of potential electron acceptors such as oxygen or sulfate to oxidize reduced organics (or reduced inorganics in the case of chemoautotrophy) during respiration. In aquatic systems, organic matter is oxidized using a predictable series of terminal electron acceptors, based on thermodynamically favorable reaction yield (Froehlich et al. 1979). Respiration occurs in all known natural aquatic environments, and subsequently at some depth it consumes all of the available oxygen, requiring organisms either to compete for incoming oxygen or switch to an alternate oxidant, such as nitrate. Such transitions are often marked with a shift in the microbial community, as well (Brune et al. 2000). This predictable stratification of oxidants often results in three distinct zones: (i) oxic (dissolved O2 >3uM), (ii) suboxic (dissolved O2 <3uM and sulfide < 1nM, and (iii) anoxic (no oxygen, often sulfidic) (e.g., Murray et al., 1995). These shifts in oxidant availability, and therefore the distribution of oxic-suboxic-anoxic zone boundaries, can have profound effects on nutrient (including Fe) bioavailability, and thus carbon cycling (e.g., Rozan et al. 2002).

1.3 Hydraulic effects on sediment geochemistry In fine-grained sediments and areas of low hydrodynamic energy, transport of dissolved species is dominated by diffusion or bio-irrigation. In permeable sediments, however, porewater advection can enhance transport several orders of magnitude relative to diffusion (Figure 1) (e.g., Janssen et al. 2005a, 2005b; Huettel et al. 2003, Falter and Sansone 2000, Hebert et al. 2007). In-situ dye injection

experiments performed at the Kilo Nalu Nearshore Reef Observatory have confirmed that dispersion coefficients are enhanced 2-3 orders of magnitude over molecular diffusion (Hebert et al. 2007). Other mechanisms, including the dynamics of localized pressure gradients associated with sand ripple formation and migration have also been proposed to explain increased rates of exchange between porewater and overlying waters (e.g., Figure 1; Shum 1996). Wave height, sediment permeability, and ripple slope all increase wave-induced pore-water advection, but little is known about how these hydrodynamic forces affect the distribution and fluctuation of oxic-suboxic-anoxic zone boundaries, and the consequent effects on biogeochemical cycling. Mounting evidence suggests that intense redox cycling on horizontal and vertical planes occurs, with extended O2 penetration at ripple troughs and focused anoxic porewater efflux at ripple peaks (Shum 1996; Precht and Huettel 2004).

Measured oxygen consumption rates in permeable sediments that rival those in fine grained sediments suggest strongly that a low organic matter pool in a permeable sediment does not imply reduced or absent biological activity (Huettel et al. 2003), but rather could imply that large mass fluxes of oxidants and metabolites could drive an active microbial community with high turnover rates, rapid mineralization, and low residence times (Rocha 2008). Our own preliminary research at the Kilo Nalu observatory reveals steep opposing gradients of oxidants and reductants in the porewaters of the upper 10 centimeters of sediment, supporting the prospect that permeable carbonate sediments act as a redox-intense filter during exchange with overlying bottom water (see preliminary results, Section 3, below). 1.4 Innovative analytical approaches The current project proposes to couple in situ voltammetry with an advanced suite of physical sensors and sophisticated modeling techniques to develop a unique characterization of in situ physical and chemical conditions, and to calculate fluxes within these sediments. Two significant challenges have limited measurement of chemical fluxes in these systems, thus restricting our understanding of their overall operations: (i) the ability to make in situ measurements of analytes on relevant spatial and temporal time scales, and (ii) the need for robust porewater transport characterizations. Traditional methods of determining speciation and concentration of analytes in seawater, porewater, and sediments have required either the retrieval of sediment cores or porewater samples for analysis, isolating the sample from the environment and producing temporally discrete samples. In recent years, in situ voltammetry has been successfully used to collect single-time-point redox analyte measurements in mid-Atlantic bays (Luther et al. 1998), salt-marsh sediments (Glazer et al. 2002), the Black Sea water column (Glazer et al. 2006a, 2006b), and hydrothermal vents (Luther et al. 2001, Glazer and Rouxel 2009), among other environments. Over the past three years, in close collaboration with Analytical Instrument Systems, Inc., we have successfully developed a next generation voltammetric analyzer capable of real-time or data-logging operation as part of the Kilo Nalu Nearshore Reef Observatory (Chen and Glazer, submitted). We propose coupling in situ voltammetry with an innovative strategy of quantifying porewater transport using a custom

Figure 1. Dominant sediment transport mode is dependent upon permeability (upper panel, from Huettel 2003). Sandy sediments have permeabilities >10-12 m2. Models predict that sediment ripples also effects porewater transport (lower panel, from Shum 1996).

miniaturized thermistor array emplaced within surficial sediments. The array will measure seawater and porewater temperature along two vertical profiles separated by a sediment ripple half-wavelength. Diurnal, episodic, and seasonal temperature changes in the overlying water column advectively propagate through the sediments, allowing temperature to be used as a natural porewater tracer. The main advantages of this method over previous fluorescent tracer methods are the capabilities to measure temperature (1) as a function of depth, (2) simultaneously under sand ripple crests and troughs, and (3) continuously for several months. 1.5 Cabled observatory infrastructure A cabled sensing/data acquisition network (e.g., Sansone et al. 2009) is ideal for characterizing geochemical and physical fluxes in the upper centimeters of permeable sediments under varying environmental conditions. Thus, all of our instruments will be connected to the Kilo Nalu Cabled Nearshore Reef Observatory (Figure 2), allowing for critical real-time interaction with instruments in order to optimize data collection. Additionally, our research will incorporate and complement existing observatory monitoring data (e.g., currents, waves, water column dissolved O2, T, S, shlorophyll fluorescence, turbidity, light).

The Kilo Nalu Reef Observatory was initiated in 2005 and supports an array of research activity that has been focused mainly on characterizing the physical environment of this sand/reef nearshore environment. The accumulated information on physical processes at this site, and the established observatory framework, make it an attractive venue for the coupled physical-biogeochemical study proposed here.

In many ways, this coastline represents an ideal setting for a study of permeable sediment biogeochemistry (Figure 2). The predominantly carbonate substrate provides a dynamic, highly permeable and biogeochemically active boundary. Close proximity to the deep ocean introduces regular exposure to offshore and sub-thermocline seawater, with variable physical forcing driven by surface waves, internal tides and mesoscale eddies (Eich et al. 2004; Lumpkin 1998; Flament et al. 1998, Sansone et al. 2009). Surface wave events have been shown to greatly enhance porewater-seawater exchange in these systems (Hebert et al. 2007), and such events are typically forecasted for Oahu’s south shore with nearly a week’s lead time. Kilo Nalu’s proximity to the University of Hawaii-Manoa campus, along with its work boats and regular field operations, makes it extremely convenient for conducting targeted studies of the coupling between physical forcing events and geochemical cycling. Furthermore, benthic fluxes are of particular importance in nutrient-depleted tropical reef systems (e.g., Herzfeld et al. 2008), giving strong scientific, environmental, and economic value to nearshore benthic boundary layer research.

The targeted 12-m site is characterized by a dynamic physical environment with significant waves, tides, winds and runoff contributing to local conditions. Primary wave forcing occurs in summer, associated with long period (14-22 s) swells from distant southern hemisphere sources, with typical significant wave heights of 2-3 m. Short period (6-8 s) swells from northeast trade winds can

Figure 2. Overview of the Kilo Nalu Observatory (http://www.soest.hawaii.edu/OE/KiloNalu/).   

also wrap around and provide weak (< 1 m) wave energy. More infrequently, local storms, characterized by strong south to west wind, can generate short period swells (6-12 s) of moderate height (1-3 m). 2.0 HYPOTHESES AND APPROACHES We propose to use innovative measurement technologies, ocean observatory science, numerical modeling, and conventional geochemical methods to calculate the fluxes of redox-sensitive chemical species across the sediment-water interface (SWI) of permeable coastal sediments, and to understand the biogeochemical transformations within the highly responsive “zone of reactivity” in the upper centimeters of these sediments. We plan a unique combination of subsurface temperature measurement, SWI morphology characterization, water column physical monitoring, and cutting-edge in situ electrochemical analytical techniques to produce interdisciplinary advances in our understanding of the biogeochemistry of permeable sediments.

Overarching Hypothesis: Coupling porewater velocity modeling methods with fine-scale, real time physical measurements (temperature profiles across the SWI, and sediment ripple topography) and chemical measurements (in situ voltammetry, pH, Eh profiles) will allow unprecedented estimations of biogeochemical fluxes across the hyperactive SWI of permeable sediments and within the upper 20cm of the sediment.

Hypothesis 1: Centimeter-scale surficial transport in permeable sediments at our nearshore 12m site can be measured and modeled using temperature as a natural tracer. Approach • Measuring temperature in surficial sediments: We will use recently developed vertical arrays of

centimeter-spaced thermistors to simultaneously measure temperature vs. depth at spatial scales of approximate sediment ripple half-wavelengths. Diurnal, seasonal, and episodic water-column temperature signals propagate advectively into the porewater, allowing quantification of water transport over a large range of temporal scales. The relative location of the array with respect to the SWI and ripple crests/troughs will be determined using downward pointing lasers, an altimeter, and a camera (see section 4.4 below).

• Modeling porewater velocity from heat transport: Shum (1992) and Webster (2003) modeled the advection and dispersion, respectively, of porewater in surficial permeable sediments. We have constructed a combined model and are uniquely positioned to validate models of transport in surficial permeable sediments with field data that span the necessary spatial and temporal scales. Key to the validation will be our ability to quantify temperature variation with depth across and below the SWI. Preliminary results indicate that transport decays exponentially with depth, with a typical e-folding scale of a few centimeters.

Hypothesis 2: Detectable concentrations of redox-sensitive chemical species (O2, Fe2+, Fe3+

aq, FeSaq, H2S/HS-, Sx

2-) important to biogeochemical cycling can be measured by solid-state in situ voltammetry on spatial and temporal scales relevant for coupling to porewater transport calculations, allowing calculated biogeochemical flux estimates across the SWI and within the upper centimeters of the sediment. We hypothesize that the oxic-suboxic boundary migrates diurnally with some modulation due to overlaying sand ripple phase. This migration will change gradients, affecting fluxes, and it implies that microbes attached to sand grains could experience a wide range of redox conditions on relatively short time scales.

Approach • In situ electrochemistry: We will deploy in situ voltammetric, Eh, and pH electrodes in a

combination of two strategies on time scales of days to week(s): (i) single-point microelectrodes vertically profiled across the sediment-water interface using an in situ micromanipulator, and (ii) a static array of voltametric microelectrodes at fixed intervals adjacent (mm’s) to the thermistor array. Preliminary thermistor array data suggest that advection dominates a region extending to at least 20 cm depth, also corresponding to the depth range previously observed to exhibit strong redox variability (Figure 5; Chen and Glazer, submitted).

• Coupled model: Concentration profiles will be combined with the validated transport model, enabling us to calculate biogeochemical fluxes as a function of depth and ripple position [flux (mol/m2/s) = conc (mol/cm3) * velocity (m/s)]. The divergences and convergences of these fluxes will be used to calculate the in situ production and consumption rates, respectively, of the measured chemical species. Thus, we are well positioned to determine the transformation rates and fluxes of the most important chemical constituents in the oxic-suboxic-anoxic transition zone of these very reactive sediments.

• Traditional geochemistry: Chemical species detected in situ can indicate dominant biogeochemical processes in the upper sediment (oxygenic photosynthesis, aerobic respiration, iron reduction, sulfate reduction, and iron-sulfur interactions), but not all species or redox couples of interest will be measurable at detectable concentrations in the upper 20cm. Thus, biogeochemical analyses will be performed on discrete samples of bottom water and porewater from oxic, suboxic, and anoxic zones to both complement and corroborate in situ measurements. Analyses using standard methods (see section 4.6 for details) will include photosynthetic pigments, dissolved Fe, dissolved Mn, and dissolved S-species. Sediments from each zone will also be collected for determining sulfate reduction rates.

• Validation using other methods: As part of the on-going studies at Kilo Nalu, J. Fram, G. Pawlak, and F. Sansone have been working with Unisense (Denmark) on an eddy correlation O2 flux measuring system (Berg et al. 2003) for deployment at Kilo Nalu. Furthermore, preliminary fluxes of O2 through the benthic boundary layer have been computed using water column O2 concentration gradients and turbulent diffusion estimates (Bandet-Chavanne 2008, Sansone et al. 2009). Continuing refinement of both techniques will produce measurements that will be available for complementing and corroborating our methods.

Hypothesis 3: Variability of porewater chemical concentrations, production/consumption rates, and fluxes can be measured, calculated, and modeled on relevant temporal and spatial scales, and this variability can be linked to specific biogeochemical or physical forcing mechanisms. Based upon preliminary results, we further propose that variability in dissolved oxygen due to sand ripple phase is greater than that due to the solar diel cycle, and that both mechanisms will be measurable and distinguishable by our approaches. Approach Targeted processes and associated time scales include:

• Benthic photosynthesis – Diel variability will be monitored by solar radiation data from the Kilo Nalu onshore meteorological station and a PAR sensor attached to a nearby SeaHorse platform that profiles the water column hourly. The diel signal of photosynthetically-affected water injected into the sediment should mirror the diel temperature signal that we will use to measure transport on this time scale. Under relatively quiescient current and wave conditions, we expect that benthic oxygenic photosynthesis will result in a localized subsurface oxygen maxima, that will be discernable from advected O2 resulting from water column primary productivity. Divergences in the O2 fluxes at these depths will provide an

estimate of net benthic oxygenic photosynthesis , and should yield gross photosynthetic rate measurements by comparing daytime and nighttime data.

• Ripple migration – Preliminary data indicate an average migration rate of a 1 ripple per day shoreward at our field site (ripples have ~20 cm wavelength, ~2 cm height). Ripple measurement techniques are described in detail in section 4.4 below.

• Currents – The M2 semi-diurnal tide dominates currents at Kilo Nalu, although the amplitude of the M2 tide changes on weekly to monthly scales. This M2 modulation is associated with a variety of processes including mesoscale eddies (J. Wells, pers. comm.). However, tidal currents near the bed are small compared to wave-driven velocities.

• Waves – Wave events from distant and local storms last several days, superimposed on seasonal modulation of wave energy (e.g., higher wave activity on Oahu’s south shore in summer than winter). Wave events are routinely forecasted (for surfing interests) with week-scale lead times, allowing for targeted instrument deployments and in situ experiments.

• Organic loading episodes – Organic loading will be monitored using real-time Kilo Nalu water-column turbidity and chl-a measurements over time periods of days to months. In situ measurements will be augmented by suspended particle measurement using conventional sampling, filtration, and CHN analyses.

3.0 PRELIMINARY RESULTS 3.1 Estimated porewater transport Preliminary results from a prototype miniTchain deployed in Fall 2009 show the water-column diel signal propagating down through 22 cm of sediment to the bottom buried thermistor as the water column warms from sunrise through mid-afternoon (Figure 3). The clear lag and decay of signal strength with depth indicate measurable porewater transport across the array on the scale of hours. Note that temperature increased with depth because of seasonal cooling of the sediments.

Our numerical model accurately simulates the temperatures measured by the miniTchain, demonstrating its usefulness for modeling porewater transport under similar time scales. The temperatures of the 10-thermistor column were

Figure 3. Temperature measured at and 6-22 cm below the SWI over 2 days.

Figure 4. Time-series of modeled porewater transport in sand with a moving ripple surface. Water parcels are color-coded to show initial depth (overlying seawater is white). Porewater exits through crests, while seawater enter through troughs.

modeled with an overall r2 of 0.97 for a 20-day period using measured water column temperature as the SWI boundary condition and assimilating time-series data on surface wave and sand ripple properties. The model also reproduces much of the diel variability, including the rate at which the diel signal propagates down through the sand.

In a summer 2008 experiment, fluorescein dye was released at ~10 cm depth and tracked fluorometrically at the release point and at four points located 1.4 cm above, below, offshore, and onshore of the release point (similar to Hebert et al. 2007); the released dye nearly always moved up and shorewards. By tagging porewater parcels in the velocity model with their initial depth (Figure 4), it is easy to see why the fluorescein dye rose and moved onshore, and why dye rise increased with benthic wave orbital velocity. If waves inject new water into the ripple troughs, then old porewater must leave the sand. Because there is no flow through the bottom or sides of the domain, transport of old porewater (and the dye tracer) in the upper sediment must be net upward. Dye, on average, moved onshore due to onshore ripple migration: dye moved towards crests that were migrating onshore. 3.2 Suboxic zone variability in permeable sediments During an instrument development project aimed at integrating voltammetry within a cabled observatory framework (Chen and Glazer, submitted), we collected a series of in situ voltammetric profiles across the sediment-water interface at the Kilo Nalu 12m site (see section 4.3 for details of technique and deployment). We detected considerable variability in both the distribution and concentration of oxygen and sulfide at different times of the year and on different days at approximately the same tidal and light regime (Figure 5). These preliminary data sets confirm: (i)

Figure 5. Discrete, remotely-acquired voltammetric microelectrode profiles from the Kilo Nalu 12m site. In each panel, the sediment-water interface is located at depth = 0. Error bars represent +/- 1 standard deviation of the mean for scans collected at a given depth (2<n<5). Data for the profiles were collected on 5/8/2008 at 13:00 (left panel), 9/16/2008 at noon (middle panel), 9/16/2008 at 16:30 (right panel). Heterogeneity in the profiles illustrate significant redox oscillation that could be attributed to a variety of factors including: (i) advection and physical forcing caused by currents and wave heights, (ii) differential pressure gradients associated with localized sand ripple migration, (iii) diurnal dissolved O2 variance associated with photosynthesis and respiration, and (iv) varying amounts or quality of organic matter delivered to the sediments.

intense redox cycling can occur within the upper centimeters of permeable sediments, resulting in steep opposing gradients of oxidants and reductants; (ii) the oxygen penetration depth and the sulfide onset depth can vary considerably over short time scales; and (iii) a well-defined suboxic zone, where no detectable overlap of oxygen and sulfide exists, is a potentially persistent feature of these permeable sediments. That oxygen and sulfide do not directly overlap is intriguing and suggests that other oxidants are involved in respiration reactions within the suboxic zone, as well as playing an important role in oxidizing the upward flux of sulfide. Transient signals of Fe(II), Mn(II), Fe(III) were all detected using the voltammetric method, and optimization techniques are being refined to lower detection limits (see section 4.3 for more details). 3.3 Estimates of oxygen consumption and biogeochemical fluxes Preliminary attempts at combining modeled transport (Figure 4) with chemical data (Figure 5) yielded a dissolved oxygen consumption flux of ~1 µmol/m2/s for Kilo Nalu sand (bulk mean), which is consistent with the published value of ~2 µmol/m2/s for a sandy river sediment (Berg et al. 2003). In the proposed research we will use this approach to calculate in situ rates and fluxes under crests and troughs as a function of depth, time, and solute concentration (see Hypothesis 2, above).  4.0 TECHNIQUES AND ANALYTICAL METHODS FOR PROPOSED WORK We propose to use exciting new technologies, ocean observatory science, and conventional geochemical methods to investigate the transport and transformations of redox-sensitive chemical species and nutrients within a “zone of reactivity” in the upper centimeters of permeable coastal sediments. We plan an optimal combination of discrete sampling with traditional wet chemistry, physical monitoring, and cutting-edge in situ electrochemical analytical techniques to produce cross-disciplinary advances in our understanding of the geochemistry and biogeochemistry of permeable sediments. In the following section, we describe components critical for making new measurements (modeling, temperature arrays, electrochemistry), details for making optimal deployments (static vertical arrays and mechanical profiling), integrated complementing and corroborating measurements (Kilo Nalu physical data and discrete sampling), and finally, details of how we intend to combine these methods to produce new estimates of biogeochemical fluxes and net in situ rates in these sediments.  4.1 Porewater velocity modeling We have developed a porewater transport model by combining models for porewater advection (Shum 1992) and dispersion (Webster 2003). We use the Shum (1992) model for the SWI pressure field, which is a function of ripple dimensions and surface gravity wave properties. Our model domain is between two ripple crests because there are no modeled lateral pressure gradients and thus no lateral flow under ripple crests. Ripples are assumed to be long and parallel to shore, which results in no alongshore flow. Porewater advection is calculated from the pressure gradients using continuity and Darcy’s Law. We employ a rectangular Cartesian grid mapped to the physical domain following Malarkey and Davies (2002). Advective flows are calculated in the Cartesian domain and then mapped to the physical domain based on methods in Shum (1992). Scalar dispersion in porewater with respect

Figure 6. Photograph of prototype miniTchain. The two columns of thermistors are perpendicular so the sensors sample one half a typical sand ripple wavelength from each other. Future models will not have an upward sensor so as not to disturb sand ripples.

to depth is from Webster (2003) and is a function of surface wave and sediment characteristics. The model assimilates SWI temperature, surface wave height and period, ripple size and migration, and SWI location measurements.  4.2 miniTchain Our prototype array includes 16 thermistors (0.002 oC accuracy, 0.4 Hz) attached to a stainless steel backbone (Figure 6). Each thermistor was potted at the end of a 10cm long cylindrical tine. The tines are long and thin so that any heat conducted along the backbone would be dissipated into the sediments before reaching the thermistors. Heat conduction was a concern because the thermal diffusivity of stainless steel is 25 times higher than the diffusivity of saltwater saturated sand. Each tine measures temperature in the water column. A column of five tines spaced 1.5 cm apart point laterally from the center of the chain. A second column, at right angles to the first, has ten tines with 1.5cm spacing between its top five tines and 2.0 cm spacing between its bottom five tines. The array and electronics package connected to it were custom-built by Precision Measurement Engineering (www.pme.com). To reduce noise, voltage was grounded to seawater through the array.

4.3 In situ electrochemistry Field techniques capable of making unobtrusive measurements are highly desirable for acquiring high-quality biogeochemical data. Likewise, high spatial and temporal resolution chemical and biological sampling is imperative to accurately define processes and biogeochemical characteristics of dynamic aquatic systems, such as the coastal ocean. Voltammetry is proving to be one of the more promising marine analytical techniques for quantifying redox couples because it allows for simultaneous measurement of several analytes in real time (Table I; e.g., Luther et al. 2008 for recent review). Using a three-electrode potentiostat, a voltage ramp is applied to the working electrode (i.e., Au/Hg electrode) versus a reference electrode (i.e., Ag/AgCl electrode). Current at the working electrode surface is simultaneously measured through a counter electrode (i.e., Pt electrode). Current is proportional to concentration (Figure 7), so analyte concentration can be calculated from current peak heights obtained in voltammograms using calibration coefficients established during laboratory standardizations.

The solid-state gold-amalgam (Au/Hg) electrode enables simultaneous voltammetric measurements of multiple redox species in situ (Brendel and Luther III 1995), and has recently been shown to also differentiate between varieties of sulfur species (Table I) (Rozan et al. 2000; Luther et al. 2001a). A key benefit to using voltammetry is the capability for collecting real-time, simultaneous measurements of dissolved O2, H2S, Mn(II), Fe(II), S2O3

2-, S4O62-, Sx

2-, S(0) and aqueous species of Fe(III) and FeS (Luther et al. 2001a; Konovalov et al. 2003; Glazer et al. 2006a, 2006b). Each redox species, if present at detectable levels, produces a current peak that can be discriminated from others in one potential scan from –0.1 V to –2.0 V (analogous to varying wavelength and measuring absorbance with spectroscopy, e.g., Figure 7). Because the voltammetric electrode scans a range of potentials, rather than constantly resting at a single potential, consumption of the chemical species measured is undetectable. At current detection limits, we may not resolve all species listed in Table I at our field site, however previous deployments have demonstrated the utility of simultaneously detecting oxygen and sulfide, and our preliminary data has revealed transient signals for Fe(II) and Mn(II), indicating the potential for our work to provide more insight into in situ cycling of Fe and Mn within the detected suboxic zones (e.g., Fig. 5).

We have had repeated success with deployments of in situ voltammetric electrodes and microelectrodes in environments ranging from coastal bays and salt marshes to hydrothermal vents (e.g., Luther et al. 2008, for recent review). In the past two years, we have worked with Analytical Instrument Systems, Inc. to make custom improvements and modifications to the in situ

electrochemical analyzer (ISEA), allowing for integration with cabled ocean observatories (e.g., Chen and Glazer submitted, Figure 5) and accommodating additional commercially-available sensors (e.g., oxygen optode, pH, Eh). We have deployed and tested the ISEA at Kilo Nalu for up to 20 continuous days, however the accessibility of Kilo Nalu allows for weekly (or even more frequent) visits to perform instrument servicing, remove biofouling, or replace failing sensors, as needed. The current proposed work is not dependent upon making deployments of individual solid-state voltammetric sensors for longer time scales than they have already been shown to be durable and stable (e.g., Chen and Glazer, submitted; Moore et al. 2009, Moore et al. 2007). Table I. Relevant electrode reactions at the Au/Hg electrode vs. the Ag/AgCl reference electrode. All data were obtained with a 100- µm diameter electrode. MDL = Minimum Detection Limit.

Ep (E1/2) (V)

MDL (µM)

O2 + 2H+ + 2e- H2O2 -0.45 2 HS- + Hg HgS + H+ + 2e- Adsorption onto Hg<-

0.62 HgS + H+ + 2e- « HS- + Hg ~ -0.62 < 0.1 S0 + Hg HgS adsorption onto Hg < -

0.60 HgS + H+ + 2e- « HS- + Hg ~ -0.62 < 0.1 Hg + Sx

2- « HgSx + 2e- adsorption onto Hg < -0.60

HgSx + 2e- « Hg + Sx2- ~ -0.62 < 0.1

Sx2- + xH+ + (2x-2)e- « xHS- ~ -0.62 < 0.1

2 RSH « Hg(SR)2 + 2H+ + 2e- typically more positive than H2S/HS-

2 S2O32- + Hg « Hg(S2O3)2

2- + 2e-

-0.15 10

S4O62- + 2e- 2 S2O3

2- -0.45 15 FeS + 2e- + H+ Fe(Hg) + HS-

-1.1 molecular species

Fe2+ + Hg + 2e- « Fe(Hg) -1.43 10 Fe3+ + e- « Fe2+ -0.2 to -0.9 molecular

species Mn2+ + Hg + 2e- « Mn(Hg) -1.55 5

The Au/Hg working microelectrodes are constructed by sealing a 0.1 mm diameter gold wire into commercially available polyethyletherketone (PEEKTM) tubing for water column deployments, or finely drawn glass or PEEK tubing for sediment profiling, using a two-part epoxy (Brendel and Luther 1995). The Au electrode surface then undergoes a series of sequential mechanical sanding and polishing steps with 400 grit sandpaper followed by diamond paste polishes and cloths (15, 9, 1, 0.25 micron). Then the highly smooth Au surface is electrochemically plated with Hg, and finally polarized in a 1 N NaOH solution at -0.9V DC for 90 seconds. We have had recent success investigating alternate techniques for building smaller scale, less labor-intensive electrodes through collaboration with microfabrication engineers and applying gold thin-film deposition techniques (Figure 8B). We intend to use previously-proven electrode contstruction techniques, as well as advance our in situ capabilities using thin-film deposition, specifically for building fine-scale static arrays (see section 4.4, Figure 8B).

Figure 7. Representative voltammograms of O2 calibration in seawater, (Glazer et al. 2004). Reduction of oxygen to peroxide at the electrode surface is measurable at -0.65V (Ep), or the half-height potential of –0.45V (E1/2), and subsequent reduction of peroxide to water at –1.67V (E1/2 = -1.35V). Current peak is proportional to O2 concentration (n = 8).

Counter (Pt) and reference (Ag/AgCl) electrodes, each of 0.5 mm diameter, are made in PEEKTM tubing. Linear sweep voltammetry (LSV), cyclic voltammetry (CV), or square wave voltammetry (SWV) is employed, scanning from -0.05 V to –2.0 V at a scan rate of 250-10,000 mVs-

1. Typically, a conditioning step of –0.9 V is first applied to remove any deposited Fe, Mn, or S-species (because none of these species are electroactive at this potential), followed by a second conditioning step at –0.05 V, to restore the electrode surface between scans (Brendel and Luther 1995). By holding an electrode’s potential at -0.9 V between scans, we have had success with avoiding sulfidic saturation of the Hg film. During preliminary deployments at Kilo Nalu biofouling has been light, and has had no observable confounding effect on electrochemical measurements, likely due to: (i) relatively oligotrophic Oahu coastal waters, (ii) physical abrasion of the sensors during sediment profiling and (iii) near-continuous voltage potentials applied to the working electrode Au/Hg surfaces.

 4.4 Active and static profiles across the sediment-water interface Because fluid transport changes with depth below the SWI and ripple phase, evaluating the temperature and geochemical data collected across and below the SWI requires precise and accurate measurement of the location of the SWI with respect to the sensors (thermistors and electrochemical, alike). We have tested two methods for resolving the SWI during time-series measurements. A Kongsberg 1007 altimeter was mounted 1.0 m directly above the 10-tine column of thermistors. It sampled a 12 cm diameter footprint at 5 Hz, and its 5 minute-average measurement is accurate to about 1 mm. Alternatively, we used a visible laser and camera combination method. A 35 mW 650 nm laser (Aixiz) was pointed at the SWI and an IP digital camera mounted at 38o 1.16 m away imaged the laser location on the SWI every 5 minutes. A lens made a ~50 cm laser line on the SWI perpendicular to the dominant direction of the sand ripple crests. From this line, calculations were made of ripple wavelength and height, as well as the SWI location above buried sensors. To better characterize the ripple field, future plans include increasing the number of laser lines using more lasers and cross-hair lenses as well as adding a camera. We also intend to evaluate the utility of a resistance sensor for identifying the SWI. Better identifying the SWI, and ripple migration, will

Figure 8. In situ sensor designs and deployment strategies: (A) Cartoon of miniTchain deployed in sediment (sample data shown in Figure 2); note that the sensor arrays are offset by approximately a half-ripple wavelength. (B) Cartoon of proposed multiplexed voltammetric microelectrode array in sediment; inset photo is a micrograph of 100-micron diameter gold thin-film lab prototype electrodes (see section 4.3 for details); vertical spacing for field array will match that of the miniTchain. (C) In Situ Electrochemical Analyzer and custom micromanipulator at Kilo Nalu 12m node, performing real-time voltammetric profiling (sample data shown in Figure 4).

allow us, among other advantages, to characterize ripples coming from more than one direction and ones that do not have long straight crests.

We will produce temperature and electrochemical profiles based upon static sensor array deployments (Figure 8A and 8B) and micromanipulator profiling of single-point custom voltammetric, and commercially-available pH and Eh sensors (Figure 8C). We have already obtained and tested with promising results, micro arrays of voltammetric sensors using Au thin-film deposition microfabrication techniques (section 4.3, Figure 8B). For deployments in the preliminary testing phases (e.g., data shown in Figure 5), we have utilized a prototype submersible micromanipulator (Figure 8C; AIS, Inc.). The submersible micromanipulator can be electronically controlled by the ISEA in real-time, or pre-programmed for automated profiling. Vertical travel resolution is up to 0.1mm increments.

 4.5 Integral cabled observatory measurements The Kilo Nalu Nearshore Reef Observatory is a cabled physical-biogeochemical ocean observing system along the south coast of Oahu, Hawaii (Fig. 1) (Sansone et al. 2009; Pawlak et al. 2009). The tropical reef seabed at this site consists of live coral, fossil limestone reef, and carbonate sands. Kilo Nalu supplies shore-based cabled 24/48V DC power, 100 Mbps Ethernet, and full-bandwidth video capability to distribution nodes at 12 m and 23 m water depth. Baseline instrumentation currently installed consists of 1200 kHz ADCP, top and bottom CTD along with DO and FLNT, water column thermistor chain, and met station. A SeaHorse (maintained by UH Kilo Nalu collaborator M. McManus) is not Kilo Nalu baseline instrumentation, but it is close enough (<2km) to use for subsurface PAR. If necessary, we will add an additional PAR unit for our deployments, which in conjuction with benthic oxygen measurements will provide a better understanding of production and respiration at the SWI.

4.6 Discrete sample analyses We will collect discrete pore water samples using previously installed 3/16-inch (0.5-cm) diameter PVC wells (Falter and Sansone 2000) with sampling ports at 7.5, 15, 20, 30, 40 and 50 cm sediment depth. Samples will be drawn by divers using 140-cc syringes (after purging stagnant water from the wells) and will be filtered, when necessary, immediately upon retrieval on the work boat. Bottom water will be similarly collected from 5-10 cm above the SWI. This sampling will be augmented by fine-scale sampling of the upper 15 cm of the sediment using temporarily inserted 16-ga needles and 50-cc syringes. Dissolved O2 samples will be analyzed immediately after collection with a stirred polarographic electrode, blank-corrected to allow low-level measurements (Falter and Sansone 2000). Push cores of the upper 20 cm of sediment will be collected by divers using 4-inch diameter polycarbonate tubes, sealed after insertion (to prevent pore water loss) by a black butyl stopper at the bottom and a plumbing test plug at the top. Filtered samples will be analyzed for dissolved nutrients (phosphate, nitrate, nitrite, ammonium, silicate) via standard automated colorimetric methods (e.g., Grasshoff 1999), dissolved iron by the Ferrozine method (modified after Stookey 1970), and dissolved Mn by the method of Brewer and Spencer (1971). Chlorophyll-a will be measured by solvent extraction and fluorometry (Sun et al. 1991). Dissolved sulfate will analyzed by ion chromatography following the methods of Werner et al. (2006). We will measure other dissolved sulfur speciation (S0, Sx

2-, S2O32-, S4O6

2-) by hanging mercury drop electrode (HMDE) and/or HPLC methods (Luther et al. 1991; Rozan et al. 2000). S8 will be determined by filtering fluid through 0.2-µm Nucleopore filters (Luther et al. 1991). The filters will be reacted with sulfite to convert S8 to S2O3

2- or be extracted in organic solvents to measure S8 directly by HPLC (Luther et al. 1991; Glazer et al. 2006b; Henneke et al. 1997). Dissolved S0 will be measured by acidifying the sample to remove volatile H2S after filtration

and measuring the electrochemical S0 adsorption peak (after Batina et al. 1992; Wang et al. 1998). Sulfate reduction rate (SRR) will be measured across the redox transition zone of push-core sediments using the 35SO4

2- radiotracer incubation methods of Jorgensen et al. (1978), as modified by de Beer et al. (2005) for permeable sediments. Although not a major focus of the proposed work, if time allows, additional radiolabeled 35SO4

2- incubations coupled to silver foil techniques (e.g., Krumholz et al. 1997; Visscher et al. 2000) will be used for resolving fine-scale distribution of H2S production, visualized as radiolabeled Ag35S precipitate on the foil. Suspended particles in overlying seawater will be filtered on site and returned to the lab for instrumental CHN analysis. Photosynthetic pigments will be determined by whole-sediment extraction and subsequent HPLC analysis with visible-light spectrophotometric detection.

4.7 Calculating biogeochemical fluxes Redox reaction fluxes and rates in the sediments will be calculated from the mass transport model (section 4.1), measured porewater chemistry profiles (sections 4.4 & 4.6), and water column oxygen data (section 4.5). Water column dissolved oxygen measurements will provide the SWI boundary condition for the model. Chemical concentrations will be advected and dispersed in the model like other scalars. Concentration profiles will be combined with the validated transport model, enabling us to calculate biogeochemical fluxes as a function of depth and ripple position [flux (mol/m2/s) = conc (mol/m3) * velocity (m/s)] at and below the SWI from crest to trough. The divergences and convergences of these fluxes will be used to calculate the net in situ production and consumption rates, respectively, of the measured chemical species. Redox reaction rates for each chemical species as a function of depth and/or concentration will be used to calibrate the model so that results fit the measured chemical profiles. For example, sulfate reduction rates of discrete samples will be used to corroborate modeled rates of sulfide production based on measured sulfide concentration profiles.  5.0 BROADER IMPACTS The project’s Broader Impacts reflect the interdisciplinary nature of the research. Permeable sediments are important habitats for bottom fish, invertebrates, and other commercially and recreationally important species. A core objective of this proposal is to provide information that can be used to support the management of these habitats and educate the public to ensure their ecological health. Thus, there is a potential economic benefit from the proposed research, in that proper management of the habitat of these species requires knowledge of sedimentary organic matter remineralization and the resultant biogeochemical fluxes from the sediments. In addition, the integration of this project with the existing Kilo Nalu infrastructure and its comprehensive array of physical measurements creates a powerful interdisciplinary collaboration for addressing complex interactions between physical and biogeochemical processes. It also is a clear example of the synergy possible with observatory-based research.

We are uniquely positioned to contribute to the education of the general public through our continued participation in outreach efforts supported by the Bishop Museum in Honolulu through our collaboration with the Kilo Nalu Cabled Observatory Program. Additionally, through a new collaboration with Hawaii Ocean Observing System Outreach Coordinator, Marcie Grabowski, we are striving to reach a broader audience by providing content and updates from our research for web sites and informative video displays in Waikiki hotels. In particular, we will promote public understanding of the key role that permeable reef sediments play in the recycling of carbon and nutrients in reef ecosystems. We have included a letter of support from Grabowski as an attached supplementary document.

Assuming funding of this NSF proposal, the designated PI, Brian T. Glazer, will be responsible for insuring compliance with the University of Hawaii’s plan for the appropriate training

and oversight in the responsible and ethical conduct of research for all undergraduate and graduate students, and postdoctoral researchers supported by NSF. Specifically, the project will support the research and career development of a post-doctoral fellow, an Oceanography graduate student, and a Global Environmental Sciences undergraduate. Underrepresented minorities constitute a great proportion of the University of Hawaii undergraduate student body, making it likely that the participating undergraduate will be from such a group. For more details on the University of Hawaii’s Responsible Conduct of Research Training Program, please see the attached supplementary document.  6.0 WORK PLAN TIMELINE The timeline for major project tasks is given Table II. These include: (a) customization of new instrumentation for Kilo Nalu integration, (b) in situ observations, (c) discrete sample collection and analysis, (d) geochemical/physical data analysis and integration with available Kilo Nalu physical data sets, (e) numerical model optimization and integration with geochemical/physical data; and (f) outreach. Note that field deployments have been designated for three time periods: (1) summer, with the biggest range in wave forcing due to southern hemisphere storms; (2) winter, with local storms featuring short-period swell and land runoff events; and (3) fall, with quiescent (background) conditions.

7.0 SIGNIFICANCE The over-arching aim of the highly interdisciplinary work proposed is to couple porewater velocity modeling with fine-scale, real time physical measurements (temperature profiles across the SWI, and sediment ripple topography) and chemical measurements (in situ voltammetry, pH and Eh profiles). This will allow calculation of biogeochemical fluxes across the hyperactive SWI of permeable sediments, and biogeochemical rates and fluxes within the upper 10cm of the sediment. The research thus specifically addresses the two main missing tools needed to understand the functioning and role of permeable sediments: how to calculate fluxes of master chemical species (e.g., dissolved

O2) from the sediment to the water column, and how to measure in situ reaction rates. Presently available methods are either very limited in scope or utility, or non-existent.

Emphasis is placed on coupling cutting-edge in situ micro-scale chemical and physical instrumentation with cabled observatory infrastructure and the utilization of existing oceanographic measurements being collected at the observatory. We aim to improve our understanding of the interaction between these active, carbon recycling sediments and the overlying water column, and to examine in detail the temporal/spatial variability and reactivity of key redox-reactive chemical species. In particular, we aim to elucidate the impact of physical forcing (e.g., waves, tides, diel lighting, runoff events) on the internal dynamics of these sediments. These goals reflect the fact that permeable sediments are known to play a major role in biogeochemical cycling (in particular, nutrient and carbon recycling) in many nearshore systems, but remain relatively poorly understood compared to fine-grained sediments. 8.0 RESULTS FROM PRIOR NSF SUPPORT 8.1 Brian Glazer: OCE 06-48637 “In situ voltammetry integrated with a cabled nearshore observatory” $250,464; 05/2007 – 08/2009; (B. Glazer, K. Binsted). This award represented Glazer’s first NSF support as lead PI. The scope of the work was to apply a cutting-edge geochemical measurement technique to existing nearshore cabled observatory infrastructure as a proof of concept for geochemical observatory science. A series of instrument developments, modifications, and new assemblies were performed to fabricate a power and communication distribution subnode for networked deployments of an In Situ Electrochemical Analyzer (ISEA) at the Kilo Nalu Nearshore Reef Observatory. Extensive laboratory bench testing was followed by five in-water deployments at the 12m node, resulting in near-continuous data collection over 3-20 day periods. We produced a robust and intuitive user interface for an automated voltammetric scan analyzer. Our prototype analysis algorithm is currently capable of batch-file analyses of oxygen and sulfide peaks. The work supported two M.S. graduate students, In Chieh Chen and Brian Jaress, and resulted in contributions to six publications and presentations; the later are listed under “References Cited”, identified by *. 8.2 Frank Sansone: “Wave-Driven Porewater-Seawater Exchange in Sandy Coastal Sediments”. OCE-0327332, 3/1/04 - 2/28/07, extended to 2/28/09. $461,553. 1 person-month. University of Hawaii. (F.J. Sansone, M.A. Merrifield, and G.R. Pawlak) The objective for this research was to develop instrumentation for measuring wave-driven porewater motion in permeable sediments, to outfit the instrumentation for in-situ experiments at the Kilo Nalu cabled underwater observatory, and to conduct field observations. The latter aimed to correlate porewater mixing with physical processes of the overlying water. We found that porewater mixing at 10 m water depth is greatly enhanced over molecular diffusion (three to four orders of magnitude greater), and that the enhanced diffusivities positively correlate with surface wave height. This project also supported work on wave-mediated diagenesis and sediment-seawater exchange in permeable sediments in both a laboratory microcosm and at field sites on Oahu and Maui. The project involved training of two postdocs, two Ph.D. students, and two undergraduates. This project has resulted so far in three published papers and one Ph.D. dissertation; these are listed under References Cited, identified by **. Six other papers and a second dissertation are in preparation. There have also been eight presentations at international meetings.

REFERENCES: * Publications/presentations resulting from grant listed for Glazer under “Results from Prior Support" ** Publications resulting from grant listed for Sansone under “Results from Prior Support" Bandet-Chavanne (2008) Dynamics of wave-induced boundary layers over very rough

boundaries: field observations over a stretch of coral reef. Ph.D. dissertation, University of Hawaii, Honolulu, 200 pp.

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sulphide and their mixtures in electrolyte solutions by a.c. voltammetry. Analytica Chimica Acta 267, 157-164.

Berg, P., et al. (2003) Oxygen uptake by aquatic sediments measured with a novel non-

invasive eddy-correlation technique. Marine Ecology Progress Series, 2003. 261: p. 75-83.

Boudreau, B.P., et al. (2001) Permeable marine sediments: overturning an old paradigm. Eos 82(11): p. 133-140.

Brendel, P.J. and G.W. Luther (1995) Development of a gold amalgam voltammetric microelectrode for the determination of dissolved Fe, Mn, O2, and S(-II) in porewaters of marine and freshwater sediments. Environmental Science & Technology. 29(3): p. 751-761.

Brewer, P. G. and Spencer, D. W., 1971. Colorimetric determination of manganese in anoxic

waters. Limnology & Oceanography 16, 107-110. Brune, A., Frenzel, P. and Cypionka, H. (2000) Life at the oxic-anoxic interface: microbial

activities and adaptations. FEMS Microbiology Reviews 24, 691-710. *Chen, IC and Glazer, BT. Integrating voltammetry with a nearshore cabled observatory:

enabling real-time and automated redox measurements in permeable coastal sediments. submitted to Limnology and Oceanography: Methods.

*Chen, IC and Glazer, BT. (2008) Connecting an in situ electrochemical analyzer to the Kilo

Nalu nearshore observatory for real-time and continuous voltammetric measurements in sandy sediments. ASLO Summer Meeting, St. John’s, Newfoundland, Canada.

*Chen, IC (2009) In situ voltammetry at the Kilo Nalu nearshore cabled observatory:

techniques for studying redox cycling in permeable sediments. M.S. thesis. University of Hawaii, Honolulu, 98 pp.

de Beer et al. (2005) Transport and mineralization rates in North Sea sandy intertidal

sediments, Sylt-Romo Basin, Wadden Sea. Limnol. Ocean. 50:113-127. Eich, M.L., M.A. Merrifield, and M. Alford (2004) Structure and variability of semidiurnal

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Froelich P. N., Klinkhammer G. P., Bender M. L., Luedtki, N. A., Heath R., Cullin P., Dauphin P., Hammond D., Hartman B., And Maynard V. (1979) Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: Suboxic diagenesis. Geochim. Cosmichim. Acta 43, 1075-1090.

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interface at the Kilo Nalu coastal observatory, Oahu, Hawaii. ASLO Aquatic Sciences Meeting, Nice, France.

Glazer, BT and Rouxel, O (2009) Redox speciation and distribution within diverse iron-

dominated microbial habitats at Loihi Seamount. Geomicrobiology Journal 26:606-622.

*Glazer, BT, Chen, IC, Briggs, RA, Ricardo, A. (2008) Biogeochemical and geomicrobial characterizations across redox gradients in diverse aquatic environments using voltammetric microelectrodes. ASLO Summer Meeting, St. John’s, Newfoundland, Canada.

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resolution real-time redox profiling. Deep Sea Research Part II: Topical Studies in Oceanography, 53:1740-1755.

Glazer, B.T. et al. (2006b) Spatial and temporal variability of the Black Sea suboxic zone. Deep Sea Research Part II: Topical Studies in Oceanography, 53:1756-1768.

Glazer, B.T. et al. (2002) In situ sulfur speciation using Au/Hg microelectrodes as an aid to microbial characterization of an intertidal salt marsh microbial mat, in Environmental Electrochemistry: Analyses of Trace Element Biogeochemistry, M. Taillefert and T.F. Rozan, Editors. American Chemical Society: Washington D.C.

Glazer,BT, A. G. Marsh, K. L. Stierhoff, G. W. Luther (2004) The dynamic response of optical oxygen sensors and voltammetric electrodes to temporal changes in dissolved oxygen concentrations Anal. Chim. Acta 518, 93.

Grasshoff, K et al. (1999) Methods of seawater analysis, 2nd edition. Wiley VCH, Weinheim. Haberstroh, P.R., Wave-forced porewater mixing and nutrient flux in a coral reef framework,

Ph.D. Dissertation in Oceanography. 1994, University of Hawaii at Manoa: Honolulu.

**Hannides, A. 2008. Organic Matter Cycling and Nutrient Dynamics in Marine Sediments. Ph.D. dissertation, Univ. of Hawaii at Manoa, Honolulu. 411 pp.

** Hebert, A. B., F.J. Sansone, and G.R. Pawlak. 2007. Tracer dispersal in sandy sediment

porewater under enhanced physical forcing . Cont. Shelf Res. 27: 2278–2287. Henneke, E., Luther, G. W., deLange, G. J. and Hoefs, J., 1997. Sulphur speciation in anoxic

hypersaline sediments from the eastern Mediterranean Sea. Geochimica Et Cosmochimica Acta 61, 307-321.

Herzfeld I, Sansone FJ, Smith C, Colgrove C, Ross M, Dailer M, Vermeij M (2008) Diurnal

dissolved inorganic C, N, P, and Fe dynamics in permeable back-reef sediments of the south shore of Maui, Hawaii. Ocean Sciences Meeting, Orlando, Florida.

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mical processes in aquatic sediments." Hydrobiologia 494: 231‐236. Huettel, M., W. Ziebis, and S. Forster (1996) Flow-induced uptake of particulate matter in

permeable sediments. Limnlogy & Oceanography 41(2): p. 309-322.

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Janssen, F., P. Faerber, M. Huettel, V. Meyer, U. Witte (2005a). "Pore‐water advection and solute fluxes in permeable marine sediments (I); Calibration and performance of the novel benthic chamber system." Limnol. Oceanogr. 50(3): 768‐778.

Janssen, F., M. Huettel, U. Witte (2005b). "Pore‐water advection and solute fluxes in permea

ble marine sediments (II): Benthic respiration at three sandy sites with different permeabilities (German Bight, North Sea)." Limnol. Oceanogr. 50(3): 779‐792.

*Jaress, B (2009) A cross-platform software package for autonomous analysis and archival

of voltammetric calibration and field data. M.S. thesis University of Hawaii, Honolulu.

Jorgensen, B B et al. (1978) Comparison of methods for the quantification of bacterial sulfate

reduction in coastal marine sediments. Geomicrobiology J. 1:11-27. Krumholz, LR et al. (1997) Confined subsurface microbial communities in Cretaceous rock.

Nature 386:64-66. Konovalov, S.K., et al. (2003) Lateral injection of oxygen with the Bosporus plume-fingers

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Oceanography. 1998, University of Hawaii: Honolulu.

Luther, GW, Glazer, BT, Ma, S, Troubworst, RE, Moore, TS, Metzger, E., Kraiya, C, Waite, T, Druschel, GK, Sundby, B, Taillefert, M, Nuzzio, DB, Shank, TM, Lewis, B. (2008) Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA). Marine Chemistry, 108: 221-235.

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