OS51C-1306 0800h
The Effect of Elevated CO$_{2}$ on the Growth Rate of Phytoplankton - Mesocosm Experiment
Recent independent lines of evidence suggest that higher CO$_{2}$ concentration in surface seawater would accelerate growth of phytoplankton. A 20-day mesocosm experiment was carried out in June 2004 in the southern coastal region of Korea to investigate the influence of elevated CO$_{2}$ concentration on the mono diatom species, {\it Skeletonema costatum}. The CO$_{2}$ concentration of a control net was being left as an ambient condition (approximately 400ppm), while that of the other treatment was being maintained approximately 900ppm. The elevated production of Particulate Organic Carbon (POC), which was generated from increasing a primary production, was not discernable in this experiment. Therefore, a new study has been carried out with some modifications to observe possible increase in POC and Dissolved Organic Carbon (DOC) productions. The new experiment includes 5 mesocosms with different CO$_{2}$ concentrations ranging from 280ppm to 900ppm. During the entire duration of this experiment, CO$_{2}$ concentration in each treatment has remained constant.
OS51C-1307 0800h
Calcification and Growth of the Marine Coccolithophorid Emiliania huxleyi in Response to Elevated Partial Pressure of Carbon Dioxide and Low Phosphate Conditions
Atmospheric carbon dioxide (CO2) is expected to reach about 780 ppm by the year 2100, under the IS92a business-as-usual scenario. This expected increase will give rise to more than a threefold increase in surface ocean CO2 concentration, cause a drop in surface seawater pH of 0.4 units, and decrease the carbonate ion concentration by 55%, relative to pre-industrial values. Previous work demonstrated that the coccolithophorid Emiliania huxleyi shows a marked decrease in calcification rates in response to elevated CO2 under nutrient-replete and nitrogen-limited conditions. Here we investigate the response of E. huxleyi to increased pCO2 under phosphate limitation. Results from laboratory and mesocosm experiments indicate that E. huxleyi can outcompete other phytoplankton in communities that are under phosphate control. Moreover, E. huxleyi has higher calcification rates under phosphate limitation, and model studies suggest that low phosphate levels are necessary for E. huxleyi to form dense blooms in the NE Atlantic. We grew E. huxleyi cells in 8-L closed systems under low phosphate conditions at present day and elevated pCO2 concentrations. Cell growth, particulate inorganic carbon, particulate organic carbon, total alkalinity and total dissolved inorganic carbon were measured over time. Results will be discussed in relation to predicted changes in the oceanic CO2/carbonate system.
OS51C-1308 0800h
The Growth Rate of Fundulus Heteroclitus: A Comparative Study of two Virginia Salt Marshes.
The growth rate of Fundulus heteroclitus (mummichog) was determined in a comparative study of Virginia tidal salt marshes. Two marshes in close geographic proximity were selected, one was considered pristine (natural) and the other impacted (urban). Monthly sampling was conducted during November 1999 and February 2000 and biweekly during May 2000 through September 2000. Stratified random samples of mummichogs were collected and brought back to the lab for otolith extraction and age determination. All other nekton were identified, measured, and enumerated. Marginal increment analysis was used to validate the use of otoliths in determining the age of mummichogs. Annulus formation was determined to occur annually; therefore counts of annuli obtained were valid and truly reflected the age of mummichogs. Difference in growth was found to exist between mummichogs from the natural and urban marshes. In the natural marsh, mummichogs grew 0.13 mm/day at age 0, 0.04 mm/day at age 1 and 0.13 mm/day at age 2. In the urban marsh, mummichogs grew 0.22 mm/day at age 0, 0.09 mm/day at age 1 and 0.13 mm/day at age 2.
OS51C-1309 0800h
Sunlight Damage To The Solitary Ascidian Chelyosoma productum
Chelyosoma productum (Stimpson) is a temperate solitary ascidian commonly found in Puget Sound and the San Juan Archipelago, Washington, USA. Adult populations are restricted to deeper subtidal regions or shaded shallow-water habitats, such as docks in shaded marinas. C. productum adults have a thin translucent outer tunic that may provide very little if any protection from solar damage. I hypothesized that sunlight may be setting limits on the distribution of this species. Since adult ascidians are sessile and rely on earlier life stages for their distribution, all life stages of Chelyosoma productum were tested. In this study, I examined the effects of sunlight exposure in embryos, larvae, juveniles and adults of Chelyosoma productum. I isolated the PAR, UVA and UVB portions of the spectrum and exposed all life stages using natural sunlight. I also sampled shallow-water dock habitats to see how adult distributions were related to light exposure. The embryonic development in C. productum was negatively affected by any solar exposure. Most embryos exposed to UV light failed to develop normally and those that did could not subsequently settle. This species produces embryos of different colors; two (purple and brown) were observed in my experiments. Damage from light exposure differed between the color morphs. Overall, the brown morph was more tolerant of light exposure than was the purple morph across all life stages. The only exception to this general pattern was that purple embryos were remarkably resistant to light damage. The distribution of C. productum is restricted to areas with no direct solar exposure. However, even within shaded environments where they were abundant, subpopulations related to the color dimorphism were observed. The significance of the brown and purple pigments in embryos and larvae remains largely unknown. However, adults with brown eggs were found to be more prevalent in edge environments where there was higher light exposure. Purple individuals were limited to the darker, more shaded areas. There is strong evidence that natural sunlight not only affects the survival and development of early life history stages of Chelyosoma productum, but through these effects, influences adult distribution as well. Lethal and sublethal effects were evident for all life stages of this species. These results suggest that the distribution of C. productum may be largely controlled by light exposure. This conclusion raises interesting questions about the influence of light intensity and quality (wavelength) on the distribution, behavior, and survival of other benthic marine organisms.
OS51C-1310 0800h
Characterization Of Sponge-Associated Microbial Communities
To more fully understand the endosymbiotic relationship between sponges and microorganisms, it is necessary to characterize the microbial communities of the sponges. In this study, DNA was extracted from each of three individual sponges from four sponge species collected in a shallow mangrove cut in Florida Bay near Key Largo, Florida. A fragment of the 16S rRNA gene from sponge-associated bacteria was amplified using the polymerase chain reaction (PCR). The resulting PCR products were analyzed by denaturing gradient gel electrophoresis (DGGE), which separates DNA fragments based on their sequence differences. Some 16S sequences appeared to be shared by each of the four sponge species, while other fragments found in only particular species likely represent unique bacterial strains that play a role in sponge nutrition.
OS51C-1311 0800h
Radiative Transfer Modeling, Spectral Analysis, and Remote Sensing of Coral Reefs
The calcium carbonate structures of tropical coral reefs protect coastlines from storms, create habitats for the world's greatest marine biodiversity, provide nurseries for many marine species; play essential roles in carbon and CO2 cycles, are major protein sources for many local populations, and are vital for sustainable economies of many societies. The world's reefs are in peril due to climate change and anthropogenic activity caused by rapidly growing populations in coastal zones. An important contribution to coral reef research is improved spectral distinction of reef components indicative of reef condition, including physical and biological degradation. Unfortunately, relatively little is known concerning the spectral properties of coral or how coral architecture reflect/transmit light. New insights into optical processes of corals can lead to improved interpretation of remote sensing data and forecasting of immediate or long-term impacts such as bleaching and disease in coral and algal overgrowth. We are investigating the spatial/spectral properties required to remotely sense changes in reef biological and physical properties by coupling spectral analysis of in situ spectra with a new coral-specific radiative transfer model. The first model development phase (CorMOD) imposes a scattering baseline that is constant regardless of coral condition, and further specifies that coral is optically thick. Evolution of the model is towards a coral-specific radiative transfer model that includes coral biochemical concentrations, specific absorptivities of coral components, and transmission measurements from coral surfaces. We present our field collected in situ spectra and resultant output relative absorption profiles of coral from CorMOD. Further, we will present NASA AVIRIS data and in situ spectra collection of coral and seagrass to support the AVIRIS mission that was collected during August 2004 for Florida Keys and Puerto Rico.
http://geo.arc.nasa.gov/sge/coral-health/
OS51C-1312 0800h
Development and Application of the SEDCON Index for Resource and Risk Assessment of Coral Ecosystems
Resource managers need inexpensive bioindicators to evaluate the health of coral ecosystems and to guide decisions on when and where to utilize more expensive assessment techniques. Following USEPA Guidelines for Evaluating Ecological Indicators, we are developing a rapid-assessment protocol, termed the SEDCON Index (SI), that utilizes reef sediment constituents to assess the integrity of coral-reef communities. Key advantages of this index are that it only requires small sediment samples and is applicable to reefs worldwide. The underlying assumption of the index is that community structure is reflected by proportions of recognizable remnants of calcareous shells and skeletal remains of autotrophic (calcareous and coralline algae), mixotrophic (zooxanthellate corals and larger foraminifers) and heterotrophic (e.g., bryozoans, molluscs, smaller foraminifers) benthic organisms, and of unrecognizable debris as a proxy for bioerosion. Implementation and assessment of this diagnostic tool is currently underway for the Florida Middle Grounds (FMG) and the Coral Reef Monitoring Program (CRMP) sites in the Florida Keys National Marine Sanctuary (FKNMS). We are calibrating SI data with benthic community data from CRMP. Data from samples collected in FKNMS between 2001 and 2004 indicate dominance of the sediments by bioerosional debris, while data from samples collected in the early 1980s from the FKNMS and from the FMG in 2003 indicate higher proportions of identifiable components of mixotrophic origin. Application of the SI provides an assessment of ecosystem condition on scales of years and will be used to supply reef baseline data for detecting changes associated with the Comprehensive Everglades Restoration Plan.
OS51C-1313 0800h
Efficient and Statistically Valid Method of Textural Sea Floor Characterization in Benthic Habitat Mapping
The advent of multibeam bathymetric sonar technology and the thematic development of benthic habitat research have spawned renewed interest in the systematic characterization and mapping of the seafloor. This necessitates the application of reliable and accurate sea floor descriptors in combination with a robust means to statistically assess descriptor associations. Traditionally, geoscientific sea floor mapping was comprised primarily of identifying the spatial extent and relationship of geological units, broadly following chronostratigraphic conventions. Classifying seafloor sediments using geological facies may not be meaningful biologically because they incorporate temporal elements that stem from a geochronological qualifier. Textural properties of geological facies are typically reliant on the application of distribution-dependent statistics, which have been shown to be inappropriate with multimodal marine sediments. While the relationship between grain size and biota appears self-evident, there is a compelling argument that granulometric properites alone are not a determinant of species distribution or community composition. The classification process is problematic because most statistical clustering techniques will, by their very nature, form clusters which may or may not represent meaningful and discernable differences. Moreover, as habitat mapping is aimed at boundary definition, the boundaries between clusters in such cases could be based on very subtle differences, or noise (e.g. sampling bias). An independent measure of the appropriate number of groups in a dataset is required. Therefore, we examine a statistical approach pioneered by Calinski & Harabasz (C-H), which was implemented by a computer routine to work in partnership with information entropy analysis of grain size data. We utilize a 30-year legacy of grain size data collected from the Scotian Shelf, Canadian Atlantic continental margin, and show that considerable improvements in textural zonation are obtained using a combined entropy-C-H technique, and these new zones better match known benthic divisions. The statistical validity of the clustering outcomes is tested at each step of the classification and the effects of data reduction resulting from archiving or data processing is examined.
OS51C-1314 0800h
Absorption Measurements from the Gulf of Maine: An Inter-Comparison of Instruments
The goal of remote sensing is to obtain quantitative and qualitative information about the constituents of natural waters from measurements of reflectance or ocean color. The shape and magnitude of these spectral measurements are related to the inherent optical properties of the water. The three main water constituents that contribute to the bulk inherent optical properties: phytoplankton, chromophoric dissolved organic matter (CDOM), and non-algal particles. In order to develop algorithms that derive information about these constituents from radiometric measurements, a large amount of in situ data must be collected from the region of interest. These measurements can be difficult to obtain due to instrumental constraints. This study focused on the inter-comparison of three different instruments designed to make absorption measurements: a Liquid Waveguide Capillary Cell (LWCC) coupled to a miniature spectrometer; multi- and hyperspectral in-situ attenuation and absorption sensors; and a benchtop spectrophotometer. Natural samples were measured in situ, on the ship, and on shore as part of the monitoring effort of the Coastal Ocean Observation and Analysis (COOA) center at the University of New Hampshire. Laboratory experiments were performed to further investigate inter-instrument differences. Preliminary results of CDOM absorption measurements made with the benchtop spectrometer and using the waveguide setup exhibited a strong correlation (R=0.993).
OS51C-1315 0800h
Variability in inherent optical properties in the Western Gulf of Maine
Inherent optical properties (IOPs) depend solely on the optically important in-water constituents, colored dissolved organic matter (CDOM), phytoplankton, and non-algal particles. As such, their variability is controlled by physical, chemical, and biological processes. Here we will examine the roles of these processes with IOPs measured as part of the University of New Hampshire's center for Coastal Ocean Observation and Analysis (COOA) monthly cruises. Much of the data was collected with a custom IOP profiling package (Wetlabs Inc.) equipped with attenuation and absorption meters, fluorometers, backscattering meters, and a CTD. Intermediate nephaloid layers in enclosed basins were among the interesting features observed.
OS51C-1316 0800h
Photochemical Formation of Hydroxyl Radical in Red-Soil-Polluted Seawater in Okinawa, Japan -Potential Impacts on Marine Organisms
Development of pineapple farmlands and construction of recreational facilities caused runoff of red soil into coastal ocean (locally termed as red-soil-pollution) in the north of Okinawa Island, Japan. In an attempt to understand the impacts of red soil on oxidizing power of the seawater, we studied formation of hydroxyl radical (OH radical), the most potent oxidant in the environment, in red-soil-polluted seawaters, using 313 nm monochromatic light. Photo-formation rates of OH radical showed a good correlation with dissolved iron concentrations (R = 0.98). The major source of OH radical was found to be the Fenton reaction (a reaction between Fe(II) and HOOH). The un-filtered red-soil-polluted seawater samples exhibited faster OH radical formation rates than the filtered samples, suggesting that iron-bearing red soil particles enhanced formation of OH radical.
OS51C-1317 0800h
Water Quality Gradients across Albemarle-Pamlico Estuarine System: Seasonal Variations and Model Applications
The seasonal variations of water quality parameters as nitrite plus nitrate (NO23), total phosphate (PO4), Chlorophyll a and dissolved oxygen (DO) are analyzed across the Croatan-Roanoke-Albemarle-Pamlico-Core Sounds Estuarine System (CAPES). Overall, several patterns are observed: The Chowan-Roanoke-Albemarle system is generally phosphorous limiting for phytoplankton growth, while both the Tar-Pamlico and the Neuse Rivers are generally nitrogen limiting. The largest PO4 gradients exist in the upper estuary of the Albemarle Sound and the largest NO23 gradients exist in the upper estuary of the Neuse and the Tar-Pamlico Rivers. Dissolved oxygen appears to have the strongest seasonal signal among the water quality variables with highest DO values observed during winter (within the CAPES and in the nearshore area) or spring (in the continental shelf and deeper ocean) and lowest during summer. Chlorophyll a concentrations are highest during spring (within the CAPES) or winter (offshore). In contrast, the NO23 and PO4 concentrations in both the Tar-Pamlico and Neuse River Estuaries are usually higher during the second half of the year. The time differences of the peak nutrient and chlorophyll a concentrations suggest that highest algal growth rate (and hence nutrient uptake rate) occur during spring while the consumed nutrients are released to the water column through a nutrient recycling method later in the year. A coupled three-dimensional hydrodynamic water quality model is then applied to the entire system. The general model set-up and parameter derivation of the model is presented in the paper. The basic observed water quality characteristics such as the nutrient limiting pattern and the spatial gradients across the system are reproduced in the model. The model results also suggest that nutrient fluxes, generated from the diagenesis of deposited organic matters and released from the sediment bed may be an important mechanism for nutrient recycling in the region.
OS51C-1318 0800h
Water Quality In The Dnipro-Buh Estuary: Assessment And Management Support Tools
The Dnipro-Buh Estuary (DBE) is the Black Sea largest estuary connected with the Black Sea through the Kinbourn strait. The sources of fresh water discharge are the Dnipro and Southern Buh rivers. The most important factor, which changed state of whole ecosystem, was construction of the Kakhovka Reservoir dam approximately 60 km from the mouth of the Dnipro River. The salt water intrusion that takes upstream of the Dnipro delta and hydrogen sulphide production in periods of summer hypoxia have adverse impacts on the DBE. The fresh water supply of city Mykolayv is provided from the Dnipro tributary, Ingulets River, that is impacted by the releases of mine waters. During the joint USA-Ukraine project an assessment of DBE water quality was provided based on monitoring data for 1984-2004, and new field data collection using modern techniques and equipment in 1998, 2003 and 2004. The 2D model CE-QUAL-W2 and 3D model consisting of linked hydrodynamic model THREETOX and 3-D version of US EPA WASP6 water quality model, were applied to the DBE. The models reproduced the behavior of the main nutrients as well as the summer hypoxia. A new module describing hydrogen sulphide in the DBE was developed and tested. A set of numerical experiments was carried out to predict and assess the impact of the Kakhovka Reservoir operational mode on the environmental situation in the downstream river/estuary system. The 1-D model of Ingulets River was developed and it was shown to be a useful tool to support the efficient operation of the pumping station for Mykolaev's drinking water supply. The developed set of the modeling tools are to be implemented in the regional Ukrainian State Ecological Inspection units of DBE area after the necessary staff training.
OS51C-1319 0800h
Reconstructing anthropogenic $\delta^{13}$C changes in the North Pacific Ocean using the MIX approach
We reconstruct anthropogenic changes in the $\delta^{13}$C of dissolved inorganic carbon (DI$^{13}$C) in the North Pacific Ocean using a multi-parameter mixing model based on the "novel approach" of Goyet et al. (1999). The approach allows us to use only the recently collected data to estimate the distribution of anthropogenic $\delta^{13}$C. The model computes tracer distributions in the basin by mixing properties of four distinct water types, roughly corresponding to North Pacific Intermediate Water, Subtropical Mode Water, tropical underwaters, and North Pacific Deep Water. Differences between $\delta^{13}$C predicted by the mixing model and measured are assumed to be due to the anthropogenic perturbation, i.e., driven by the atmospheric $\delta^{13}$C decrease since $\sim$1800. The cross-isopycnal penetration of the anthropogenic perturbation within each water type is determined iteratively. The mixing model's $^{13}$C change reconstruction is validated using known anthropogenic tracers such as chlorofluorocarbons and using an ocean general circulation model's simulated $\delta^{13}$C changes. We applied the MIX approach to data collected along WOCE line P13N in 1992. Total (i.e., since the 1800s) anthropogenic DI$^{13}$C changes are detectable to about 1200 meters in the western North Pacific (165$\deg$E). The surface ocean $\delta^{13}$C change in the surface ocean was largest in the subtropical gyre (30$\deg$N), where the $\delta^{13}$C decrease was about 60$%$ of the decrease in the atmosphere. Surface ocean changes were smaller in the tropics (40$%$ of the atmospheric change at 10$\deg$N) and much smaller in the subpolar gyre (only 20$%$ at 50$\deg$N). These century-scale oceanic changes relative to the atmosphere are smaller than observed over the past two decades, suggesting that recent (1970-1990s) decreases in upper-ocean $\delta^{13}$C may be enhanced by possible changes in carbon cycling rates in the North Pacific.
OS51C-1320 0800h
230Th In The Semi-closed Basins
230Th (half life 75.2 ky) is produced by decay of 234U (half life 4.47 Gy) with a constant rate in the water column. Thorium is a particle-reactive element scavenged easily by settling particles and removed into the deep-sea sediments. The vertical distribution of thorium is well described by the reversible scavenging model [Nozaki et al., 1981; Bacon and Anderson, 1982; Nozaki et al., 1987]. The model could predict the vertical profile of 230Th, increasing linearly from the surface to the deep. However, concave profiles with higher or lower concentrations in deep waters than those predicted by the reversible scavenging model were often reported and explained by the scavenging-mixing model [Rutgers van der Loeff and Berger., 1993]. In this model, 230Th vertical profiles in seawater were governed not only by the settling particle dynamics and adsorption/desorption equilibrium but also by lateral transport with water ventilation. We applied the scavenging-mixing model to this vertical profile in the Andaman Sea, and estimated the upper limit of renewal time to be 6 yr. We compared 210Pb/ 226Ra ratios among deep waters of various oceanic basins to constrain the application of 230Th as a tracer of deep-water renewal. The 210Pb/ 226Ra ratios were almost identical for the deep-water of the Andaman Sea and the inflow water from the Bay of Bengal, suggesting that the deep water in the Andaman Sea is replaced rapidly without bottom scavenging effects on the 210Pb/ 226Ra ratio. We will discuss the scavenging process of thorium in semi-closed basins; the Sulu Sea, the South China Sea and the Japan Sea. In those basins, whose residence time of deep water is relatively long and whose specific ratio of surface sediment area to the water mass volume is higher than in oceanic regions, the bottom scavenging seems to affect the 230Th distribution in seawater.
OS51C-1321 0800h
Mercury speciation in the Mediterranean Sea
An interesting feature of mercury biogeochemistry in the Mediterranean is that several fish species from the Mediterranean show higher concentrations of Hg in their tissues than same fish species in the Atlantic ocean. although the concentrations of mercury in the open waters of both oceans are similar. It has been suggested that the higher mercury levels noted in many larger pelagic fish species in the Mediterranean are not related to anthropogenic inputs, but rather are due to the higher than average natural environmental levels of this metal originating from the Mediterranean mercury anomaly. Although elevated Hg levels have been noted in environmental matrices from the Mediterranean regions adjacent to known mercury anomalies, the data do not clearly indicate that the effects of these anomalies have been transmitted to open waters or to lower trophic level species living in these waters. In the present contribution data obtained during three oceanographic cruises carried out in the framework of the MERCYMS project (An integrate approach to assess mercury cycling in the Mediterranean basin) funded by EU in the period between 2000 and 2003 will be presented. Measurements included total mercury measurements and its speciation (reactive Hg, total Hg and monomethylmercury (MMHg) in filtered and non-filtered sea water samples, dissolved gaseous mercury (DGM) and dimethylmercury (DMHg) in open and coastal waters of the Mediterranean Sea. Radon, as a tracer gas of tectonic activity was also measured in depth profiles. The results presented clearly show that hg species distribution in surface and deep oceanic waters is affected by several dynamic processes such as photochemical transformation at the surface, phytoplankton biomass stratification in the photic zone, development of an oxygen depletion zone at intermediate depths and diffusion from deeper layers due to biological and/or tectonic activities.
OS51C-1322 0800h
Comparative study on deficiency of N-nutrient deduced from Beaufort and Laptev Sea expedition data (JWACS and NABOS cruises)
Arctic shelf and its vicinity are posted to be the most active area for denitrification in the world ocean. The recent stable nitrogen isotope study suggests that there is no appreciable evidence for denitrification in water column although there is substantial deficiency in nitrogen in water column. Nitrogen isotope study revealed that the water column deficiency is due to unidirectional nitrogen uptake by sediments, which is driven by sedimentary denitrification (T. Tanaka et al., Cont. Shelf Res., 2004). Nitrogen loss by dinitrification in the area was posted as large as 20 Tg-N/year, which corresponds 15-25 % of nitrogen loss in the world ocean, if entire shelf area in arctic and its vicinity is active in denirification. JWACS (Joint Western Arctic Climate Study) and NABOS (Nansen & Amundsen Basin Observational System) has been carried out hydrographic observation cruises by Japanese R/V Mirai, Canadian icebreakers and Russian icebreaker in the last 3 years to understand Arctic Ocean Response to the Climate Change and its feed back to the global climate system. Those cruises gave us unique opportunity to examine nutrient dynamics in surface stratified water layers, which the upmost response and affect climatic system in the Arctic, which include physical climate and biological response forcing physical climate system. In this study, N*=(NO3-+NO2--16PO4+2.9)x0.87 is estimated in Laptev Sea and Beaufort Sea. N* in Laptev Sea shows all positive values averaged at 3.8, indicating typical Atlantic surface layer signature. Whereas N* values in Canada Basin showed startling negative values as low as -13. The lowest value was found in the nutrient maximum subsurface layer with almost freezing water temperature (Cold Halocline Water). N* -phosphate diagram and N*-nitrate diagram revealed remarkably weak denitrification signature in Laptev Sea.
OS51C-1323 0800h
Interannual Variability in Carbon and Nitrogen Stable Isotopic Signatures of Size-Fractionated POM from the South Florida Coastal Zone
Environmental conditions in South Florida coastal waters have been of local and national concern over the past 15 years. Attention has focused on the ecosystem impacts of salinity increases, seagrass die-off, increased algal bloom frequency, waste water influence, groundwater discharge, and exchange between Florida Bay, the Gulf of Mexico, and the Atlantic Ocean. Changes in water quality and productivity levels may be reflected in the isotopic signatures of coastal zone primary producers. Recent work with seagrasses in South Florida has demonstrated high seasonal and spatial variability in C and N isotopic signatures and decoupling between the two isotopic systems as they vary. To better understand the sources of seasonal and spatial fluctuation, size fractionated POM (particulate organic matter) samples have been collected on a quarterly basis since Sept. 2002. Fractions collected include $>$150$\mu$m, 50-150$\mu$m, and 0.1-50$\mu$m using Nitex mesh sieves and a portable pump system deployed from a small boat at 10 sites around the Florida Keys and Florida Bay. It was hypothesized that planktonic groups respond more quickly to changes in water quality then seagrasses, and thus variations may be more clearly attributed to environmental parameters. Significant spatial and temporal variability is evident both within site between size fractions and between sites. Seasonal oscillations of up to 4$\permil$ were observed in N isotopic values and 6$\permil$ in C isotopic values of the 50-150$\mu$m size fraction, which is dominated by diatoms and dinoflagellates. $\delta$$^{13}$C values are depleted in the late winter/early spring sampling period possibly reflecting decreased productivity stress on available C pools. $^{13}$C depletion is generally coincident with $\delta$$^{15}$N enrichment in the late winter/early spring, possibly demonstrating changes in DIN pools (NO$_{3}$$^{-}$ and NH$_{4}$$^{+}$ concentrations) or changes in decomposition or denitrification rates. Broad groupings appear to separate Atlantic coral reef sites, interior Florida Bay sites, and western boundary Florida Bay/Florida Keys channel sites in isotopic signature and the magnitude of seasonal variation. Additionally, results utilizing flow cytometry in conjunction with isotopic analyses of the $<$50$\mu$m POM fraction from Florida Bay show a correlation between low DIN availability, cyanobacterial population abundance, and more depleted $\delta$$^{15}$N signatures, possibly indicating N-fixation as a supplemental nutrient source, favoring N-fixing cyanobacterial blooms.
OS51C-1324 0800h
Marine DOC Radiocarbon Methods and DOC/POC Exchange
Dissolved Organic Carbon (DOC), defined as the carbon contained in that fraction of organic matter which passes through a 0.2-1.0 micrometer filter, is the largest oceanic reservoir of organic carbon with approximately 600 Gt C. Sources and sinks of this carbon pool are not yet well constrained, with some suggestions that a portion exchanges with the Particulate Organic Carbon pool (POC), i.e. that fraction retained by filters. Progress in examining this proposed phenomenon necessitates accurate and precise methods for quantifying DOC concentrations and isotope ratios. A simple experiment was performed whereby deep seawater was inoculated with dried, ground plankton as a known source of POC, and incubated two weeks in darkness at ambient temperature (Jeomshik Hwang, "Radiocarbon in Organic Compound Classes of Particulate and Sedimentary Organic Matter in the Northeast Pacific Ocean", Ph.D. Thesis, University of California, Irvine, 2004). The final DOC concentrations and isotope ratios were measured via prototype UV oxidation/vacuum line collection systems. The method performs with a system blank of 15 micrograms carbon, achieves 100% yield for the oxidation of ca. 1 liter solutions of NBS oxalic acid I, and preserves the standard's isotopic signature. Analytical performance of the DOC systems and results of the addition experiment are presented.
OS51C-1325 0800h
The effect of sediment trap poisons on particulate phosphorus integrity
The biogeochemical cycling of phosphorus (P) in marine systems has been complicated by a lack of information regarding the flux of particulate P from surface waters to the seafloor. This is because one of the most common ways to collect sinking particles is through the use of sediment traps where poisons are often added to reduce post depositional biological processing. Although few in number, several studies have suggested that these poisons may also affect sample integrity, particularly with respect to P. In this study, we examined the effects of three preservatives (mercuric chloride, formalin, and sodium azide) on P concentrations in marine sediments collected from a range of coastal and open ocean environments: the Black Sea (BS), Cariaco Basin (CB), Gulf of Mexico (GoM), and Winyah Bay (WB). Duplicate samples with controls were exposed to each preservative, and the loss of P to the supernatant was monitored over a period of six months. P losses to the supernatant happened rapidly, with most of the P loss occurring within the first 2 - 5 days of exposure. Formalin was consistently the least effective in preserving P sample integrity, with ~ 5 % of the initial P found in the supernatant for sediments of the BS, ~12 % from the GoM, ~ 20 % in CB, and as much as 40 % in WB. Mercuric chloride was the second least effective preservative, with P losses of 20 % in WB and $<$ 5 % in the other sediments. In contrast, sodium azide, appeared to be the most effective trap solution, with P losses never exceeding more than 5 % of the total P measured in the sediment. In most of our experiments with formalin and sodium azide, the dominant form of P found in the supernatant occurred as soluble reactive P. However, mercuric chloride consistently had dissolved organic P concentrations greater than 50 % of the total P measured in the supernatant, confirming earlier studies that mercuric chloride releases ATP during preservation. Our results suggest that P losses in sediment traps may vary widely, depending on the region and initial composition of the material. In addition, sodium azide appears to be the best trap solution for preserving P integrity and should be used whenever possible.
OS51C-1326 0800h
Carbonate Removal from Sediment Samples for Elemental and Isotopic (\delta$^{13}$C and \Delta$^{14}$C) Analyses: Comparison of HCl Vapor and Sulfurous Acid
Removal of carbonate minerals from environmental samples is critical for accurate determination of organic carbon (OC) content. Vaporous HCl and sulfurous acid (H$_{2}$SO$_{3}$) were compared as decarbonation agents for a series of particulate samples ranging from dolomitic shale to marine sediment. The performance of these acids was compared under two contexts: (1) for simultaneous determination of percent OC (%OC) and \delta$^{13}$C of OC using coupled elemental analyzer-isotope ratio mass spectrometry, and (2) for determination of \Delta$^{14}$C of OC using accelerator mass spectrometry (sealed-tube combustion followed by reduction to graphite). In case (1), HCl vapor and H$_{2}$SO$_{3}$ treatments both sufficiently removed carbonates from all samples tested. Percent OC and \delta$^{13}$C of OC obtained by these two methods were similar, although H$_{2}$SO$_{3}$ treatment may underestimate %OC due to sample loss. Overexposure to HCl vapor also resulted in significantly lower \delta$^{13}$C values depending on sample type. In case (2), it was possible to successfully decarbonate all samples using HCl vapor with minimal introduction of blank C. In contrast, effervescence made acidification by H$_{2}$SO$_{3}$ difficult when handling sample sizes required for accelerator mass spectrometry. Incomplete removal of S (as SO$_{2}$) may also pose negative effects on the graphitization process.