OS11B-1116
Dissolved Zinc Measurements Using Shipboard FIA During the 2008 GEOTRACES Cruise
Zinc concentrations in the open ocean have been measured accurately by only a few investigators due to the extreme difficulties of collecting and processing seawater samples without introducing Zn contamination. Accurate measurements of dissolved Zn are important for understanding the biogeochemical behavior of this important biochemically required element in the open ocean. Historically, reliable samples for dissolved Zn were collected using Teflon-coated GO-FLO bottles individually hung on Kevlar line. To speed up sample collection, two "Trace Metal" rosette systems were tested during Leg 1 of the GEOTRACES 2008 intercalibration cruise: a large GEOTRACES 24-bottle rosette and the smaller Measures and Landing "CLIVAR" 12-bottle rosette. Both rosettes use 12-liter, Teflon-coated GO- FLO bottles equipped with Teflon spigots and modified air-relief fittings, allowing for pressure filtration. Contamination for dissolved Zn was eliminated in the 12-liter Teflon-lined GO-FLO bottles by repeated deployments ("flushing") on both rosette systems. A Flow Injection (FIA) technique for shipboard determination of total dissolved Zn was utilized to test rosette sampling methods for Zn contamination. Samples were acidified to 0.024M HCl (pH 2) for 16 hours. Samples were buffered to pH 5.5 using ammonium acetate buffer. Dissolved Zn was pre-concentrated using a small- volume column of 8-HQ cation exchange resin. After column rinsing, Zn was eluted into the flowing stream of organic reagent p-Tosyl-8-aminoquinoline (pTAQ), which forms fluorescent complexes with Zn. A flow- through fluorometer was used to record peak heights. Calibration was performed via standard additions. Accuracy of this method was established by measuring standard SAFe D2 and S1 samples, as well as multiple samples collected and analyzed throughout Leg 1 of the GEOTRACES 2008 cruise. Dissolved Cadmium (Cd) can additionally form fluorescent complexes with pTAQ. Thus, when necessary, a small, positive, Cd interference can be corrected for using established Cd-PO4 relationships. Dissolved Zn profiles from both rosette systems agree extremely well with previously published Zn data from this region.
OS11B-1117
Distributions of Eight Trace Elements From a North-South Transect of the Pacific Ocean During the CLIVAR/Repeat Hydrography P16S and P16N Cruises
A key objective of the GEOTRACES program is to determine water column distributions of selected trace elements and isotopes in each ocean basin. The Climate Variability and Predictability (CLIVAR)/CO2 Repeat Hydrography program is engaged in studying the worlds oceans in order to describe and understand the physical processes responsible for climate variability. An integral part of this program is the investigation of biochemically required trace elements and their distributions in the upper water column (1000m) where the majority of trace metal uptake and recycling occurs. Sampling on the CLIVAR (P16 north and P16 south transects) cruises during 2005-2006 using the CLIVAR Trace Metals rosette has produced high-resolution data (1-2 degree spacing) for a suite of trace elements in the upper 1000m of the Pacific Ocean between 55.8°N and 71.0°S from Kodiak, Alaska to Antarctica along 150°W. Total dissolved Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb were extracted from stored (acidified) samples (after UV oxidation) using Nitrilo-triacetic Acid (NTA) chelating resin and determined using isotope dilution ICP-MS (Mn and Co were calibrated by the method of standard additions). Analytical accuracy was established by repeated analysis of the S1 (surface) and D2 (1000m) seawater standards produced from the SAFe intercalibration experiment. Observed trends will be compared to hydrographic, nutrient, and transient tracer data in order to interpret and understand elemental distributions, sources, biogeochemical cycling rates, and transport in the water column.
OS11B-1118
The Effect of Supersaturation on the Ca and Sr Composition in Synthetic Barite Precipitated From Seawater
An area of intense chemical oceanographic research effort in the past few decades has been the study of marine minerals as there is ample evidence that buried ocean sediments contain important information on past seawater environmental conditions such as temperature, productivity, alkalinity, phosphate, and pH, among others. A key oceanic mineral that could hold robust records of seawater Sr and Ca composition is barite. Marine barites typically contain 1-3% Sr and 0.01-0.1% Ca; concentrations that are evidently controlled by conditions under which barite formation occurs thereby potentially linking sediment composition to oceanic chemistry at the time of formation. The key objective of this work is to develop a better understanding of the connection between solution and solid chemistry that will be applicable to natural marine barites over a broad range of environmental conditions. Recent data from our precipitation experiments from natural seawater spiked with BaCl2 suggest that the Sr/Ca ratio in the barite precipitates is not only a function of the corresponding ratio in seawater via the distribution coefficient, but that supersaturation with respect to barite also plays an important role in governing the precipitate composition. We will report the results of barite precipitation experiments carried out in seawater solutions at room temperature as a function of supersaturation and as a function of the solution barium ion to sulfate ion ratio. Empirical modeling results from this data will be presented along with the interpretations in terms of the kinetics of ion incorporation during crystallization.
OS11B-1119
Distribution of seawater Cd in the Ulleung basin, East/Japan Sea
In order to understand controlling factors of Cd concentration and Cd/PO4 ratios in water column, we collected seawaters from surface (10m) to bottom (2000m) at 12 sites during three surveys (July 2005, April 2006, May 2007) using acid-cleaned Niskin bottles. Seawater, suspended particulate material and phytoplankton samples in surface layers (10 or 20m) were also collected on spring seasons (April 2006, May 2007). Dissolved, total dissolvable and particulate Cd was quantified using ICP/MS. The concentration of dissolve Cd and PO4 showed similar vertical profiles regardless of seasons and locations. Minimum concentrations of Cd and PO4 in surface waters were observed 0.07-0.13 nM Cd and 0.03-0.33 uM PO4 , respectively. The concentration increased rapidly to maximum of 0.28-0.33 nM Cd and 1.72-1.98 uM PO4, respectively, at 500-600 m, and then they increased steadily to the bottom. Concentration in surface waters and the rapid increasing depth were modified by the existence of anti- cyclone eddies and depth of thermocline. Plots of Cd against PO4 concentration showed fairly good linearity when the water depth was divided between upper and lower layers based on the bottom of thermocline; for the upper layer, [Cd](nM) = 0.08¢®¢¯[PO4](uM)+0.07 (r2= 0.78) and for the lower layer, [Cd](nM)= 0.15¢®¢¯[PO4](uM)-0.04 (r2= 0.66)). Cd/PO4 ratios in surface waters were in the range of 0.23-2.21 and they rapidly decreased in depth to constant deep water values (0.12-0.16 nM/ uM). Two characteristic features were identified from the Cd and PO4 distribution in this study. The one was very high intercept values (~0.07) in the relationships between Cd and PO4 concentration, which had also been reported in northern East/Japan Sea (0.1-0.2). And the other was very low slope (~0.15) in deep layer, which were lower values than those found in the northern Atlantic Ocean. From the relationships between Cd concentration and salinity, fractionation coefficient (d[Cd]/d[PO4]=Kln(Cd)/ln(PO4)), the separation of preformed and regenerated parts and Cd/PO4 ratios in phytoplanktons, it might be suggested that both the input of external Cd source and the preferential uptake of PO4 relative to Cd maintained the high Cd/PO4 ratios in surface waters. The low Cd/PO4 ratios in deep waters might implicate that bottom water from the northern East/Japan Sea would rapidly flow through the basin.
OS11B-1120
Processes Controlling Trace Metal Distributions Within the Sub-surface Waters of a Mesoscale Anti-cyclonic Eddy
In 2000 and 2001, a series of cruises were undertaken to study the physical, chemical and biological processes occurring within large eddies that form off the coast of British Columbia and travel westward into the Gulf of Alaska. This project allowed for the study of processes affecting trace metal distributions as coastal water ages. A simple physical mixing box-model for the sub-surface waters of an eddy was developed based on the change in the average salinity within the core of the eddy over time. This physical mixing model was found to produce results, such as initial salinity, lifetime prediction, and volume exchanged, similar to the observations and published estimates from other studies. With the use of the physical mixing model, the major controls on trace metals in the eddy core were studied. The average dissolved aluminum and manganese concentrations decreased within the eddy core as it aged. For aluminum it was found that 51% of the average dissolved decrease within core waters could be attributed to physical mixing with surrounding waters, whereas 49% was a result of particle scavenging. For manganese, 61% of the overall decrease in dissolved manganese concentration could be explained by the mixing of the eddy with the waters surrounding the eddy while 39% is presumably due to oxidative scavenging. From the model predictions the removal rates for aluminum and manganese were determined to be 4.0 ± 0.2pM/day and 0.68 ± 0.03pM/day respectively. Also, residence times of 3.2 ± 0.2 years for aluminum and 6.5 ± 0.3 years for manganese were calculated. The average dissolved cadmium and copper concentrations within the core of the eddy increased as the eddy traveled offshore into HNLC waters. For both cadmium and copper, the amount of the dissolved metal concentration increase within the core of the eddy at 16 months was not significantly different from the amount predicted from the physical mixing model. This suggested that between the depths of 40 to 400m within the eddy any recycling occurring from biological uptake in surface waters was minimal.
OS11B-1121
The Effects of Nutrient and Trace Metal Enrichment on Coastal and Oceanic Strains of Synechococcus
The availability of nutrients and trace metals in the oceans is determined largely by terrestrial inputs, from erosion, rivers, and atmospheric deposition. Because biologically important trace metals and nutrients are known to be transported from land to the coastal and open ocean in different amounts, we set out to determine the impact of several terrigenous metals on Synechococcus, a unicellular cyanobacterium, which is globally ubiquitous, with diverse strains living throughout the world's oceans in coastal and open ocean environments. In our research, we measured the physiological responses (growth rate, photosynthetic efficiency, and cellular composition) of cultured Synechococcus isolates to various trace metal and nutrient addition treatments. Our preliminary results suggest dissimilar physiological adaptations between coastal and oceanic isolates. In general, coastal isolates were characterized by higher growth rates and greater resistance to metal toxicity than oceanic isolates. The diversity of these physiological responses may influence Synechococcus' geographical distribution throughout the world's oceans.
OS11B-1122
Nitrogen Cycling in the Oligotrophic Ocean: How Seasonal Physical Processes Determine Biologically-Mediated Nitrogen Transformations
Two mechanisms have been proposed to describe how nitrite maxima form: (1) spatially segregated microbial oxidation of ammonium and nitrite during nitrification; and (2) incomplete nitrate reduction to ammonium by light limited phytoplankton. Nitrite maxima throughout the world's oceans are generally attributed to one of these two processes; however, in situ measurements from the oligotrophic Red Sea suggest that they may co-occur within the water column. In winter, light limitation from deep mixing may cause incomplete nitrate reduction by phytoplankton, leading to an inverse correlation between nitrate and nitrite levels. In summer, stratification increases light availability, and shallow nitrite maxima during summer may indicate that microbial nitrification plays a larger role in nitrite formation during summer months. Bioassay incubation experiments with various 15N labeled nitrogen (N) sources suggest that light availability strongly affects cellular uptake of N from nitrate and urea, while ammonium and nitrite uptake are unaffected by light. N mass balance in these incubations will be presented. These results indicate that it is likely that the combined physical, chemical, and biological characteristics of the water column determine which of the two nitrite formation processes becomes dominant at a given time or location.
OS11B-1123
Parameterizing the Marine Silicon Cycle: Effects on Modern Ocean Biogeochemistry
The oceanic biogeochemical silicon cycle plays a significant role in the climate system, due to its strong
influence on marine planktonic production. Silicic acid, along with other nutrients, controls production of
siliceous plankton, which compete with calcareous plankton. Through this competition, and the biological
carbon pump, these organisms make an important impact on the carbon cycle.
In this study, parameterizations of the marine silicon cycle are added to a biogeochemical model derived from
the Ocean Carbon Model Intercomparison Project (OCMIP-2) biotic carbon model. This is coupled to a
model from the Parallel Ocean Program (POP), which is the active ocean component of the Community
Climate System Model version 3.0.
Three parameterizations of the silicon cycle are tested in three different cases. Each case is initiated with
observed modern silicic acid concentrations, provided by the World Ocean Atlas (2005), and is integrated for
1000 model years. In all cases, biogenic silica (opal) production is controlled by light and silicic acid
concentrations. In case 1, opal production is not limited by any additional nutrients. In case 2, opal
production is limited by phosphate, the original limiting nutrient in OCMIP. In case 3, opal production is
limited by iron, which has been included as a limiting nutrient within OCMIP for its incorporation in CCSM
POP.
The parameterization that yields output closest to observed data is used in a fourth case, in which the silicon
cycle modulates the carbon cycle. In this formulation, opal production controls production of calcium
carbonate, to represent competition between siliceous and calcareous organisms. This impacts the carbon
cycle within the model through changes in dissolved inorganic carbon (DIC) and alkalinity. This case is
compared to a control run, which does not contain a silicon cycle parameterization, and to observed data.
http://www.uta.edu/faculty/awinguth/PETM-Home.html
OS11B-1124
Cd/Ca, Ba/Ca and Pb/Ca Records of Porites Coral from Lanyu Islet, Northwestern Pacific: Contribution of Natural and Anthropogenic Sources to Seawater Trace Metal Variability
Coralline Cd, Ba, and Pb can reflect sensitively of marine environmental variability (i.e., upwelling, river flood and anthropogenic activity). To assess impacts of erosion input and anthropogenic pollution on seawater chemistry along the Kuroshio pathway, Southwestern Taiwan, Cd, Ba and Pb in coralline skeleton were examined in a Porites core (1966-1996). Monthly Cd/Ca and Pb/Ca results show large enhanced ratios during spring and winter, which can be referred to wind-blown dust during monsoon activity. On the other hand, Ba/Ca ratios reflect riverine discharge peak intensity during spring and autumn. It is clear in the long- term trend that low Cd, Ba and Pb appeared in 1966-1979, high Pb in 1979-1988, and high Cd and Ba in 1988-1994. In particular, Ba/Ca baseline increases gradually since 1985, which is corresponding to a period of heavy local reconstruction in Lanyu islet.
OS11B-1125
Sources and Evolution of Anthropogenic Lead in Northwestern Pacific Seawater: High Resolution Coral Pb Isotope Record
Lattice-bound Lead in scleractinian coral skeletons provides a potential tracer to investigate the historical anthropogenic disturbance in the surface ocean. In this study, a Porites coral core collected from an islet offshore southeastern Taiwan was used to reconstruct decadal lead variation in surface seawater at northwestern Pacific. Seasonal Pb/Ca peaks are in accordance with rainfall episodes, while the long-term trend shows high lead input before 1970s. This can be attributed to extensively use of alkyl-lead in the region. Moreover, temporal variations of lead isotope display a significant change of lead sources in mid-20 th, coinciding with the Australian Pb imported period. These isotopic signatures also indicate contribution from China/Japan pollutant through atmospheric circulation during 1962-1998. This preliminary study infers that Pb in surface seawater is dominantly transported by ocean current and aeolian deposition from adjacent urban area, while Pb concentration may not reflect entirely the source flux due to potential loss during transportation.
OS11B-1126
PB CONCENTRATION AND STABLE PB ISOTOPES IN DATED-CORE SEDIMENTS IN THE ULLEUNG BASIN, EAST/JAPAN SEA
This study investigated temporal and spatial variation of Pb and stable Pb isotopes accumulated in Ulleung Basin core sediments (12) using MC ICP/MS in order to identify the sources of anthropogenic Pb in the East/Japan Sea. Leached (1M HCl) Pb concentration and isotope ratios (207Pb/206Pb and 208Pb/206Pb) ware constant at around 20 mg/kg and 0.845 and 2.092 from 1700 to 1930 year, respectively and increased steadily up to 40 mg/kg and 0.873 to 2.129 at the beginning of 2000s, increased up to twice in concentration and as much as 3.31% and 1.64%. On the other hand, residual Pb concentrations were nearly constant for past 400 yrs. From the vertical profiles of Pb concentration and two end-members mixing model, anthropogenic Pb concentration and isotope ratios were estimated. The transport pathways of anthropogenic Pb could be estimated from 1) the comparison between the inventories of excess 210Pb in each sediment column and the input fluxes from the atmosphere and seawater column, 2) between the accumulation rate of anthropogenic Pb and mass accumulation rate of sediments. From the detailed evaluation for the pathways and isotope ratios of anthropogenic Pb, we proposed probable source of anthropogenic Pb. Pb emission by coal burning from the China and Korea initiated the accumulation of anthropogenic Pb in the sediments of East/Japan Sea from 1930s. The accumulation of Pb increased by the addition of anti-nocking agents from both countries untill beginning of 1990s, but from the middle of 1990s to the present, the phase-out of gasoline additives and the rapid increase of coal burning from China maintained the atmospheric Pb levels in the Ulleung basin nearly similar to before. However the local sources (e.g. ocean dumping) within this basin might take an important role in the rapid increase of anthropogenic Pb accumulation in slope areas from the middle of 1990s.
OS11B-1127
Heavy Metals Contamination in Coastal Sediments of Karachi, Pakistan
Toxic compounds such as heavy metals exert chronic and lethal effects in animals, plants, and human health. With the rapid industrialization, urbanization, and economic development in Karachi, heavy metals are continuing to be introduced to estuarine and coastal environment through rivers, runoff and land-based point sources. Pollution in the Karachi coastal region (167 km long) is mainly attributed to Lyari and Malir Rivers flowing through the city of Karachi. Both rivers are served by various channels of domestic and industrial wastes carrying more than 300 million gallons per day untreated effluent of 6000 industries and ultimately drain into the beaches of Arabian Sea. Concentrations of selected heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in surface sediments from eighty-eight sites in Karachi coastal region were studied in order to understand metal contamination due to industrialization, urbanization, and economic development in Karachi. Sediment samples were collected in 2005 and 2006. We have found that heavy metal concentrations in surface sediments varied from 0.006 to 24.3 ug/g for Cd, 5.1 to 95 ug/g for Co, 2.9 to 571 ug/g for Cr, 6.9 to 272 ug/g for Cu, 0.55 to 6.5% for Fe, 1.2 to 318 ug/g for Mn, 7.5 to 75 ug/g for Ni, 6.3 to 121 ug/g for Pb, and 3.3 to 389 ug/g for Zn. Enrichment factors (EFs) were calculated to assess whether the concentrations observed represent background or contaminated levels. The highest levels of metals were found to be at the confluence of the Lyari and Malir River streams at the Arabian Sea, indicating the impact of the effluents of the highly urbanized and industrialized city of Karachi. Furthermore, this study assessed heavy metal toxicity risk with the application of Sediment Quality Guideline (SQG) indices (effect range low/effect range median values, ERL/ERM). Results indicated that the potential toxicity of marine environment can cause adverse biological effects to the biota directly and the human health indirectly through food web chain.
OS11B-1128
Determination of Bimolecular Rate Constants for Reactions of Hydroxyl Radical with Pharmaceutical and Cosmetics Chemicals - Implications to the Fate in the Aquatic Environment
Large organic compounds such as hyaluronic acid and chondroitin sulfate are often used in pharmaceutical and cosmetics products, but their chemical degradation pathways are not well understood. To better elucidate their fate in the aquatic environment, we initiated a study to determine bimolecular rate constants between these organic compounds and hydroxyl radical (OH), which is a potent oxidant in the environment. The lifetimes of many organic compounds are determined by reactions with OH radicals, and the lifetime of OH is often controlled by reactions with organic compounds. To determine these bimolecular rate constants we used a competition kinetics technique with either hydrogen peroxide or nitrate as a source of OH and benzoate as the competing sink. Since the molecular weights of some of the large organic compounds we studied were not known, we used dissolved organic carbon (DOC) concentrations to determine mole-carbon based bimolecular rate constants, instead of the commonly used molar-based bimolecular rate constants. We will report the mole-carbon based bimolecular rate constants of OH, determined at room temperature, with hyaluronic acid, chondroitin sulfate and some other large organic compounds.
OS11B-1129
Quantitative Applications of Deep-Sea Raman Spectroscopy: Geochemistry of 1,4- thioxane in sea water
We have developed quantitative Raman spectroscopic techniques for the novel detection of dissolved species in sea water to determine their fundamental properties. In this example we use a field-deployable Raman system to determine the solubility of 1,4-thioxane (TO) in sea water as 0.65 to 0.63 mol/kg H2O between 4.5°C and 25.0°C (which varies greatly from an earlier report of 2.75 mol/kg H2O), and to assess the conditions under which it may form a hydrate. TO is of unusual environmental interest as a breakdown product of the chemical weapon mustard gas, and thus development of non-contact field- deployable sensing techniques is highly desirable. Raman spectroscopy has typically been considered as only a qualitative technique due to the complexity of the optical path and the substantial changes in components between different instruments. We show here that by self-referencing to the ubiquitous water peaks (the water ν2 mode from 1500 to 1800 cm-1) we can derive quantitative information with a precision of ± 4%, and provide essential new information. The long-term fate of large quantities of chemical weapons disposed of in the ocean some 50 years ago is poorly known. Part of this lacking knowledge can be attributed to the hazards associated with the direct study of these materials leaving ocean scientists vulnerable when sampling in inadequately marked sites. Mustard gas (1,1'-thiobis[2-chloroethane]) represents the largest tonnage of material disposed of until the 1972 London Convention banned such activities. Thus there is strong interest in determining the fate and lifetime of these materials, their decomposition products, and the extent of the affected zones. We have earlier shown that TO forms a hydrate with a help-gas, such as methane or hydrogen sulfide, and that the temperature, pressure and reducing conditions required for hydrate formation commonly occur at known disposal sites. In fact, a mixed TO hydrate is more stable than methane hydrate by almost 10°C. Here we show that in the presence of hydrate formation, as with other hydrate guest molecules, the TO solubility trend was reversed and solubility decreased in response to lower temperatures. The relatively low solubility in water coupled with the ability to form a hydrate within marine sediments can greatly decrease molecular mobility and increase chemical lifetime. Mixing will reduce concentrations of TO in the ocean water column below the detection limits established here. But the solubility data reveals the concentrations that will characterize marine pore waters at such sites, and these are readily detectable. Development of pore water Raman sensing techniques are underway.
OS11B-1130
UV-Induced Serial-oxidations of Marine Dissolved Organic Carbon (DOC) and Biogeochemical Implications
Serial-oxidation of dissolved organic carbon (DOC) to CO2 via a 1200 W medium-pressure Hg lamp revealed an inverse relationship between the proportion oxidized and radiocarbon content (Δ14C). In samples from both 20 m and 2000 m depth of the NE Pacific (Station M, 34° 50' N, 123° 00' W), ~50 % of the DOC was significantly enriched relative to bulk DOC Δ14C values. In 20 m DOC, the initial 1 % oxidized was significantly depleted relative to DIC Δ14C, indicating concurrent photo-mineralization of Δ14C-depleted material. These results are consistent with molecular and isotopic heterogeneity throughout the water column, as well as preliminary evidence for a photochemical sink of Δ14C-depleted DOC. Modified procedures and a well-constrained DOC isotopic composition may improve estimates of the natural mineralization of Δ14C-depleted DOC by sunlight.
OS11B-1131
Hurricane Contribution to pCO2 Distribution in the Gulf of Mexico
The influence of hurricanes on the ocean carbon cycle and air-sea carbon exchange is not well understood. It has been suggested that hurricanes play an important role in the global ocean-atmosphere CO2 exchange; however, uncertainty is large. One of the factors that contributes to such uncertainty is limited partial pressure of CO2 (pCO2) data. Therefore, the purpose of this study is to develop a regional satellite-based technique that extends the spatial and temporal coverage of pCO2 in order to assess the impact hurricanes have upon pCO2 distribution. The technique involves creation of a multiple linear regression from in situ observations and application to MODIS-Aqua satellite data. The approach will be described and demonstrated for hurricanes from the 2005 season in the Gulf of Mexico.
OS11B-1132
Improved Segmented-Flow Tracer-Monitored Titration for Automated Measurement of Total Alkalinity in Seawater
The four measurable inorganic carbon parameters commonly measured as part of oceanic carbon cycle studies are total dissolved inorganic carbon (DIC), total alkalinity (AT), hydrogen ion concentration (pH) and partial pressure of CO2 (pCO2). AT determination is critical for anthropogenic CO2 inventory calculations and for quantifying CaCO3 saturation. Additionally, measurement of AT in combination with one other carbonate parameter can be used to describe the inorganic carbon equilibria. Current methods for measuring AT require calibrated volumetric flasks and burettes, gravimetry, or precise flow measurements. These methods also require analysis times of ¡Ý15 min and sample volumes of ¡Ý200 mL, and sample introduction is not automated, resulting in labor-intensive measurements and low temporal resolution. The Tracer Monitored Titration (TMT) system was previously developed at the University of Montana for AT measurements. The TMT is not dependent on accurate gravimetric, volumetric or flow rate measurements because it relies on a pH-sensitive indicator (tracer) to track the amount of titrant added to the sample. Sample and a titrant-indicator mixture are mechanically stirred in an optical flow cell and pH is calculated using the indicator equilibrium constant and the spectrophotometrically determined concentrations of the acid and base forms of the indicator. AT is then determined using these data in a non-linear least squares regression of the AT mass and proton balances. The precision and accuracy of the TMT are 2 and 4 micromol per kg in 16 min using 110-mL of sample. The TMT is dependent on complete mixing of titrant with the sample and accurate absorbance measurements. We have developed the segmented-flow TMT (SF- TMT) to improve on these aspects and decrease sample analysis time. The TMT uses segmented flow instead of active mixing and a white LED instead of a tungsten-halogen light source. Air is added to the liquid flow stream, producing segments of liquid separated by air bubbles. Because liquid is not transferred between flow segments, there is rapid flushing which reduces sample volume to <10 mL. Additionally, the slower movement of liquid at the tube walls compared to that at the tube center creates circulation within each liquid segment, mixing the sample and eliminating the need for mechanical stirring. The white LED has higher output at the wavelengths of interest, thus improving the precision of absorbance measurements. These improvements result in a faster, simpler method for measuring AT.
OS11B-1133
Widespread influence of resuspended sediments on oceanic particulate organic carbon
Particulate organic carbon (POC) in the ocean oftentimes exhibits lower radiocarbon isotope ratios (Delta C- 14) than expected if its sole source were POC recently produced by primary production and export from the overlying surface waters. We have observed a strong correlation between Delta C-14 values of organic carbon and aluminum content in sinking particles. This correlation is remarkably consistent over a range of oceanic settings. The correlation implies that old organic carbon associated with lithogenic material from sediment resuspension is responsible for the radiocarbon-depleted values of oceanic POC (as opposed to other processes such as incorporation of dissolved inorganic carbon or dissolved organic carbon into POC at depth). Resuspension of sediment and its subsequent lateral transport therefore appears to be an important component of oceanic carbon cycle, particularly over or adjacent to continental margins, and requires consideration in models of carbon export and burial.
OS11B-1134
Isotopic Signatures of Particulate Organic Matter Sources, Transport Pathways and Diagenesis on the Waiapu Margin, New Zealand
The significant contribution of short mountainous river systems, including the Waiapu River on New Zealand's East Cape, to the global fluvial sediment supply necessitates further investigation into the processes that influence the character and composition of organic carbon associated with these high sediment discharge systems. Organic matter preserved on the continental margin originates from terrestrial sources such as ancient, 14C-dead kerogen and fresh and aged soil carbon, and marine sources of carbon produced in the water column. Carbon and nitrogen isotopic compositions of rocks and soils in the watershed and sediment and benthic biota from the margin have been used to a) investigate possible sources of organic carbon to the margin, and b) consider potential transport, burial, and preservation processes that may alter the isotopic signature of the carbon source out on the continental margin. Carbon and nitrogen isotopic signatures of sediment typically become more enriched in the heavier isotope with increasing distance from the river mouth, indicative of a transition from terrestrial to marine carbon sources. In addition to source variation, possible explanations for these geochemical trends include diagenetic alteration and particle sorting. Structural deformation of the shelf complicates the sediment dynamics, resulting in localized areas that deviate from these trends, which suggests potential routing of sediment deposition and burial that also influences geochemical composition. One such area south of the river mouth near the shelf break is a bathymetric high where winnowing effects may have led to coarser particle sizes. An enrichment in 13C relative to 12C is consistent with this being a region of low sediment accumulation experiencing either a replacement of terrestrial carbon by marine OC or an enrichment of kerogen by the loss of more reactive OC phases. In contrast, several bathymetric lows near the river mouth have served as accumulation zones for terrestrial carbon and fine sediments.
OS11B-1135
Use of Carbon and Nitrogen Stable Isotopes to Study Late Pleistocene to Holocene Environmental Change in the Waipaoa Sedimentary System, New Zealand
The stable isotopic composition of organic matter in continental margin sediments provides a useful, long- term record of environmental change. The Waipaoa River watershed, New Zealand, represents a system of interest due to its very large sediment supply and well known, relatively recent history of anthropogenic disturbance. Three cores taken by the RV Marion Dufresne in January 2006 on the continental shelf offshore from the river mouth provide a record extending into the late Pleistocene, dating as far back as 14,000 years. Analyses of terrestrial sources, soil profiles, sedimentary rocks and riverine sediments from within the watershed create a more holistic understanding of the current and past source to sink relationships associated with the Waipaoa sedimentary system and its influence upon the marine isotopic record. Shoreline progradation, hillslope erosion and gully incision, and the capture of river tributaries are examples of terrestrial processes that are hypothesized to influence isotopic ratios and may leave identifiable imprints in the marine stratigraphic record. By coupling the carbon and nitrogen stable isotope records with radiocarbon data a timeline of environmental processes in the area is derived as well as more detailed source apportionments.
OS11B-1136
Tidal Inundation Control on Foraminiferal Biofacies and Stable Isotope Distributions in a Shallow Arid System Lagoon: Sur, Sultanate of Oman
This study examined the interrelationship between benthic foraminifera, stable isotopes (Δ18O) and elevation in a small micro-tidal lagoon in Sur, Sultanate of Oman. Sur Lagoon is a shallow, tidally controlled system that communicates with the open sea through a narrow subtidal entrance channel. The lagoon is largely composed of intertidal sand and mudflats with fringing mangroves. A total of three wadis empty into the lagoon, supplying freshwater and sediment during the rainy season. Q-mode cluster analysis of the foraminiferal data (n=54) revealed three main biofacies related to elevation (E): Subtidal (Eavg = -0.829 m.s.l.), mid to low intertidal (Eavg = 0.315 m.s.l.), and high intertidal (Eavg = 0.582 m.s.l.). The subtidal biofacies is largely controlled by the presence of Amphistegina sp. and Ammonia inflata. Ammonia parkinsoniana dominates the mid to low intertidal zone; whereas miliolids characterize high intertidal areas. Stable isotopic analysis on Ammonia parkinsoniana discriminated between subtidal and intertidal zones. Subtidal locations which are always inundated, have more negative Δ18O values (Δ18Oavg = -1.652 ± 0.096 ‰) than intertidal zones which experience high evaporation during exposure (Δ18Oavg = -1.347 ± 0.411 ‰). In the intertidal environment, exposure resulting between tidal cycles ranges from 8.2 to 11.5 hrs/day. As exposure time increases with elevation, surface evaporation rates increase leading to more positive Δ18O values. The combined use of foraminiferal and stable isotopic analysis could prove useful in reconstructing sea level and in discriminating between marine incursions associated with storms and tsunamis.