OS44B-01 16:00h
The Marine Carbon Cycle - A Global View From the Deep
In this study we present a global distribution pattern and budget of the minimum flux of particulate organic carbon to the sea floor (J$_{POC\alpha}$). The estimations are based on regionally specific correlations between the diffusive oxygen flux across the sediment-water interface, the total organic carbon content in surface sediments, and the oxygen concentration in bottom waters. For this, we modified the principal equation of Cai and Reimers (1995) as a basic monod reaction rate, applied within 11 regions where in situ measurements of diffusive oxygen uptake exist. By application of the resulting transfer functions to other regions with similar sedimentary conditions and areal interpolation, we calculated a minimum global budget of particulate organic carbon that actually reaches the sea floor of $\sim$0.5 GtC yr$^{-1}$ ($>$1000 m wd), whereas approximately 0.002-0.12 GtC yr$^{-1}$ is buried in the sediments (0.01-0.4 % of surface primary production). Despite the fact that our global budget is in good agreement with previous studies, we found conspicuous differences among the distribution patterns of primary production, calculations based on particle trap collections of the POC flux, and J$_{POC\alpha}$ of this study. These deviations, especially located at the southeastern and southwestern Atlantic Ocean, the Greenland and Norwegian Sea and the entire equatorial Pacific Ocean, strongly indicate a considerable influence of lateral particle transport on the vertical link between surface waters and underlying sediments. This observation is supported by sediment trap data. Furthermore, local differences in the availability and quality of the organic matter as well as different transport mechanisms through the water column are discussed.
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OS44B-02 16:15h
Carbon Fluxes to the Sediment in Monterey Bay: August 2001-Febuary 2002
Carbon and nitrogen content of oceanic sinking particulate matter collected in sediment traps between August 2001 and February 2002 in Monterey Bay on the northern California Coast was measured. This time interval captures seasonal changes from the end of the summer and until the end of winter, and characterized by a transition from high to low sea surface temperatures and no significant upwelling. The carbon (C) and nitrogen (N) fluxes to the deep ocean were estimated and the isotopic composition of the sinking particulate matter determined. A decrease in the fluxes of carbon and nitrogen over this interval was observed. This decrease corresponded to a decrease in total phytoplankton abundance. The isotopic composition of the sinking particulate matter is consistent with a marine origin with minimal terrestrial input. The data point to a close relation between primary production and carbon and nitrogen fluxes in Monterey Bay during the sampling interval.
OS44B-03 16:30h
Composition and Sources of Suspended Particulate Organic Carbon (POC) in the Ocean Implied by Radiocarbon and Stable Carbon Isotope Ratios of its Organic Fractions
Suspended particulate organic carbon (POC) is a dynamic carbon pool in the ocean and is expected to exchange carbon with other organic carbon pools such as sinking POC and dissolved organic carbon (DOC). To study carbon cycling through suspended POC, radiocarbon and stable carbon isotope ratios of three organic fractions (extractable lipids, acid-soluble, and acid-insoluble fractions) were measured on samples collected from various depths at an abyssal station (Station M, 220km off the central California coast). Stable carbon isotope ratios of the acid-insoluble fraction were distinctly lower than those of the acid-soluble fraction, but similar to those of the extractable lipids. This trend was persistent throughout the water column. A similar trend was observed for sinking POC from 3450m depth at the same station (Hwang and Druffel, 2003). Radiocarbon isotope ratios of suspended POC are also presented and compared to the results of sinking POC and DOC. Implications of these isotope results on the composition of the acid-insoluble fraction and exchange among the organic carbon pools in the ocean are discussed.
OS44B-04 16:45h
A modeling study using the mineral ballasting tecnique for POC flux prediction in the ocean with a focus on comparison with sediment trap data and interactions with the sediments.
The fluxes of POC below the euphotic zone in the ocean are modeled using a mineral ballasting approach with the HAMOCC5.1 Carbon Cycle Model. {\it Armstrong et al.}[2002] and {\it Klaas and Archer}[2003] have shown that particulate organic carbon(POC) fluxes at depths of 2,000m and more in the ocean have a statistically significant correlation to the fluxes of the biominerals CaCO$_{3}$ and opal, and also lithogenic material, at those depths. Utilizing their parameterization, the goal of this study is to improve agreement between modeled POC fluxes and sediment trap data over the previous approach, a distribution curve modified from {\it Martin et al.}[1978] to include an iron dependency. A baseline run of the model with the mineral ballasting parameterization has been integrated for 10,000 years and is compared with a reference run of the model and with data. The long integration time is especially useful for studying the interactions with the sediments. The modeled POC fluxes do not significantly improve in agreement with sediment trap data from the reference run, but the overall distribution of CO$_{2}$ in the ocean does improve. At 3,000m, the modeled CO$_{2}$ is nearly the same as the values from GLODAP data, with model-data differences not exceeding about 60 mol/kg or 2%. The alkalinity distribution at 3,000m is similar to the reference run and agrees reasonably well with data. In addition to the baseline run of the model with the ballast parameterization, sensitivity experiments were conducted to test the response of the ballast model to changes in the e-folding penetration depth of CaCO$_{3}$ and opal, the sediment dissolution constant, and the PIC:POC ratio. Each of the experiments was integrated 10,000 years to allow for interactions with the sediments. The model was sensitive to each of these parameters, and in the case of increasing the PIC:POC ratio from 0.20 to 0.25, improved the tracer distributions.
OS44B-05 17:00h
A High Iron, Low Chlorophyll Coastal Ecosystem: the Gulf of Aqaba, Red Sea
The Gulf of Aqaba, Red Sea, is a deep, narrow, semi-enclosed oligotrophic basin surrounded by desert. Precipitation and runoff are close to zero and benthic sources of iron are minimized by the steep shelf and intense summertime stratification. Exchange of seawater between the Gulf and the Red Sea proper occurs only across a 250 m sill at the southern end. This system represents an end-member with respect to aeolian dry deposition of iron to the ocean. We have measured dissolved and total iron concentrations in the Gulf during the stratified summer (August 2003) and well mixed winter (March 2004) seasons. Profiles from the middle of the Gulf in summer show a strong surface maximum in dissolved ($<$0.2 $\mu$m) and total dissolvable (dissolved plus particulate) iron. Dissolved concentrations are 6-10 nM at the surface and decrease abruptly to ~0.7 nM below the surface mixed layer (50 m). Total dissolvable concentrations are 10-40 nM at the surface and decrease to ~ 4 nM below the mixed layer. In winter, profiles are uniform throughout the water column, with dissolved iron about 1 nM and total dissolvable iron about 3 nM. Coupled with a yearlong record of dust deposition from an on-site aerosol collector, these data provide insight into the residence time and solubility of iron in an oligotrophic coastal system. Preliminary analysis suggests residence times in the mixed layer with respect to dust deposition in both seasons are on the order of a day for total iron, and a week for dissolved iron. Although observed iron concentrations are high compared to the open ocean, given the extremely high dust deposition to the Gulf, and very low biological productivity, the fact that the concentrations are not much higher suggests a low solubility for dry-deposited aerosol iron.
OS44B-06 17:15h
Effects of an Asian Dust Storm on the Gulf of Alaska: Trace Metal Evidence and Biological Consequences
In April 2001, a large dust storm originating in the Gobi and Takla Makan deserts resulted in large quantities of dust to be transported to the northeastern Pacific Ocean. Off the California coast, dissolved iron and aluminum concentrations determined before and after the dust traversed the North Pacific show increases of 0.5nM and 2nM respectively (Johnson, 2003). The most concentrated plume of dust traveled toward the eastern Gulf of Alaska. Every year anticyclonic mesoscale eddies, transporting coastal waters offshore, form off the coast of the Queen Charlotte Islands, British Columbia. These Haida eddies begin with high concentrations of trace metals which deplete over time. Evidence of 2001-dust deposition is seen in elevated dissolved aluminum concentrations (up to 7nM) in the eddy, which stay elevated months after the dust was deposited. By June 2001, dissolved zinc concentrations in the eddy surface mixed layer are low (below 0.3nM) and decrease slightly by September 2001. Dissolved cadmium concentrations dropped drastically (from 0.4nM to 0.09nM) from June to September 2001 in the Haida-2001 eddy coinciding with a large increase in coccolithophore production. This coccolithophore increase was five times greater than what was seen in the Haida-2000 eddy and twenty times that of the reference station. Based on our observations and by comparison with a shipboard Zn-Fe-enrichment study, we hypothesize that dust deposition into surface waters promotes growth first of diatoms and then of coccolithophores once zinc is depleted. The presence of dust remnants held within a quasi-isolated mesoscale eddy allows us to draw conclusions about succession following dust deposition events and yields further information regarding interactions between trace metal supply and primary production in the NE Subarctic Pacific.
OS44B-07 17:30h
Evaluation of Electrodialysis as Part of an Improved Method to Concentrate Dissolved Organic Matter from Seawater
A major obstacle in the study of marine dissolved organic matter (DOM) has been isolating from seawater sufficient quantities for analysis of this highly dilute and chemically complex material. This research explores the application of electrodialysis (ED) in combination with reverse osmosis (RO) as a method to concentrate DOM from seawater. RO methods recover a significant fraction (90%) of DOM from fresh waters with little physical or chemical alteration, and similar high recoveries of DOM have been observed in preliminary tests using estuarine waters of varying salinity. Unfortunately, the extent to which DOM in saline waters can be concentrated by RO is very limited, because RO membranes co-concentrate inorganic salts with DOM. At an early stage of processing, osmotic pressures become too high and/or inorganic salts precipitate from solution and foul the RO membrane. To realize the potentially high recoveries of DOM from saline waters, RO must be coupled with an independent method for removal of inorganic salts. Electrodialysis, which is a well-established process for removal of inorganic salts from aqueous solutions, is such a method. In ED, a feed stream of the sample to be de-ionized and a receiving stream of a solution that will accept the removed ions are pumped through adjacent layers of a membrane stack, which consists of several layers of alternating anion and cation exchange membranes. The membranes are made from highly crosslinked polymers and are non-porous. The direction and velocity of diffusion of the cations and anions are further mediated by a DC electrical current that flows through the membrane stack. In the first stage of testing of the ED process, samples of near-seawater salinity (28 ppt) containing 4 ppm of dissolved organic carbon were collected at the Skidaway Institute of Oceanography in Savannah Georgia. Using ED, salinity was reduced by 87% in these samples with retention of more than 95% of the DOM. These experiments indicate that ED can significantly reduce salt concentrations in saline waters with little or no loss of DOM, thus making it possible to use efficient RO methods to concentrate marine DOM.
OS44B-08 17:45h
Microscale Phosphorus Distribution and Chemistry in Marine Particles: New Insights From X-ray Absorption Near Edge Structure (XANES) Spectroscopy and X-ray Microscopy
Dissolved and particulate organic materials are a significant source of bioavailable phosphorus (P) in many aquatic environments. In order to gain a better understanding of marine P cycling, the bulk composition of dissolved and particulate materials has been the focus of studies using nuclear magnetic resonance (NMR) techniques. One puzzling observation of NMR studies is the high proportion of P as phosphonate compounds (containing a direct C-P bond) in dissolved organic matter (DOM) compared to the almost undetectable quantities of phosphonates in most living organisms and particulate organic matter. The source of phosphonates in DOM has remained a mystery and has driven the search for new methods to examine P cycling in natural samples. Scanning tandem fluorescence and transmission X-ray microscopy, together with P x-ray absorption near edge structure spectroscopy (P-XANES), provide a way to examine P composition in natural samples on sub-micron scales. These techniques were used to compositionally characterize Cariaco Basin sediment trap particulates as well as freeze-dried DOM. Elemental mapping of particulates revealed a heterogeneous P distribution characterized by several micron diameter P rich regions associated with organic phases. The proportion of P esters and phosphonates in these regions varied from 100% P esters to some areas containing greater than 50% phosphonates. The results imply a source or concentrating mechanism capable of producing highly phosphonate rich particulates. Solubilization of such particulates along with selective decompostion of non-phosphonate P may be one possible mechanism to explain the high proportion of phosphonates in DOM.