Organic Geochemical Studies in the Southern Ocean

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9531759 Wakeham This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. This work is one of forty-four projects that are collaborating in the Southern Ocean Experiment, a three-year effort south of the Antarctic Polar Frontal Zone to track the flow of carbon through its organic and inorganic pathways from the air-ocean interface through the entire water column into the bottom sediment. The experiment will make use of the RVIB Nathaniel B. Palmer and the R/V Thompson. This component concerns a cooperative study of organic matter cycling in the water column and in the surficial sediments of the Southern Ocean. The main goals of the effort are: (1) to determine how the composition and fluxes of organic material vary regionally and seasonally within the Southern Ocean, (2) to relate these variations to biological processing of the punctuated organic input and its siliceous matrix, (3) to follow the downward diagenetic fate of planktonic remains through the water column and into the underlying sediments, with special emphasis on biochemical trends reflecting substrate quality (freshness), and (4) to holistically account for total organic matter at all stages of degradation by carbon-13 analysis of bulk trap and sediment samples. The shipboard work involves collecting suspended and raining particulate material within the water column and from the underlying sediment at several sites along the proposed study transect. Suspended particles will be collected both by plankton net tows and high volume filtration of surface water. Sinking particles will be collected with modular sediment traps deployed in arrays of four. Individual traps will be designed to selectively collect sinking particles and reject swimming zooplankton without loss of sample or biocide. Two of the four traps on each array will be fitted with 12-tube subsampling carousels to study shorter term variations. The collected trap and sediment core samples will be analyzed for their basic biochemical building blocks, such as carbohydrates, amino acids, lipids, lignins, and pigments. These make up the bulk of the organic matter produced in the upper water column and are an important fraction of the material buried in the sediment. At the molecular level they can provide unequivocal information on the sources of organic matter and its decomposition at depth, and on the pathways by which biogenic material is transferred to the sediment. These data will be combined with information obtained during prior JGOFS experiments to produce a global picture of the organic chemistry of particulate matter in the ocean. ***