Seasonal and Spatial Variations in the Flux of Particulate Organic Carbon Derived from Thorium-234 in the U.S. JGOFS Southern Ocean Process Study

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9530861 Buessler 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. The objective of this component is to provide a quantitative estimate of upper ocean export fluxes of particulate organic carbon on spatial and temporal scales relevant to understanding biological and physical processes. The approach is to measure the concentration of thorium-234, a particle reactive tracer with a half-life of 24.1 days, and its ratio to particulate organic carbon (POC) and particulate organic nitrogen (PON) in order to derive the appropriate export data. The research activities include the collection of thorium-234 and POC samples on cruises spanning the seasonal production cycle in the Antarctic Polar Front Zone. The results will be used to constrain the upper ocean sinking fluxes and to derive relationships between production and export across physical gradients (i.e. fronts) during seasonal transitions between low and high productivity. The sensitivity of these rate estimates to model assumptions and data quality will also be examined. ***