Physical and Biological Controls of CO2 Levels in the Southern Ocean: A Multi-Tracer Approach

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9530824 Quay 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 threeyear 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 two ships, the RVIB Nathaniel B. Palmer and the R/V Thompson. The Southern Ocean has been implicated, by ocean models, as an important region of oceanic uptake of anthropogenically produced carbon dioxide. There is however, little data to corroborate these model predictions. There are three characteristics of the Southern Ocean that likely have a major impact on the strength of this region as a carbon dioxide sink: deep waters upwell close the surface, high wind speeds cause rapid air-sea exchange of heat and gases, and biological productivity occurs both in the open ocean and at the ice edge. The interplay between these three processes controls the surface carbon dioxide concentrations and thus the direction and magnitude of air- sea gas exchange. This project will use a combination of chemical measurements and a wind-driven circulation model to determine how deep water upwelling in this region exchanges carbon dioxide with the surface layer, and how air-sea exchange and biological productivity offset the effects of upwelling on the surface carbon dioxide levels. The measurement and modeling activities will yield a quantitative explan ation of how the air-sea flux of carbon dioxide in the Southern Ocean is affected by circulation, gas exchange and biological productivity. The model results will be used to predict how the surface carbon dioxide levels and the ratio of carbon isotopes in the dissolved inorganic carbon pool of the ocean respond to changes in circulation rates and pathways caused by different atmospheric conditions. These results will help reconstructions of past conditions of CO2 levels in the Southern Ocean that are based on proxy measurements in marine sediments and continental ice cores. ***