Oxygen Dynamics During the JGOFS Southern Ocean Process Study

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95-30746 BENDER 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. One of the primary goals of the JGOFS program in general, and of the Southern Ocean initiative in particular, is to constrain the carbon flux in order to evaluate whether this region is a net sink or source of carbon. Interest in this program is directed towards gaining an understanding of the environmental factors that affect rates of primary production and the extrapolation of these rates over broad spatial and temporal scales. Research will focus on using oxygen to constrain carbon fluxes on three scales; large, meso and local. 1) For the large scale, air samples will be collected and the O2/N2 ratio will be measured. Oxygen concentrations in the atmosphere vary on seasonal time scales due to primary production in the spring and summer months and ventilation of the ocean in the fall and winter. Thus knowledge of the amplitude of the O2/N2 signal will provide a measure of the magnitude and timing of net production for the Southern Ocean. Air samples will be collected daily from ships that will participate in the JGOFS experiment to have high resolution records of zonal and temporal variations of the atmospheric oxygen field over the Southern Ocean. 2) Similarly, net primary productivity will be determined from the mesoscale oxygen field in two ways: first by measurement of O2/Ar ratios and del 18O of O2 in seawater collected from the mixed layer and second by continually measuring subsurface oxygen concentrations along the cruise track. These two approaches, together with the air sampling program, wi ll provide a temporally and spatially integrated estimate of net production. 3) Carbon flow will be constrained by undertaking daily measurements of gross and net oxygen production, and nitrate assimilation. Gross oxygen production is calculated by spiking and incubating seawater samples with 18O-labelled water and measuring the del 18O of the photosynthetically produced oxygen. Net oxygen production is measured by comparing the relative change in the oxygen concentration between initial and incubated samples by automated high precision Winkler titrations. These measurements will provide daily depth integrated gross and net production rates in addition to respiration rates. Furthermore, photosynthesis-irradiance experiments will measure gross and net production during cruises to extrapolate local measurements up to meso and large scale using bio-optical data from moorings and satellites.