New estimates of Southern Ocean biological production rates from O sub(2)/Ar ratios and the triple isotope composition of O sub(2)

We report O sub(2)/Ar ratios (a constraint on net community production) and the triple isotopic composition of dissolved O sub(2) (a constraint on gross primary production) in samples collected from the surface mixed layer on 23 Southern Ocean transits. Samples were collected at 1-2 super(o) meridional resolution during the austral summer. Methodological limitations notwithstanding, the results constrain the net/gross production ratio, net O sub(2) production, and gross O sub(2) production at unprecedented resolution throughout the Southern Ocean mixed layer. Gross O sub(2) production rates inferred from the oxygen triple isotopes are greater than production rates calculated from a model based on remotely sensed chlorophyll. This result agrees with previous super(1) super(8)O and super(1) super(4)C incubations along 170 super(o)W. O sub(2)/Ar ratios exceeding saturation are consistently observed within the Subantarctic and Polar Frontal Zones south of New Zealand and Australia, showing that a net autotrophic community predominates during austral summer. Lower O sub(2)/Ar values are observed within the Drake Passage and Antarctic Zone, suggesting unresolved influences of low net community production, net heterotrophy, and upwelling of O sub(2)-undersaturated waters. In autotrophic waters of the austral summer mixed layer, ratios of net community production/gross O sub(2) production scatter about 0.13, corresponding to f ratios of similar to 0.25. Net community/gross O sub(2) production ratios show no meridional gradient across the Antarctic Circumpolar Current, suggesting that an approximately constant fraction of gross primary productivity is regenerated or exported. Our calculated net O sub(2) production rates are in satisfactory agreement with comparable published estimates. Net and gross O sub(2) production rates are highest in the Subantarctic and decline to the south, paralleling the well-known trend of chlorophyll a concentrations. In an analysis of variance of net O sub(2) production and gross O sub(2) production with other environmental variables, the strongest correlations are between net O sub(2) production and sea surface temperature (SST) (direct correlation), climatological [NO sub(3) super(-)] (inverse correlation), and estimates of primary productivity derived from a remote sensing (direct correlation). These trends are as expected if aerosol iron input is the most important influence on production. They are unexpected if upwelling-derived S