We determined the in situ primary productivity, particle absorption, pigment concentrations, and photosynthetic quantum yields during two Southern Ocean cruises in 1997 and 1998 in the Pacific sector of the Antarctic Circumpolar Current (ACC), and in the Ross Sea. Integrated primary productivity in the Ross Sea during the austral summer averaged 762 mg Cm-2 d(-1) (range: 413-1200 mg Cm-2 d(-1)), and mean integrated chlorophyll a levels were 80.6 mg m(-2) (range: 47.8-155 mg m(-2)). The mean (+/-standard deviation) quantum yield was 0.09 (+/-43%)mol C Ein(-1) during summer in the Ross Sea. Less than 2% of the depth variability in quantum yield in the Ross Sea was attributable to light absorption by photoprotective pigments. There was an inverse relationship found between the value of the in situ maximum quantum yield (phi[max]) and the ratio of particulate organic carbon to nitrogen (POC:PON), indicating that variations in quantum yields were controlled largely by nutrient availability. POC:PON ratios near Redfield ratio of 6.6 were found to have in situ phi(max) values near the theoretical maximum of 0.12 mol C Ein(-1). POC-to-particulate iron values were also found to have been lower in high phi(max) regions. Integrated primary productivities and chlorophyll a levels in the ACC during the early summer were similar to those in the Ross Sea. The mean integrated primary productivity was 734 mg C m(-2) d(-1) (range: 606-839 mg Cm-2 d(-1)), and the mean integrated chlorophyll equaled 56.2 mg m(-2) (range: 33.3-71.9 mg m(-2)). The mean (+/-standard deviation) quantum yield was 0.04 (+/-28%) mol CEin(-1) and was less than the mean value measured for the Ross Sea. As in the Ross Sea, light absorption by photoprotective pigments was responsible for <2% of the variability in quantum yield. There was no discernable relationship found between in situ phi(max) and elemental ratios of the particulates, although the sample size for the ACC was smaller (n = 4) compared to the Ross Sea (n = 10). Overall, the phytoplankton of the ACC required higher irradiance than the phytoplankton of the Ross Sea to saturate photochemistry. (C) 2003 Elsevier Science Ltd. All rights reserved.
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