| Summary: | Measurements of surface total carbon dioxide (TCO 2 ), alkalinity, and calculated pCO 2 , along with water column nutrients and hydrography, were made on two cruises to the Ross Sea polynya (NBP 94-6, November-December 1994 and NBP 95-8, December 1995 to January 1996). The polynya experiences an intense phytoplankton bloom during a short period of open water conditions from mid-December to mid-February each year. Our biogeochemical observations were used to determine the temporal variability of CO 2 , fluxes of carbon within the ocean, and rates of air-sea exchange of CO 2 . Depletions of TCO 2 , pCO 2 , and nitrate+nitrite were considerable (~70–150 µmol kg -1 , 80–150 µatm, and 10–20 µmol kg -1 , respectively) and associated primarily with biological uptake during Phaeocystis and diatom blooms. Alkalinity was a conservative tracer of salinity and nitrate+nitrite. Surface pCO 2 was undersaturated by ~50–150 µatm, and air-sea gas exchange of CO 2 during open water conditions was directed from atmosphere to ocean. Observed surface stoichiometric C:N ratios were 6.66: 1 and 6.77:1 for the 2 years, consistent with global “Redfield” ratios, while C:P and N:P ratios were variable (75–141:1, 12–18:1). Estimates of net community production (NCP) rates were made using in situ changes in TCO 2 and nitrate+nitrite across repeated transects along 76°30'S. Mean NCP rates across the polynya ranged from 0.86 to 0.98 g C m -2 d -1 . These values may be underestimated by 5–25% because of the contribution of atmospheric CO 2 to the surface layer through gas exchange. Export of carbon from the surface to depth was at least 55–60% of NCP rates.
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