Distribution of CO sub(2) species, estimates of net community production, and air-sea CO sub(2) exchange in the Ross Sea polynya

• Published in: Journal of Geophysical Research, Washington, DC Washington, DC, 1998-02, Vol.103 (C2), p.2883-2896
• Main Authors: Bates, N R, Hansell, DA, Carlson, CA, Gordon, LI
• Format: Article
• Language: English
• Subjects: Marine; Phaeocystis
• ISSN: 0148-0227

Measurements of surface total carbon dioxide (TCO sub(2)), alkalinity, and calculated pCO sub(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 sub(2), fluxes of carbon within the ocean, and rates of air-sea exchange of CO sub(2). Depletions of TCO sub(2), pCO sub(2), and nitrate+nitrite were considerable ( similar to 70-150 mu mol kg super(-1), 80-150 mu atm, and 10-20 mu mol kg super(-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 sub(2) was undersaturated by similar to 50-150 mu atm, and air-sea gas exchange of CO sub(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 sub(2) and nitrate+nitrite across repeated transects along 76 degree 30'S. Mean NCP rates across the polynya ranged from 0.86 to 0.98 g C m super(-2) d super(-1). These values may be underestimated by 5-25% because of the contribution of atmospheric CO sub(2) to the surface layer through gas exchange. Export of carbon from the surface to depth was at least 55-60% of NCP rates.