Distribution of CO₂ species, estimates of net community production, and air-sea CO₂ exchange in the Ross Sea polynya

Bates, Nicholas R., Hansell, Dennis A., Carlson, Craig A. and Gordon, Louis I. (1998) Distribution of CO₂ species, estimates of net community production, and air-sea CO₂ exchange in the Ross Sea polynya. Journal of Geophysical Research, 103 (C2), 2883-2896. (doi:10.1029/97JC02473).

Abstract

Measurements of surface total carbon dioxide (TCO₂), alkalinity, and calculated pCO₂, 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 CO₂, fluxes of carbon within the ocean, and rates of air-sea exchange of CO₂. Depletions of TCO₂, pCO₂, 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 pCO₂ was undersaturated by ~50–150 µatm, and air-sea gas exchange of CO₂ 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 TCO₂ 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 CO₂ 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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