The role of phytoplankton in carbon dioxide exchange between the atmosphere and the ocean in the Weddell Sea

DI FIORI, E; SCHLOSS, I. R.; FERREYRA, G. A.; PAPARAZZO, F.E.; RUPOLO, V; ALMANDOZ G. O.; ESTEVES, J.L.; POISSON, A.

Buenos Aires

Conferencia; XXXI SCAR, Open Science Conference; 2010

The objective of this study was to identify the potential role of Weddell Sea (Antarctica) phytoplankton communities in CO2 exchange between the ocean and the atmosphere through the balance between net primary production (NPP) and respiration (R) rates. Surface samples were collected during summers 2002 - 2005 on board ¨Almirante Irizar¨ as part of the French-Argentinean “Argau” Project. Water temperature, salinity, CO2 partial pressure (pCO2) in water and atmosphere, and dissolved oxygen were continuously measured. Oxygen saturation (%O2) and the difference between oceanic and atmospheric pCO2 (_pCO2) were calculated. Inorganic nutrients concentration and chlorophyll-a fractions (<5 ìm, 5- 10ìm and >10ìm) were determined. For 40 stations, NPP and R rates were estimated in incubations through oxygen exchange. Nutrient concentration was high in the studied area. High phytoplankton biomass, high NPP and low _pCO2 characterised frontal areas (Weddell Front and Antarctic Slope Front) as well as the ice edge and coastal areas. Areal averages were 1.05 mg m-3 chlorophyll-a, 98% %O2 and -42ppm _pCO2. The NPP:R ratio was >1 for most of the area, indicating that although %O2 was slightly subsaturated, the area would be acting as CO2 sink during austral summers, mainly due to phytoplankton activity. Phytoplankton >10 ìm contributed in more than half of total chlorophyll-a, suggesting that diatoms are mainly responsible for the NPP. Nonetheless, quali-quantitative analyses for 2004 campaign indicate that flagellates <5 ìm and diatoms represent 43% each of total phytoplankton abundance, alternatively dominating phytoplankton assemblages, both therefore contributing to CO2 sink in the Weddell Sea.