Role of plankton communities in pCO2 sea-air variation in the southwestern Atlantic Ocean

SCHLOSS, IRENE R., G. A. FERREYRA, M .E. FERRARIO, G. O. ALMANDOZ, R. CODINA, A. BIANCHI, C. F. BALESTRINI, H. A. OCHOA, D. RUIZ PINO AND A. POISSON

MARINE ECOLOGY PROGRESS SERIES

Inter-Research

Año: 2006 vol. 332 p. 93 - 106

0171-8630

The influence of the plankton community structure on carbon dynamics was studied on the surface waters of the Argentinean continental shelf (SW Atlantic Ocean) in summer and fall 2002, 2003 and 2004. The horizontal changes in plankton community respiration (R), net community production (NCP) and gross primary production (GPP) were (i) compared with the difference in the partial pressure of CO2 (pCO2) between the sea surface and the atmosphere (.pCO2), (ii) compared with oxygen saturation and (iii) related to the microscopic phytoplankton assemblages. This area, which has recently been shown to be a CO2 sink, had an average surface oxygen saturation of 108.1%, indicating that net photosynthesis could have played a dominant role in the CO2 dynamics. At most stations, the production:respiration (GPP:R) ratio was greater than 1, indicating that planktonic communities were autotrophic; the average GPP:R ratio for the whole study was 2.99. Phytoplankton biomass (chlorophyll a) and NCP showed inverse relationships with .pCO2 and direct relationships with %O2 saturation when phytoplankton assemblages were dominated by diatoms (30% of the stations). This was not the case when small (¡Â 5 ¥ìm) flagellates were the most abundant organisms. Although NCP was mostly positive for both groups of stations (i.e., diatom dominated or small flagellate dominated), other physical and biological processes are thought to modify the CO2 dynamics when small flagellates are the prevailing phytoplankton group.