CO2 dynamics in the Southern Ocean: the role of biology

SCHLOSS I.R. (1,2), FERREYRA G.A.(1), FERRARIO M.E.(2,3), BALESTRINI C.F.(4), RUIZ-PINO D.(5), POISSON A.(5)

Bremen, Alemania

Simposio; XXVIII SCAR Science & XVI COMNAP; 2004

Models dealing with CO2 dynamics mostly assign a key role to the Southern Ocean, even though its surface represents only 12% of the total oceanic surface. In situ observations have shown that, at least in the summer period, several areas of the Southern Ocean act as a sink for atmospheric CO2, but data are still scarce. The role of the different processes involved in CO2 dynamics, i.e., physical (temperature, winds, vertical mixing), chemical (carbonates chemistry) and biological uptake or release of CO2 is controversial. In this frame, a scientific co-operative program has been developed (ARGAU), based on oceanographic cruises onboard the Argentinean Icebreaker #Almirante Irizar#, allowing the continuous sampling of water to study oceanographic surface variability. This is a long term (10 year) program carried out by the Laboratoire de Biogéochimie et Chimie Marines (LBCM), UPMC, Paris VI, France, the Instituto Antártico Argentino (IAA) and the Servicio de Hidrografía Naval (SHN), both from Buenos Aires, Argentina, which started in March 2000. The difference between sea water and atmospheric CO2 content (dpCO2) is calculated, and several related physico-chemical of the different water masses, as well as meteorological parameters are measured. Phytoplankton biomass and communities composition are also studied. Community production:respiration ratios (P:R) were experimentally measured onboard since year 2002 by means of incubations of waters from different regions: the Argentinean shelf, the Antarctic Peninsula and the Weddell Sea. Results show that areas with negative dpCO2 values presented higher P:R and phytoplankton biomass than CO2 source areas. Moreover, the highest production values were associated to communities dominated by diatoms in the Southern Ocean. In this area, whenever phytoflagellates dominated the community, a P :R <1 was found, and no clear trend in dpCO2 was measured. A different pattern was found in the Southern Atlantic Ocean, when phytoflagellates where associated to negative dpCO2 values, and coccolithophoriids characterised the areas where P:R>1. It is concluded that the knowledge of the community composition is essential in understanding the fluxes of CO2 in the ocean.    Presenting Author: Dr Irene Schloss / Instituto Antártico Argentino, Depto. Ciencias del Mar / C1010AAZ Buenos Aires / Cerrito 1248 / Argentina / +54-11-4812-1689 / ischloss@dna.gov.ar  Abstract Reference No.:   ABS-2198-00199