Temporal variability of CO₂ flux at the air-sea interface in the Indian and Southern ocean, south of Tasmania

Measurements of fCO2, TCO2, nutrients and Chl-a were performed between Hobart, Australia and Dumont D'Urville, Antartica during the Austral Spring and Summer (October to March) in 1996/97 (4 sections) and 2002/03 (8 sections). The results show that :During the spring and summer the SubAntarctic Region (43°S - 53°S) is a large CO2 sink and the interannual variability is not significant.South of 62°S, there is a large spatio-temporal variability, mainly influenced by sea-ice dynamics.High summer interannual variability in the Permanent Open Ocean Zone (POOZ) (53°S -62°S) is evident. Our results show contrasted values, close to equilibrum in 1997 (–0.3 mmol/m2/d) and with a strong sink in 2003 (–20.6 mmol/m2/d). An increase in phytoplankton biomass accounts for this large CO2 sink. This increase in biomass cannot be a consequence of changes in SST, light/mixing regime and/or stratospheric ozone total amount, but may be due to episodic iron deposition coming from Australia and could be linked with 2002/03 ENSO event.