Changes of the oceanic CO2 sink in the Eastern Indian sector of the Southern Ocean

Changes in the carbon dioxide fugacity (fCO2) and air–sea CO2 flux observed in the Southern Ocean, south of Tasmania were analysed and compared for two different years: 1996/1997 and 2002/2003. The CO2 flux showed large and contrasting interannual changes in the permanent open ocean zone (POOZ, 53–61◦S) between the 2 yr where the oceanic CO2 sink increased from about −0.3 mmol m−2 d−1 in February 1997 to −20.6 mmol m−2 d−1 in February 2003. The strong sink in February 2003 was associated with increased phytoplankton biomass in this High-Nutrient, Low- Chlorophyll (HNLC) region. Three hypotheses that may have influenced the biomass and fCO2 changes in the POOZ were investigated: sea surface temperature (SST) and El Ni˜no/ Southern Oscillation (ENSO) event, total stratospheric ozone column and ultraviolet (UV) radiation, and atmospheric dust inputs. The strong CO2 sink in 2003 in the POOZ cannot be explained by the observed changes in SST or UV, but would be qualitatively consistent with the presence of episodic atmospheric dust inputs