Australian dust storms in 2002-2003 and their impact on Southern Ocean biogeochemistry

Abstract

During late 2002 and early 2003 southern Australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent Southern Ocean. We use meteorological records of dust activity, satellite ocean colour and aerosol optical depth data, and dust transport modeling to investigate the transport and deposition of mineral dust from Australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll-a concentration in five-degree latitude bands from 40-60°S. Seasonal maxima in mean surface chlorophyll-a of ~0.5 mg m-3 were not achieved until late Jan 2003 or during February in the more southerly bands, which when compared with a 9-year satellite mean climatology suggests the phenology of the bloom in 2002-03 was atypical. Contemporaneous field data on CO2 fugacity collected on transects between Tasmania and Antarctica show that significant atmospheric CO2 drawdown occurred as far south as 60°S during February 2003. Our results provide strong evidence for a large-scale natural dust fertilization event in the Australian sector of the Southern Ocean, and highlight the importance of dust-derived nutrients in the marine carbon cycle of the Southern Ocean.