Tasman Sea biological response to dust storm events during the austral spring of 2009

Abstract

During the austral spring of 2009 several significant dust storms occurred in south-east Australia including the so-called ‘Red Dawn’ event in late September. Estimates of 2.5 Mt total suspended particulate sediment lost off the Australian coast in the 3000 km long dust plume make it the largest off-continent loss of soil ever reported. Much of this material was transported over the coastline of New South Wales and into the adjacent Tasman Sea. Long-term model simulations of dust deposition over the south-west Tasman Sea suggest the amount deposited during the spring of 2009 was approximately three times the long-term monthly average. Previous satellite-based analyses of the biological response of Tasman Sea waters to dust-derived nutrients are equivocal or have observed no response. Satellite-derived surface chlorophyll concentrations in the southern Tasman during the spring of 2009 are well above the climatological mean, with positive anomalies as high as 0.5 mg m–3. Dust transport simulations indicate strong deposition to the ocean surface, which during both the ‘Red Dawn’ event and mid-October 2009 dust storm events was enhanced by heavy precipitation. Cloud processing of the dust aerosol may have enhanced iron bioavailability for phytoplankton uptake.