Vrginie Biophysical couplings in South Australian shelf waters under conditions of summer upwelling and winter downwelling - Results from the Southern Australian Integrated Marine Observing System (SAIMOS)

Abstract

The Southern Australia Integrated Marine Observing System, or SAIMOS, is one of five nodes operating as part of the Australia-wide Integrated Marine Observing System (IMOS). This collaborative program is designed to observe Australia’s oceans, both coastal and bluewater. Since February 2008 Physical Data has been collected for SAIMOS in both summer and winter months during 8 surveys. The data collected during summer are used to characterise the nature and dynamics of the Kangaroo Island-Eyre Peninsula upwelling system during a record upwelling event in February 2008. During this event a plume of very cool water was observed along the bottom from South of Kangaroo Island up to the Eyre Peninsula. This plume dissipated rapidly after the end of upwelling favourable winds and by March 2008 had disappeared entirely from the observations. The data are also used to study the dense high salinity outflow from Spencer Gulf observed during the winter months, and resulting from surface cooling of high salinity waters at the head of Spencer Gulf. The outflow occurs during a series of strong pulses with a period of approximately 2 weeks and duration of 1-3 days, with bottom velocities at 100 m exceeding 1 m s-1. The abundance and composition of viral, bacterial and pico- and nanoplankton communities have concurrently been investigated. In summer, the space-time dynamic of viral, bacterial and pico- and nanoplankton communities is generally driven by the plume of upwelled, cool and nutrient rich water that flows across the continental shelf, and is locally heavily influenced by the level of vertical stability of the water column. In winter, the structure of the plankton community is related to the local physical properties of the water column, i.e. dense plume of bottom waters outflowing from the Spencer Gulf, vertical stability of the water column and presence of a deep chlorophyll maximum.