CSIRO Marine and Atmospheric Research
Past Seminars

Friday 16 April 2004, 11.30 am (Tas time)

CSIRO Auditorium, Hobart and via videoconference to Floreat and Cleveland

Helen Phillips
CSIRO Marine Research, Hobart

Analysis of ARGO data -
Anomalously fresh conditions off NW Australia during 2000-2002

During La Nina, when the Southern Oscillation Index is positive and the eastern Pacific Ocean is cooler than average, the Indonesian region experiences unusually wet conditions. At the end of the 1990s, a La Nina event occurred that persisted for much longer than usual: 2 years (1998-2000) instead of the more typical 9-12 months.

In 1999, CSIRO Marine Research began deployment of Argo profiling floats off northwest Australia. From the floats, which measure temperature and salinity profiles every 10 days, we now have a 4 year record of ocean conditions in the region. This record reveals very fresh conditions from 1999 to the end of 2002 in the upper 200 metres of the water column over the entire region of ocean between Indonesia and Australia. Averaging over the region 100ºE-125ºE, 25ºS-5ºS, and the depth range 0-200m, the water is fresher than climatology by approximately 0.2 psu.

We compare the float results with historical CTD sections dating back to 1989, thermosalinograph data during 1999-2002, and surface freshwater flux time series from NCEP and ECMWF. Together these show strong interannual variability in the upper ocean freshwater content of the region and that the recent freshening is unprecedented in the last 20 years.

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