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Salinity change in the southeast Indian Ocean

Salinity change in the southeast Indian Ocean. Helen Phillips, Susan Wijffels and Ming Feng CSIRO Marine Research Australia. The study region and example time series. WMO 53547. T. S. WMO 56509. T. S. The CARS-2000 climatology (CSIRO Atlas of Regional Seas).

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Salinity change in the southeast Indian Ocean

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  1. Salinity change in the southeast Indian Ocean Helen Phillips, Susan Wijffels and Ming Feng CSIRO Marine Research Australia

  2. The study region and example time series WMO 53547 T S WMO 56509 T S

  3. The CARS-2000 climatology (CSIRO Atlas of Regional Seas) • 4-D interpolation based on locally weighted least squares • Loess filter to interpolate data onto a uniform grid (.5 x .5) • Weighting is adjusted to allow for influence of bathymetry and land barriers • Isobaric averaging • WOD1998 supplemented by regional hydrographic data • Fairly even spread of data between 1960 and 2000 • Ridgway, Dunn and Wilkin (J. Tech. V19, 1357-1375, 2002) Temp 100m Sal 100m

  4. Float – CARS salinity difference

  5. Argo floats show very strong freshening of the upper layers from end 1999 to end 2002 Θ=22º 0.7 0 -0.7 Θ=16º Θ=10º -0.3 0 0.3

  6. Argo floats show the freshening wanes after end 2002until Nov 2003 Θ=22º 0.7 0 -0.7 Θ=16º Θ=10º -0.3 0 0.3

  7. 5 CTD sections in 1995 recorded strong salinity increases across the southeast Indian Ocean Θ=22º 0.7 0 -0.7 Θ=16º Θ=10º -0.3 0 0.3

  8. Salinity changes 1995-2003 1995 - CTD Oct 1999-Sep 2002 Oct 2002-Sep 2003

  9. NCEP Reanalysis 2 Area-averaged P-E seasonal anomaly

  10. Spatial distribution of P-E Jul 1995 – Jun 1997 Banda Sea mm/day Indo-Australian Bight Jul 1997 – Sep 1998 Oct 1998 – Mar 2002

  11. Predicted salinity change over the top 180 metres in the Indo-Australian Basin and observations Change due to P-E in Indo-Australian Basin Change due to combined P-E of Indo-Australian Basin and Banda Sea (lagged by 1 year) Predicted change = Vorig – (Vorig.Sorig + Vfresh.Sfresh) / (Vorig + Vfresh) Vorig = 180 m3, Sorig = 34.5, Sfresh = 4

  12. Summary • Argo floats have recorded a large amplitude, broad scale freshening of the upper layers of the Indo-Australian Basin during 2000-2002. • CTD data collected in 2000 supports the float data • Historical CTDs document strong interannual variation in the freshwater content • Local P-E can account for the observed salinity changes • In years of strong Indonesian Throughflow P-E from the Banda Sea can boost freshening (e.g. 1989) • The present Argo sampling strategy has worked well in this case. Profiles to 2000m provide for stable salinity calibration and high-frequency variability has not masked the large scale signal

  13. Salinity changes 1995-2003 1995 - CTD Oct 1999-Sep 2002 Oct 2002-Sep 2003

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