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, , 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
-0.7
Θ=16º
Θ=10º

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

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

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

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
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