Coral oxygen isotope reconstruction of sea surface salinity variability in the southern Makassar Strait since 1938 C.E. and its influence on the Indonesian Throughflow
Abstract
The Indonesian Throughflow (ITF) annually transports surface and thermocline depth water from the Pacific Ocean north of the equator to 12°S in the Indian Ocean. Today, the net result of the ITF is a cooling and freshening of the Indian Ocean thermocline. One mechanism to explain this relatively cool ITF comes from limited instrumental data suggesting that the seasonal influx of low salinity surface water from the South China and Java Seas into the southern Makassar Strait lowers surface salinity by 2 to 3 SP and generates a northward pressure gradient during the winter monsoon (Dec-Mar). The low salinity "plug" seasonally inhibits the flow of warm surface water in the far western Pacific Ocean from freely flowing southward into the Indian Ocean. However, little is known about interannual and lower frequency salinity changes in the Makassar Strait due to a lack of instrumental and detailed paleoceanographic data. We present new sub-seasonally resolved δ18O and Sr/Ca records from a 0.8 m Porites sp. coral core collected from Kapoposang in the Makassar Strait near southwest Sulawesi. The coral series span 2004 to 1938 (66 years). Annual δ18O variations of 1-1.5 ‰ and thin but distinct fluorescent banding coincident with δ18O minima were used to develop the chronology. Sub-seasonal δ18O is highly correlated (r2 = 0.74, 1980-2004) to the gridded instrumental sea surface salinity (SSS) dataset (Simple Ocean Data Assimilation; SODA) at this location. The coral δ18O record demonstrates that the annual 2-3 SP surface salinity reduction during the winter monsoon (Dec- Mar) is a consistent pattern. During El Niño conditions, the freshening in the strait is reduced by ~50% for moderate events, and by up to 90% for "very strong" El Niño's such as the 1982/83 and 1997/98 events. Interannual coral δ18O variability closely tracks Niño3.4 SST, the Southern Oscillation Index, and additional equatorial Pacific coral δ18O records. The fact that interannual Sr/Ca variability is correlated with interannual coral δ18O in this colony, but not with interannual Extended Reconstructed Sea Surface Temperature (ERSST) suggests that interannual coral δ18O variability in this setting is primarily driven by SSS changes. This also suggests that interannual Sr/Ca at this location is in part due to SSS variability. At lower frequencies, no distinct relationship was found between coral δ18O or Sr/Ca to the Pacific Decadal Oscillation/Interdecadal Pacific Oscillation indices of Pacific-wide decadal-scale SST variability. Analysis of a second coral core is underway that will extend this reconstruction back to the early 1800s.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP21B2014L
- Keywords:
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- 4215 OCEANOGRAPHY: GENERAL / Climate and interannual variability;
- 4522 OCEANOGRAPHY: PHYSICAL / ENSO;
- 4916 PALEOCEANOGRAPHY / Corals