Sea Surface Salinity and Temperature’s Impact on Coral Geochemistry

The Influence of Sea Surface Salinity and Temperature on Coral Geochemistry in the Makassar Strait Results Introduction This study was conducted to determine if coral Sr/ Ca and δ18O at Kapoposang in the Makassar Strait could be used to reconstruct oceanographic and climatic conditions over time. • • Figure 2: Sea Surface Salinity during the NW Monsoon (Jan-March) (left) and SE Monsoon (July-Oct) (Right). The study site at Kapoposang is indicated by a purple dot near SW Sulawesi in the S. Makassar Strait. Salinity data is from Conkright et al. (1998)1. Kapoposang coral d18O and SODA Salinity (Makassar Strait, Indonesia) -7 -6.5 32 -6 33 -5.5 34 -5 SSS SODA KC4 site -4.5 1970 1975 1980 1985 1990 1995 2000 35 2005 year Figure 3: KC4 δ18O plotted with SODA sea surface salinity from 1970 to 2005 1930 0.3 1940 1950 1960 YEAR 1970 1980 1990 2000 Maiana coral d18O ENSO-band (Urban et al., 2000) -2 0.2 -1 0.1 0 0 -0.1 EN -0.2 1 EN EN EN -0.3 EN EN -0.4 2 EN EN EN NINO 3.4 SST Anomaly ˚C EN -0.4 EN Kapoposang core KC4 d18O ENSO band vs Maiana ENSO band (*-1) KC4 d18O ENSO-band (3-8yr) Maiana d18O (*-1) ENSO-band (3-8yr) -0.3 Oxygen Isotopes (per mil) -3 -0.2 -0.1 0 0.1 EN ? 0.2 0.3 0.4 1930 EN EN EN 1940 EN EN EN 1950 1960 EN 1970 YEAR EN EN EN 1980 1990 2000 3 NINO 3.4 SST Anomaly (˚C) oxygen isotopes (per mil) 0.4 • A 0.8 meter Porites sp. coral from Kapoposang (KC4) in the southern Makassar Strait near S.W. Sulawesi (4˚41’S, 118˚55’E) was analyzed • δ18O and Sr/Ca were measured on 1mm-scale samples (~10-14 samples per year) • The annual δ18O peaks were used to construct a time series with 2 age control points per year. • Time series then compared to climate indices such as sea surface temperature, sea surface salinity (SSS), SE Asian monsoon, and El Niño Southern Oscillation 31 KC4 d18O UV age 12/y Maiana Coral d18O ENSO band Variability and Niño 3.4 SST Methods KC4 coral core dates back to 1938 KC4 coral skeletal δ18O signal is highly correlated with SODA SSS (Fig. 3) Skeletal Sr/Ca influenced by more than SST alone KC4 δ18O ENSO-band inversely related to Maiana δ18O ENSO-band and NINO 3.4 SST anomaly Conclusions SSS SODA (Sp units) KC4 Site Objectives • • Figure 1: KC4 coral core X-Ray composite Oxygen Isotopes (per mil, PDB) The Indonesian throughflow (ITF), located in the far western equatorial Pacific, annually transports surface and thermocline depth water from the western Pacific Ocean to the eastern Indian Ocean. The Makassar Strait is the main pathway. Porites sp. corals here have strong annual Sr/Ca and oxygen isotope signals. During the boreal winter monsoon buoyant, low salinity Java Sea surface water is driven by the wind into the southern Makassar Strait. This creates a north pressure gradient in the surface layer. This “freshwater plug” inhibits warm surface water from the Pacific Ocean from flowing south into the Indian Ocean and thus, the Indian Ocean cools. This plug is eliminated when the summer winds reverse and more saline Banda Sea surface water is brought in (Gordon 2003)3. This study has important implications not only for the Indonesian throughflow, but also oceans world wide, as the ITF is an important part of global thermohaline circulation (Gordon, 1986)2. Figure 4 (Left): (Top) δ18O ENSO-band (3-8 years) values from a Maiana coral in the Equatorial Pacific (Urban et al., 2000)4 plotted with the NINO 3.4 sea surface temperature anomaly from 1930-2000. (Bottom) δ18O ENSO-band (3-8 years) values from Maiana coral plotted with the δ18O ENSO-band from the KC4 coral from Kapoposang, Indonesia. • KC4 coral δ18O is a good proxy for SSS in the Makassar Strait • KC4 coral Sr/Ca could be influenced by SSS as well as SST • KC4 δ18O ENSO-band shows an inverse interdecadal relationship with SST Future Work A  3.3  meter  Porites  sp.  core  from  Gili  Meno  (GM5A)   collected  by  Michael  Moore  in  1990  will  be  analyzed.   Gil  Meno  is  located  east  of  Bali  at  8˚15’S  and   115˚30’E.  Preliminary  analysis  dates  this  core  back   around  200  years.