Reconstruction of PALeo-sea water properties in the tropical western Indian Ocean for the last 470 kyrs using Mg/Ca and stable isotopes on planktonic foraminifera: atmospheric versus oceanographic influences (PALIO).
Oceanography
Final Report Abstract
The tropical Indian Ocean is a key location for paleoclimate research affected by different oceanographic and atmospheric processes. Annual climate variations are strongly controlled by the Indian and Asian Monsoon characterized by bi-annually reversing trade winds. Inter-annual climate variations in the Walker circulation are caused by the Indian Ocean Dipole and El Niño-Southern Oscillation resulting in either heavy flooding or severe droughts like for example the famine of 2011 in eastern Africa. Oceanographically the tropical western Indian Ocean receives water masses from the Indonesian Gateway area, sub-Antarctic waters that upwell south of the equator, and the outflow waters from the highly saline Red Sea. On the other hand, the tropical western Indian Ocean is a major source for providing water masses to the Agulhas Current system. Although the eastern Indian Ocean has been studied extensively, the tropical western Indian Ocean was still lacking in high quality climate-archives that have the potential to provide important information to understand how the ocean and atmospheric zonal circulation have changed in the past, and possibly will change in the future. Until now there were no long sediment cores available covering several glacialinterglacial cycles in the tropical western Indian Ocean. Core GeoB 12613-1, recovered during RV Meteor Cruise M75/2 east of the island of Pemba off Tanzania, provides an open-ocean core with well-preserved sediments covering the last five glacial-interglacial cycles (~500 kyr). Mg/Ca and stable isotopes on both surface- and thermocline dwelling foraminifera have been performed to test how changes in sea water temperatures and relative sea water salinity were coupled on orbital time scales. The results are compared with similar records generated for the tropical eastern Indian Ocean in core SO139-74KL off Sumatra. Variations in water column stratification on both sides of the Indian Ocean and the tilt of the thermocline across the Indian Ocean are strongly controlled by precession. The tilt of the thermocline is a proxy for the strength of the Walker circulation showing that it is primarily controlled by low-latitude changes in insolation although high-latitude climate impacts may have an influence too. The results of the PALIO project show for the first time how the tilt of the thermocline changed through time. Opposed to previous model studies our records prove an increase in the strength of the Walker circulation during the last glacial in comparison to today, with a deeper thermocline and more precipitation in the eastern Indian Ocean, and a shallow thermocline and dry conditions in east Africa.
Publications
- The consequences of opening the Sunda Straiton the hydrography of the eastern tropicalIndian Ocean. Paleoceanography 30
Setiawan, R. M. Mohtadi, J. Southon, J. Groeneveld, S. Steinke, D. Hebbeln
(See online at https://doi.org/10.1002/2015PA002802) - 500 kyr of Indian Ocean Walker circulation variability. AGU 2017, New Orleans
Groeneveld, J., M. Mohtadi, A. Lückge, J. Pätzold
- Insolation forcing of coccolithophore productivity in the western tropical Indian Ocean over the last two glacial-interglacial cycles. Paleoceanography, 32
Tangunan, D., K.-H. Baumann, J. Pätzold, R. Henrich, M. Kucera, R. De Pol-Holz, J. Groeneveld
(See online at https://doi.org/10.1002/2017PA003102)
