Climate variability in the Eastern Indian Ocean during Marine Isotope Stage 3: high-resolution proxy studies from the Timor Sea
Paleoclimate reconstructions based on marine sediment proxy data are important to understand the mechanisms of past climates and to test the predictability of climate models with regard to future climate predictions. Marine Isotope Stage 3 (MIS 3), a time period of high climate variability on millennial timescales with different shapes of temperature increases in the Northern and Southern Hemispheres as firstly detected in Greenland and Antarctica ice core records, is therefore subject of this thesis. During MIS 3 high-latitude Northern Hemisphere temperatures abruptly shifted to interstadial conditions (Dansgaard-Oeschger events) followed by gradual decreases to stadial conditions (Heinrich events), whereas the high-latitude Southern Hemisphere experienced gradual temperature in- and decreases. In contrast to the wealth of information concerning the regional climate impacts in the Northern Hemisphere high latitudes, relatively little is known about the low-latitude responses to these climate fluctuations and about the role of the tropics. To elucidate high- and low-latitude interactions in the tropics and to gain insights into the regional climate changes during MIS 3 high-resolution marine sediment multi-proxy records from the tropical eastern Indian Ocean (Timor Sea) were analyzed. Today, this area is influenced by the Intertropical Convergence Zone, which drives monsoonal winds, and by the Indonesian Throughflow (ITF), which represents a key component of the global thermohaline circulation system connecting the Pacific with the Indian Ocean. Thus, cores from the Timor Sea are ideally situated to monitor the linkages between tropical and high-latitude climate as well as regional paleoceanography and climate settings. Benthic d18O data (P. wuellerstorfi) clearly covary with Antarctic warm events as recorded in Southern Hemisphere ice cores. This southern high-latitude signal is transferred by Antarctic Intermediate Water flowing northward from the Southern Ocean into the Indian Ocean. Planktonic d18O (G. ruber) records show close affinity to northern high-latitude records and covary with Greenland temperature signals. These northern high-latitude signals in the tropical surface water are probably transmitted through atmospheric teleconnections and a tight coupling of the Asian-Australian monsoon system. Regional monsoon variability in the Timor Sea during D-O interstadials are estimated with respect to modern temperature and salinity conditions. Planktonic foraminiferal stable isotope values, Mg/Ca temperature and d18O-seawater estimates (G. ruber and P. obliquiloculata) reveal a weaker ITF intensity with a reduced transport of less saline water from the Pacific into the Indian Ocean during Heinrich events. During these stadials, when sealevel was extensively lowered, the regional paleoceanography in the outflow area of the ITF was influenced by a northward moving hydrological front between the West Australian Current and the Leeuwin Current. This front is probably associated with a change in food export to the seafloor as indicated by changing benthic foraminiferal accumulation rates of globocassidulinids. In contrast carbon-flux sensitive buliminids reveal increased abundances during Southern Hemisphere stadials due to higher paleoproductivity modulated by changes in the Asian-Australian monsoon system.
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