BENTHIC FORAMINIFERA OXYGEN AND CARBON ISOTOPIC RECORD FROM THE TROPICAL INDIAN OCEAN DURING THE LAST GLACIAL TERMINATION

Abstract

By volume, the Indian Ocean governs ~19.8 % of global oceanic water. The Northern Hemispheric section of the Indian Ocean, Northern Indian Ocean, operates as the upwelling regime of the global Thermohaline Circulation. In spite of being the third largest ocean with a diverse and significant oceanographic characteristic, the role of Northern Indian Ocean in defining the global climate at the time span of the Last Glacial Termination, has been deprived from major attention and well documentation. Carbon and Oxygen isotopic compositional value (18O and 13C) derived from benthic foraminiferal calcium carbonate test has been considered to provide information about variation in past deep-ocean circulation, air–sea transaction, changes in global carbon cycle and variation regarding temperature within different water masses. This analysis presents oxygen and carbon isotopic values of benthic foraminiferal i.e., Cibicides wuellerstorfi and Cibicides kullenbergi, calcium carbonate test, from sediment core SSD004 GC03, recovered from 1540-meter water depth, from the Laccadive Sea, with an age range of ~23 Ka to 8 Ka. Being situated within the intermediate depth, the benthic foraminiferal 18O and 13C isotopic ratio has been expected to be influenced by the deep-water bodies i.e., North Atlantic Deep Water (NADW), Antarctic Bottom Water (AABW), intermediated water mass i.e., Antarctic Intermediate Water (AAIW) as well as by Red Sea Outflow Water (RSOW). Apart from that situated within intense upwelling zone the values are also expected to get effected by this oceanographic phenomenon. The trend of the 18O and 13C curve reveals the expectations to be true. The uprising trend of the 18O reveals a gradual increase in temperature from the Last Glacial Termination to Holocene. Evaluation of 18O value shows an overall ~2.08o C increase in temperature throughout the Last Glacial Termination. Comparison with LR04 benthic stack, reveals that the identical event had been happened throughout the globe as well. Being situated in the upwelling zone, the region has been affected by surface productivity, which reflects in Glacial Termination. Finally, corelating the 18O and 13C data of SSD004 GC03 with Mg/Ca, Cd/Ca, Nd from different cores of the adjacent regions and 230Pa/232Th and 230Pa/238Th derived from the cores within Atlantic Ocean, ultimately leads to a conclusion of interrelation between the variation in the intensity of Atlantic Meridional Overturning Circulation (AMOC) with changes in the oceanographic condition within the Northern Indian Ocean (NIO), e.g., an weakened AMOC is related with an cold NIO, whereas a strong AMOC indicates a warm NIO. At the very end, interlinkage of the different intermediate and bottom-water hydrographic phenomenon with changes in global climate at the time span of the Last Glacial Termination has also been established and the global consequence of the same has also been explicated with the modern-day reference frame.