Deep-Water Evolution in the Southwest Indian Ocean and Its Response to Global Climate Change During the Last 300 ka: Evidence from Sedimentary and Stable Isotopic Records

Abstract

Benthic δ18O and δ13C values, as well as the mean grain size (MS) of sortable silt (SS), were used to construct the records of deep-water ventilation during the last 300 ka, at core GC02. This core is located at 4430 m water depth on the Madagascar basin near the Southwest Indian Ocean mid-ridge (SWIR). Decreased values of MS of SS reveal a weakened Antarctic Bottom Water (AABW) in the glacial periods, while increased values indicate enhanced AABW in the interglacial periods. The MS of SS record in GC02 exhibited a particularly good synchronization with a record based on the δ13C gradient between the North Atlantic and tropical Pacific Ocean, indicating that AABW is dominated by the overturning strength of the Atlantic meridional overturning circulation (AMOC), and showed a higher generation rate in the early stages of the glacial periods. A rapid reduction in δ13C occurred in MIS 2, 4, and 6; the MS values in GC02 and winter sea ice (WSI) also exhibited significant decreases and increases, respectively. By controlling the transport of ventilated water mass to deep waters and polar heat transport, in the Indian Ocean, both the change in AABW intensity and the Southern Ocean ice volume result from changes in the AMOC under the orbital modulation background. In the Southwest Indian Ocean, AMOC has a larger effect on ice volume during glacial periods, while its effect on AABW is relatively strong during interglacial periods.

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