Michael Lis

Date of Award

Summer 2019

Document Type

Open Access Thesis

Department

Earth and Ocean Sciences

First Advisor

Claudia Benitez-Nelson

Abstract

The Indo-Pacific Warm Pool exerts a strong influence on the global climate system because it partially controls heat and moisture exchange (pressure gradient) between the atmosphere and ocean, and thus, the intensity of the Indonesian throughflow (ITF) via the Makassar Strait, the main passage of water connecting the Pacific and Indian Oceans. The magnitude of ITF is reflected by the structure of the oceanic thermocline. Here, we use shell δ18O signatures and trace element composition of foraminifera (Globigerinoides ruber, Pulleniatina obliquiloculata, and Globigerinoides menardii) in two sediment records spanning the past 30 kya collected from the northern and southern openings of the Makassar Strait. Reduced differences in δ18O records between thermocline species suggest a stronger thermocline at both sites during the deglaciation (19 to 11.7 kya), signifying a weaker ITF. During the Holocene, greater differences among δ18O records from all species indicate a weaker thermocline and a shallow mixed layer, indicating stronger ITF. Paired Mg/Ca -δ18Ocalcite records in the mixed layer-dwelling species Globigerinoides ruber (G. ruber) allow us to derive δ18Oseawater across the strait and indicates a substantial decrease in salinity and an increase in freshwater during the Holocene compared to the last glacial maximum (LGM). Ba/Ca ratios remain consistently high throughout our records, likely due to constant riverine input. Combined, our data suggest that there was decreased ITF during the LGM and deglaciation and increased ITF during the Holocene, which we hypothesize is due to sea

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© 2019, Michael Lis

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