The Upper Ocean at the End of an Ice Age: Using Proxies in Benthic Foraminifera to Investigate Intermediate Water Changes During the Last Glacial Termination

Author

Cassandre R. Stirpe, University of MaineFollow

Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Katherine Allen

Second Committee Member

Elisabeth Sikes

Third Committee Member

Brenda Hall

Additional Committee Members

Aaron Putnam

Alicia Cruz-Uribe

Abstract

The ocean is an important component of the global climate system and plays a key role as a storage reservoir for heat and carbon. Under glacial conditions, the ocean sequestered carbon from the atmosphere, contributing to a cooler global climate. During the last glacial termination, that carbon was released back into the atmosphere, but the exact timing and mechanisms of this transfer are still not fully understood. This study examines waters from the intermediate depths of the Southern Ocean to gain insight into deglacial processes. Intermediate waters are capable of reacting to climate change on decadal timescales, making them a good candidate for catching the early part of deglacial changes. Geochemical proxies in benthic foraminifera provide information on the physical and chemical conditions of these water masses. Prior to applying the Mg/Ca–temperature proxy downcore, we performed a coretop calibration using the species Uvigerina peregrina for our southwest Pacific site. Thorough examination of coretop conditions and foraminifer chemistry yieled a globally-applicable Mg/Ca–temperature calibration, and a series of recommendations

for utilizing U. peregrina in paleotemperature reconstructions. Using the resulting calibration as well as a calibration for a second species, Hoeglundina elegans, we reconstructed a paleotemperature record for site 79JPC (1163 m water depth), located in New Zealand’s Bay of Plenty. Temperatures of Antarctic Intermediate Water (AAIW) at this site support the hypothesis of a rapid global warming early during the last glacial termination, and provide further evidence for deglacial changes occurring on timescales much more rapid than those of the continental ice sheets. For a second perspective on deglacial changes in AAIW, we applied a similar approach to site 50GGC, located in the Indian Sector of the Southern Ocean. Using Cibicidoides wuellerstorfi and Cibicidoides kullenbergi, we reconstructed paleotemperature as well as carbonate ion concentrations. Unlike AAIW records from the Pacific and Atlantic basins, those at 50GGC show greater stability and a lower magnitude of change. The uniqueness of the records from 50GGC highlights the need for further study in this basin, and the need to separate concepts of “Indo-Pacific” deglacial change into “Indian sector” and “Pacific sector” components.

Recommended Citation

Stirpe, Cassandre R., "The Upper Ocean at the End of an Ice Age: Using Proxies in Benthic Foraminifera to Investigate Intermediate Water Changes During the Last Glacial Termination" (2023). Electronic Theses and Dissertations. 3833.
https://digitalcommons.library.umaine.edu/etd/3833