Date of Award

8-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Stefanie Brachfeld

Committee Member

Claus-Dieter Hillenbrand

Committee Member

Ying Cui

Committee Member

Matthew Gorring

Abstract

The mid-Pleistocene transition (MPT) was a period spanning ~1.2-0.7 Ma when glacial-interglacial cyclicity changed from 41 kyr obliquity paced to 100 kyr eccentricity paced cycles with increased glacial-interglacial contrast post-MPT. Marine Isotope Stage (MIS) 31 was a “super-interglacial” within the MPT and occurred in the recent geological past (1.08-1.06 Ma). During MIS 31, the tectonic configuration resembled the present day, but Earth’s orbital parameters were marked by maximum values of eccentricity and obliquity while atmospheric CO2 remained at pre-industrial levels (below 280 ppm). MIS 31 therefore offers a valuable baseline for testing the impacts of modern anthropogenic CO2 levels combined with maximum values of solar insolation in climate models. This dissertation investigates MIS 31 in both the southern and northern polar regions using rock magnetic signatures of marine sediments from two International Ocean Discovery Program (IODP) expeditions: Expedition 382 (Iceberg Alley, Scotia Sea) and Expedition 403 (Eastern Fram Strait). Grain-size-specific studies of Fe-oxide mineralogy, concentration, and magnetic grain size (Scotia Sea) yield information about glacial margin position and changes in sources of current-sorted material, while paleomagnetic studies (Fram Strait) yield improved magnetostratigraphic age control in order to identify MIS 31. In the Southern Hemisphere, Scotia Sea sediment assemblages reflect East Antarctic Ice Sheet (EAIS) influence during interglacials and West Antarctic Ice Sheet (WAIS) and/or Antarctic Peninsula Ice Sheet (APIS) input during glacials. Magnetic provenance data show declining WAIS/APIS detrital input starting in late MIS 32, while lower ice rafted debris concentrations across the MIS 32/31 deglaciation relative to other deglaciations suggest reduced calving, smaller ice sheets, more distant iceberg sources, or warmer ocean conditions. In the Scotia Sea, MIS 31 warmth began ~10,000 years earlier and persisted ~12,000 years longer than the boundaries defined by the Lisiecki and Raymo 2004 oxygen isotope stack (LR04) (1.081-1.062 Ma), as indicated by primary productivity proxies that suggest peak warmth occurred after 1.07 Ma and persisted to 1.048 Ma. Magnetic data point to a diminished WAIS/APIS and dynamic EAIS margins during MIS 31, consistent with WAIS/APIS collapse and EAIS retreat. WAIS/APIS advance resumed during glacial MIS 30. Dove Basin in the Scotia Sea is well situated to record variations in both the Antarctic Circumpolar Current (ACC) at its southern boundary and Weddell Sea Deep Water (WSDW) outflow. Bottom current changes across MIS 33-30 are evident in compositional shifts of current-sorted silt. Rock magnetic characteristics of bulk sediment and the silt-sized fraction combined with a Zr/Rb-derived current speed proxy indicate periods of dominance by each current/water mass. The ACC signal is pronounced in Dove Basin during interglacials, especially during late-stage super interglacial MIS 31, and absent during glacials. WSDW influence strengthens during glacial inceptions, and is absent when WAIS extent and sea ice production are minimal, such as during the MIS 32/31 deglaciation and the interglacial MIS 31. In the Arctic, IODP Expedition 403 sediments in the Fram Strait sediments exhibit a pervasive chemical remanent magnetization (CRM) carried by the authigenic ferrimagnetic mineral greigite. This complicates the detection of MIS-31 via the onset of the Jaramillo normal-polarity subchron at ~1.07 Ma. This study assesses the degree of remagnetization at Site U1623, Bellsund Drift, and refines the stratigraphic position of the Jaramillo onset in order to improve age control and establish the stratigraphic position of MIS 31. Findings also reveal that greigite is more pervasive than originally believed during Expedition 403, with greigite signatures documented in horizons with low magnetic susceptibility. By addressing key uncertainties in the magnetostratigraphic record, this work establishes a foundation for future investigations of interactions between the paleo Svalbard-Barents Sea Ice Sheet and the West Spitsbergen Current during MIS 31. Combining Fram Strait findings with the Scotia Sea data will enable investigations of interhemispheric phase relationships during the MPT and will contribute to our understanding of polar climate systems under varying climate conditions.

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