2025 Theses Doctoral

The Evolution of the Antarctic Ice Sheet Over the Plio-Pleistocene Inferred from Scotia Sea Sediments

Jasper, Claire Elizabeth

Our ability to predict future global sea level rise is limited by our understanding of the fundamental ice dynamics that govern ice sheet retreat and collapse. The Antarctic Ice Sheet holds the vast majority of potential sea level rise, and understanding the primary controls of retreat is crucial for understanding the evolution of the ice sheet and identifying key parameters to monitor for the future. Antarctica has extensive marine-based margins, characterized by large, fringing ice shelves. Icebergs calve off the margins of these ice shelves and, with them, they carry and deposit poorly- sorted terrestrial iceberg-rafted debris (IRD) into ocean sediments. Therefore, paleoceanographic records of IRD allow us to quantify the timing and provenance of major iceberg discharge events in the past.

In this dissertation, I employed a range of quantitative, sedimentological, and geochronological techniques to study the history of Antarctic IRD over the late Pliocene and Pleistocene. The key problems that I aim to address in this dissertation are: what are the main controls on the stability of the Antarctic Ice Sheet in the past, and what are the major factors that drove iceberg discharge and inland retreat of the ice sheet margins in the past? To answer these questions, I have focused on deep-sea sediment drill cores collected during the International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea, a region in the Southern Ocean, where the vast majority of Antarctic icebergs pass through.

In Chapter 1, I developed a novel artificial intelligence (AI) algorithm that was trained to identify iceberg rafted debris in X-ray images of sediment drill cores. By applying this new AI model to hundreds of meters of cores, I created a 3.3 million-year (Myr) record of Antarctic iceberg discharge. I observe an increase in the flux of IRD just after 1.8 million years ago (Ma), which likely represents an expansion of the Antarctic Ice Sheet from a primarily terrestrial-based to a marine-based ice sheet after this time.

In Chapter 2, I focus on an increase in the flux of IRD after 0.43 Ma, which is aligned with the Mid-Brunhes Event. I suggest that increased iceberg discharge is related to the enhanced retreat of marine-based margins at glacial terminations, which is linked to the southward shift in the Southern Hemisphere Westerlies and the Antarctic Circumpolar Current, driving increased basal melt and iceberg calving. I also suggest that the Northern Hemisphere-triggered thermal bipolar seesaw could be an additional factor in driving Antarctic iceberg discharge during both glacial inception and glacial terminations.

Finally, in Chapter 3, I created a high-resolution 1.2 Myr record of IRD discharge using physical samples spanning the early to mid-Pleistocene, and I considered the provenance and pacing of iceberg discharge throughout this period. I find that after 1.7 Ma, the dominant provenance of IRD is from the West Antarctic Ice Sheet. After this time, iceberg discharge is primarily driven by the glacial-interglacial variability of the Antarctic Circumpolar Current and modulated by the variance in summer insolation. Taken collectively, the chapters of this dissertation suggest that the early Pleistocene expansion of the marine-based margins of the Antarctic Ice Sheet established an inherently unstable system, in which perturbations in ocean and atmospheric circulation could trigger significant iceberg discharge events throughout the Pleistocene.