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Thesis defended by Michael Bollen, August 29, 2025 – Institute of Earth sciences (ISTE).
This thesis investigates how the Antarctic Ice Sheet and Southern Ocean have interacted over the past 30,000 years—a period marked by Earth’s transition from a glacial world with vast ice sheets, low atmospheric CO₂, and sea levels 120 m lower than today, to our current interglacial climate. The Antarctic Ice Sheet is divided into two distinct sectors: East Antarctica, grounded mostly above sea level on ancient bedrock, and West Antarctica, grounded largely below sea level on younger, more vulnerable terrain. Because West Antarctica sits below sea level, it is particularly sensitive to ocean temperature changes, especially where warm water reaches the ice base via ocean currents. The Southern Ocean plays a dual role in this system. It not only transports heat toward Antarctica, influencing ice sheet stability, but also helps regulate Earth’s climate by storing or releasing carbon dioxide, depending on the relative intensity of water masses mixing, upwelling, and bottom water formation.
This research focuses on the Weddell Sea, a key drainage outlet for the Antarctic Ice Sheet and a major source of Antarctic Bottom Water, the cold, dense water that spreads through the global ocean. Using high-resolution seafloor mapping, sediment core analysis, and geochemical fingerprinting with neodymium and lead isotopes, we reconstruct how ice and ocean conditions changed since the last ice age. These records show that ice retreat in the Weddell Sea may have commenced relatively early in the deglaciation, with a warm, deep water current inflowing across the continental shelf to the ice margin that prevailed across the deglaciation. The formation and export of bottom water also persisted across periods of rapid climate change, hinting at a regional stability in oceanographic circulation in the Weddell Sea Embayment. We also identified a major shift during the Younger Dryas interval (12.5 – 11.5 ka), when inflows of warm water and increased glacial melt disrupted deep water formation. This event coincided with ice sheet thinning in East and West Antarctica, suggesting a feedback loop between ocean warming and ice loss. Ultimately, our findings show that the Weddell Sea is not just a passive responder to global climate, but it actively shapes it. Understanding these dynamics is essential for predicting future Antarctic ice sheet behavior, global carbon cycling, and global sea-level rise.
