(Un)coupling of Global Temperature and Ice Volume in Marine Isotope Stage 3: Quantitative Constraints from Ice Core Noble Gases

Understanding the relationship between temperature and ice sheet changes in the past is key to understanding ice sheet vulnerability to future warming. While geological evidence for past sea level and ice volume changes are ample for the last 25,000 years, the data become sparse before this interval. Therefore, more indirect evidence of ice volume change is used to understand ice sheets further in the past. This indirect information primarily comes from foraminifera (‘forams’), single-celled marine dwelling organisms. However, forams respond to the combination of two effects: ocean temperature and ice volume changes. This research will resolve past ice volume using foram records by calculating and removing the ocean temperature effect. The work will focus on a past interval where a growing body of geological evidence suggests that – although global temperatures were quite cold – ice sheet volume was relatively reduced. However, this has yet to be corroborated by the foram record. If confirmed, this has important implications for how ice sheets respond (or do not respond) to global temperature change. The research team will employ a new tool that uses past changes in the composition of our atmosphere to calculate past changes in ocean temperature. Because colder water can hold more dissolved gas, ocean cooling leads to a net transfer of gases from the atmosphere into the ocean, implying that cooler or warmer ocean conditions can be detected by measuring minute changes in atmospheric gases in response to ocean temperature change. Ancient samples of the atmosphere, trapped as bubbles in ice sheets, will be sampled from existing ice core samples previously collected in Antarctica. Researchers will investigate the evolution of ocean temperature and ice volume changes across Marine Isotope Stage (MIS) 3 using a proxy for mean ocean temperature based on noble gases trapped in polar ice cores, providing the first global constraints on total ocean heat content and will provide unique insight into oxygen isotope records for this interval. The apparent uncoupling of climate and ice volume during MIS 3 offers a valuable test for models of glaciation. Techniques developed will build on previous research demonstrating that this ice core-based tool is particularly well suited for interpreting foram records. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.