Collaborative Research: Mechanisms of moisture-driven ice growth: a warm Miocene data-model comparison

One of the biggest unknowns in projecting future sea level is how fast the Antarctic Ice Sheet will melt in response to continued warming. An increase in high-latitude snowfall may offset some ice sheet melt due to warming of surrounding ocean and atmosphere, though it is not yet known how effective this compensating mechanism is, or under what timescales or conditions it might be important. To better understand these competing processes, researchers are investigating moisture-driven mechanisms of ice sheet growth during a past interval in Earth’s history where the climate was warm (the Miocene Climate Optimum, about 17 to 14.8 million years ago). During this time, Earth was warmer than today, yet geologic records hint at episodes where Antarctica was gaining ice. This project brings together an interdisciplinary team of experts across three institutions to investigate the potential for moisture-driven ice growth using a combination of advanced Earth system models and geologic data, while providing hands-on interdisciplinary geoscience training for graduate and undergraduate students. Researchers will use isotope-enabled climate and ice sheet models to test a suite of hypothesized mechanisms for precipitation-driven Antarctic ice growth during the Miocene Climate Optimum. Each model simulation tracks the oxygen isotopic concentration of ice, generating a modeled oxygen isotope signal that can be compared directly against deep-sea isotopic records. To evaluate model simulations, the team will generate a new high-resolution record of Antarctic Ice Sheet volume using paired benthic foraminiferal oxygen isotopes and Mg/Ca measurements from a deep-sea sediment core from 17-15 Ma, providing a key dataset for model validation alongside a synthesis of published geologic records spanning this time. Data-model comparisons will evaluate how well each modeled mechanism can explain the observed ice volume and oxygen isotope changes recorded in deep sea sediments. Specifically, investigators will explore the ice-growth potential of local polar mechanisms (such as ice-proximal ocean warmth and sea ice cover), as well as global hemispheric processes (such as CO2 and orbital forcing) that influence the heat and moisture transport to the ice sheet. Miocene data and model output will contribute to international community synthesis efforts, and project results will provide critical context for understanding long-term trajectories of global sea level. 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.