REGENTS OF THE UNIVERSITY OF MINNESOTA

Intellectual Merit: This grant will support the development of calibrated, highly-resolved, and absolute-dated stable isotopic and trace-metal time series from multiple speleothems preserved in multiple cave systems along a N-S transect from East Tennessee, through southern West Virginia, to northeastern West Virginia. Modern regional climate is demonstrably sensitive to sea-surface variability of the North Atlantic and Pacific Oceans, and climate variability, in particular the occurrence of drought and paleo-drought, has been linked to large-scale oceanic and atmospheric patterns in the instrumental record (e.g., AMO, PDO/NPO) and in the paleo-record (e.g., Bond-scale cyclicity, 8200-year event). In addition, the team will investigate the geochemical response on land and in the ocean to climatic changes at the onset of the Younger Dryas, using a fully coupled climate model including a carbon cycle. When integrated, the work will yield a unique data product that evaluates the timing, magnitude, and underlying causes for climatic change in the region for at least the last six glacial/interglacial cycles. The specific deliverable for the speleothem-based portion of the project is a well-dated composite time series that can be used to assess the modes and timescales of climate variability, and, in the context of proximal marine and more distal speleothem (e.g., China, Oman) and ice-core records, evaluate the potential driving mechanisms responsible for climate instability and mode-shifts. Time series from individual sites along the N-S transect will also be compared in order to assess the importance of shifts in climatic boundaries. Geochronological control (230Th ages) on 43 speleothems from the study transect demonstrate that exceptional potential exists for reconstructing regional climate change back through Marine Isotope Stage 15 (~600 kyr BP). The 230Th-dated time series will help define climate shifts on timescales of human activity. Specifically, the integration of several highly-resolved (multidecadal-scale) Holocene speleothem records from multiple sites will 1) define the timing of, and 2) resolve the basis for abrupt climate change (e.g., 8200-year event) during the past ten millennia. Furthermore, similar studies of late Pleistocene speleothems will yield a more comprehensive understanding of how specific climate modes evolved in the past when climate was presumably similar to (e.g., MIS-5, 7, 9, 11, 13, 15) or different from (MIS-2, 6, 8, 10, 12, 14) today. Interpretation of the late Quaternary climate history will be strengthened using results from a proposed isotopic/geochemical calibration study of cave drip waters (del-18O, del-13C, trace-metal), cave environment (temperature, humidity, pCO2), and the atmospheric/hydrological conditions above the cave. Results from the modeling-part of the project will contribute to the understanding of geochemical feedbacks and possible amplifying or stabilizing factors at times of rapid climate change, such as the Younger Dryas. The proposed study addresses key initiatives of P2C2, including 1) assessment of sensitivity and response to climate mode changes in a region with demonstrable linkages to large-scale coupled climate systems, 2) assessment of responses to abrupt and extreme climate events, and 3) data-model synthesis. Broader Impacts: The proposed research will define the history of climate change during the last ~600,000 years for the mid-Atlantic/Appalachian region of eastern North America, a highly-populated region of national importance. The project is designed to provide meaningful lab- and field-based mentorship/traineeship opportunities that couple undergraduates with graduate-level and faculty mentors across three universities. The PIs represent three diverse research groups committed to recruitment of underrepresented groups, including females and minorities.

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