Consolidation and Calibration of the New England Varve Chronology (NEVC): An Annual Continental Record of Ice Dynamics and Terrestrial Change, 18-11.5 kyr BP

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Rapid climate change during deglaciation is linked to interactions between the ice sheet, the ocean, and the atmosphere. Understanding these interactions requires high resolution comparisons of climate and continental ice. Although general patterns of Laurentide Ice Sheet variation have been found, they are not continuously resolved at a sub-century scale. This lack of continuous, high-resolution terrestrial glacial chronologies with accurate radiometric controls continues to be a limiting factor in understanding deglacial climate. Such records, especially from the southeastern sector of the ice sheet can provide critical comparisons to N. Atlantic climate records (marine and ice core) and a rigorous test of hypotheses linking glacial activity to climate change.Consolidation of the New England Varve Chronology, and the development of records of glacier dynamics and terrestrial change, is a rare opportunity to formulate a complete, annual-scale terrestrial chronology from 18,000 -11,500 years before present. Glacial varve deposition, which is linked to glacial meltwater discharge, can be used to monitor ice sheet retreat and has a direct tie to glacier mass balance and climate. Complete records of readvances, ice recession rates, and annual meltwater discharge of the southeastern ice sheet could be compared to climatic events in the N. Atlantic region to determine whether the ice sheet was in lock-step with climate and ice rafting events, whether it was a driver or responder, or whether it behaved independently or with time lags. The varve chronology's use as a precise regional chronology of glacial events, including floods that may have been triggers for rapid climate change, would be critical to evaluating climate models and the thresholds necessary for individual floods to influence ocean circulation and climate.The project will be to join sequences of the New England Varve Chronology, forming a single sequence spanning over 6000 years (18.0-11.5 kyr BP). This will be the longest continuous, high resolution record of terrestrial ice front changes, ice recession rates, and glacial lake history in North America. Cores will be collected in critical areas to join existing sequences of the varve chronology and new Carbon-14 ages will be used to improve its calendar-year calibration.Broader impacts:1) The exceptional accuracy and precision of the New England Varve Chronology will demonstrate the potential usefulness of glacial varve chronology in other regions of North America where glacial varve sequences have not been studied for either their glacial chronologies or climate records. This project will serve as a stepping stone to an expansion of the chronology to cover the entire last deglaciation (~24-11.5 kyr BP) and is likely to stimulate varve studies in many other regions of the United States and Canada. 2) Varve chronology will serve as a calibration or consistency test of other dating techniques. The NEVC represents the most precise and accurate opportunity for comparison of cosmogenic-nuclide ages for deglaciation with an independently-calibrated deglacial chronology. Refinement of the varve chronology will dramatically improve the accuracy and confidence in this geological calibration.3) Dissemination of results, in addition to normal publication in scientific journals, will include internet availability of a library of varve records and images for other researchers; instructional presentations on how to collect, formulate, and match varve records; and an image glossary of varve characteristics and features as a reference for students and instructors.4) This project will expand the research program at Tufts University. Undergraduates (two per summer for three years), will be active research participants in field and laboratory phases of the project. Each student will be supervised through a start-to-finish analysis of a complete varve section leading to a year-long thesis or research project. Over three years the project will effectively double the number of people in the United States trained in the analysis of glacial varve cores.