A High-Resolution Stalagmite Record of East-Central North America Hydroclimates during Marine Isotope Stages 3-5

Abstract:

Long-term, high-resolution stalagmite carbon and oxygen isotope records from eastern North America (ENA) provides a mid-latitude history of relative changes in moisture availability and climate states during the last interglacial and glacial inception (127.7 to 41.6 ka before present). The West Virginia carbon record (δ¹³C) shows low-amplitude variability at orbital time scales, superimposed on a long-term asymmetric pattern similar to global sea level changes. Relative moisture availability peaked at ~114ka and following a brief dry interval at ~96ka, moisture availability gradually decreased. The gradual changes in moisture availability over ENA may reflect similarly gradual changes in mid-latitude zonal circulation as the polar cell and Laurentide Ice Sheet expanded or decreased. However, high frequency isotopic fluctuations are present and correlative with climatic phenomena recorded in Greenland. In contrast to the gradual changes in carbon isotopes, our oxygen record (δ¹⁸O) is precession-modulated and in phase with spring insolation, perhaps due to changes in precipitation seasonality. Altered precipitation seasonality or seasonal moisture availabilities would, as a result of annual variability in meteoric δ¹⁸O, have caused a weighting effect in stalagmitic calcite precipitation. However, this explanation for changes in δ¹⁸O does not explain why the two isotopic records of eccentricity (carbon) and precession (oxygen) are paced differently because moisture availability might resonably be expected to covary with precipitation seasonality. The same pattern is observed in a stalagmite from the previous interglacial-glacial cycle, so it is a persistent feature in our study area. We will present possible explanations.