HOLOCENE CLIMATE VARIABILITY FROM CHESAPEAKE BAY SEDIMENTS

The modern Chesapeake Bay, a large partially mixed estuary, experiences seasonal and interannual salinity variability mainly caused by changes in river discharge, which in turn is strongly correlated (r²=0.84) with regional precipitation. The oxygen isotopic composition of modern Chesapeake water (d18Obay) is a function of the mixing of fresh and marine water and d18Obay is strongly correlated with salinity (r²=0.96). Holocene mid-Atlantic precipitation was reconstructed from oxygen isotope (d18O) records of benthic foraminifera (Elphidium) obtained from multiple Chesapeake Bay sediment cores. The d18Ocalcite of Holocene foraminifers were used to reconstruct temporal trends in d18Obay using ostracode Mg/Ca paleothermometry from paired specimens to correct for the influence of water temperature on d18O. Results from the mesohaline and polyhaline regions of the bay indicate Holocene variability in d18Obay ranging from ~-0.5 to –3.5 per mil, which converts to paleosalinities between ~ 14 to > 30 ppt. Important observations include evidence of late Holocene multi-decadal and centennial droughts and wet intervals, higher and more variable 20th century precipitation than the prior 2000 years, and ~ 30% drier mean early Holocene conditions than those of the late Holocene.