Late Holocene Climate and Ecosystem History from Chesapeake Bay Sediment Cores

^1#Willard, D.A., ¹Cronin, T.M, and ^1,2Verardo, S.

¹U.S. Geological Survey, 926A National Center, Reston, VA 20192, USA

^#phone (703) 648-5320; fax (703) 648-6953; dwillard@usgs.gov

²Atlantic Geoservices, Inc., Oakton, VA, USA.

        Paleoclimate records from late Holocene sediments in Chesapeake Bay, the largest estuary in the United States, provide evidence that both decadal to centennial climate variability and European colonization had severe impacts on the watershed and estuary. Using pollen and dinoflagellate cysts as proxies for mid-Atlantic regional precipitation, estuarine salinity, and dissolved oxygen (DO) during the last 2,300 years, we identified four dry intervals, centered on 50 AD (P1/D1), 1000 AD (P2/D2), 1400 AD (P3), and 1600 AD (P4). Two centennial-scale events, P1/D1 and P2/D2, altered forest composition and led to increased salinity and DO levels in the estuary. Intervals P3 and P4 lasted several decades, leading to decreased production of pine pollen. Periods of dry mid-Atlantic climate correspond to "megadroughts" identified from tree-ring records in the southeastern and central United States. The observed mid-Atlantic climate variability may be explained by changes in atmospheric circulation resulting in longer-term, perhaps amplified, intervals of meridional flow. After European colonization in the early 17th century, forest clearance for agriculture, timber, and urbanization altered estuarine water quality, with dinoflagellate assemblages indicating reduced DO and increased turbidity.