Holocene Climate and Water Quality Variability Inferred from Estuarine Sediments in the Chesapeake Bay: a Phytoplankton-Based Reconstruction

The Chesapeake Bay is one of the best and most closely monitored estuarine systems in the world. Since 1986 a continuous monitoring program measures water quality indicators such as water temperature, salinity, nutrient status, oxygen levels, and suspended sediment. We collected surface samples of sediment at monitoring sites throughout the bay to identify major phytoplankton (primarily diatom) assemblages and correlate them with water-quality parameters. Using statistically based relationships between phytoplankton assemblages and water quality, we created a data-based transfer function to interpret fossil diatom assemblages extracted from well dated (14C) sediment cores taken from the Chesapeake Bay. Sediment cores retrieved from the Bay reveal an excellent proxy record of late Holocene (circa last 2300 years) regional palaeoclimate on decadal to millennial timescales, as well as local ecosystem variability. Within the entire Holocene, however, temporal resolution varies, with decadal resolution in much of the early and late Holocene but sub-centennial resolution in the middle Holocene. It is important to consider the longer-term record of the Holocene to understand relative roles of human induced changes in the environment from supposed anthropogenic forcing of the climate system, and natural variability. Results indicate a slow down (or hiatus) in sedimentation in the bay during the period 3.9 - 5.5 ka B.P which may be linked to the North American regional climate event some 4200 years ago. We integrate detailed phytoplankton and pollen analyses of this interval to evaluate the impact of that event on water quality and terrestrial environments in Chesapeake Bay and its watershed.