Chesapeake Bay Foraminifera Counts and Paleosalinity Estimates. Age model
developed from lead-210, cesium-137, pollen stratigraphy, and C-14 dates.
Salinity estimates in ppt based on the relative proportions of salinity
sensitive benthic foraminifera described in Cronin et al. 2000 Geology.
Salinity oscillations caused by multidecadal climatic variability had major
impacts on the ... Chesapeake Bay estuarine ecosystem during the past 1000 yr.
Microfossils from sediments dated by radiometry (14C, 137Cs, 210Pb) and pollen
stratigraphy indicate that salinity in mesohaline regions oscillated 10-15 ppt
during periods of extreme drought (low fresh-water discharge) and wet climate
(high discharge). During the past 500 yr, 14 wet-dry cycles occurred,
including sixteenth and early seventeenth century megadroughts that exceeded
twentieth century droughts in their severity. These droughts correspond to
extremely dry climate also recorded in North American tree-ring records and by
early colonists. Wet periods occurred every ~60-70 yr, began abruptly, lasted
<20 yr, and had mean annual rainfall ~25%-30% and fresh-water discharge
~40%-50% greater than during droughts. A shift toward wetter regional climate
occurred in the early nineteenth century, lowering salinity and compounding
the effects of agricultural land clearance on bay ecosystems.