A Submergence Curve for the Connecticut River Estuary

Two submergence curves for the Connecticut River estuary define the position of relative sea level in the estuary for the last 4000 years. An upper submergence curve is defined by the stratigraphic position and radiocarbon age of (1) buried soils that formed on upland surfaces and are now buried by estuarine mud and (2) by the occurrence of drowned floodplain forests. A second submergence curve, based on the stratigraphic position of intertidal peat deposits, is offset 0.5 m below the upper submergence curve. The lower curve has two inflection points that define three time periods with different rates of relative sea level rise. Between 4000 and 1700 yBP sea level rose at an average rate of 1.9 mm/yr. During this time interval floodplains and terrace surfaces that border the estuary were flooded. After 1700 yBP and perhaps until about 300 yBP sea level rose at a rate of only 0.9 mm/yr. Over this time interval marshes expanded across the previously created shallow water environments along the margins of the estuary. Since 300 yBP sea level has begun to rise at a rate of 2.2 mm/yr. Sedimentation rates on the high marshes are apparently sufficient to maintain the marsh surface during this phase of increased submergence. The submergence curve for the Connecticut River is similar to those proposed for other coastlines in southern New England. The greatest deviation is with the submergence curve for the Hammock River in Clinton, Connecticut, which falls above the upper submergence curve for the Connecticut River estuary