Response of the Connecticut River estuary to late Holocene sea level rise

Abstract

The morphology of the modern Connecticut River estuary has been inherited from an earlier tidal river. The Holocene evolution of the estuary has been dictated by the relative submergence of the coastline and the sediment trapping efficiency of the estuary and tidal river system. The mid-Holocene tidal river system extended to the modern mouth of the estuary and subaerial floodplains stretched across the modern submerged shoals of the estuary. Submergence in excess of the long-term sedimentation rate converted these floodplains into open backwater coves beginning about 4000 yr BP in the southern estuary and about 2700 yr BP in the upper estuary and it also initiated estuarine circulation in the tidal river. Approximately 1700 yr BP an abrupt decrease in the submergence rate caused freshwater marshes to prograde across the coves and across the remaining floodplain surfaces. At 1000 yr BP salt marsh peat at the mouth of the estuary indicates estuarine circulation similar to that of t he modern estuary. The marshes in the northern estuary have supported freshwater vegetation since their inception. Thus the continuum of modern environments present along the length of the estuary models the evolution of a single reach of the estuary through time. Continued submergence will increase the tidal prism and intensify estuarine circulation. This effect will be regulated by the large excess sediment supply available to fill the volume of the estuary created by relative sea level rise.