A HIGH-RESOLUTION SEA-LEVEL CURVE FROM BARN ISLAND, CONNECTICUT

Geologic records of sea-level rise (SLR) in southern New England indicate a deceleration in the rate of rise from 3 mm/year to 1 mm/year over the last 6000 years. Tide gauge data indicate that sea-level has been rising between 2 to 3 mm/year over the last 60-150 years. This apparent acceleration in the rate of SLR is often attributed to increases in global temperatures over the past 150 years, possibly related to “green-house” gas emissions. In order to establish the timing and magnitude of any changes in the rate of SLR, we produced a high-resolution sea-level chronology from eastern Connecticut for the last 1400 years by dating basal high-marsh peat deposits which grow close to mean high water (MHW). We excavated a 1.4 meter section of marsh peat accreted over a glacial erratic at Barn Island Marsh, Stonington, CT. We dated a series of the high-marsh peat samples from the erratic contact using C-14, Pb-pollution horizons and pollen stratigraphic ages. In order to estimate the relationship of the marsh sediments to MHW at the time of their formation, we related the elevation of modern marsh flora to tide observations.

Preliminary results indicate that MHW has increased at this site approximately 1.4 meters in the last 1400 years. From the 7th century A.D. to roughly the 18th or 19th century A.D., MHW rose at a rate of close to 1 mm/year. In the last few hundred years, MHW has risen at a rate of between 2 and 3 mm/year. Our data suggest that the acceleration of sea-level rise may coincide with the rise in northern hemisphere temperatures, but further work is required in order to better constrain the timing of change in the rate of SLR. This record potentially represents only local changes in sea level, so additional records need to be developed to determine if a regionally-coherent pattern of sea-level changes exist.