Sedimentary records of late Holocene salt marsh development, storms and sea levels in the northeastern United States

Analysis of late Holocene relative sea level (RSL) changes from northern Massachusetts and Cape Cod using radiocarbon-dated basal salt-marsh peat confirms a pattern of differential subsidence in the northeastern United States. In the last 4,000 calendar years RSL has risen approximately 4 meters in northern Massachusetts in contrast to Cape Cod where RSL has risen 7 meters in that time. An investigation of changes in salt-marsh vegetation community composition at two Rhode Island marshes indicates a shift towards more flood-tolerant vegetation in the last 150 years. This alteration of marsh community composition is likely the result of increased flooding frequency associated with an increased rate of sea-level rise. Accretion rates in the Spartina patens and Distichlis spicata dominated high marsh are equal to or less than rates of RSL rise measured by local tide gauges. Conversely, portions of New England marshes dominated by Spartina alterniflora are accreting at rates equal to or greater than local RSL rise. Given Intergovernmental Panel on Climate Change (IPCC) projections of changes in global sea level by 2100 A.D., salt marshes in New England will likely continue to move towards cordgrass dominance with significant loss of marshes possible.; Mapping and dating of overwash fans preserved within backbarrier marsh sediments provide a means of developing records of past intense storms. Using these techniques several proxy records of storm activity have been developed for southern Rhode Island and central New Jersey. At Succotash Marsh, Rhode Island four overwash fans deposited within the historic period are attributable to hurricanes in 1954, 1938, 1815, and 1635. Two prehistoric overwash deposits date to 1295–1407 A.D. and 1404–1446 A.D. and likely result from hurricane strikes. Stratigraphic analysis of backbarrier marshes at Whale Beach and Brigantine, New Jersey reveal storm deposition associated with historic storms in 1962 and 1944 and a large-scale overwash fan that dates to the early 19th century and was most likely deposited by the hurricane of September 3, 1821. An additional large-scale overwash fan dates to between 600 and 1400 A.D. and likely represents a hurricane strike.