Coastal salt marshes of Northeastern United States (Maine to New Jersey) formed within the last 4000 to 7000 years, following deglaciation of the last Ice Age initiated about 15,000 years ago. As sea-level slowed, a string of highly productive, peat-forming coastal wetland marshes extending from the easternmost tip of Long Island to what is now New York City, and north along the Hudson River developed. More recently, alterations in marsh geomorphology consists of a reversal of the marsh-building process through land loss from marsh erosion and inundation.
The rate of local SLR is about 2.7mm per year as determined by tide gauge data (1961-1990) from Battery Park in Manhattan. This can be compared to the mean global sea-level rise (SLR) of 1.8 mm/yr since the 1900s, due in part to anthropogenic causes. The difference between the global and the New York average sea-level rise is due, in part, to local subsidence resulting from retreat of the last ice age. Using current trends and three GCMs, local SLR projections indicate that by the 2020s SLR is estimated to be between 2.7 and 7.3 mm/yr, by the 2050s it will likely range between 2.7 and 13.7 mm/yr, and by the 2080s SLR is estimated to be between 2.7 and 22.7 mm/yr. Erosion of Jamaica Bay marshes is likely to continue, caused by a combination of SLR, changes in inshore wave energy, dredging and channel modification, and lowered sediment levels available to nourish vertical marsh accretion. GCM scenarios, accounting for marsh accretion, indicate that future loss of New York Citys salt marshes may be greater than fifty percent due to erosion and inundation.
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