Last Millennium Relative Sea-Level Change on the Western Coast of Southern New Jersey

Abstract

The main goal of this study was to reconstruct last millennium sea-level changes on the western coast of southern New Jersey (Delaware Bay) shore. The project used proven paleoecological techniques (sediment archives/cores) to provide quantitative information on sea level/subsidence in Dennis Creek over the last millennium through analysis of biogeochemical indicators accumulated and preserved in Dennis Creek wetland sediments. Salt-marsh sediment cores were used to understand the underlying stratigraphy, and cores were analyzed using foraminifera, geochemistry, and sediment characteristics. Results from this investigation were used to analyze relative sea-level changes associated with extensive subsidence previously observed at Dennis Creek. The timing of subsidence and relative sea-level change at Dennis Creek were determined with radiocarbon dating and pollution chronomarkers. Changes in fossil foraminifera species abundances isolated from dated core intervals were used to reconstruct relative sea level changes through time.

The results from this project were compared to the available sea-level studies on the east coast of New Jersey to determine whether similar processes are occurring on both the Delaware Bay and a Cape May site located on the Atlantic Ocean-facing coast of New Jersey. Understanding the local and regional physical processes controlling relative sea-level change is crucial for sea-level projections and future mitigation efforts, especially at locations where such high rates of change are documented. Project results revealed that relative sea-level started to accelerate earlier in Delaware Bay’s Dennis Creek than sites located along the New Jersey Atlantic coast, and also maintains present day higher rates. This finding underscores that there could be significant differences in local processes contributing to relative sea-level change at individual locations along the New Jersey coast. At Dennis Creek, relative sea-level rise reached a rate of 2 mm/yr by the mid 1600s and 3 mm/yr by 1800 CE, roughly a hundred years earlier than a site located at Cape May Courthouse, around 15km from Dennis Creek. In the 20th century, relative sea-level rise was approximately 3.6 mm/yr at Cape May Courthouse, but 4.2 mm/yr at Dennis Creek. Results from this project have profound implications for understanding local and regional processes controlling relative sea-level change and projections into the future. As the present results suggest, potentially significant local differences in relative sea-level rise could highlight important implications for how individual coastlines respond to accelerating sea-level rise. The protection and mitigation strategies that wetland stakeholders will need to provide at local levels may need to correspond with local conditions.