East Coast Sea Level

Exposures of 200,000 year-old marine sediments, near Ponzer, North Carolina, deposited during a warm interglacial period. These and other sediments along the eastern US record past periods of reduced polar ice volume and higher-then-present sea level.
Exposures of 200,000 year-old marine sediments, near Ponzer, North Carolina, deposited during a warm interglacial period. These and other sediments along the eastern US record past periods of reduced polar ice volume and higher-then-present sea level.

Sea-level rise and associated storm surges are major threats to low-lying areas of US coastal zones, including much of the east coast. To fully understand how high and how fast sea level will rise and what the impacts will be, it is necessary to examine past geological sea level records preserved in ancient marine shorelines (barrier islands, scarps) and sediments deposited along the Atlantic Coastal Plain (ACP) of the eastern US. The geology of the ACP, from New Jersey to the Florida Keys, is dominated by geological features formed during periods of higher-than-present sea level evident in geological maps of the region. Thus, the US ACP and adjacent continental margin are important regions to examine the combined factors that influence the elevation of paleo-shorelines: global climate [both warmer and colder than present], changes in ice sheet volume (glacio-eustasy), glacio-isostatic adjustment (GIA, also called post-glacial rebound), regional tectonics, and ocean dynamics.

The main objectives of this project are: (1) to apply stratigraphy, geomorphology, physical, biological and chemical proxies and geochronology to marine deposits from Virginia, North Carolina, South Carolina and Florida to quantify maximum relative sea level during past warm periods; (2) to reconstruct sea level variability within Marine Isotope Stages 11, 9, 7 and 5 (400,000-100,000 years ago) through analyses of benthic microfaunal assemblages, shell geochemistry, and pollen assemblages. Lithologic units to be studied in Virginia, North and South Carolina, and Florida include the Norfolk-Kempsville, Omar, Kent Island, Tabb, Wachapreague, Nassawadox, Socastee, Canepatch, Fort Thompson and Bermont Formations; (3) to reconstruct late Holocene sea-level variability in the Chesapeake Bay-Potomac-Rappahannock River estuaries using tidal marsh sediments; (4) to reconstruct glacial and deglacial sea-level history on the outer continental shelf and upper slope; and (5) to estimate regional tectonic and isostatic adjustment by correlating the ACP sea level record to global sea level curves from coral reefs, deep-sea oxygen isotope curves, and ice-sheet modelling.

Why is this research important?

This research is important because international, national, regional, and local decision-makers charged with managing coastlines and preparing for future sea level rise need baseline information on past rates and impacts of sea level rise. Understanding past regional sea level variability is particularly important due to the complex interplay between global factors and short and long-term oceanographic and geophysical processes affecting particular coastlines such as the eastern US.

Project Lead:

Thomas M. Cronin, Eastern Geology and Paleoclimate Science Center

Project Team:

G. Lynn Wingard, Laura Gemery, Marci Robinson, Michael Toomey, Robert Poirier

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