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East Coast Sea Level

Sea-level rise and associated storm surges are major threats to low-lying areas of U.S. coastal zones, including much of the east coast. In order to fully understand how high and how fast sea level will rise and what the impacts will be, it is necessary to examine paleo-sea level records preserved in ancient marine shorelines (barrier islands, scarps) and sediments deposited along the eastern U.S. In fact, the geology of the east coast from New Jersey to the Florida Keys is dominated by geological features formed during periods of higher-than-present sea level. The most prominent sea-level high stands represent warm interglacial periods including Marine Isotope Stage (MIS) 11, 7, 5e, and 5a. MIS 11, ~400,000 years ago, is of particular interest to climate scientists due to the unique orbital configuration (earth's tilt, precession, eccentricity of orbit), warm climate in polar regions, and high sea level and reduced land ice volume. MIS 5 ~125,000 years ago, has also been the focus of intense paleo-sea level research and climate modeling because the high sea level (~6-8.5 m) at that time is thought to results from partial melting of the Greenland and West Antarctic ice sheets.

Policymakers, especially those dealing with international issues such as the IPCC, and local and regional decision makers managing coastline threatened by sea level rise, need information on past periods of high sea level and impacts.

The U.S. Atlantic Coastal Plain (ACP) is an ideal place to examine the combined effects of reduced high-latitude land-ice volume (glacio-eustacy), glacio-isostatic adjustment and regional tectonics on the elevation of paleo-shorelines and marine deposits. Geological formations are well mapped, some are well dated, and, in the central and northern ACP, paleoclimate proxies are common (marine macrofossils, benthic forams, ostracodes, pollen). This is important to allow analyses of sea-level variability within interglacial periods. Proper analysis of paleo-sea levels requires state-of-the art geochronology, which along the ACP can take the form of Optically Stimulated Luminescence, Uranium-series and Amino Acid Dating, augmented by paleomagnetic and biostratigraphic analyses.

The two main objectives are: 1) Southern ACP (non-fossiliferous soils, weathered sediments): to use new dating methods on the series of shorelines in the Georgia/South Carolina border region, expanding Markewich, Pavich et al. (2013, QSR), who dated MIS 11 deposits. Seaward of the MIS 11 shoreline, there are post-MIS 11 interglacial and perhaps interstadial shorelines; 2) Central/Northern ACP (fossiliferous sediments): Reconstruct sea level variation within MIS 11, 7 and/or 5 through detailed proxy analyses of the Formations found in the coastal plain [Lithologic units go under various names in Virginia, Delmarva Peninsula, North and South Carolina, including Norfolk-Kempsville, Omar, Kent Island, Tabb, Wachapreague, Nassawadox, Canepatch Formations]. Additional geochronology will be carried out where needed by obtaining new U-series dating.

Understanding sea level variability during warm interglacial periods is critical to understanding background rates of the current Holocene interglacial and for detecting anomalous human-induced sea level rise. In addition, we ought to be able to estimate regional tectonic and isostatic adjustment by correlating the ACP record of sea level positions to global sea level curves from reefs, deep-sea oxygen isotope curves, and modelling.

contact: Thomas Cronin

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