This research will produce high-resolution reconstructions of sea-level change for the last 2000 years along the latitudinal gradient of the Atlantic Coast of the United States from Connecticut to Florida. Accurate estimates of sea-level rise in the pre-satellite era are needed to provide an appropriate context for 21st century projections and to validate geophysical and climate models. Documenting geographic trends in sea level is important because sea-level changes are not globally uniform owing to isostatic (land-level) movements of the solid Earth, gravitational and rotational changes driven by the exchange of mass between oceans and ice sheets, ocean density (steric) changes from temperature and salinity variations, and other factors. Analysis of microfossils from salt marsh sediments will generate transfer functions that document prehistoric sea level at a vertical resolution of ±0.1-0.3m. The age of the sediments will be determined from complementary dating methods. Sea-level reconstructions will be adjusted for land-level movements and ocean density influences to address the underlying mechanisms of sea-level change, focusing on the interplay between the contrasting influences of both the Greenland and Western Antarctic Ice Sheets. Whereas the Greenland Ice Sheet produces a significant latitudinal gradient in the magnitude of sea-level rise from north to south along the Atlantic Coast of the United States, the influence of Western Antarctic Ice Sheet is spatially uniform. Four specific research hypotheses related to the timing and magnitude of sea-level rise will be tested: (1) The timing of 20th century sea-level rise was synchronous between sites and the magnitude of this rise increased from north to south; (2) The magnitude of a deceleration in sea-level rise associated with the Little Ice Age (AD 1500-1850) increased from south to north; (3) The magnitude of sea-level rise during the Medieval Climate Anomaly (AD 1000-1500) increased from south to north; and (4) The rate of sea-level rise was constant from AD 0 to 1000.
Sea-level rise is a vital barometer of climate change, with potentially devastating consequences in the 21st century for coastal landforms, populations and infrastructure. Knowledge of sea-level variability during the past 2000 years is limited and the response to known climate deviations such as the Medieval Climate Anomaly, Little Ice Age and 20th century warming is unknown. This project will increase comprhension of the driving mechanisms of sea-level change and enhance the ability to predict 21st century sea-level rise. Such predictions must be validated against observations that constrain spatial and temporal variability in sea-level. The results of this project will contribute to the assessment of national hazards with respect to sea-level rise and coastal responses.
The rate of sea-level rise along the US Atlantic and Gulf coasts increased throughout the 20th century. Whilst there is widespread agreement that it will continue to accelerate during the 21st century, great uncertainty surrounds its magnitude and geographic distribution. Key uncertainties include the role of continental ice sheets, mountain glaciers and ocean density changes. Insufficient understanding of these complex physical processes precludes accurate prediction of sea-level rise. The time span of instrumental sea-level records is insufficient to adequately constrain the climate-sea level relationship. Therefore, we will produce new high-resolution proxy sea-level reconstructions to provide crucial additional constraints to such semi-empirical models. The new datasets from Connecticut, New Jersey, North Carolina and Florida span the alternation between the "Medieval Climate Anomaly" and "Little Ice Age". Before the climate models can provide appropriate data for coastal management and planning, they must be complemented with regional estimates of sea-level rise. Therefore, the proxy sea-level data has been collected from four study areas to accommodate the required extent of regional variability. The data from North Carolina, New Jersey, and Connecticut reveal four phases of persistent sea level change after correction for land level change. Sea level was stable in the first millennia. It then increased around the Medieval Climate Anomaly, followed by a further period of stable, or slightly falling, sea level associated with the Little Ice Age. In contrast Florida shows a linear rate of rise during the past 2000 years. All study sites show an increase in the rate of rise in the 20th century, representing the steepest, century-scale increase of the past two millennia. Based upon these and other results, thirteen peer reviewed papers, four book chapters and one edited volume have been accepted for publication. The results to informed national and state sea-level rise committees. Project funding has supported one post-doctoral scientists, one graduate student and four undergraduates. Our published work has been used in National Geographic Magazine.
