Accurate projections of future relative sea-level (RSL) rise are crucial for effective management of coastal populations, infrastructure, and ecosystems including salt marshes. Sea-level reconstructions from the last 4000 years provide a context for understanding modern and projected rates of sea-level rise because Earth's climate system is relatively unchanged. We will develop two new proxy RSL reconstructions from North Carolina to identify positive and negative departures from the perceived stability of sea level during the last 4000 years and support development of new predictive models in which the sea level-climate relationship can vary through time. The reconstructions will test the widely held assumption that sea-level rise from melting of large ice sheets was negligible during the last 2000 years and will help constrain rates of vertical land level movement. Data generated for the reconstructions will be used to further develop a model of salt-marsh response to sea-level rise that will provide a valuable service and tool to the coastal management community for informing policy decisions.
While there are compilations of global and regional proxy temperature data for the late Holocene, little is known about sea-level variability during this period and the response of sea level to known climate deviations such as the Medieval Climate Anomaly, Little Ice Age, and 20th century warming is unknown. Using foraminifera preserved in North Carolina salt-marsh sediments, we will produce the first continuous, high resolution (decadal and decimeter) RSL reconstruction spanning the last ~4000 years. The sea-level reconstructions will calibrate new predictive models of sea-level rise to improve the accuracy and regional validity of projections. The new record will extend existing reconstructions to test the following hypotheses that are vital for understanding the climate sea-level relationship: (1) regional RSL was stable before AD 1000; and (2) the contribution from melting of large ice sheets sea-level rise ended 2000 years ago. Reconstructions derived from salt marsh sediment also provide a paleo perspective for predicting the ecological effects of future sea-level rise. The proxy sea-level record will validate, for the first time, the Marsh Equilibrium Model (MEM). The MEM describes the regulation of salt-marsh vegetation by changes in sea level. If sea-level rise is faster than the rate of salt-marsh sediment accretion, the productivity of salt-marsh vegetation will decline, resulting in the degradation or loss of these important coastal ecosystems. The proxy sea level record will test a central premise of the MEM that (3) Stable sediment organic matter (SOM) concentration varies inversely with the reconstructed rate of RSL-rise.
