13 Sea Level in the Southeast: Past, Present, and Future

Thursday, 29 March 2007
1:20 PM - 5:00 PM

EXAMINING THE EVIDENCE FOR A RECENT ACCELERATION IN THE RATE OF SEA-LEVEL RISE USING COMBINED INSTRUMENTAL AND PROXY DATA FROM THE PAMLICO-ALBEMARLE ESTUARINE SYSTEM, NORTH CAROLINA, USA

Paper number: 13-9
Program: THEME SESSIONS
Time: 4:00 PM – 4:20 PM

Authors

Abstract

We provide a high resolution relative sea-level (RSL) history for the last ~2000 years from the Pamlico – Albemarle estuarine system. The need for high resolution, late Holocene RSL reconstruction has increased with the realization that global warming may accelerate the rate of sea-level rise resulting in increased coastal flooding. Determining the physical response of a coastline to sea-level rise is an important problem to be addressed by applied coastal geology. This concern is acute for the Outer Banks and its back barrier estuary system which are considered as very vulnerable to sea-level rise. North Carolina does not have a reliable, long term tide gauge record to provide an instrumental measure of historical sea level. In order to consider the potential impacts sea-level rise may have on the Outer Banks it is necessary to place them in an appropriate geological framework. Scenarios for future sea-level rise are concerned with decadal to centennial timescales; as such they must be viewed in light of geologically derived sea-level reconstructions at a comparable temporal resolution. The foraminifera based transfer function approach is a quantitative methodology which can be effective in establishing these records.

Contemporary foraminifera were collected from 5 back barrier marshes to create a regional scale modern training set. The use of multiple marshes from a region increases the ecological and environmental diversity included within the training set and reduces the probability of a no modern analogue outcome. In order to merge the five spatially distinct sites and to relate each to local tide levels we used the VDatum transformation tool. This method relates all samples to a common orthometric datum (NAVD88) and reduces error.

A transfer function was developed to reconstruct former sea-levels based upon the modern, observable relationship between foraminiferal distributions and elevation (m MSL). Foraminifera were counted in a core of saltmarsh sediment from Sand Point, North Carolina. A high resolution age-depth model was produced from composite chronologies of 210Pb, 14C and pollen chrono-horizons. Application of the transfer function to fossil foraminifera was used to produce a late Holocene RSL record. There is an increase in the rate of sea-level rise at the commencement of the Industrial Revolution.