Early Onset of Historical Accelerated Relative Sea Level Rise in North Carolina, USA

We present an 800 year, high resolution record of relative sea level rise (RSLR) change from foraminifera preserved in salt-marsh sediments on Roanoke Island, North Carolina. In the absence of long term instrumental records, geological derived estimates of former sea level are necessary to detect changes in the rate RSLR. Using a foraminifera-based transfer function we show that RSLR increased at the start of the 19th Century from a previous rate of 0.8mm/yr ± 0.04mm to 1.5mm/yr ± 0.16mm. We identify a second acceleration around 1900AD to ~4.3mm/yr. This current rate of RSLR has been reconciled with the available tide gauge record data and validates our approach.

Contemporary foraminifera were collected from eight salt marshes in North Carolina representing a wide range of physiographic settings. The strong relationship between foraminifera and elevation in the modern environment was used to develop a regional scale transfer function. We reconstructed RSLR by applying this transfer function to assemblages of foraminifera in a core of salt-marsh peat recovered from Sand Point on Roanoke Island, NC. The timing of RSLR changes is constrained by an age model developed from a composite chronology of five AMS 14C dates, 210Pb, 137Cs dating and a pollen chrono-horzion (Ambrosia).

Recent geological investigations of historic RSL in North America (e.g. Maine and Connecticut) have identified accelerated rates of rise beginning in the late 19th and early 20th Centuries. Our study suggests that in North Carolina the onset of rapid RSLR change began earlier (at the beginning of the 19th Century) and comprises of two distinct accelerations. High resolution studies of RSLR change and accurate dating of accelerations may be able to provide new information pertaining to the mechanisms behind historical RSLR.