Examining the evidence for a recent acceleration in the rate of sea-level rise using combined instrumental and proxy data, North Carolina, USA

Whilst accelerated rates of relative sea-level (RSL) rise are potentially one of the most devastating impacts of future climate change, our understanding of decadal scale changes in sea-level is poor. This paper seeks to address this knowledge gap by combining tide gauge and high-precision geological reconstructions of relative sea-level of sufficient resolution and duration to detect any recent acceleration in the rate of sea-level rise. We offer a high resolution relative sea-level history for the last ~2000 years from the Albemarle - Pamlico Estuarine System in North Carolina. Contemporary foraminifera were collected from five 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. 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. We developed an accurate and precise transfer function to reconstruct former sea levels based upon the modern observable relationship between foraminifera and elevation with respect to the tidal frame. We applied the transfer function to salt-marsh core(s) from Sand Point (Roanoke Island), North Carolina to produce a late Holocene RSL record. An age-depth model was produced from composite chronologies of 210Pb, 14C and pollen chrono-horizons. We validated our approach by comparing geological based reconstructions and instrumental tide gauge records. Our records show that in the last ~2000 years sea level has risen at a background rate of ~1.1mm/yr. There is evidence for two recent accelerations in the rate of sea-level rise during the late 19th and 20th centuries to a current rate of ~4mm/yr.