20th Century Sea-Level Rise on the US Atlantic Coast: Greater Than the Global Average

We have assembled a database of late Holocene (last ~4000 a BP) basal sea level index points (SLI) based on saltmarsh deposits from the Atlantic Coast of the United States of America. We have standardized these SLI both by relating their elevation to a geodetic datum (NAVD88) and by developing reference water levels (RWL) that relate the sea level indicators to the tidal frame.

This validation results in 21 sites with three or more basal SLI from Maine to South Carolina. Using this dataset, we can subdivide the US Atlantic Coast into three zones of differing modern day subsidence. The first zone from Maine to Boston shows rates of subsidence less than 0.3 mm yr^-1. The second zone from Barnstable to the Outer Banks shows rates of 0.3 – 0.6 mm yr^-1 and the third zone from Southport to Beaufort shows a return to rates less than 0.3 mm yr^-1.

Evidence obtained by decontaminating the tide gauge record of the Atlantic Coast of the United States of America with this geological dataset, documents the rate of sea level rise during the 20th century. Utilizing the nine reliable, long term (> 50 years) tide gauges where we have associated geological data, we highlight a 20th century rate of sea level rise of c. 2 mm yr^-1. This is higher than most previous global estimates derived from geophysical models, tide gauge analysis and global positioning systems although is in agreement with a number of studies concentrating solely on the US East Coast. Our results suggest that 20^th century sea level rise on the US Atlantic Coast was greater than the global average of 1.8 mm yr^-1.