A METHODOLOGY FOR ANALYSES OF RELATIVE SEA-LEVEL DATA: A CASE STUDY FROM NORTH CAROLINA

High quality sea-level data reveal spatial and temporal variations in crustal movements since the Last Glacial Maximum (LGM). Current concerns about the potential sea-level rise associated with anthropogenic warming of the atmosphere and ocean, and its impacts on coastal resources have resulted in increased attention focused on evidence of former sea-level fluctuations. Rates of sea-level rise obtained since the LGM represent the fundamental basis for comparison with the historical and present day changes. They provide an essential benchmark against which one must measure the additional sea-level rise that has occurred over the last 100 years. Sea-level histories since the LGM from sites along the Atlantic coast of the United States constitute an extremely important constraint upon the dynamical models of the Glacial Isostatic Adjustment process). There exists a systematic misfit of the model to sea-level observations along the United States Atlantic coast greater than a few thousand years. It is presently unknown whether these misfits derive from a fundamental flaw in the model of the GIA process or in the interpretation of former sea-level measurements from this critical region.

In this paper we have validated existing sea-level observations from North Carolina and combined these with new high precision data. To reconstruct former sea level we have followed the common language developed during numerous IGCP projects, with rigid operational definitions, for classification, statistical analysis and hypothesis testing. North Carolina sea levels rise from -35m at 11ka cal yrs BP with a discernable slow down c. 6.5ka cal yrs BP. Using the linear regression the late Holocene (last 4 ka cal yrs BP) the uplift rate for North Carolina was c. 0.8mm/yr. The Wilmington tidal station estimates the twentieth century mean sea level trend is and c. 2.2 mm/yr. This implies an additional rate of mean sea-level change during the twentieth century of the order of over 1 mm/yr, which agrees with the consensus of opinion that global sea levels have increased between 10 and 20 cm over the past century. It is assumed that thermal expansion of sea water and the melting of mid-latitude glaciers have been the major contributors to this.