Global Sea-Level Changes During the Past Century
An updated and expanded data base of tide-gauge measurements and late Holocene sea-level indicators is used to obtain a revised global average sea-level rise, corrected for long-range glacio-isostatic and/or tectonic trends. The global average is determined using two methods: (1) the arithmetic mean of all stations, and (2) a new technique which weights contributing stations by distance from a given cell and relative coastal area. A least-squares regression line is then fitted to the composite regional sea-level curve. In the second method, the global average is derived by averaging 11 regional sea-level curves, weighting each region equally, and also according to the relative reliability of the regional data. This latter step is designed to reduce the influence of regions with few stations or poor data.
The “corrected” average eustatic sea-level rise for both methods is 1.2 ± 0.3 and 1.0 ± 0.1 mm/yr, respectively. Weighting for regional reliability does not alter the global average significantly. The results agree with those of previous studies and provide an independent verification for a global increase in sea level during the past century. The closeness in values between the two averaging methods used here and those of earlier studies suggests that the observed change represents a true eustatic sea-level rise in spite of noisy data, geographic bias, and differences in approach and techniques.
Sea level, corrected for long-term movements, is found to be rising in all but three regions, which have small station populations, sparse long-range data or are tectonically active. Along the east coast of North America, an apparent maximum sea-level rise is observed in both tide-gauge and late Holocene sea-level indicators between Chesapeake Bay and New Jersey (36°–40°N). This enhanced mid-Atlantic subsidence, possibly indicating neotectonic activity or sediment loading, has persisted for at least the last 7,000 yrs. Subsidence of northern New England-Maritime Canada (44°–46°N) may be caused by a migrating crest of the peripheral forebulge at the edge of formerly glaciated areas. Sea-level changes in western North America show greater spatial variations than for the east coast, which can be related to more active tectonism in California and British Columbia and to strong, localized isostatic rebound in Alaska.
Most of the recent sea-level rise can be accounted for in terms of the thermal expansion of the upper layers of the ocean and by melting of alpine glaciers.
Figures & Tables
Sea-Level Fluctuation and Coastal Evolution - This Special Publication is the result of a symposium in honor of W. Armstrong Price held at the first SEPM Midyear Meeting at San Jose, California, on August 12, 1984. The factors controlling relative sea-level change along our shores are varied and, at best, imperfectly understood. Yet, the relative rate of change is what controls shoreline erosion, the arrangement of sedimentary facies of the coastal zone, and the character of deformities within the coastal stratigraphic record. Therefore, these papers address sea-level changes, shoreline responses, and the controls on the three-dimensional geometry of the consequent lithosomes; in short, the architecture of the coastal depositional systems.