Recent Sea-Level Changes in the North Atlantic

Abstract

Most of the tide-gauge stations still active, for which long series of almost continuous records are available, are located on both sides of the North Atlantic. Only records starting earlier than 1925 have been considered in this paper: 17 stations on the American side, and 58 on the European one. In addition records in the Bermudas starting in 1933 have been used for regional comparisons. All the stations indicate secular trends of relative sea-level variation which change from place to place. The data have been grouped in 5-yr periods, but the secular trends have been left out of the data in order to remove crustal movements.

Short term (5 to 20-yr) regional oscillations appear. Average 5–10 yr changes in sea level on the American coasts (where a north-south gradient is frequent) differ from those on the European ones. They often differ too between the American and the Bermuda coasts. This suggests that changes in the sea-surface topography across the Gulf Stream and in the sea-level slope occur in the North Atlantic, making regional sea levels change from one area to the other, with average differences in level reaching as much as one decimetre over 5-yr periods. Also on the European coasts changes in sea level often differ from one region to the other.

After an estimation of the eustatic component obscured by the local secular trends, the conclusion is reached that the average sea level, which shows faster rates of change on the American coasts, rose on both sides of the Atlantic from 1920 to 1950, and then remained stable or dropped slightly between 1950 and 1980, in spite of the increasing CO₂ atmospheric content. In Europe, the sea-level rise during the last century that can be ascribed to eustatic changes is only a few centimetres.