ABSTRACT: Recent coastal submergence of the Maritime Provinces

CGRG Bibliography of Canadian Geomorphology
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Abstract

For more than a century it has been known that the Maritimes are submerging. This report describes the extent, age, sequence, rate and causes of the relative rise of sea level, primarily by determining the radiocarbon and calendar ages of submerged features that originated at or near former high tide, and measuring their depths below present high tide. Variations in the rate of sea-level rise, and a recent acceleration are reflected in stratigraphy of coastal deposits and discontinuities of beach morphology. Evidence of submergence during the last 5000 years is recorded by tree-stumps and other freshwater vegetation overridden by transgressing barrier beaches, and buried beneath tidal marshes. Supplementary evidence for the last 1000 years includes drowned Indian campsites, colonial artifacts buried in tidal mud, and the rise of high tide at the fortress of Louisbourg. Tide-gauge records and geodetic re-levelling confirm that the coast is still submerging today. Forty-seven age and depth determinations on former lower positions of high-tide datum indicate the region is submerging 30 cm (one foot) per century, whereas average world-wide rate of sea-level rise is only 6 cm/century. Excessive submergence in the Maritimes is believed due to subsidence of the earth's crust as a former glacier-marginal bulge collapses. In the Bay of Fundy an additional factor has been the amplification of tidal range as world- wide rise of sea level widened and deepened the entrance, and optimized basin geometry. Both subsidence and tidal change are indirect consequences of climatic change. Details of past climatic variation, and indications of future change, can be deciphered from the shape and composition of Maritime coastal features.

Bibliography of Canadian Geomorphology