Holocene eustatic sea level change

Abstract

RELATIVE sea level changes result from eustatic variations in water level and vertical movements of the land, from tectonic or isostatic causes. If these changes are to be properly understood, it is important to define the eustatic component. Devoy1 has presented a relative Holocene sea level curve for the Thames Estuary, an area of known downwarping throughout the Quaternary and earlier time. If predictions of future relative sea levels in South-east England are to be made, the contributions of the worldwide post-glacial rise of sea level and of regional subsidence in the Flemish Bight have to be evaluated. One approach to the problem is to compare results from areas of tectonic instability with those from more stable areas. In the British Isles, the only area which can be regarded as stable is in the south and west, as far removed as possible, on the one hand, from the subsidence of the south-east, and on the other hand from isostatic rebound from ice-loading centred in North-west Scotland. Although theoretical objections to long-term stability, even in this region, can be adduced2, the geomorphological evidence in South-west England suggests that, at least in the Holocene and later Pleistocene, the area can be regarded as stable3. We presented in 1973 (ref. 4) a sea level curve based on detailed work in the Bristol Channel, which we regarded, in the absence of any evidence of Holocene isostatic and tectonic activity, as representative of the eustatic sea level rise. In view of evidence of continuing isostatic rebound in South-west Scotland5, studies were subsequently initiated in Cardigan Bay, particularly in the neighbourhood of Aberystwyth and Borth, to try to circumscribe the areas of stability and those of continuing recovery from ice-loading. The results are compared here with our previous ones.