Marine molluscs and late quaternary environmental studies with particular reference to the late-glacial period in Northwest Europe: A review

Abstract

Although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates, particularly on a local scale, there is evidence to suggest that some boreal molluscs, particularly those which occur in similar environments on both sides of the North Atlantic, are valuable as oceanic temperature indicators. This applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature. The oceanography of the eastern North Atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas. Most glaciomarine molluscan faunas are not specific to that environment, an exception being that dominated by the bivalve Portlandia arctica. The role of marine molluscs in palaeoenvironmental research at the local level for the 13-11 ka BP period is illustrated by a site at Inchinnan, Scotland; it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition. During the same time interval, the changing composition of molluscan faunas on the NW European seaboard suggests that a weak drift of North Atlantic water replaced polar water at or a little later than 13 ka BP off Scotland and a few hundred years later off northern Norway. Evidence for relatively ‘warm’ intervals early and late in the 13-11 ka BP period has been found particulary on the Scottish coast and (to a lesser extent) more generally. The later ‘warm’ interval may be related to the southward movement of the polar front at the beginning of the Younger Dryas. The value of the bivalve shell itself in the determination of temperature, seasonality and calendar years is briefly discussed.