Recent and fossil growth rates of marine bivalves, Canadian Arctic, and Late-Quaternary Arctic marine environments

Abstract

Growth rates of three marine bivalves - Mytilus edulis, Serripes groenlandicum and Clinocardium ciliatum-are used to elucidate Late-Quaternary marine conditions in the Canadian Arctic and Subarctic. Present-day growth rates in Subarctic waters are statistically faster than those for the same species in Arctic waters. Fossil growth rates are analysed for a 6,000- and 8,500-year sequence from central Hudson Bay and east Baffin Island. These data suggest that growth rates and the size of coexistent clams, Mya truncata and Mya pseudoarenaria, increased to a maximum about 3,500 B.P. and have since declined. Growth rates did not increase to Subarctic values and hence the increase is related to temperature and salinity changes of the surface layer rather than by vertical mixing with the Atlantic water layer at depth. During the period 8,000-2,500 B.P. M. edulis and Macoma balthica extended up the east coast of Baffin Island and across the entire Arctic mainland coast; Chlamys islandicus does not appear to have been as widespread. In the last 2,500 years or so these species have retreated to the west and south. A comparison of raised, Late-Quaternary marine deposits throughout the North-Atlantic Arctic indicates similar biostratigraphic zones. Warmer conditions than today prevailed between 8,500-2,500 B.P. with an optimum ∼ 3,500 B.P. These dates suggest that marine conditions lagged behind terrestrial climatic changes, thus superimposing (in time) a cool atmosphere/warm ocean system that might explain the renewed glacierization of Arctic regions in the Neoglacial.