Holocene boreal molluscs in Greenland — palaeoceanographic implications

Abstract

Boreal molluscs, now extinct in Greenland waters, occur as subfossils in West Greenland between lat. 65°30′ and 68°30′N. A number of new localities for these warmth demanding molluscs are described, and the list of species now comprises the gastropod Emarqinula fissura and the bivalvalves Heteranomia squamula, Modiolus, Arctica islandica, Panopea norvegica, and Zirphaea crispata. During their time the molluscs formed an isolated northern outpost, located in the area which — as a result of the complex oceanic circulation — today has Greenland's highest ocean surface temperatures. The occurrences are 14C dated to the interval 8400–4900 yr B.P., and summer surface temperatures were 1–3°C higher than now. For its beginning this period coincides with similar “marine optimal periods” in East Greenland and on the Baffin Island shelf, whereas it took 1000 years before the beginning of warmer than present temperatures on land. On the basis of this evidence it is concluded that the rise of sea surface temperatures was afforded by a decrease in inflow of cold polar water and/or increase in inflow of warm atlantic water into Davis Strait, rather than climatic change.