Evidence for Postglacial Paleoceanographic and Paleoclimatic Changes in Lake Melville, Labrador, Canada

Abstract

Foraminifera, dinoflagellates, and pollen in a radiocarbon-dated piston core from Lake Melville have been used to reconstruct a postglacial history of the fiord oceanography and regional climate. Present bottom water salinity in Lake Melville is about 5± lower than on the inner Labrador Shelf because of a shallow sill in the Narrows at the fiord entrance. Foraminiferal assemblages suggest that about 5000 yr BP, the fiord salinity was about the same as the inner shelf. The postglacial change in fiord salinity is best explained by a shallowing of the sill, preventing the entry of saline inner shelf bottom water. A model of relative sea-level changes at the Narrows is proposed which shows that at 5000 yr BP, the sill was about 20 m deeper than present; at 7000 yr BP it was 50 m deeper, and it was 90 m deeper until the end of the marine maximum at 7500 yr BP.

Pollen assemblages in the piston core indicate a succession of four major vegetation types in the Lake Melville drainage basin: from ca. 8000 to 7500 yr BP, low arctic tundra was replaced by shrub tundra; around 6000 yr BP, shrub tundra gave way to spruce woodland, which was followed by boreal forest around 5000 yr BP. A decline in absolute pollen concentrations during the past 4000 yr may indicate a recent climatic deterioration. Before forestation of the Lake Melville watershed, sedimentation in the fiord basin was three to four times higher than at present, but the maximum sedimentation rate of 0.26 cm yr^-1 is much lower than in other large Canadian fiords, e.g., Knight Inlet.