Holocene glaciation and climate evolution of Baffin Island, Arctic Canada

Abstract

Lake sediment cores and cosmogenic exposure (CE) dates constrain the pattern of deglaciation and evolution of climate across Baffin Island since the last glacial maximum (LGM). CE dating of erratics demonstrates that the northeastern coastal lowlands became ice-free ca.14 ka as the Laurentide Ice Sheet (LIS) receded from its LGM margin on the continental shelf. Coastal lakes in southeastern Baffin Island started to accumulate sediment at this time, whereas initial lacustrine sedimentation was delayed by two millennia in the north. Reduced organic matter in lake sediment deposited during the Younger Dryas chron, and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall. Ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the LIS and local mountain glaciers ∼9.6 ka (Cockburn Substage). A second readvance occurred just before 8 ka during a period of unusually cold summers, corresponding to the 8.2 ka cold event in the Greenland Ice Sheet. Most local glaciers were behind their present margins before 7 ka, and in some instances much earlier, although the Foxe Dome of the LIS continued to slowly retract toward the present day Barnes Ice Cap throughout the Holocene. Pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka. Subsequently, grass tundra became established, followed by modern tundra vegetation ca. 8 ka, with subtle changes in pollen assemblages in the late Holocene. Lake primary productivity peaked in the early Holocene, before terrestrial vegetation or marine surface waters reached their apparent thermal maxima. Lacustrine, marine, and glacial proxies all reflect significant late Holocene cooling. The onset of Neoglaciation is well dated in lacustrine records at ca. 6 ka, with intensification after 2.5 ka. The expansion of local glaciers during the Little Ice Age represents the most extensive advance since 7 ka. We suggest that the replacement of Atlantic surface waters by cold, low-salinity Arctic Ocean water, coupled with the steady reduction of summer insolation, resulted in a significant positive sea-ice feedback that produced a larger late Holocene summer temperature depression over the Baffin region than in the Pacific sector of the Arctic.