Late Quaternary chronology and environments of Square Lake, Torngat Mountains, Labrador

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Abstract
Sediment, pollen, and diatom records from Square Lake, a small lake dammed by a segment of Saglek Moraine, cover the period of deposition of and deglaciation from the Saglek Moraine. The basal radiocarbon date (18 210 ± 1900 years BP) is on sediment contaminated by reworked pollen and is thus a maximum age. However, the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the Saglek Moraine and thus establishes a Late Wisconsinan age for the Saglek Moraine. Vegetation on the ice-free upland surrounding Square Lake at this time was a sparse tundra vegetation dominated by grasses and herbs. The absence of diatoms indicates perennial lake-ice cover. A major transition is recorded by pollen and diatoms at > 8.5 ka. Vegetation probably remained sparse tundra, but birch and willow may have arrived in the area by 8 ka. Diatoms are first dominated by alkaliphil species, reflecting continued influence of glaciolacustrine sedimentation. An abrupt change in depositional environment ≥ 8 ka indicates ice retreat from the Saglek Moraine and start of nonglacial lacustrine sedimentation that has continued to the present. This was accompanied by an increase in organic matter, reflecting the newly established rich shrub tundra. At this time the diatoms also change, suggesting development of acidic organic soils around the lake. At 7.5 ka, diatoms indicate continued evolution of water chemistry and nutrient availability in the lake. Diatom concentrations and transfer function analyses of the pollen record identify the Holocene climatic optimum at 6.5 ka in the southern Torngat Mountains. The modern diatom flora was established at that time, but a decrease in diatom concentrations and estimated July temperatures suggest climatic deterioration in the area since 6.5 ka.