Changes in lake-sediment stratigraphy associated with late glacial climatechange: examples from western Nova Scotia

An investigation of lake-sediment stratigraphy in western Nova Scotia has f ocused on determining the environmental response to late-glacial climate ch ange. Sediment records from five headwater lakes were recovered and sedimen t stratigraphy from four of the lakes was used to reconstruct late-glacial environments for this region. Results from Sand Lake and Canoran Lake (South Mountain) indicate that the South Mountain was deglaciated by about 11,500 B.P. The North Mountain was deglaciated slightly earlier. All cores contained till (unit 1) which was o verlain by a fine-grained diamicton (unit 2) that was deposited after ice h ad receded. A gyttja with varying mineral sediment concentrations (unit 3) overlies unit 2. Unit 2 is interpreted as sediment that was transferred to the basin as the basin and catchment stabilized. The North Mountain sites a re characterized by lack of a Younger Dryas-equivalent loss-on-ignition or mineral oscillation. The South Mountain sites both contain a thin (2 cm) Yo unger Dryas-equivalent mineral horizon (unit 4) bounded above and below by sandy gyttja (units 3 and 5). Image and grain size analysis of units 3, 4 a nd 5 indicate that these units differ primarily in their amounts of fine si lt and clay, as maximum grain size is similar in each unit. This result ind icates that changes in sediment transfer mechanisms in response to climate change were subtle. The formation of unit 4 (YDimh) was primarily a consequ ence of intrabasin sediment transfer and reduced productivity; an increase in the extent and/or duration of lake ice cover may have been an important factor. The catchment response to Younger Dryas climate change in western N ova Scotia was probably subdued. Though aufeis and perennial snow cover may have existed at some sites, the presence of Younger Dryas-equivalent glaci al ice in western Nova Scotia is unlikely.