Rapid climate change and spruce-climate disequilibrium in lateglacial Nova Scotia
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Date
2015
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University of New Brunswick
Abstract
A network of 25 lateglacial-aged lakes was sampled in Nova Scotia to examine the relationship between climate and vegetation at the end of the last Ice Age. Nova Scotia lake sediments are sensitive to the rapid climate events that typify the lateglacial and possess some of the best records for millennial-decadal scale climate change outside the Greenland Ice Core records. The presence of spruce in lateglacial Nova Scotia has been previously estimated using the 20% spruce pollen limit. Using fossil stomates and plant macrofossils, I have refined this limit to 8%, potentially eliminating significant underestimates of the distribution of spruce. The 8% limit was then used to determine if spruce was in equilibrium with climate during the lateglacial at 4 time intervals. Evidence for spruce was found at numerous sites with chironomid inferred July temperatures as low as 13°C. Sites where the temperature was at, or above, 13°C but spruce was absent indicated that spruce was not in equilibrium with climate at that time interval as the result of a migration or population expansion lag. Significant portions of northeastern Nova Scotia and all of Cape Breton Island remained in vegetation-climate disequilibrium during the lateglacial, while a small portion of southwestern Nova Scotia also exhibited disequilibrium conditions.
While reconstructing the thermal regime in lateglacial Nova Scotia, evidence for the Older Dryas (GI-1d) and the recently discovered GI-1c2 was observed and confirmed with chironomid inferred temperature reversals >3 °C. The discovery of these two events indicates that brief cooling events typical of NW European records also occurred in North America. Furthermore, chironomid and LOI records from Nova Scotia also provide evidence for a potential decade-scale cooling event analogous to the current slowdown in the rate of global warming. These data, indicating cooling between 1.6-6.4 °C, have been correlated to over 30 marine and terrestrial sites throughout the North Atlantic and beyond.