SENSITIVITY OF DIMICTIC LAKES TO CLIMATE CHANGE: A PALEOLIMNOLOGICAL PERSPECTIVE

Lake sediment cores obtained from dimictic lakes in southwestern Nova Scotia commonly contain the Younger Dryas inorganic marker horizon (YDimh), a stratigraphic layer thought to have formed as climate deteriorated and lake productivity declined. However, the distribution of lakes containing the YDimh is erratic and does not appear to be related to external conditions or processes. Because the YDimh is present only in lakes with complex basins connections may exist between lake morphometry, productivity and climate.

In order to investigate the relationship between lake basin morphometry, thermal structure and climate, the thermal structures of a suite of lakes of similar volume, area, depth, chemistry etc. but in which the YDimh is either present or absent were studied for up to 7 years. These data were then compared to weather (temperature, precipitation, pressure) records to determine the relationship between short-term meteorological events and lake thermal regimes. Thermal data (2002 – 2009) indicate that during periods of frequent low pressure episodes, lakes with simple basins (no YDimh) exhibit strong metalimnetic entrainment and rapid downwards displacement of the thermocline. Under similar conditions lakes with complex basins (YDimh present) experienced strong stratification and a stable thermocline. Climate change prediction for Atlantic Canada indicates the likelihood of more frequent and more intense low pressure influxes, conditions that would favour cold water habitat resilience in complex lake basins. This study indicates that lake basin morphometry may be an important indicator of the relative sensitivity of dimictic lakes to short term climate change.