POST-GLACIAL CLIMATE CHANGE AND ITS EFFECT ON THE THERMAL STRUCTURE AND HABITAT IN A SHALLOW DIMICTIC LAKE, NOVA SCOTIA, CANADA

To provide context for the recent loss of cold-water habitat for Brook Trout (Salvelinus fontinalis) in shallow (<6m av. depth), dimictic lakes in Nova Scotia, a high resolution (decadal- centennial scale) and well dated (7 ¹⁴C dates, ¹³⁷Cs, ²¹⁰Pb) record of post-glacial climate change has been reconstructed for Canoran Lake, Nova Scotia.  Chemostratigraphic (organic carbon, total nitrogen, stable isotopes (d¹⁵N and d¹³C), Hydrogen Index), biostratigraphic (pollen), and lithostratigraphic (magnetic susceptibility and smear slides) proxies were used to understand how past shifts in climate and basin infilling have affected primary productivity and the thermal regime of Canoran Lake. 

Canoran Lake reacted strongly to rapid climate change events associated with Late Glacial and Early Holocene cooling events including the Younger Dryas (13 000 - 11 500 cal. yr BP) and the 8.2 kyr event (8200 cal yr BP).  During the Younger Dryas cooling, Canoran Lake became a cold monomictic lake with short ice free periods (anomalously high d¹³C, low C/N ratios, low %TOC, low %N, low HI), paludified shorelines (wetland pollen, d¹⁵N, d¹³C), and a destabilized watershed (clastic sedimentation).  Rapid climatic cooling that was coincident with the 8.2 kyr event resulted in an increase in clastic input and/or a decrease in primary productivity (decrease in bulk density, %TOC, %N).  However, the response of d¹³C and d¹⁵N values to 8.2 kyr event was delayed or buffered by lakeside wetland development.  After ~8000 cal. yrs BP, proxies indicate that the climate was relatively stable, warm, and dry until ~5900 - 4600 cal. yr BP when a change in precipitation patterns resulted in wetland formation.  Climate change apparent in historical records (1800 AD – present) did not strongly effect the proxy record of Canoran Lake even though 3 years of water temperature monitoring indicated that modern-day climate variability has a significant effect on the hypolimnic water temperatures and cold-water habitat for Brook Trout.