Post-glacial climate change and its effect on the thermal structure and habitat of a shallow dimictic lake, Nova Scotia, Canada: A chemostratigraphic and lithostratigraphic investigation.

摘要

To provide context for recent loss of cold-water habitat for brook trout (Salvelinus fontinalis) in shallow ( 6 m av. depth), dimictic lakes in Nova Scotia, Canada, a high resolution (decadal-centennial scale) and well-dated (7 14C and 1 137Cs dates) record of post-glacial climate change has been reconstructed for Canoran Lake, a shallow lake that has been stocked with brook trout in the past. This study is a pioneering attempt to quantify hypolimnetic conditions using delta 15N, delta13C, HI, %C, magnetic susceptibility, and pollen.; Canoran Lake reacted strongly to rapid cooling events including the Younger Dryas. The climate during the Early and Late Hypsithermal (∼11500--8500 cal. yr BP and ∼8000--3500 cal. yr BP, respectfully) was stable, warm, and dry. The Early Hypsithermal was interrupted by minor increase in clastic input between 9100 and 8500 cal. yr BP but delta15N, delta 13C, and HI values imply that the lithostratigraphic response is not indicative of climatic-induced change; the cause remains enigmatic. The proxy response between 8500 and 8000 cal. yr BP is interpreted to be due to the southward displacement of the polar jet stream that is coincident with the 8.2 kyr event. The 5500 cal. yr BP hemlock decline recorded in the pollen record is not coincident with drought-like conditions and a pathogen attack is likely. The Late Hypsithermal was followed by a subtle increase in precipitation and cooler air temperatures, which marked the onset of the Post-Hypsithermal (∼3500 cal. yr BP--AD 1200). The proxy response during the Medieval Warm Period (∼AD 1200--AD 1550) was a smaller-magnitude equivalent of the 8.2 kyr event and was followed by an increase in precipitation during the Little Ice Age (AD 1550--present). The lake was anthropogenically acidified from ∼1860--present; consequently, the proxy trends were neutral and did not react to modern climate change.; Post-glacial habitat quality and quantity for brook trout has been highly variable, and dependent on air temperature and effective moisture (precipitation - evapotranspiration). Air temperature change strongly affected the quality of brook trout habitat (water temperatures (delta13C) and hypolimnetic dissolved oxygen concentrations (HI)). The quantity of brook trout habitat was predominantly controlled by effective moisture and ultimately lake levels (delta15N; C/N ratios; %C).