Early Holocene climate of southwestern Alberta, Canada, reconstructed from lake sediment cores.

摘要

Beginning at about 10,000 BP, immediately following the Younger Dryas cold period, climate warmed dramatically and precipitation decreased. Previous research has identified this warm interval; however new results described herein have improved resolution of regional scale effects, timing and severity.; Sediment cores from 3 glacially-fed subalpine lakes indicate that sedimentation in southern Canadian Rocky Mountain lakes changed from allochthonous to autochthonous between 10,000 and 9400 BP, suggesting that suspended sediment influx terminated in response to increasing climatic warmth and aridity which caused alpine glaciers to completely melt. Clear water resulting from termination of suspended sediment influx allowed filter-feeding molluscs to colonize lower Burstall Lake, and greatly increased organic productivity in all three lakes through increased photosynthesis. Stable oxygen and carbon isotope measurements on organic and carbonate fractions of these cores suggest minimal glacial influence on subalpine lakes between 10,000 and shortly after 6734 BP.; Additional sediment cores from 7 closed basin lakes in the subalpine, montane and foothills of southwestern Alberta suggest increased warmth and aridity between 10,000 and sometime after 6734 BP. An erosional unconformity indicates that Cartwright Lake had completely dried out by 6734 BP. Peat facies in two other lakes also indicate low water levels during the early Holocene. The distance between the unconformity and peat facies, and modern water level suggest possible regional scale water table lowering of at least 6.5 m. Stable oxygen values from the organic fraction of Sibbald Lake become progressively heavier after 10,000 BP, indicating a negative water balance existed for most of the early Holocene.