The ostracode record from Harris Lake, southwestern Saskatchewan: 9200 years of local environmental change

Holocene paleoenvironments of Harris Lake, southwestern Saskatchewan, are r econstructed from the ostracode stratigraphy of a 10.4 m sediment core. Twe nty three taxa, representing nine genera, were identified and counted from 113 samples. At each depth, a theoretical faunal assemblage was derived fro m the raw counts. The mean and variance of chemical, climatic and physical variables were inferred from modern analogues of the fossil assemblages, us ing existing autecological data from 6720 sites, mostly in western Canada. These data suggest four paleoenvironments: an early-Holocene (9240-6400 yea rs BP) variable climate supporting aspen parkland vegetation; the warm dry hypsithermal (6400-4500 years BP); a short transitional period of ameliorat ing climate and expanding subboreal forest (4500-3600 years BP); and the pr esent environment since 3600 years BP. A change in regional climate with th e draining of Glacial Lake Agassiz (ca. 8500 years BP) and landsliding in t he watershed (ca. 4000 years BP) caused relatively rapid environmental chan ge. The ostracode record generally corroborates the interpretations of othe r proxy data previously published for Harris Lake. Most of the discrepancy involves the timing and severity of maximum Holocene warmth and aridity. Pe ak aridity interpreted from the pollen data is earlier than in the other pr oxy records. Both the diatoms and ostracodes indicate highest paleosalinity between ca. 6500 and 5000 years BP, but maximum salinity in the diatom rec ord occurs between ca. 6000-5700 years BP, whereas the ostracode-inferred s alinity is relatively low at this time and peaks later at ca. 5000 years. N either of these reconstructions suggests the short episodes of hypersalinit y interpreted from the mineralogy.