Diatom-inferred records of paleolimnological change and Holocene paleoclimate variability from the Altai Mountains (Siberia) and Columbia Mountains (British Columbia).

摘要

Sediment collected from lakes in two mid-continental regions was analyzed for evidence of Holocene paleoclimatic change. The lakes, situated within interior mountain ranges of British Columbia and Siberia at similar latitudes, are subject to similar insolation forcing. The primary proxy of climatic or environmental change in each set of lakes is the diatom record, including species assemblages and biogenic silica concentrations, a proxy for diatom productivity. The sedimentary diatom records of three shallow lakes in the Altai Mountains were dominated for the entire period of record by small benthic Fragilariaceae taxa. Uncertainties in the ecological affinities of the dominant taxa make direct interpretation of the diatom record difficult. However, the chironomid record at one lake suggests that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata reflect cooling possibly correlative to the Younger Dryas Stade and maximum Holocene warmth prior to 6000 cal year BP. In a second lake, accumulation rates of biogenic silica appear to have tracked summer insolation trends over the last 8000 years. In the Columbia Mountains of western Canada, reconstructions of paleo-lake levels, and, by extension, changes in regional water balance, are based on variability in preservation and composition of the diatom records and are consistent with existing paleoclimate data from British Columbia, which indicate a transition to higher effective moisture between ∼7000 and 6000 cal year BP. Broad trends in climate appear related to atmospheric circulation patterns with PNA- and PDO-like modes of variability. Spectral analysis reveals periodicities of 92 to 910--970 years, all of which have been reported previously from sites from the Northern Great Plains to Alaska.; Morphometric and SEM analysis of several Cyclotella populations with affinities to Cyclotella bodanica v. lemanica is also described. This diatom is a common element of the planktonic flora in deep, alkaline montane lakes in western North America, including those discussed in this dissertation.