ABSTRACT: Paleohydrology of a Canadian Shield lake inferred from 18O in sediment cellulose

CGRG Bibliography of Canadian Geomorphology
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Abstract

Oxygen- and carbon-isotope analyses on cellulose in the postglacial sediment of Weslemkoon Lake, southern Ontario, show that the cellulose came mainly from aquatic plants or algae, rather than from terrestrial sources. If a wholly aquatic source is assumed, the oxygen-isotope content permits inferences of lake-water 18-O values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis. Chronological control is provided by pollen analysis and six 14C dates. Our reconstruction shows lake-water 18-O fluctuated from about 5o/oo lower than present in the early postglacial to 5 o/oo or more above present values during the mid-postglacial. These broad, secular shifts reflect a combination of fluctuating mean annual 18-O of local precipitation, evaporative isotopic enrichment of surface waters, and snowmelt-bypass effects. The first two factors reflect the changing paleotemperature and paleohydrology, respectively, whereas the third factor is a more speculative interpretation of isotope effects during snowmelt delivery to the lake. The snowmelt-bypass mechanism is supported by parallel changes in the overall abundance and seasonal distribution of precipitation. This effect is probably responsible for pronounced isotopic enrichment of the water throughout the moist climate of the past 6000 years.

Bibliography of Canadian Geomorphology