Paleohydrology of a Canadian Shield lake inferred from 18O in sediment cellulose
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 δ18O 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 δ18O fluctuated from about 5‰ lower than present in the early postglacial to 5‰ or more above present values during the mid-postglacial. These broad, secular shifts reflect a combination of fluctuating mean annual δ18O 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 interp...