LAKE WINNIPEG WATER ISOTOPIC COMPOSITIONS INFERRED FROM δ~(18)O AND δ~2H MEASUREMENTS OF SEDIMENT PORE WATER AND ORGANIC MATTER

摘要

The oxygen and hydrogen isotopic composition of lake water is dependent on the varying isotopic composition of meteoric water supplying it, the hydrology of the lake basin and the effects of evaporation. Therefore, a record of the oxygen and hydrogen isotopic composition of lake water could be used to document past changes in the isotopic composition of the mean annual precipitation (related to changes in atmospheric circulation and mean annual temperature), basin hydrology and moisture regimes. Oxygen and hydrogen isotopic values of sediment pore water extracted from two 7.0 m cores taken from the north basin of Lake Winnipeg (23 698.4 km~2) provide evidence of distinct climate intervals during the Holocene in central North America. Since these lake sediments are underlain by Precambrian bedrock it is unlikely that their pore water oxygen isotopic compositions have been modified by the infiltration of formation waters. Major ion chemistry of the pore water also suggests that it is indeed preserved lake water.