ABSTRACT: A 1000-year record of climate in the Eastern Canadian Prairies reconstructed from lake sediment organic isotope measurements.

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Abstract

A short sediment core (1.62 m), covering the period between A.D. 920 – 1999, was sampled from the south basin of Lake Winnipeg for a suite of multi-proxy analyses leading towards a detailed characterization of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Of specific interest here is information on the frequency and duration of major dry periods in southern Manitoba in light of the changes that are likely to occur as a result of an increasingly warming atmosphere. In this study, intervals of relatively enriched lake sediment cellulose oxygen isotope values (?18Ocellulose) occur from A.D. 1180 – 1230 (range: A.D. 1104 –1231 to 1160 –1280), 1610 –1640 (range: A.D. 1571–1634 to 1603–1662); 1670 –1720 (range: A.D. 1643–1697 to 1692–1738) and 1750–1780 (range: A.D. 1724 –1766 to 1756 –1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (?18Oinf-lw), suggest that the ratio of lake evaporation to catchment input may have been 25 to 40% higher during these isotopically distinct periods. Reasonably correlated with the enriched ?18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (?13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimized input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the A.D. 1180-1230, 1610 –1640; 1670 –1720; 1750 –1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba,Canada. Additionally, lower magnitude and duration dry periods may have also occurred from 1320 –1340 (range: A.D. 1257–1363), 1530–1540 (range: A.D. 1490 –1565 to 1498–1572) and 1570 –1580 (range: A.D. 1531–1599 to 1539–1606).

Bibliography of Canadian Geomorphology