Lake of the Woods is one of North America's largest lake complexes, covering an area of ~4000 km2 in Ontario, Manitoba, and Minnesota. Multiple proxies and 38 new accelerator mass spectroscopy (AMS) radiocarbon dates from six sediment cores in the basin were used to interpret the Holocene paleoenvironmental history of Lake of the Woods, including the late history of glacial Lake Agassiz. Sediments cored consist mainly of lacustrine silty clay to clayey silt. A distinct pink lamina in one core is associated with overflow into Lake Agassiz from the Superior basin related to the Marquette readvance of the Laurentide Ice Sheet 11,300 cal (9900 14C) yr B.P. Pedogenic zones developed in the sediment reflect periods when the lake floor was dry and exposed to weathering, specifically (1) during an initial phase after the Lake of the Woods basin became isolated from Lake Agassiz ca. 10,500-10,000 cal yr B.P. but before differential isostatic rebound caused water in the northern end of the basin to transgress south over the exposed lake floor, and (2) during a 3600-yr-long negative hydrological budget and chronological hiatus related to the mid- Holocene Hypsithermal warming and drying event, which is represented by < 1 m of sediment. Diatoms first appear in the record after the Lake of the Woods became separated from Lake Agassiz shortly after 10,500 cal yr B.P. Ostracodes are present in sediments as young as ca. 7600 cal yr B.P., disappearing above the uppermost pedogenic zone; thecamoebians first appear after this. Distinct shifts in diatom assemblage composition and in sedimentary chlorophyll-a in one core track late Holocene changes in Lake of the Woods.
Bibliographical noteFunding Information:
We thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for support for the coring and research of Teller and Mellors and a Best in Science Grant to Smol from the Ontario Ministry of the Environment for the enumeration and interpretation of the diatom data. Personnel and equipment for the coring by Teller and Mellors came from the Limnological Research Center (LRC) at the University of Minnesota in Minneapolis; the coring team consisted of Kristina Brady, Amy Mybro, Anders Noren, and Mark Shapley from LRC, and Jim Teller and Trevor Mellors from the University of Manitoba in Winnipeg. We are grateful to the LRC for allowing use of their laboratory facilities to study and store our cores, and we thank members of the coring team who helped while at LRC. Particular thanks are owed to Alice Telka (Paleotec Services, Ottawa), who carefully selected and identified organics from the cores for dating. Steve Colman provided important insight into our interpretations and a detailed review of an early version of this paper. We thank Brandon Curry of the Illinois Geological Survey for help in identifying ostracodes. Devin Vessey and Graeme Patrick helped with laboratory analyses at the University of Manitoba. Thanks to Jim McPhee for boat transportation on Shoal Lake. Special thanks go to Z. Yang, who revised the original paleotopography maps published in Yang and Teller (2005). Financial support from the Clayton H. Riddell Faculty of Environment, Earth, and Resources at the University of Manitoba helped bring this research to completion.
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