Evolution and paleohydrology of glacial Lakes Barlow and Ojibway

Abstract

The evolution of Lakes Barlow and Ojibway, two large ice-contact glacial lakes that covered parts of northern Ontario and western Québec from about 10.1–8.0 ka BP, during the retreat of the Laurentide Ice Sheet, was reconstructed using deglaciation landforms, ice-flow indicators inscribed on bedrock, 14C dates of early postglacial vegetation accumulated in lake basins, the distribution of Mysis relicta (a biological indicator of lacustrine submergence), varve chronology, and a detailed photogrammetric survey of the lake limit. Although the rate of ice retreat varied greatly throughout the basin, the average rate in Lake Barlow-Ojibway was 450 m/year. Rates of ice retreat deduced from varve chronology were assessed using predictable relationships between the lake limit, the shoreline gradient, and the rate of relative uplift. Over a 590 km long profile, the gradient on the maximum elevation of the lake defines a parabola that is attributed to restrained rebound, although in part it could be due to the position of the profile with respect to the overall uplift pattern generated by the ice sheet. The life span of the lake determined from varve chronology (2110 years) shows excellent agreement with the age difference obtained between that of marine shells overlying Lake Ojibway sediments at its northern end in Hudson Bay, and the oldest radiocarbon ages on basal organics in lakes in the southern part of the Barlow-Ojibway basin.Both lakes drained eastward through the Ottawa River between 10.1 and 8.0 ka BP, and the average yearly discharge to the North Atlantic Ocean during the last 1000–1500 years is estimated at about 946 km3. At break-up of the ice sheet in southern Hudson Bay at about 8.0 ka BP, Lake Ojibway drained abruptly, releasing an estimated 114,396 km3 of freshwater into the Tyrrell Sea and raising sea level by about 30 cm.