The geomorphic and paleoenvironmental record in the sediments of Atlin Lake, northern British Columbia

Atlin Lake in northern British Columbia and southern Yukon Territory is the largest natural lake in the North American Cordillera (791 km2). Inflow from the Juneau Ice Field delivers large volumes of sediment to the proximal basins of Willison Bay and Llewellyn Inlet. Sediment is distributed by interflow and underflow through these basins. Based on acoustic data, each of these basins contain Holocene deposits about 120 m thick, representing mean annual accumulation since deglaciation of more than 1 cm/a. Cores confirm this, except that the formation of a small lake at the toe of Llewellyn Glacier during about the past 50 years is trapping sediment and has reduced accumulation in Llewellyn Inlet by an order of magnitude. Sills separate these basins from the main body of Atlin Lake and Torres Channel where accumulation is much less, averaging about 1–4 mm/a during the history of the lake. Late Pleistocene glacilacustrine sediment occurs as a thin, patchy deposit and is overlain by up to 10 m of Holocene lacustrine deposits. Unlike other large lakes in the Cordillera with thick late Pleistocene deposits indicating large volumes of sediment contributed by glaciers in the lakes and their basins, the pattern in Atlin Lake documents rapid retreat of glaciers from the lake and much of the drainage basin.