A LATEGLACIAL AND HOLOCENE LACUSTRINE RECORD OF PALEOENVIRONMENTAL CHANGE FROM LOST LAKE, INTERIOR ALASKA

Sediment cores collected from Lost Lake, Alaska, are used to reconstruct relative lake-level change and shifting moisture balance conditions from the latest Pleistocene to the present. Sedimentological analysis of core-transects from closed-basin lakes in the interior of Alaska indicate a period of aridity during the Last Glacial Maximum, higher, variable lake-levels during the Lateglacial period, and high, generally stable lake-levels since the early Holocene. However, after lake-levels increased and stabilized during the early Holocene, many lacustrine systems became largely insensitive to subsequent smaller scale fluctuations. Lost Lake is a relatively shallow (~11 m max. depth) closed-basin lake, which we hypothesize makes it sensitive to lower magnitude lake-level changes. Three sediment cores were collected along a transect from the shoreline to the central depocenter in July of 2012 in 10.6 m, 6.8 m, and 3.1 m water depths. The cores were analyzed for bulk density, grain size, organic matter, high-resolution imagery, grayscale, magnetic susceptibility, and are dated using radiocarbon analysis on terrestrial macrofossils. Basal radiocarbon ages for the deep and intermediate water depth core sites indicate the start of fine-grained, banded to laminated (lacustrine) sedimentation at ~12 ka cal BP. A basal radiocarbon age for the shallow water core (D-12 core) indicates that lacustrine sedimentation began at ~8.1 ka cal BP. Combined, these results suggest dry conditions prior to ~ 12 ka, an increase in lake levels ~ 12 ka, and a further increase to high lake levels ~ 8.1 ka. Abrupt changes in grain size and the presence of coarse sandy layers in the D-12 core suggests the presence of several unconformities and fluctuating lake-levels through the mid to late Holocene. Radiocarbon dating and statistical analyses of a high-resolution (0.1 cm) grayscale record will be used to detect shifts in sedimentology to further constrain lake level variability.