HOLOCENE FLUCTUATIONS OF A MEROMICTIC LAKE IN SOUTHERN BRITISH-COLUMBIA

Holocene deposits of Mahoney Lake, a meromictic saline lake located in a closed basin in the semi-arid Okanagan Valley, contain evidence of frequent and marked changes in lake depth (up to >12 m/100 C-14 yr) pr obably caused by short-term changes in effective precipitation. We stu died a 5.45-m-long core comprising a basal layer of inorganic mud over lain by a succession of layers of calcareous laminated and nonlaminate d organic mud, marl, and sand. We used Mazama tephra to adjust nine ra diocarbon ages for the hardwater effect. Meromixis developed ca. 9000 C-14 yr B.P., and the lake has been episodically meromictic for about half the time since. Because of close linkages between sediments and d epositional environments in meromictic and saline lakes, we infer that laminated sediments indicate meromictic conditions and high lake leve ls (>ca. 12 m water depth), whereas thick marl layers and nonlaminated sediments indicate nonmeromictic conditions and thus low lake levels (<ca. 8 m depth). Many of the inferred shortterm climatic changes have not been identified in previous studies in northwestern North America , perhaps because of insensitive climatic proxies, inadequate temporal resolution, or discounting Of anomalous findings. (C) 1997 University of Washington.