Effects of Holocene Climate Change on Mercury Deposition in Elk Lake, Minnesota: The Importance of Eolian Transport in the Mercury Cycle

Authors

W.F. Cannon, U.S. Geological Survey, M.S. 954, Reston, Virginia 20192, USA
Walter E. Dean, U.S. Geological Survey, M.S. 980, Denver, Colorado 80225, USA
John H. Bullock Jr., U.S. Geological Survey, M.S. 973, Denver, Colorado 80225, USA

Document Type

Article

Date of this Version

2-2003

Comments

Published in Geology; February 2003; v. 31; no. 2; p. 187–190; 4 figures.

Abstract

Sediments in Elk Lake, Minnesota, consist of 10,400 varve layers that provide a precise chronology for Holocene fluctuations in climate and biota recorded in the strata. Progressively greater concentrations and accumulation rates of mercury since ca. A.D. 1875 reflect deposition of anthropogenic mercury additions to the atmosphere. Within the Holocene record are numerous short intervals in which mercury concentrations and accumulation rates exceed the modern values. The highest mercury concentrations formed ca. 8 ka, coincident with a rapid change from cool, moist conditions to warm, dry conditions. A related change in flora from pine forest to prairie caused destruction of organic forest soils and the release of mercury that had been sequestered in them, resulting in a short-lived pulse of mercury to the lake. Accumulation rates of mercury were highest during the 4 k.y. mid-Holocene dry interval and show a correlation with periods of rapid deposition of eolian dust. The mercury was probably bound to wind-borne mineral particles, which were derived from an unidentified mercury-rich source region west of Elk Lake.