Changing Climate and Sea Level Alter Hg Mobility at Lake Tulane, Florida, U.S.

Abstract

Between 45,000 cal years BP and the beginning of the Holocene, the accumulation rate for Hg in sediments of Lake Tulane, Florida ranged from ≈2 to 10 μg m(-2) yr(-1), compared with 53 μg Hg m(-2) yr(-1) in the 1985-1990 period of anthropogenic input. The locality experienced regional draw-down of the water table during the Wisconsinan glaciation, which lowered global sea level by nearly 130 m. Natural atmospheric deposition of Hg to the surrounding area resulted in long-term (ca. 100,000 years) sequestration of this atmospheric flux of Hg, primarily by adsorption in the oxic Al- and Fe-hydroxide-rich sandy subsoil. Global sea level rise during deglaciation led to a rising regional water table, flooding the oxidized soils surrounding Tulane. Iron and adsorbed Hg were mobilized by reductive dissolution and transported by groundwater flow to Lake Tulane and ultimately to the accumulating sediment. The accumulation rate of Hg (and Fe) increased rapidly about 16,000 cal years BP, peaked at nearly 60 μg Hg m(-2) yr(-1) ca. 13,000-14,000 cal years BP, declined sharply during the Younger Dryas, and then increased sharply to a second 60 μg Hg m(-2) yr(-1) peak about 5000 cal years BP. Thereafter, it declined nearly to background by 900 cal years BP. In similar geologic situations, rapid modern sea level rise will initiate this process globally, and may mobilize large accumulations of Hg and lesser amounts of As, and other redox sensitive metals to groundwater and surface water.