Isotopic Composition of Hg in Fogwaters of Coastal California
Spencer J. Washburn, Joel D. Blum, Laura C. Motta, Bridget A. Bergquist, P. S. Weiss‐Penzias
Abstract
We present the first measurements of the isotopic composition of mercury (Hg) in fogwater, measured in samples collected across coastal California. Coastal California fogwater samples exhibit a relatively narrow range of Hg isotopic compositions {δ202Hg = −0.60‰ to 0.38‰, average of −0.10 ± 0.33‰ [one standard deviation (1SD)]; Δ199Hg = 0.04–0.75‰, average of 0.28 ± 0.17‰ (1SD); Δ200Hg = −0.16‰ to 0.24‰, average of 0.08 ± 0.10‰ (1SD)}. The isotopic composition of fogwater samples did not exhibit any spatial trends, either with distance from the Pacific Ocean coastline or with the latitude of sampling locations. The Hg isotopic composition of coastal California fogwater samples is not significantly different from that of precipitation collected across coastal California and the North Pacific, suggesting that marine-derived atmospheric Hg has a relatively homogeneous isotopic composition across the North Pacific. Fogwater samples exhibit a Δ199Hg/Δ201Hg slope of 1.03 consistent with Hg(II) photoreduction, highlighting the importance of photoreduction mechanisms in controlling the odd-MIF isotopic composition of atmospheric Hg wet deposition. Overall, the need for an improved understanding of the processes that control atmospheric Hg deposition is revealed by this data set, as such knowledge will be required to more accurately model global atmospheric Hg cycling.