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Research article - Peer-reviewed, 2021

Critical Observations of Gaseous Elemental Mercury Air-Sea Exchange

Osterwalder, S.; Nerentorp, M.; Zhu, W.; Jiskra, M.; Nilsson, E.; Nilsson, M. B.; Rutgersson, A.; Soerensen, A. L.; Sommar, J.; Wallin, M. B.; Wangberg, I; Bishop, K.;

Abstract

Air-sea exchange of gaseous elemental mercury (Hg-0) is not well constrained, even though it is a major component of the global Hg cycle. Lack of Hg-0 flux measurements to validate parameterizations of the Hg-0 transfer velocity contributes to this uncertainty. We measured the Hg-0 flux on the Baltic Sea coast using micrometeorological methods (gradient-based and relaxed eddy accumulation [REA]) and also simulated the flux with a gas exchange model. The coastal waters were typically supersaturated with Hg-0 (mean +/- 1 sigma = 13.5 +/- 3.5 ng m(-3); ca. 10% of total Hg) compared to the atmosphere (1.3 +/- 0.2 ng m(-3)). The Hg-0 flux calculated using the gas exchange model ranged from 0.1-1.3 ng m(-2) h(-1) (10th and 90th percentile) over the course of the campaign (May 10-June 20, 2017) and showed a distinct diel fluctuation. The mean coastal Hg-0 fluxes determined with the two gradient-based approaches and REA were 0.3, 0.5, and 0.6 ng m(-2) h(-1), respectively. In contrast, the mean open sea Hg-0 flux measured with REA was larger (6.3 ng m(-2) h(-1)). The open sea Hg-0 flux indicated a stronger wind speed dependence for the Hg-0 transfer velocity compared to commonly used parameterizations. Although based on a limited data set, we suggest that the wind speed dependence of the Hg-0 transfer velocity is more consistent with gases that have less water solubility than CO2 (e.g., O-2). These pioneering flux measurements using micrometeorological techniques show that more such measurements would improve our understanding of air-sea Hg exchange.

Keywords

evasion; flux; REA; transfer velocity; uptake

Published in

Global Biogeochemical Cycles

2021, volume: 35, number: 8, article number: e2020GB006742
Publisher: AMER GEOPHYSICAL UNION

Authors' information

Osterwalder, Stefan
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Osterwalder, Stefan
Université Grenoble Alpes
Nerentorp, M.
IVL Swedish Environmental Research Institute
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Jiskra, M.
University of Basel
Nilsson, E.
Uppsala University
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Rutgersson, A.
Uppsala University
Soerensen, A. L.
Swedish Museum of Natural History
Soerensen, A. L.
Stockholm University
Sommar, J.
Guiyang Institute of Geochemistry, CAS
Uppsala University
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Wangberg, I
IVL Swedish Environmental Research Institute
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment

Associated SLU-program

Non-toxic environment

UKÄ Subject classification

Oceanography, Hydrology, Water Resources
Meteorology and Atmospheric Sciences

Publication Identifiers

DOI: https://doi.org/10.1029/2020GB006742

URI (permanent link to this page)

https://res.slu.se/id/publ/113579