Preprints
https://doi.org/10.5194/gmd-2024-81
https://doi.org/10.5194/gmd-2024-81
Submitted as: development and technical paper
 | 
06 May 2024
Submitted as: development and technical paper |  | 06 May 2024
Status: this preprint is currently under review for the journal GMD.

An improved model for air–sea exchange of elemental mercury in MITgcm-ECCO v4-Hg: the role of surfactants and waves

Ling Li, Peipei Wu, Peng Zhang, Shaojian Huang, and Yanxu Zhang

Abstract. The air–sea exchange of elemental mercury (Hg0) plays an important role in the global Hg cycle. Existing air–sea exchange models for Hg0 have not considered the impact of sea surfactants and wave breaking on the exchange velocity, leading to insufficient constraints on the flux of Hg0. In this study, we have improved the air–sea exchange model of Hg0 in the three-dimensional ocean transport model MITgcm by incorporating sea surfactants and wave breaking processes through parameterization utilizing the total organic carbon concentration and significant wave height data. The inclusion of these factors results in an increase of over twofold in the transfer velocity of Hg0 relative to the baseline model. Air–sea exchange flux is increased in mid- to high-latitude regions with high wind and wave breaking efficiency, while it is reduced by surfactant and concentration change at low latitudes with low wind speeds and nearshore areas with low wave heights. Compared with previous parameterizations, the updated model demonstrates a stronger dependence of Hg0 air–sea exchange velocity on wind speed. Our results also provide a theoretical explanation for the large variances in estimated transfer velocity between different schemes.

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Ling Li, Peipei Wu, Peng Zhang, Shaojian Huang, and Yanxu Zhang

Status: open (until 01 Jul 2024)

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Ling Li, Peipei Wu, Peng Zhang, Shaojian Huang, and Yanxu Zhang
Ling Li, Peipei Wu, Peng Zhang, Shaojian Huang, and Yanxu Zhang

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Short summary
The estimation of Hg0 fluxes is of great uncertainty due to neglecting wave breaking and sea surfactant. Integrating these factors into MITgcm significantly rise Hg0 transfer velocity. The updated model shows increased fluxes in high wind and wave regions and vice versa, enhancing the spatial heterogeneity. It shows a stronger correlation between Hg0 transfer velocity and wind speed. These findings may elucidate the discrepancies in previous estimations and offer insights into global Hg cycling.