Earth system modelling of mercury using CESM2 – Part 3: Oceanic model POP2/Hg v1.0
- 1Tulane University (New Orleans, United States of America)
Abstract
Mercury (Hg) is a globally distributed toxicant with complex cycling in the ocean, involving redox reactions, air–sea exchange, and microbial methylation. We present POP2/Hg v1.0, a new global ocean mercury model developed within the ocean component of CESM2 (POP2) and coupled to the Marine Biogeochemistry Library (MARBL). POP2/Hg v1.0 simulates dissolved elemental Hg (Hg ⁰ ), oxidized Hg (Hg II ), particulate-bound Hg (Hg P ), and methylmercury (MeHg = MMHg + DMHg), linking their transformation to ecosystem processes and dynamics of particulate organic carbon (POC). The model captures observed large-scale features of marine Hg. Surface Hg ⁰ concentrations range from 0.01 to 0.12 pmol L ⁻¹ (pM, 1 pM = 10 ⁻¹² mol L ⁻¹ ) and are elevated in tropical and subtropical oceans due to strong photoreduction and limited evasion. Subsurface Hg ⁰ maxima emerge in upwelling zones, reflecting remineralization-driven Hg II reduction. Surface Hg II concentrations peak in regions of high atmospheric deposition and productivity and rise at depth in oxygen-deficient zones. Hg P is closely associated with high POC and Hg II levels in the surface ocean but attenuates rapidly with depth due to remineralization. MeHg accumulates in the subsurface and deep sea, broadly consistent with observations. Total Hg (Hg T ) at surface generally falls within the range of open-ocean observations, with values of 0.1–1.0 pM across most regions and localized concentrations exceeding 1.2 pM. The biological pump strongly shapes vertical Hg transport. Above 1000 m, soft POC carries 98.55 % of Hg P flux, driving export and remineralization. Below 1000 m, hard POC becomes relatively more important and accounts for 43.94 % of the integrated Hg P flux reaching seafloor cells, locally contributing up to over 99 %, although the total flux is small (16.86 Mg yr ⁻¹ ). Sensitivity tests show that altering redox rates significantly affects the vertical distribution of Hg transformations. Reduced surface reduction and oxidation rates increase Hg ⁰ concentrations in the upper ocean, decrease Hg II concentrations, and weaken seasonal variability. By embedding mercury chemistry into a biogeochemical and physical ocean model which can be potentially fully coupled, POP2/Hg v1.0 offers a process-resolving platform for assessing mercury cycling and its response to environmental change. It enables future integrated Earth system simulations and provides a foundation for simulating marine mercury under future climate and policy scenarios.
Versions
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BibTeX
@article{mao2026earth,
title = {{Earth system modelling of mercury using CESM2 – Part 3: Oceanic model POP2/Hg v1.0}},
author = {Mao Mao and Yujuan Wang and Peng Zhang and Ling Li and Shaojian Huang and Chen Zhou and Yanxu Zhang},
journal = {Geoscientific Model Development},
year = {2026},
month = nov,
doi = {10.5194/gmd-19-10551-2026},
url = {https://gmd.copernicus.org/articles/19/10551/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Earth system modelling of mercury using CESM2 – Part 3: Oceanic model POP2/Hg v1.0
AU - Mao Mao
AU - Yujuan Wang
AU - Peng Zhang
AU - Ling Li
AU - Shaojian Huang
AU - Chen Zhou
AU - Yanxu Zhang
PY - 2026
DA - 2026/11/06
JO - Geoscientific Model Development
DO - 10.5194/gmd-19-10551-2026
UR - https://gmd.copernicus.org/articles/19/10551/2026/
AB - Mercury (Hg) is a globally distributed toxicant with complex cycling in the ocean, involving redox reactions, air–sea exchange, and microbial methylation. We present POP2/Hg v1.0, a new global ocean mercury model developed within the ocean component of CESM2 (POP2) and coupled to the Marine Biogeochemistry Library (MARBL). POP2/Hg v1.0 simulates dissolved elemental Hg (Hg ⁰ ), oxidized Hg (Hg II ), particulate-bound Hg (Hg P ), and methylmercury (MeHg = MMHg + DMHg), linking their transformation to ecosystem processes and dynamics of particulate organic carbon (POC). The model captures observed large-scale features of marine Hg. Surface Hg ⁰ concentrations range from 0.01 to 0.12 pmol L ⁻¹ (pM, 1 pM = 10 ⁻¹² mol L ⁻¹ ) and are elevated in tropical and subtropical oceans due to strong photoreduction and limited evasion. Subsurface Hg ⁰ maxima emerge in upwelling zones, reflecting remineralization-driven Hg II reduction. Surface Hg II concentrations peak in regions of high atmospheric deposition and productivity and rise at depth in oxygen-deficient zones. Hg P is closely associated with high POC and Hg II levels in the surface ocean but attenuates rapidly with depth due to remineralization. MeHg accumulates in the subsurface and deep sea, broadly consistent with observations. Total Hg (Hg T ) at surface generally falls within the range of open-ocean observations, with values of 0.1–1.0 pM across most regions and localized concentrations exceeding 1.2 pM. The biological pump strongly shapes vertical Hg transport. Above 1000 m, soft POC carries 98.55 % of Hg P flux, driving export and remineralization. Below 1000 m, hard POC becomes relatively more important and accounts for 43.94 % of the integrated Hg P flux reaching seafloor cells, locally contributing up to over 99 %, although the total flux is small (16.86 Mg yr ⁻¹ ). Sensitivity tests show that altering redox rates significantly affects the vertical distribution of Hg transformations. Reduced surface reduction and oxidation rates increase Hg ⁰ concentrations in the upper ocean, decrease Hg II concentrations, and weaken seasonal variability. By embedding mercury chemistry into a biogeochemical and physical ocean model which can be potentially fully coupled, POP2/Hg v1.0 offers a process-resolving platform for assessing mercury cycling and its response to environmental change. It enables future integrated Earth system simulations and provides a foundation for simulating marine mercury under future climate and policy scenarios.
SN - 1991-9603
ER -