Investigating mercury’s ocean-atmosphere exchange: a global perspective

Mercury’s exchange between the ocean and atmosphere is a critical component of its global cycle, influencing environmental and public health.

At a recent conference, Koketso Molepo, a PhD researcher at the Helmholtz Centre for Environmental Research in Germany, presented findings from her ongoing study into this phenomenon. The session explored long-term atmospheric mercury observations and their implications.

Understanding mercury’s movement

Research indicates that the global surface ocean is supersaturated with elemental mercury compared to the atmosphere.

This results in significant net emissions of gaseous elemental mercury (GEM) from the ocean into the atmosphere. Making it the largest individual source of mercury to the atmosphere.

The process, driven by photoreactions and influenced by wind speed, exhibits seasonal and regional variations.

Molepo highlighted that while mercury ocean-atmosphere exchange is well-documented, the intricacies of the involved processes remain underexplored.

Her work aims to bridge this gap by analyzing GEM data from six coastal monitoring stations in both hemispheres, including Cape Point, Amsterdam Island, and Cape Verde Observatory.

Key findings

The study revealed that five of the six stations showed weak seasonal and diurnal variations in GEM concentrations linked to marine air masses. This suggests a limited or absent ocean-atmosphere exchange signal at these locations.

However, at Dumont d’Urville in Antarctica, strong seasonal and diurnal patterns were observed. GEM concentrations peak around midday in spring and summer.

Existing research attributes these patterns to emissions from snowpack and soils influenced by daytime heating and air mass transport from the Antarctic plateau.

Methodology and validation

The research utilized hourly GEM measurements and classified air mass origins using back-trajectory analysis.

This approach was validated with radon data from Cape Point, which acts as a proxy for continental air influence.

Marine air masses consistently showed lower radon concentrations, reinforcing the reliability of the classification method.

Implications and future research

The findings challenge assumptions about the strength of ocean-atmosphere mercury exchange globally.

While the Dumont d’Urville site highlights localized processes, the weak signals at other stations raise questions about the proposed global net mercury flux from oceans to the atmosphere.

Molepo emphasized the need for further modeling to quantify these fluxes and understand regional differences.

This work will contribute to more accurate assessments of mercury’s environmental impact and inform global mercury management strategies.

A call to action

This research underscores the complexity of mercury’s global cycle and the need for continued monitoring and advanced modeling.

For those monitoring and analyzing mercury in the environment, the findings highlight the importance of localized studies to complement global assessments.

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