Sea-Ice-Driven Mercury Depletion over the Arctic Marginal Ice Zone Revealed by Direct Shipborne Observations

The Arctic is undergoing
rapid environmental change, with sea-ice
loss altering key exchanges among the cryosphere, atmosphere, and
biosphere. During spring, atmospheric mercury and ozone depletion
events (AMDEs and ODEs) drive rapid declines in gaseous elemental
mercury (Hg0) and ozone (O3), promoting mercury
deposition to snow, ice, and marine ecosystems. Despite three decades
of research, AMDEs have been documented almost exclusively at coastal
land-based stations, leaving their occurrence and mechanisms over
oceanic sea-ice poorly constrained. To address this gap, we conducted
a research cruise in the Arctic marginal ice zone to study the connections
between sea-ice and atmospheric Hg chemistry. We measured atmospheric
Hg0, reactive gaseous Hg (RGM), and O3 along
the cruise track, identifying the simultaneous occurrences of AMDEs
and ODEs. Air mass back-trajectory analysis combined with sea-ice
images from satellite remote sensing revealed that these depletion
events occurred exclusively when air masses originated from over sea-ice
and were near its surface. Our findings confirm that Arctic sea-ice
plays a pivotal role in initiating AMDEs observed in the marginal
ice zone, driven by halogen release from the sea-ice surface. This
study advances understanding of the interplay between sea-ice dynamics
and atmospheric chemistry, with important implications for Hg deposition
in polar ecosystems and the consequences for human and wildlife health,
given the potential impacts of a rapidly changing Arctic.