The reduction of Arctic sea ice occurred as a result of the sharp rise in temperature during the transition between the last glacial period and the warmest current climatic period has favored the release of oceanic mercury into the atmosphere and its deposition in the environmentsuggesting that the effects of climate change on the environment may contribute to increasing levels of this pollutant in Arctic ecosystems.
This was revealed by a new paleo-climate study just published in Nature Geoscience, conducted by researchers from theCa’ Foscari University of Venice and the Institute of Polar Sciences of National Research Council (CNR-ISP), in collaboration with other international partners.
Mercury, a toxic metal for health and the environment
The mercury emissionscarefully monitored internationally, are not only of anthropic origin.
The biogeochemical cycle of this metal is in fact also controlled by different sources naturalsuch as volcanic eruptions, geothermal activities, forest fires and a multitude of physical, chemical and biological processes that occur in the soil, ocean and atmosphere.
Due to its particular physical and chemical characteristics, mercury is distributed in the environment in various forms and can be transported for long distances, even depositing itself very far from the place of emission, where it persists, not being subject to degradation.
In the form of a compound called methyl mercuryaccumulates in the adipose tissues of living beings and undergoes biomagnification, i.e. increases in concentration going up along the levels of the food chain, thus finding itself in considerable quantities in large predators, especially marine ones, such as swordfish, tuna and sharks .
Extremely toxic to health and the environment, mercury is a pollutant of great global interest, especially for the arctic regions, where it tends to accumulate in large quantities in aquatic and terrestrial ecosystems, transported through long-range atmospheric, oceanic and fluvial routes.
Climate change and mercury levels in the Arctic environment, the study
To study the relationship between past climate variations and mercury levels in the Arctic, the team of scientists developed a model of atmospheric chemistry of mercury and analyzed the available palaeoclimatic archives, including an ice core extracted from the Greenland ice cap as part of the EastGRIP project (East GReenland Ice core Project), which made it possible to reconstruct the temperature profile and the dynamics of mercury and other elements between 9,000 and 16,000 years ago, i.e. during the transition between the last glacial period and the current warmer climatic period, the Holocene.
EastGRIP project: the remote ice core field in East Greenland
Delia SegatoPhD student in Science and Management of Climate Change at the Ca’ Foscari University of Venice, and first author of the publication, explains that mercury deposition in the Arctic tripled as a result of abrupt global warming 11,700 years agodue to the loss of sea ice in the sub-polar Atlantic Ocean, especially perennial sea ice.
The melting of sea ice would in fact have caused a higher release of oceanic mercury into the atmosphere, and the replacement of multi-year ice with seasonal one would have favored the complex chemical reactions that promote the deposition of this pollutant.
Profiles of accumulation and concentration of mercury (Hg) in the period between 9000 and 15,700 years ago, derived from the analysis of the EGRIP ice core.
Dark areas indicate colder periods; lighter areas highlight warmer periods: early Holocene (9,000–11,700 years ago) and Bølling–Allerød (12,900–14,700 years ago), a relatively warm period during the final stages of the last glacial period. The dotted line indicates the Holocene–Glacial transition, which occurred 11,700 years ago.
Da: Segato, D., Saiz-Lopez, A., Mahajan, A.S. et al. Arctic mercury flux increased through the Last Glacial Termination with a warming climate. Nat. Geosci. 16, 439–445 (2023). Fonte: ResearchGate.
“Perennial sea ice, several tens of meters thick, has been shown to prevent the transfer of mercury from the ocean to the atmospherewhich would otherwise happen due to the volatility of this metal,” he explains Andrea Spolaorresearcher at the CNR-ISP of Venice and co-author of the study.
«In contrast, seasonal sea ice, being more thin, permeable and salineallows mercury transfer and promotes complex atmospheric reactions involving bromine and increase the frequency of mercury atmospheric depletion events, causing faster deposition in the Arctic environment,” continues the scientist.
Emission, transport, chemistry and deposition of mercury (Hg) during the end of the last glaciation (LGT, Last Glacial Termination) and the early Holocene.
a) LGT (11,000–15,700 years ago): Stronger transport of dust to the Greenland ice sheet by winds; weaker oceanic mercury release, lower reactive bromine (Br) emission from First Year Sea Ice (FYSI), and reduced bromine atmospheric chemistry. The overall result is low mercury deposition.
b) Primo Olocene (9,000–11,700 years ago): weak dust transport, heavy release of oceanic mercury due to low multi-year sea ice extent (MYSI, Multi Year Sea Ice), higher bromine emission from thinner seasonal ice and, consequently, stronger bromine atmospheric chemistry. The early Holocene scenario thus results in increased mercury deposition.
Da: Segato, D., Saiz-Lopez, A., Mahajan, A.S. et al. Arctic mercury flux increased through the Last Glacial Termination with a warming climate. Nat. Geosci. 16, 439–445 (2023). Fonte: ResearchGate.
What future scenarios?
What could happen today and in the future, given the rapid global warming we are experiencing, particularly accelerated in the Arctic regions, and also considering anthropogenic emissions?
Il mercurio it is in fact issued and issued by several anthropic activitieswhich include the burning of carbone fossilsome industrial processes related tochemical industryai cement factories and refining the petroliumthe mining activity in the mercury mines (banned in the European Union, but still present in some countries) and that linked to small-scale mining in the gold mines. Mercury is also present in some commonly used products.
«Due to the current climate warming – explains Spolaor -, Arctic perennial sea ice extent decreased by more than 50% compared to the beginning of satellite measurements in the 1970s. Future studies will help us estimate how this phenomenon will affect mercury levels e what are the risks partners for Arctic peoples and ecosystems”.
