New study: Greenland’s melting ice sheet releases mercury into the Arctic Ocean

As the Greenland Ice Sheet melts, it can transport more than water. Meltwater also mobilises chemical elements stored in ice and rock, transporting them towards rivers and the ocean.

New research, co-authored by Guillaume Lamarche-Gagnon and Jon Hawkings from the iC3 Polar Research Hub, explores how Greenland Ice Sheet meltwater contributes to the transport of mercury, a toxic element that can accumulate in food webs and threaten Arctic wildlife and human health.

Figure: a) discharge (black) and precipitation (green vertical bars); c) mercury (Hg) species and fractions (particulate total Hg (pTHg, red), filtered total Hg (fTHg, blue), and monomethylmercury (MMHg, yellow). Modified from Youssef et al. (2026), Commun Earth Environ.

Tracking mercury from ice to ocean

Mercury occurs naturally in the environment, but human activities have substantially increased the amount circulating globally. Its presence in Arctic ecosystems is a concern because it can accumulate in organisms and become more concentrated higher up the food chain.

To understand how the Greenland Ice Sheet contributes to mercury budgets in the Arctic, the researchers measured mercury concentrations and mercury stable isotope ratios along a pathway from the ice sheet to meltwater rivers and fjord waters in southwest Greenland during the summer of 2023.

The results show that mercury concentrations and sources change as the summer melt season progresses and as meltwater rivers move through the landscape towards the coast. Early in the season, rainfall-driven permafrost runoff contributed to the highest dissolved mercury concentrations observed. As ice melt increased with warming summer temperatures, hidden rivers and streams developed beneath the ice sheet and the meltwater river in front of the ice sheet grew in size. During this period, particulate mercury concentrations approximately doubled, pointing to the importance of processes occurring beneath the ice, most importantly, the physical grinding of the bedrock by the moving glaciers.

The researchers also found that water in nearby fjords contained elevated concentrations of dissolved mercury, including the most toxic bioaccumulating form, monomethylmercury, compared with river water. This suggests that mercury continues to be transformed and supplemented by additional sources once it reaches coastal waters.

Why the subglacial environment matters

The team combined mercury measurements with mercury stable isotope analyses to determine the source of the mercury in the meltwater river. Using these geochemical fingerprinting techniques, they estimated that ice and snow melt from the glacier surface contributed around 20–48% of the mercury exported from the ice sheet. This indicates that inputs from beneath the ice sheet (i.e., mercury in rocks) must instead dominate the remaining seasonal mercury export.

The study estimated a mercury yield of approximately 23 millimoles per square kilometre per year, comparable to estimates for Arctic rivers. As climate change accelerates ice loss, mercury export from Greenland could increase, although its future trajectory will depend on changing hydrology and the how the processes controlling mercury mobilisation respond.

Jon Hawkings, iC3 researcher and co-author of the study, explains:

“Understanding what happens beneath the ice sheet is essential for tracing how elements such as mercury move from glacial environments into downstream ecosystems. Following these pathways from ice to ocean over seasonal timescales helps us better understand the role of melting ice sheets in polar biogeochemical cycles and how these systems might change in a future warmer environment.”

The findings highlight the importance of studying the entire ice-to-ocean system rather than considering glaciers or downstream regions in isolation. Understanding how mercury is released, transformed and transported will help researchers assess how a changing Greenland Ice Sheet may affect Arctic coastal environments.

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Find out more

The paper “Mercury mobilization and export from the Greenland Ice Sheet using an ice-to-ocean approach” is available open access in Nature communications earth & environment.

Lead author Amina Youssef is a PhD student at the University of Pennsylvania.

Co-author Guillaume Lamarche-Gagnon is an environmental microbiologist and biogeochemist, with interests in understanding the interplay between the biological, geological, and hydrological interfaces within the cryosphere. Within iC3, he leads Research Unit 2: Methane, nutrients and carbon. He is based in the Department of Geosciences at UiT The Arctic University of Norway, Tromsø. To find out more about his work, see his list of publications, or contact him by email.

Co-author Jon Hawkings is a researcher investigating how glaciers mobilise and transport nutrients and carbon, and their effects on downstream ecosystems and global biogeochemical cycles. He is based at both UiT and at the University of Pennsylvania. Within iC3, he is part of Research Unit 2: Methane, nutrients and carbon. To find out more about his work, please check out his interview, his list of publications, or contact him by email.