Constraining Mercury Sources to the Arctic Ocean Using Mercury Stable Isotopes

Mercury (Hg) concentrations in Arctic biota are elevated relative to lower latitudes, posing an increased risk of adverse health effects for Arctic populations that rely on them as an important food source. Hg readily cycles through different environmental compartments such as air–soil–river before reaching sea waters where it becomes available for methylation to methylmercury and is readily taken up and magnified in the marine food web.

Warming climate is expected to further enhance air-soil-river exchange, increase river discharge, mobilize additional Hg loads from thawing permafrost, erosion melting glaciers and sea ice. A recent Arctic Ocean (AO) Hg mass budget indicates that Hg inputs exceed outputs, indicating either a missing sink or an imbalance due to ongoing changes. 

We determined Hg stable isotope endmember signatures of Hg sources, including western Siberian organic-rich permafrost and mineral soils, and compile those with available literature data on endmembers. Central AO surface seawater samples were collected under trace metal clean conditions in Summer 2025 aboard RV ODEN and zooplankton samples in Summer 2015 aboard RV Polarstern. Solid samples were pre-concentrated using a double tube furnace set-up, while 40 L of sea water were pre-concentrated using a two-step purge and trap method. Hg stable isotopic composition was measured via online cold-vapor generation multicollector ICP-MS analysis.

We use the new Hg stable isotopes measurements together with available literature data to better constrain the Arctic Hg cycle by disentangling the relative importance of different Hg sources to AO surface waters, the entry point of Hg into the marine food web.