Quantifying Ice‐Sheet Derived Lead (Pb) Fluxes to the Ocean; A Case Study at Nioghalvfjerdsbræ

• Published in: Geophysical Research Letters
• Main Authors: Krisch, Stephan, Huhn, Oliver, Al‐Hashem, Ali, Hopwood, Mark J., Lodeiro, Pablo, Achterberg, Eric P., 3 Institute of Environmental Physics University of Bremen Bremen Germany, 1 GEOMAR Helmholtz Centre for Ocean Research Kiel Kiel Germany
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: ddc:551; Greenland ice sheet; Arctic; marine‐terminating glacier; Nioghalvfjerdsbrae; lead fluxes; GEOTRACES; Greenland; glacier; Ice Sheet
• Online Access: https://doi.org/10.1029/2022GL100296; http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11181

Concentrations of the toxic element lead (Pb) are elevated in seawater due to historical emissions. While anthropogenic atmospheric emissions are the dominant source of dissolved Pb (dPb) to the Atlantic Ocean, evidence is emerging of a natural source associated with subglacial discharge into the ocean but this has yet to be constrained around Greenland. Here, we show subglacial discharge from the cavity underneath Nioghalvfjerdsbræ floating ice tongue, is a previously unrecognized source of dPb to the NE Greenland Shelf. Contrasting cavity‐inflowing and cavity‐outflowing waters, we constrain the associated net‐dPb flux as 2.2 ± 1.4 Mg·yr−1, of which ∼90% originates from dissolution of glacial bedrock and cavity sediments. We propose that the retreat of the floating ice tongue, the ongoing retreat of many glaciers on Greenland, associated shifts in sediment dynamics, and enhanced meltwater discharges into shelf waters may result in pronounced changes, possibly increases, in net‐dPb fluxes to coastal waters. Plain Language Summary: Lead (Pb) is a toxic element. Hundreds of thousands of tons have historically been emitted into the atmosphere through use of leaded gasoline, ore‐smelting and coal‐combustion which led to large‐scale deposition of Pb into the ocean and onto the Greenland Ice Sheet. Since the phase‐out of leaded gasoline, concentrations of dissolved Pb in the surface ocean have declined, increasing the relative importance of other, natural sources of Pb to the marine environment. In 2016, we conducted a survey near Nioghalvfjerdsbræ, one of Greenland’s largest marine‐terminating glaciers, to investigate if Greenland Ice Sheet discharge is a source of Pb to the Northeast Greenland Shelf. We observed elevated dissolved Pb concentrations at intermediate depths within a ⁓60 km radius downstream of the Nioghalvfjerdsbræ terminus. The Pb enrichment originates from underneath the glacier’s floating ice tongue. Lead sources underneath Nioghalvfjerdsbræ likely include Pb from eroded bedrock and exchange with ...