Publication Date:
2023-11-17
Description:
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.
Description:
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 fjord sediments. Our calculations suggest that Nioghalvfjerdsbræ dissolved Pb discharge is comparable to that from small Arctic rivers. Given the widespread occurance of Pb‐rich minerals across Greenland, observed increases in meltwater discharge and the retreat of marine‐terminating glaciers could increase dPb supply to Greenlandic shelf regions.
Description:
Key Points:
Helium and neon show strong evidence for a subglacial source of Pb discharging onto the NE Greenland Shelf.
Contrasting inflowing and outflowing waters beneath the floating ice tongue of Nioghalvfjerdsbræ shows a 2‐3‐fold dPb enrichment.
The dissolved Pb flux from Nioghalvfjerdsbræ (2.2 ± 1.4 Mg·yr−1) is comparable to small Arctic rivers, with ∼90% of a sedimentary origin.
Description:
Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659
Description:
Bundesministerium für Bildung und Forschung
http://dx.doi.org/10.13039/501100002347
Description:
Kuwait Institute for Scientific Research
http://dx.doi.org/10.13039/501100005074
Description:
Swiss Polar Foundation
Description:
https://doi.pangaea.de/10.1594/PANGAEA.871028
Description:
https://doi.pangaea.de/10.1594/PANGAEA.871030
Description:
https://doi.pangaea.de/10.1594/PANGAEA.879197
Description:
https://doi.pangaea.de/10.1594/PANGAEA.905347
Description:
https://doi.pangaea.de/10.1594/PANGAEA.933431
Description:
https://doi.pangaea.de/10.1594/PANGAEA.931336
Description:
https://doi.org/10.5194/essd-8-543-2016
Keywords:
ddc:551
;
Greenland ice sheet
;
Arctic
;
marine‐terminating glacier
;
Nioghalvfjerdsbrae
;
lead fluxes
;
GEOTRACES
Language:
English
Type:
doc-type:article
