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

Abstract

Lead (Pb) is a toxic element to humans (Carrington et al., 2019;Wani et al., 2015) and accumulation in marine biota a pathway of exposure (Burger et al., 2012;Zimmer et al., 2011). Lead emissions from coal combustion and the use of tetraethyllead as an additive to gasoline through the twentieth century (McConnell & Edwards, 2008;Pacyna & Pacyna, 2001) resulted in large scale atmospheric deposition of anthropogenic Pb across the surface ocean (Boyle et al., 2014). Whilst Pb concentrations across the North Atlantic are now declining, they remain above pre-industrial concentrations (Kelly et al., 2009;Noble et al., 2015). The ultimate fate of Pb in the marine environment is governed by its high affinity to particles (Dewey et al., 2021;Yang et al., 2015), which results in a dissolved Pb (dPb) distribution strongly affected by lateral transfer within sinking matter and burial in sediments (Bruland et al., 2013). However, a growing number of studies have shown intermittent release of dPb from shelf sediments (Cobelo-García & Prego, 2004;Kalnejais et al., 2007;Martino et al., 2002). This suggests that shelf sediments affected by a legacy of anthropogenic Pb deposition may continue to act as a dPb source to the water column (Rusiecka et al., 2018;Vieira et al., 2019).

Glacier‐Derived Particles as a Regional Control on Marine Dissolved Pb Concentrations

“…In two Antarctic coastal regions, median dPb was 23 pM with a range of 7.8-107 pM Across five Greenlandic coastal regions the median dPb was 38 pM with a range of 3.2-252 pM (excludes one outlier of 1,246 pM). While there are sparse data sets to compare to, measured dPb concentrations fall within the range reported from similar geographic environments in the Arctic and Antarctic (Colombo et al, 2019;Kim et al, 2015;Krisch et al, 2022;Ndungu et al, 2016;Schlosser & Garbe-Schönberg, 2019). The February 2018 transect in Maxwell Bay (dPb concentrations 29-107 pM) is close to Marion Cove (3-6 km distance), both in King George Island, where similar concentrations were observed, 30-120 pM, in January 2012 (Kim et al, 2015).…”

“…Similarly, near‐surface dPb concentrations reported at two stations close to Devon Island (Canadian Arctic Archipelago) of 10.4 and 10.8 pM were elevated compared to both adjacent stations and values expected from conservative mixing of dPb concentrations (Colombo et al., 2019). Altogether, these studies consistently appear to show evidence of an additional dPb source at intermediate salinities across diverse glaciated regions worldwide (Colombo et al., 2019; Kim et al., 2015; Krisch et al., 2022; Ndungu et al., 2016; Schlosser & Garbe‐Schönberg, 2019). There is also some evidence in the paleorecord to suggest elevated Pb deposition in the ocean associated with subglacial weathering (Crocket et al., 2013), however our mechanistic understanding of the effect of this process on marine dPb concentrations is limited.…”

“…Precipitation and ice core Pb concentrations (for Greenland) have a very broad range from 2 to 800 pM suggesting that 1,200 km 3 yr −1 of freshwater discharge (Bamber et al., 2018) corresponds roughly to an annual release of between 2.4 and 960 kmol yr −1 total Pb into the ocean. However, this approach ignores the potential role of subglacial and proglacial weathering as Pb sources (Hawkings et al., 2020; Krisch et al., 2022). At Leverett Glacier (west Greenland), a seasonal time series of dPb in runoff suggests a discharge weighted mean of 182 pM with a range from below detection to 666 pM (Hawkings et al., 2020).…”

“…Similarly, based on its isotopic composition, a mineral source of dPb has been suggested to account for 95% of the 4–89 pM dPb observed close to the Dotson Ice Shelf (Antarctica) (Ndungu et al., 2016). Dissolved Pb concentrations of 30–120 pM in one survey of Maxwell Bay (King George Island) were also noted to be higher than could be explained by dilution of dPb in freshwater sources (Kim et al., 2015) and dPb concentrations of 12 pM emerging from beneath the floating ice tongue of Nioghalvfjerdsbræ (NE Greenland) suggest a twofold to threefold enrichment of dPb compared to concentrations in inflowing Atlantic water (Krisch et al., 2022). Similarly, near‐surface dPb concentrations reported at two stations close to Devon Island (Canadian Arctic Archipelago) of 10.4 and 10.8 pM were elevated compared to both adjacent stations and values expected from conservative mixing of dPb concentrations (Colombo et al., 2019).…”

Dissolved, Labile, and Total Particulate Trace Metal Dynamics on the Northeast Greenland Shelf

“…Due to the long residence time (∼162 days, data from GN05 cruise) of inflowing AIW inside the subglacial cavity (Schaffer et al, 2020), the freshwater signals in the mAIW (denoted as submarine meltwater) may reflect extensive homogenization and equilibration of AIW with particle and dissolved inputs from ice melt, and sediment-water exchange. Cavity outflow has previously been observed for dFe and dissolved lead (dPb) at 79NG (Krisch, Hopwood, et al, 2021;Krisch, Huhn, et al, 2022). Here, we used noble gases as a tracer to distinguish the influence of submarine meltwater from Arctic waters on TM distributions on the NE Greenland shelf, following the methods of Huhn, Rhein, .…”