Tracing Dissolved Lead Sources in the Canadian Arctic: Insights from the Canadian GEOTRACES Program

Abstract

This study addresses an important knowledge gap in the distribution of lead (Pb) in the Arctic Ocean, by presenting dissolved Pb concentrations from samples collected during the GEOTRACES Canadian cruise in 2015. Dissolved Pb showed an increase in concentration from the Canada Basin toward Baffin Bay and the Labrador Sea. Canada Basin was the most isolated region from anthropogenic Pb inputs with low background concentrations (1.4−6.2 pmol kg −1 ) across most of the basin, although higher Pb features from the advection of Pacific-derived waters and sea ice meltwater were present. Likewise, high-Pb peaks (13.5−26.6 pmol kg −1 ) along narrow isopycnal surfaces (σ θ , 27.4−27.6) in Baffin Bay were attributed to the advection of North Atlantic waters spreading a high-Pb signature into the bay, contrasting with the low values (2.5−7.4 pmol kg −1 ) present in the mixed layer, Arctic and Baffin Bay deep waters. The Labrador Sea, largely influenced by the recirculation of North Atlantic waters, had the highest Pb concentrations (∼17−34 pmol kg −1 ) measured in this study. The Canadian Arctic Archipelago (CAA) represents a transition environment influenced by Arctic waters imprinting a low-Pb signature in the western CAA and the southern side of Parry Channel, while Baffin Bay waters prevailed in the eastern CAA recirculating westward along the northern side of Parry Channel and progressively losing their relatively high Pb signature. Extremely low concentrations were measured in Canada Basin and CAA waters, which reflect the remoteness of this region from anthropogenic inputs as well as the old ventilation age of deep waters' masses, providing a baseline for assessing future Pb studies. Finally, we successfully integrate modeling data with field observations demonstrating that dissolved lead, due to its distinctive anthropogenic signature in North Atlantic waters, can be a useful complementary tracer of water masses in the Canadian Arctic Ocean.

Canadian Arctic Archipelago Shelf‐Ocean Interactions: A Major Iron Source to Pacific Derived Waters Transiting to the Atlantic

“…In addition to the particulate trace metal enrichment documented here, a similar glacially derived peak of dissolved lead and Mn has been described at station CAA1 (Colombo et al, 2020;Colombo, Rogalla, et al, 2019), and adds to the growing evidence that glacial meltwater runoff could be a significant source of Fe and other trace elements to coastal waters (Bhatia et al, 2013;Kanna et al, 2020). Baffin Bay and the Labrador Sea are surrounded by extensive glacial ice-sheets (e.g., Greenland, Ellesmere Island, Devon Island, Baffin Island), and therefore, receive large amounts of glacial meltwaters and associated trace elements (Bhatia et al, 2013;Kanna et al, 2020).…”

“…At CAA1 station, a unique subsurface plume highly enriched in dissolved and particulate Fe, as well as pAl, pV, and pMn, was present between approximately 30 and 200 m ( σ θ = 25.92–27.15; Figures 3 and 4), at the same density range where transmissivity values dropped and Chl‐a increased (Colombo, Rogalla, et al., 2019). This subsurface feature is most probably related to sediment‐laden meltwater inputs from glaciers along the western side of Devon Island (Lenaerts et al., 2013; Figure 5b), which deliver extremely high loads of particulate and dissolved elements (e.g., dFe: 212 nM, pFe: 13,980, pAl: 19,355, and pMn: 151 μg L −1 ; Colombo, Brown, et al., 2019) to CAA1 station, located 5 km offshore of the Devon coast (Figure 5b).…”

“…In the CAA, small permafrost draining rivers and glacially fed streams are common, and their combined outflow delivers 201–257 km 3 yr −1 of freshwater (Alkire et al., 2017) along with a high load of dissolved and particulate elements. For some elements, such as Fe, their riverine concentrations are many times greater than those in transiting AW (Colombo, Rogalla, et al., 2019). These augmented freshwater sources in the CAA—including land fast sea ice melt–, likely explain the high dFe concentrations (AVG ± SD: 0.939 ± 0.368 nmol kg −1 ; Figure 3a) measured in surface waters ( d < 40 m), compared with deeper Canadian Arctic basins such as the CB, BB, and the LS (Colombo et al., 2020).…”

Arctic – Atlantic Exchange of the Dissolved Micronutrients Iron, Manganese, Cobalt, Nickel, Copper and Zinc With a Focus on Fram Strait

“…Based on available data from GEOTRACES cruise GA01 sampling the West Greenland Current entering the Labrador Sea off the southern tip of Greenland, concentrations of dFe, dMn, dCo and dCu in the Baffin Current were almost consistently higher, up to one order of magnitude in the case of dMn, than those observed in the water column of the West Greenland Current, the only notable exception being dFe in Surface Water of the Baffin Current at 150 and 200 m depth (Figure S9 in Supporting Information S1). Consequently, a strong gradient in dissolved micronutrient concentrations between regions influenced by the North Atlantic inflow (along the West Greenland coastline) and Arctic Ocean outflow (coastal Canada) is expected in Davis Strait (Colombo et al, 2019(Colombo et al, , 2020. Calculating micronutrient fluxes only from concentrations of dFe, dMn, dNi, dCu, dZn and the labile fraction of dCo in the Baffin Current herein likely overestimates Arctic contributions to outflow across Davis Strait.…”

Physical and Biogeochemical Influences on Nutrients Through the Canadian Arctic Archipelago: Insights From Nitrate Isotope Ratios

“…While not evident at CAA9, elevated proportions of Pacific NO 3 − deriving from remineralization were otherwise apparent at CAA1 and CAA5 (discussed below), suggesting that the remineralized Pacific NO 3 − at CAA6 is imported from northern Lancaster Sound. Based on measurements of dissolved lead and other tracers along the same hydrographic line, Colombo et al (2019) similarly concluded that water column properties at CAA6 showed traceable input from Lancaster Sound, entrained across Barrow Strait as part of the westward counter-current in northern Parry Channel. This conclusion is contrary to previous notions, however, as the T-S characteristics suggest that the westward flow from Lancaster Sound does not penetrate further west than Resolute Bay (Jones & Coote, 1980;.…”