Trace Element (Fe, Co, Ni and Cu) Dynamics Across the Salinity Gradient in Arctic and Antarctic Glacier Fjords

Abstract

Around the Greenlandic and Antarctic coastlines, sediment plumes associated with glaciers are significant sources of lithogenic material to the ocean. These plumes contain elevated concentrations of a range of trace metals, especially in particle bound phases, but it is not clear how these particles affect dissolved (<0.2 µm) metal distributions in the ocean. Here we show, using transects in 8 glacier fjords, trends in the distribution of dissolved iron, cobalt, nickel and copper (dFe, dCo, dNi, dCu). Following rapid dFe loss close to glacier outflows, dFe concentrations in particular showed strong similarities between different fjords. Similar dFe concentrations were also observed between seasons/years when Nuup Kangerlua (SW Greenland) was revisited in spring, mid- and late-summer. Dissolved Cu, dCo and dNi concentrations were more variable and showed different gradients with salinity depending on the fjord, season and year. The lack of consistent trends for dCu and dNi largely reflects less pronounced differences contrasting the concentration of inflowing shelf waters with fresher glacially-modified waters. Particles also made only small contributions to total dissolvable Cu (dCu constituted 83 ± 28% of total dissolvable Cu) and Ni (dNi constituted 86 ± 28% of total dissolvable Ni) within glacier plumes. For comparison, dFe was a lower fraction of total dissolvable Fe; 3.5 ± 4.8%. High concentrations of total dissolvable Fe in some inner-fjord environments, up to 77 µM in Ameralik (SW Greenland), may drive enhanced removal of scavenged type elements, such as Co. Further variability may have been driven by local bedrock mineralogy, which could explain high concentrations of dNi (25–29 nM) and dCo (6–7 nM) in one coastal region of west Greenland (Kangaatsiaq). Our results suggest that dissolved trace element distributions in glacier fjords are influenced by a range of factors including: freshwater concentrations, local geology, drawdown by scavenging and primary production, saline inflow, and sediment dynamics. Considering the lack of apparent seasonality in dFe concentrations, we suggest that fluxes of some trace elements may scale proportionately to fjord overturning rather than directly to freshwater discharge flux.

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

“…Conversely, dCo, dNi and dCu showed surface layer maxima and decreasing concentrations with depth only in the EGC and waters on the NE Greenland Shelf. There, Surface Water were 1.7–2.7‐fold (dCo), ⁓1.4‐fold (dNi) and 2–2.5‐fold (dCu) enriched relative to mean bottom layer concentrations, potentially related to glacial meltwater addition (Krause et al., 2021) and sea ice input (Tovar‐Sánchez et al., 2010) and likely aided through organic stabilization of dCo (Bundy et al., 2020), dNi (Van Den Berg & Nimmo, 1987) and dCu (Coale & Bruland, 1988) in near‐surface waters. In the WSC and parts of western Fram Strait, dCo showed surface layer minima (60 ± 10 pM in the WSC; 47 ± 12 pM at stations 6, 15 and 16) and subsurface layer maxima (86 ± 13 pM in the WSC, 93 ± 9 pM at stations 6, 15 and 16) which, corroborated by observations of increasing dNi and dCu concentrations with depth in the WSC, suggests the influence of drawdown by primary production and regeneration at depth (Krisch et al., 2020).…”

“…Shelf processes that affect fluxes on the NE Greenland Shelf are Greenland Ice Sheet discharge and sedimentary release of micronutrients such as dFe and dMn (Krause et al., 2021; Krisch, Hopwood, et al., 2021). We estimated the glacial micronutrient supply from Nioghalvfjerdsbrae to Fram Strait (Table S6 in Supporting Information S1) following the approach outlined in Krisch, Hopwood, et al.…”

“…Although glacial discharge is likely the source of observed dFe, dMn, dCo, dNi and dCu maxima near coastal Greenland (stations 20–22, Figure 2; Krause et al., 2021; Krisch, Hopwood, et al., 2021), Greenland Ice Sheet discharge is unlikely a substantial contributor to the EGC beyond the shelf break (Huhn et al., 2021; Laukert et al., 2017). Efficient estuarine removal, particularly of dFe (Krause et al., 2021; Zhang et al., 2015), and the limited potential to stabilize additional quantities of ligand‐bound micronutrients (Ardiningsih et al., 2020; Krisch, Hopwood, et al., 2021) are major constraints on Greenland Ice Sheet micronutrient export. Concentrations in the surface EGC at 78°50’N (0.56 ± 0.14 nM dFe, 0.96 ± 0.30 nM dMn, 85 ± 28 pM dCo, 3.19 ± 0.22 nM dNi and 1.45 ± 0.32 nM dCu for <500 m at stations 14, 15 and 26) were similar to observations in Atlantic Water of the WSC.…”

“…In contrast, net southbound transport of Arctic dNi and dCu across Fram Strait is ∼5-10-fold greater than the combined riverine supply by the Lena, Ob and Yenisey which may be related to the addition from smaller rivers (Guay et al, 2010) and sedimentary release in Siberian Shelf regions (Guieu et al, 1996). Advected with the Transpolar Drift toward the North Atlantic Ocean, southbound Arctic dFe transport in EGC Surface Water (1.4 ± 1.0 Gg•a −1 ) may be comparable in magnitude to Greenland ice sheet-toocean dFe export (1.6 Gg•a −1 as per Krause et al, 2021).…”

“…Shelf processes that affect fluxes on the NE Greenland Shelf are Greenland Ice Sheet discharge and sedimentary release of micronutrients such as dFe and dMn (Krause et al, 2021;Krisch, Hopwood, et al, 2021). We estimated the glacial micronutrient supply from Nioghalvfjerdsbrae to Fram Strait (Table S6 in Supporting Information S1) following the approach outlined in Krisch, Hopwood, et al (2021), using the mean cavity volume overturning rate (46 ± 11 mSv, Schaffer et al, 2020) and the difference in dissolved micronutrient load between station 19 (cavity-entering Atlantic Intermediate Water) and station 22 (cavity-exiting, glacially modified Atlantic Intermediate Water).…”