Trace Element Biogeochemistry in the High‐Latitude North Atlantic Ocean: Seasonal Variations and Volcanic Inputs

Abstract

We present dissolved and total dissolvable trace elements for spring and summer cruises in 2010 in the high-latitude North Atlantic. Surface and full depth data are provided for Al, Cd, Co, Cu, Mn, Ni, Pb, and Zn in the Iceland and Irminger Basins, and consequences of biological uptake and inputs by the spring Eyjafjallajökull volcanic eruption are assessed. Ash from Eyjafjallajökull resulted in pronounced increases in Al, Mn, and Zn in surface waters in close proximity to Iceland during the eruption, while 3 months later during the summer cruise levels had returned to more typical values for the region. The apparent seasonal removal ratios of surface trace elements were consistent with biological export. Assessment of supply of trace elements to the surface mixed layer for the region, excluding volcanic inputs, indicated that deep winter mixing was the dominant source, with diffusive mixing being a minor source (between 13.5% [dissolved Cd, DCd] and −2.43% [DZn] of deep winter flux), and atmospheric inputs being an important source only for DAl and DZn (DAl up to 42% and DZn up to 4.2% of deep winter + diffusive fluxes) and typically less than 1% for the other elements. Elemental supply ratios to the surface mixed layer through convection were comparable to apparent removal ratios we calculated between spring and summer. Given that deep mixing dominated nutrient and trace element supply to surface waters, predicted increases in water column stratification in this region may reduce supply, with potential consequences for primary production and the biological carbon pump.

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

“…Similarly, dissolved Co, Ni and Cu in Atlantic Water from Fram Strait and the Barents Sea Opening (Table S3 in Supporting Information S1) matched observations in the Iceland and Irminger Basins (87 ± 20 pM dCo, 3.90 ± 0.52 nM dNi, 1.25 ± 0.08 nM dCu, Achterberg et al., 2021). Dissolved Mn on the other hand was ∼2‐fold elevated in Atlantic Water at Fram Strait (0.96 ± 0.32 nM) relative to observations from Atlantic Water in the Iceland and Irminger Basins (0.50 ± 0.37 nM, Achterberg et al., 2021). This suggests that during northward transport in the high latitude North Atlantic and across the Nordic Seas, sources and sinks of dFe, dCo, dNi and dCu are roughly balanced, whereas other micronutrients such as dMn and dZn are subject to ongoing net inputs, for example, from Svalbard shelf sediments (Gerringa, Rijkenberg, et al., 2021), before entering the Arctic Ocean.…”

“…In the Irminger Basin, dissolved Fe, Mn, Co, Ni, Cu and Zn in surface waters are progressively depleted and exported to depth because of primary production in spring and summer, followed by deep winter mixing which resupplies dissolved micronutrients to surface waters. Dissolved micronutrient concentrations in deeper waters (>500 m) remained fairly constant (Figure S10 in Supporting Information S1) as a consequence of the young age of these waters and an established equilibrium between dissolution and scavenging (Achterberg et al., 2018, 2021). For Fram Strait, the same is to be expected.…”

“…Unfortunately, data on seasonal micronutrient concentrations in the Arctic Ocean boundary regions considered herein are lacking. Two sampling campaigns in spring and summer 2010 to the Irminger and Iceland Basins are the only available datasets showing seasonal cycling of dFe, dMn, dCo, dNi, dCu and dZn in the high latitude North Atlantic to date (Achterberg et al., 2018, 2021).…”

“…Classical error propagation would lead to an over-estimation in the calculated error for net annual Arctic-Atlantic micronutrient exchange. We explore the potential implications of seasonal variations for annual fluxes based on the limited multi-seasonal micronutrient data available for the high latitude North Atlantic (Achterberg et al, 2018(Achterberg et al, , 2021.…”

“…A plume with elevated concentrations of shelf-derived radium and micronutrients including dFe and dCo, which are effectively stabilized by organic complexation, is subsequently advected offshore across the central Arctic Ocean within the Transpolar Drift (Bundy et al, 2020;Slagter et al, 2017). This results in pronounced near-surface dFe and dCo concentration maxima in the Central Arctic Ocean (Charette et al, 2020;Kadko et al, 2019;Klunder, Bauch, et al, 2012) and an inverted depth distribution of these elements compared to the North Atlantic (Achterberg et al, 2018(Achterberg et al, , 2021Rijkenberg et al, 2014). The southward extent of these elevated surface concentrations is so far undetermined.…”