Dissolved Cd, Co, Cu, Fe, Mn, Ni, and Zn in the Arctic Ocean

Abstract

During the Polarstern (PS94) expedition, summer 2015, part of the international GEOTRACES program, sources and sinks of dissolved (D) Cd, Co, Cu, Fe, Mn, Ni, and Zn were studied in the central Arctic Ocean. In the Polar Surface Water in which the TransPolar Drift (TPD) is situated, salinity and δ18O derived fractions indicated a distinct riverine source for silicate DCo, DCu, DFe, DMn, and DNi. Linear relationships between DMn and the meteoric fraction depended on source distance, likely due to Mn‐precipitation during transport. In the upper 50 m of the Makarov Basin, outside the TPD core, DCo, DMn, DNi, DCd, and DCu were enriched by Pacific waters, whereas DFe seemed diluted. DCo, DFe, DMn, and DZn were relatively high in the Barents Sea and led to enrichment of Atlantic water flowing into the Nansen Basin. Deep concentrations of all metals were significantly lower in the Makarov Basin compared to the Nansen and Amundsen, the Eurasian, Basins. The Gakkel ridge hydrothermal input and higher continental slope convection are explanations for higher metal concentrations in the Eurasian Basins. Although scavenging rates are lower in the Makarov Basin compared to the Eurasian Basins, the residence time is longer and therefore scavenging can decrease the dissolved concentrations with time. This study provides a baseline to assess future change, and additionally identifies processes driving trace metal distributions. Our results underline the importance of fluvial input as well as shelf sources and internal cycling, notably scavenging, for the distribution of bio‐active metals in the Arctic Ocean.

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

“…Comparing the zero salinity intercepts for Greenland data herein (24 nM dFe, 11 nM dNi, 2.7 nM dCo and 7.4 nM dCu) with mean concentrations in the Transpolar Drift (2 nM dFe, 7 nM dNi, 150 pM dCo and 5 nM dCu, Gerringa et al, 2021) suggests that trace metal concentrations along the east Greenland shelf may be more influenced by trace metal fluxes exiting the Arctic than they are by local freshwater discharge from Greenland. The high dNi and dCu concentrations over the shelf may thus simply reflect a signal exported southwards (Gerringa et al, 2021). It remains to be quantified how far this Transpolar Drift signal is propagated.…”

“…A further confounding influence, especially given the location of most shelf measurements in east Greenland, is that the Transpolar Drift appears to drive elevated trace metal signatures in the East Greenland Current (Krisch et al, 2021). Comparing the zero salinity intercepts for Greenland data herein (24 nM dFe, 11 nM dNi, 2.7 nM dCo and 7.4 nM dCu) with mean concentrations in the Transpolar Drift (2 nM dFe, 7 nM dNi, 150 pM dCo and 5 nM dCu, Gerringa et al, 2021) suggests that trace metal concentrations along the east Greenland shelf may be more influenced by trace metal fluxes exiting the Arctic than they are by local freshwater discharge from Greenland. The high dNi and dCu concentrations over the shelf may thus simply reflect a signal exported southwards (Gerringa et al, 2021).…”

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

“…Samples from GN04 were analyzed via solid‐phase extraction and HR‐ICP‐MS (Thermo Finnigan Element 2) as described in Gerringa, Rijkenberg, et al. (2021). Briefly, 30 mL of UV‐digested sample were pre‐concentrated using an automated SeaFAST system (SC4 DX SeaFAST pico; ESI) through addition of ammonium acetate buffer that was prepared from ammonium hydroxide and sub‐boiled glacial acetic acid (Suprapur grade, Merck).…”

“…Macronutrient data can be obtained from: https://doi.pangaea.de/10.1594/PANGAEA.868396 (GN04/PS94, van Ooijen et al., 2016), and https://doi.pangaea.de/10.1594/PANGAEA.905347 (GN05/PS100, Graeve et al., 2019). Dissolved micronutrient data can be obtained from: https://dataportal.nioz.nl/doi/10.25850/nioz/7b.b.jc (GN04/PS94, Gerringa, Middag, et al., 2021), and https://doi.pangaea.de/10.1594/PANGAEA.933431 (GN05/PS100, Krisch, Roig, et al., 2021). Radium isotope data can be obtained from: https://www.bco-dmo.org/dataset/718440 (GN01/ HLY1502, Charette & Moore, 2021), the supplement to the publication of Rutgers van der Loeff et al.…”

“…Dissolved micronutrient fluxes to the Arctic Ocean are dominated by advection of the Atlantic WSC. Recirculation of Atlantic waters (de Steur et al., 2014; Hattermann et al., 2016) may thus exert a strong control on the amount of micronutrient import to the Arctic Ocean with possible knock‐on effects on phytoplankton productivity in regions downstream of the WSC such as the Nansen Basin (Rijkenberg et al., 2018) where shelf inputs, for example, through the Transpolar Drift (Gerringa, Rijkenberg, et al., 2021), are lacking. Seasonal and interannual variability in Atlantic Water transport have been observed (Hattermann et al., 2016; Tsubouchi et al., 2021).…”