A Refinement of the Processes Controlling Dissolved Copper and Nickel Biogeochemistry: Insights From the Pan‐Arctic

Abstract

Recent studies, including many from the GEOTRACES program, have expanded our knowledge of trace metals in the Arctic Ocean, an isolated ocean dominated by continental shelf and riverine inputs. Here, we report a unique, pan‐Arctic linear relationship between dissolved copper (Cu) and nickel (Ni) present north of 60°N that is absent in other oceans. The correlation is driven primarily by high Cu and Ni concentrations in the low salinity, river‐influenced surface Arctic and low, homogeneous concentrations in Arctic deep waters, opposing their typical global distributions. Rivers are a major source of both metals, which is most evident within the central Arctic's Transpolar Drift. Local decoupling of the linear Cu‐Ni relationship along the Chukchi Shelf and within the Canada Basin upper halocline reveals that Ni is additionally modified by biological cycling and shelf sediment processes, while Cu is mostly sourced from riverine inputs and influenced by mixing. This observation highlights differences in their chemistries: Cu is more prone to complexation with organic ligands, stabilizing its riverine source fluxes into the Arctic, while Ni is more labile and is dominated by biological processes. Within the Canadian Arctic Archipelago, an important source of Arctic water to the Atlantic Ocean, contributions of Cu and Ni from meteoric waters and the halocline are attenuated during transit to the Atlantic. Additionally, Cu and Ni in deep waters diminish with age due to isolation from surface sources, with higher concentrations in the younger Eastern Arctic basins and lower concentrations in the older Western Arctic basins.

Spatial Complexity in Dissolved Organic Matter and Trace Elements Driven by Hydrography and Freshwater Input Across the Arctic Ocean During 2015 Arctic GEOTRACES Expeditions

“…(2019, 2020, 2022) for GN01 Fe and Mn, Gerringa et al., and Jensen et al. (2022) for GN01 Cu and Ni. The isotope data were from Pasqualini et al.…”

“…(2020) for GN01 Cd, Jensen et al. (2019, 2020, 2022) for GN01 Fe and Mn, Gerringa et al., and Jensen et al. (2022) for GN01 Cu and Ni.…”

“…The dZn (Jensen et al, 2019), dCd (Zhang et al, 2019), dCu, dNi (Jensen et al, 2022), and dMn (Jensen et al, 2020) have elevated concentrations throughout the UHC in the Canada Basin water column (Fig. S5, S6).…”

“…The DOC data are available online (Hansell, 2017;. Dissolved Fe and other TE data were obtained from Jensen et al, (2019) for GN01 Zn, Zhang et al, (2020) for GN01 Cd, Jensen et al, (2019,2020,2022) for GN01 Fe and Mn, Gerringa et al, and Jensen (2022) for GN01 Cu and Ni. The isotope data were from Pasqualini et al, (2017) and Paffrath et al, (2021).…”

“…Dissolved Fe and other TE data were obtained from Jensen et al (2019) for GN01 Zn, Zhang et al (2020) for GN01 Cd, Jensen, et al (2019Jensen, et al ( , 2020Jensen, et al ( , 2022 for GN01 Fe and Mn, Gerringa et al (2021) for GN04 trace metals, and Jensen et al (2022) for GN01 Cu and Ni. Sample collection and analyses followed GEOTRACES protocols (Cutter et al, 2010(Cutter et al, , 2014Rijkenberg et al, 2018).…”