ALBERT

Description: Highlights • Cu complexation was measured for the first time in the Fram Strait region. • Cu-binding ligand concentrations and binding strength varied longitudinally in the Fram Strait. • More than 99 % of dCu was organically complexed by strong ligands. • On the Greenland shelf the Transpolar Drift and the coastal processes were the main sources of Cu ligands. Abstract The Fram Strait represents the major gateway of Arctic Ocean waters towards the Nordic Seas and North Atlantic Ocean and is a key region to study the impact of climate change on biogeochemical cycles. In the region, information about trace metal speciation, such as copper, is scarce. This manuscript presents the concentrations and conditional stability constants of copper-binding ligands (LCu and log KcondCu2+L) in the water column of Fram Strait and the Greenland shelf (GEOTRACES cruise GN05). Cu-binding ligands were analysed by Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using salicylaldoxime (SA) as competitive ligand. Based on water masses and the hydrodynamic influences, three provinces were considered (coast, shelf, and Fram Strait) and differences were observed between regions and water masses. The strongest variability was observed in surface waters, with increasing LCu concentrations (mean values: Fram Strait = 2.6 ± 1.0 nM; shelf = 5.2 ± 1.3 nM; coast = 6.4 ± 0.8 nM) and decreasing log KcondCu2+L values (mean values: Fram Strait = 15.7 ± 0.3; shelf = 15.2 ± 0.3; coast = 14.8 ± 0.3) towards the west. The surface LCu concentrations obtained above the Greenland shelf indicate a supply from the coastal environment to the Polar Surface Water (PSW) which is an addition to the ligand exported from the central Arctic to Fram Strait. The significant differences (in terms of LCu and log KcondCu2+L) between shelf and coastal samples were explained considering the processes which modify ligand concentrations and binding strengths, such as biological activity in sea-ice, phytoplankton bloom in surface waters, bacterial degradation, and meltwater discharge from 79NG glacier terminus. Overall, the ligand concentration exceeded those of dissolved Cu (dCu) and kept the free copper (Cu2+) concentrations at femtomolar levels (0.13–21.13 fM). This indicates that Cu2+ toxicity limits were not reached and dCu levels were stabilized in surface waters by organic complexes, which favoured its transport to the Nordic Seas and North Atlantic Ocean and the development of microorganism.

Description: Copper (Cu) is a bio-essential trace metal involved in many phytoplankton metabolic processes. In seawater, its bioavailability is controlled by the formation of organic complexes with binding ligands which also controls the toxicity of free cupric ion (Cu²⁺). Despite this key role, information about Cu speciation is scarce, especially in the Arctic Ocean. However, this oceanographic region is essential to understand the copper biogeochemical cycle. This dataset contains the results of Cu complexation measurements in station depth profiles sampled in Fram Strait and Greenland Shelf. Samples were collected during GEOTRACES expedition GN05 (PS100) between 21 July and 1 September 2016, following GEOTRACES guidelines (https://www.geotraces.org). Copper binding ligand concentrations (LCu) and conditional stability constants (logKcond) were measured by Competitive-Ligand Exchange Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using Salicylaldoxime (SA) as competitive ligand (Campos and van den Berg, 1994). The concentration of dissolved copper has been reported by Krisch et al. (2021) (doi:10.1594/PANGAEA.933431).

Description: Copper (Cu) is an important micronutrient involved in different phytoplankton metabolic processes. In seawater, Cu speciation is controlled by the formation of organic complexes with natural binding ligands, which controls its bioavailability and toxicity. The information about Cu organic speciation in the ocean is scarce, particularly in the Arctic Ocean where the ongoing climate change is altering the seawater chemistry. This dataset contains measurements of Cu-binding ligands from station depth profiles sampled between from the Norwegian Coast to the Central Arctic Ocean. Samples were collected during GEOTRACES expedition GN04 (Polarstern cruise PS94) between 17 August and 14 October 2015, following GEOTRACES guidelines (https://www.geotraces.org). The Competitive-Ligand Exchange Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV), using Salicylaldoxime (SA) as competitive ligand (Campos and van den Berg, 1994), was the technique applied to determine the Cu-binding ligand concentrations (LCu) and conditional stability constants (logKcu2+L). The concentration of dissolved copper used for the analysis has been reported by Gerringa et al. (2021) (doi:10.1594/PANGAEA.932797).