Copper-binding ligands in the Arctic Ocean and the role of the Transpolar Drift


The extension of shelf areas, the riverine inputs and the sea-ice coverage make the Arctic Ocean a unique biogeochemical environment. The surface waters of the Arctic Ocean receive a large amount of freshwater from rivers, sea-ice melt and glacial meltwater that act as a source of trace metals and dissolved organic matter. These substances are transported from the Siberian Shelves to the central Arctic toward the Fram Strait by the Transpolar Drift (TPD). Related to this transport, high surface concentrations of dissolved copper (dCu), a bio-essential trace metal, were observed in the Central Arctic (3 – 8 nM) and the Fram Strait (4 – 5 nM). The speciation and bioavailability of dCu are mainly controlled by organic binding ligands present in seawater, but the information about ligands in the Arctic Ocean is limited. The concentration and the conditional stability constants of Cu-binding ligands (LCu and log KcondCu2+L) were studied in the Arctic Ocean, Greenland Shelf and Fram Strait in 2015 and 2016 (GEOTRACES cruises GN04 and GN05). High concentrations of LCu were observed in surface waters (77 m) Greenland shelf samples (mean: 2.16 ± 0.47 nM; range: 1.41 – 3.37 nM). However, the log KcondCu2+L values observed in Fram Strait and deep Greenland shelf (range: 14.25 – 16.33) were slightly higher than in the other Arctic regions (range: 13.83 – 16.00). The high LCu concentration in the Arctic Ocean was related to the transport of organic matter by the TPD and Greenland coast processes while the low concentrations observed elsewhere were associated with the effect of Atlantic Waters. The transport of ligands within the TPD and the inputs from the Greenland coasts stabilize the dCu concentration, control the Cu2+ toxicity and could favour the phytoplankton development inside and outside the Arctic Ocean.