Elevated sources of cobalt in the Arctic Ocean

• Published in: Biogeosciences
• Main Authors: R. M. Bundy, A. Tagliabue, N. J. Hawco, P. L. Morton, B. S. Twining, M. Hatta, A. E. Noble, M. R. Cape, S. G. John, J. T. Cullen, M. A. Saito
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Arctic Ocean; North Pole; Arctic Basin; International Polar Year; Phytoplankton; Sea ice
• Online Access: https://doi.org/10.5194/bg-17-4745-2020; https://doaj.org/article/c8710e4963d74742898ed37918c57f3a

Cobalt (Co) is an important bioactive trace metal that is the metal cofactor in cobalamin (vitamin B 12 ) which can limit or co-limit phytoplankton growth in many regions of the ocean. Total dissolved and labile Co measurements in the Canadian sector of the Arctic Ocean during the U.S. GEOTRACES Arctic expedition (GN01) and the Canadian International Polar Year GEOTRACES expedition (GIPY14) revealed a dynamic biogeochemical cycle for Co in this basin. The major sources of Co in the Arctic were from shelf regions and rivers, with only minimal contributions from other freshwater sources (sea ice, snow) and eolian deposition. The most striking feature was the extremely high concentrations of dissolved Co in the upper 100 m, with concentrations routinely exceeding 800 pmol L −1 over the shelf regions. This plume of high Co persisted throughout the Arctic basin and extended to the North Pole, where sources of Co shifted from primarily shelf-derived to riverine, as freshwater from Arctic rivers was entrained in the Transpolar Drift. Dissolved Co was also strongly organically complexed in the Arctic, ranging from 70 % to 100 % complexed in the surface and deep ocean, respectively. Deep-water concentrations of dissolved Co were remarkably consistent throughout the basin ( ∼55 pmol L −1 ), with concentrations reflecting those of deep Atlantic water and deep-ocean scavenging of dissolved Co. A biogeochemical model of Co cycling was used to support the hypothesis that the majority of the high surface Co in the Arctic was emanating from the shelf. The model showed that the high concentrations of Co observed were due to the large shelf area of the Arctic, as well as to dampened scavenging of Co by manganese-oxidizing (Mn-oxidizing) bacteria due to the lower temperatures. The majority of this scavenging appears to have occurred in the upper 200 m, with minimal additional scavenging below this depth. Evidence suggests that both dissolved Co (dCo) and labile Co (LCo) are increasing over time on the Arctic shelf, and these ...