Physical and remineralization processes govern the cobalt distribution in the deep western Atlantic Ocean

• Published in: Biogeosciences
• Main Authors: Dulaquais, G., Boye, M., Rijkenberg, M. J. A., Carton, X.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Antarctic; The Antarctic; Antarc*; Northeast Atlantic
• Online Access: https://doi.org/10.5194/bg-11-1561-2014; https://www.biogeosciences.net/11/1561/2014/

The distributions of the bio-essential trace element dissolved cobalt ( D Co) and the apparent particulate Co ( P Co) are presented along the GEOTRACES-A02 deep section from 64° N to 50° S in the western Atlantic Ocean (longest section of international GEOTRACES marine environment program). P Co was determined as the difference between total cobalt ( T Co, unfiltered samples) and D Co. D Co concentrations ranged from 14.7 pM to 94.3 pM, and P Co concentrations from undetectable values to 18.8 pM. The lowest D Co concentrations were observed in the subtropical domains, and the highest in the low-oxygenated Atlantic Central Waters (ACW), which appears to be the major reservoir of D Co in the western Atlantic. In the Antarctic Bottom Waters, the enrichment in D Co with aging of the water mass can be related to suspension and redissolution of bottom sediments a well as diffusion of D Co from abyssal sediments. Mixing and dilution of deep water masses, rather than scavenging of D Co onto settling particles, generated the meridional decrease of D Co along the southward large-scale circulation in the deep western Atlantic. Furthermore, the apparent scavenged profile of D Co observed in the deep waters likely resulted from the persistence of relatively high concentrations in intermediate waters and low D Co concentrations in underlaying bottom waters. We suggest that the 2010 Icelandic volcanic eruption could have been a source of D Co that could have been transported into the core of the Northeast Atlantic Deep Waters. At intermediate depths, the high concentrations of D Co recorded in the ACW linearly correlated with the apparent utilization of oxygen (AOU), indicating that remineralization of D Co could be significant (representing up to 37% of the D Co present). Furthermore, the preferential remineralization of phosphate (P) compared to Co in these low-oxygenated waters suggests a decoupling between the deep cycles of P and Co. The vertical diffusion of D Co from the ACW appears to be a significant source of D Co into the surface waters of the equatorial domain. Summarizing, the dilution due to mixing processes rather than scavenging of D Co and the above-mentioned remineralization could be the two major pathways controlling the cycling of D Co into the intermediate and deep western Atlantic.