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

• Main Authors: G. Dulaquais, M. Boye, M. J. A. Rijkenberg, X. Carton
• Format: Article
• Language: English
• Published: Copernicus Publications 2014-03-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/11/1561/2014/bg-11-1561-2014.pdf
• ISSN: 1726-4170; 1726-4189

The distributions of the bio-essential trace element dissolved cobalt (<i>D</i>Co) and the apparent particulate Co (<i>P</i>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). <i>P</i>Co was determined as the difference between total cobalt (<i>T</i>Co, unfiltered samples) and <i>D</i>Co. <i>D</i>Co concentrations ranged from 14.7 pM to 94.3 pM, and <i>P</i>Co concentrations from undetectable values to 18.8 pM. The lowest <i>D</i>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 <i>D</i>Co in the western Atlantic. In the Antarctic Bottom Waters, the enrichment in <i>D</i>Co with aging of the water mass can be related to suspension and redissolution of bottom sediments a well as diffusion of <i>D</i>Co from abyssal sediments. Mixing and dilution of deep water masses, rather than scavenging of <i>D</i>Co onto settling particles, generated the meridional decrease of <i>D</i>Co along the southward large-scale circulation in the deep western Atlantic. Furthermore, the apparent scavenged profile of <i>D</i>Co observed in the deep waters likely resulted from the persistence of relatively high concentrations in intermediate waters and low <i>D</i>Co concentrations in underlaying bottom waters. We suggest that the 2010 Icelandic volcanic eruption could have been a source of <i>D</i>Co that could have been transported into the core of the Northeast Atlantic Deep Waters. At intermediate depths, the high concentrations of <i>D</i>Co recorded in the ACW linearly correlated with the apparent utilization of oxygen (AOU), indicating that remineralization of <i>D</i>Co could be significant (representing up to 37% of the <i>D</i>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 <i>D</i>Co from the ACW appears to be a significant source of <i>D</i>Co into the surface waters of the equatorial domain. Summarizing, the dilution due to mixing processes rather than scavenging of <i>D</i>Co and the above-mentioned remineralization could be the two major pathways controlling the cycling of <i>D</i>Co into the intermediate and deep western Atlantic.