High Resolution Distributions of Dissolved Iron and Manganese in the North Atlantic Ocean during the 2010 and 2011 US GEOTRACES cruises
Abstract
Bioactive metals, especially Fe, are essential for biological activity in the surface ocean. The high-resolution distribution of dissolved Fe along with other metals such as Al and Mn help us to understand the mechanisms responsible for their distributions in the ocean. Dissolved Al, Fe, Mn and Zn were measured in vertical profile seawater samples collected during the US GEOTRACES North Atlantic expeditions, from 37N to 17N along 22W (October-November, 2010) and from 70W to 25W (November-December, 2011). Samples were collected at approximately two-degree intervals using the GEOTRACES clean rosette sampling system, and dissolved trace metal concentrations were determined at-sea using Flow Injection Analysis. Our trans-basin survey revealed dissolved trace metal enrichments coincident with major physical features. While Al concentrations were elevated in the Mediterranean outflow plume at 1300 m, Fe was not similarly enriched, due to preferential Fe scavenging and removal before this water mass exited the Strait of Gibraltar. In contrast, dissolved Fe was enriched in sub-surface waters at the shelf margins in both the eastern and western basins. A strong Fe enrichment (>2 nM) off the African coast (17N) coincided with the Mauritanian oxygen minimum zone. The lack of a corresponding Mn enrichment in this 90-600 m zone suggests that Fe is remineralized in situ during vertical transport, but does not originate from coastal reducing sediments. Subsurface Fe was similarly enriched (1.2 nM, 800-1200 m) in the western basin, again without a concurrent Mn enrichment. However, this feature paralleled elevated CFC-12 and dissolved oxygen concentrations, consistent with transport by North Atlantic Deep Water. The highest dissolved Fe and Mn concentrations originated from the Trans-Atlantic Geotraverse (TAG) hydrothermal vent site, between 3000 and 4000 m at 26N, 44.7W in the axial valley of the Mid Atlantic Ridge.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS24E..02H
- Keywords:
-
- 4805 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Biogeochemical cycles;
- processes;
- and modeling;
- 4825 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Geochemistry;
- 4875 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Trace elements