Speciation and export of particulate iron from the Northwest African continental margin into the water column
Abstract
The tropical North Atlantic receives the highest inputs of mineral dust in the world oceans, and this aeolian supply is thought to be the primary source of iron to this region. Both the path and magnitude of atmospheric dust delivery change seasonally, however, allowing the possibility that lateral input of iron from the continental margin may be important at some times of the year. Here we use a new technique called chemical mapping that allows a quick and statistically meaningful assessment of the speciation of marine particulate iron in a sample. Chemical mapping is a powerful synchrotron x-ray technique that incorporates the chemical speciation insight from X-ray Absorption Spectroscopy with the wealth of spatial and distribution information from XRF mapping. We mapped African dust aerosol samples and sediment samples from the African continental margin, the two putative end-member sources of iron to the Eastern Tropical North Atlantic. The resultant chemical maps show that 40% of the particulate iron in a sediment sample was pyrite, with the balance consisting of Fe(III)-compounds (40%) and Fe(II)-silicates (20%). In contrast, pyrite was absent in African dust, which was composed of Fe(III)-compounds (85%) and Fe(II) silicates (15%). The presence of pyrite in water column marine suspended particles thus indicates a margin source of iron. We determined the speciation of marine particulate iron in a coastal to open ocean transect between the Mauritanian upwelling region to the Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) in September 2008. We found the presence of pyrite in suspended marine particles as far as the TENATSO station, ~900km from the Mauritanian coast, indicating long-distance influence of Fe from the margin. Pyrite was not a significant component of total particulate Fe, however, which was instead dominated by Fe(III)-compounds (80-90%), and some Fe(II)-silicates (10-20%).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMOS32B..05L
- Keywords:
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- 4805 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Biogeochemical cycles;
- processes;
- and modeling;
- 4807 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Chemical speciation and complexation;
- 4845 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Nutrients and nutrient cycling;
- 4875 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Trace elements