Nanoparticulate iron oxyhydroxides dominate iron speciation in hydrothermal plumes over the 1-100 km distance from vent source
Abstract
Iron (Fe), a limiting nutrient for phytoplankton productivity, connects hydrothermal vents to surface waters. Formerly, dust deposition was considered the main source of iron to the oceans, but recent work suggests hydrothermal vents could also be an important source of iron to the surface ocean via upwelling at high latitudes. Dissolved iron concentrations in hydrothermal fluids are a million times those of surrounding ocean water. Considerable iron (>90%) precipitates close to vent sources, but in a major breakthrough, the international GEOTRACES program revealed signatures of hydrothermally derived iron transported across deep ocean basins worldwide. Models show that through density-controlled upwelling, this iron could support up to 10% of primary production in the North Pacific Ocean and up to 30% in the Southern Ocean. It remains unclear how some iron persists in dissolved form in the water column rather than being sequestered into sinking particles. The fate of iron likely depends on speciation and aggregate size, with organic ligand-bound iron, pyrite, and iron oxyhydroxide nanoparticles all having different lifetimes in hydrothermal plumes. Critical processes constraining export of iron from vent sources to open ocean waters occur within the first ~100 km of plume evolution.
We show that particulate iron speciation within the first 70 km of dispersing plume evolution is dominated by aggregates of morphologically uniform iron oxyhydroxide nanoparticles. We work with samples from Rainbow vent system (Mid Atlantic Ridge) and vent fields between 15-18S along the Southern East Pacific Rise. We use synchrotron-based methods (bulk extended X-ray absorption fine structure spectroscopy, X-ray fluorescence spectromicroscopy, and scanning transmission X-ray microscopy) and electron microscopy. These results increase our understanding of iron export mechanisms and support conservation of hydrothermal vent systems due to the global significance of iron export.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMOS55B..07M