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Titel |
Inferring source regions and supply mechanisms of iron in the Southern Ocean
from satellite data |
VerfasserIn |
Robert M. Graham, Agatha M. de Boer, Erik van Sebille, Karen E. Kohfeld, Christian Schlosser |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250126850
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Publikation (Nr.) |
EGU/EGU2016-6636.pdf |
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Zusammenfassung |
In many biogeochemical models a large shelf sediment iron flux is prescribed through the
seafloor over all areas of bathymetry shallower than 1000 m. Here we infer the likely location
of shelf sediment iron sources by identifying where mean annual satellite chlorophyll
concentrations are enhanced over shallow bathymetry ( > 1000 m). We show that mean
annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry
located more than 500 km from a coastline. Chlorophyll concentrations > 2 mg m-3 are only
found within 50 km of a continental or island coastline. These results suggest that
large sedimentary iron fluxes only exist on continental or island shelves. Large
sedimentary iron fluxes are unlikely to be found on isolated seamounts and submerged
plateaus.
We further compare satellite chlorophyll concentrations to the position of ocean fronts to
assess the relative role of horizontal advection and upwelling for supplying iron
to the ocean surface. Sharp gradients in chlorophyll concentrations are observed
across western boundary currents. Large chlorophyll blooms develop where western
boundary currents detach from the continental shelves and turn eastwards into the
Southern Ocean. Chlorophyll concentrations are enhanced along contours of sea
surface height extending off continental and island shelves. These observations
support the hypothesis that bioavailable iron from continental shelves is entrained into
western boundary currents and advected into the Sub-Antarctic Zone along the
Dynamical Subtropical Front. Likewise, iron from island shelves is entrained into nearby
fronts and advected downstream. Mean annual chlorophyll concentrations are very
low in open ocean regions with large modelled upwelling velocities, where fronts
cross over topographic ridges. These results suggests that open ocean upwelling is
unlikely to deliver iron to the surface from deep sources such as hydrothermal vents. |
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