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Please join us for this week's EOAS Colloquium at 3pm Friday Jan 19
in EOAS 1050:
<p>Dr. Lisa Herbert; EOAS, Florida State University</p>
<p><font size="5"><b><span style="line-height: 107%; font-family: "Times New Roman", serif;">Title:
<span style="mso-spacerun:yes"> </span>Seafloor
sources of nutrient iron to a coastal Antarctic ecosystem
revealed by a coupled
modeling-observational approach </span></b></font></p>
<p class="MsoNormal"><font size="4"><span style="line-height: 107%; font-family: "Times New Roman", serif;">Abstract:
<span style="mso-spacerun:yes"> </span></span></font></p>
<p class="MsoNormal"><font size="4"><span style="line-height: 107%; font-family: "Times New Roman", serif;">The
Amundsen Sea Polynya in the coastal Antarctic hosts
a vibrant ecosystem with some of the highest productivity
rates in the Southern
Ocean. This productivity is limited by the availability of
iron (Fe), and the
sources of Fe to the region are not yet well described. Past
research has
suggested Fe released from the seafloor may provide a key
source of this
micronutrient to the local ecosystem. However, the mechanisms
and magnitude of
this benthic Fe source have not been fully explored. In
austral summer 2022, we
collected sediment cores from the Amundsen Sea Polynya,
analyzing sediment
geochemistry and calculating diffusive Fe fluxes. Pore water
data indicate the consolidated
surface sediment hosts little Fe reduction, and fluxes are
therefore low (<0.2
µmol m<sup>-2</sup> d<sup>-1</sup>) and nonreductive. The
fluxes were then
incorporated into a high-resolution numerical circulation
model. By comparing
the model results to observations, we show that these low
fluxes are sufficient
to explain bottom water Fe observations in shallow regions
(<300m) close to
the coastline but cannot explain high bottom water Fe (3-4 nM)
in the deeper
regions. We propose that rapid remineralization in a seasonal
fluff layer observed
in the deep region may drive mineral dissolution in reducing
microenvironments.
This process releases dissolved Fe which can enrich inflowing
deep water and
upwell at the grounding line to sustain further productivity
at the polynya
surface. This previously unidentified Fe source is likely
dependent on the
strength, timing, and community structure of the phytoplankton
bloom, so recent
changes in glacial melt rates, sea ice cover and shelf
circulation may disrupt
this fragile feedback.</span></font></p>
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