[Eoas-seminar] EOAS Colloquium Fri Jan 19

[eoas-seminar at lists.fsu.edu]

Please join us for this week's EOAS Colloquium at 3pm Friday Jan 19 in 
EOAS 1050:

Dr. Lisa Herbert; EOAS, Florida State University

*Title: Seafloor sources of nutrient iron to a coastal Antarctic 
ecosystem revealed by a coupled modeling-observational approach *

Abstract:

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^-2 d^-1 ) 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.
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