Katherine Mateos, University of California, Santa Cruz

Abstract

Particulate Iron Sources and Bioavailability in the Amundsen Sea: Determining Mineralogy and Speciation using K-edge XAS spectroscopy 

Katherine Mateos, Phoebe J. Lam, Samuel Webb, Sharon Bone, Robert Sherrell 

The Amundsen Sea is undergoing rapid changes due to the melting of the West Antarctic Ice Sheet. The basal meltwater from these glaciers is altering the biogeochemistry of the region and is strongly correlated to the rate of photosynthesis. One proposed explanation for this link is that the meltwater delivers the essential micronutrient iron, stimulating primary productivity. Although iron comes in both dissolved and particulate forms, photosynthetic rates are more closely tied to the concentration of particles, implying their bioavailability is crucial. Particulate iron can enter the sea directly through glacial outflow or indirectly as the meltwater stimulates buoyancy-driven circulation that brings up iron-rich sediment. Each of these processes may provide a different chemical form of particulate iron with implications for bioavailability. We used Fe K-edge XAS spectroscopy to characterize the mineralogy of iron particles from both sediments and glacial outflow. Using a combination of 𝜇XANES and 𝜇EXAFS at beamlines 2-3 and 7-2, we characterized water-column particle samples collected near a glacial outflow site and near the bottom sediment at an inflow site. Both sample types (outflow and near bottom) contained a diversity of both Fe 2+ and Fe 3+ minerals, including 2-line ferrihydrite, green rust, and magnetite. These findings suggest that the particles delivered to the Amundsen Sea via glacial meltwater may be highly amorphous and partially reduced, making them highly bioavailable.