Biogeochemistry of iron in coastal Antarctica:isotopic insights for external sources and biological uptake in the Amundsen Sea polynyas

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Tian, Hung An, van Manen, Mathijs, Bunnell, Zach B., Jung, Jinyoung, Lee, Sang Hoon, Kim, Tae Wan, Reichart, Gert Jan, Conway, Tim M., Middag, Rob
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Biogeochemistry; GEOTRACES; Isotopic compositions; Trace metals; Amundsen Sea; Antarctic; Austral; Dotson Ice Shelf; The Antarctic; Antarc*; Ice Shelf
• Online Access: https://hdl.handle.net/11370/70ffa9fd-05d7-4082-b055-2f123395fa7a; https://research.rug.nl/en/publications/70ffa9fd-05d7-4082-b055-2f123395fa7a; https://doi.org/10.1016/j.gca.2023.10.029; https://pure.rug.nl/ws/files/890556138/1-s2.0-S0016703723005239-main.pdf; http://www.scopus.com/inward/record.url?scp=85176269993&partnerID=8YFLogxK

Seasonal phytoplankton blooms in the Antarctic Amundsen Sea Polynyas are thought to be supported by an external supply of iron (Fe) from circumpolar deep waters, benthic sediments, and/or ice shelf meltwaters. However, largely due to the limited amount of Fe data reported for the Amundsen Sea Polynyas, understanding of the sources and processes that affect the biogeochemistry of Fe in this region (notably within the ice shelf system) remains limited. Here, we present the first investigation of dissolved Fe isotope distributions (δ 56 Fe) along the conveyer belt of waters into and through the Amundsen Sea, via the Dotson Ice Shelf, from samples collected during austral summer (2017–2018). Our dataset allows us to characterize and compare the dissolved δ 56 Fe signatures of incoming modified Circumpolar Deep Water (mCDW) and of sedimentary sources on the continental shelf. The range in dissolved δ 56 Fe (–1 to +0.1 ‰) observed in the Amundsen Sea close to the seafloor, coupled with elevated dissolved Fe concentrations (up to 1.6 nmol/L), suggests that Fe is released from shelf sediments via a combination of reductive and non-reductive processes, with non-reductive dissolution input being relatively more important (20–56 %) than reductive dissolution (4–12 %). Near the Dotson Ice Shelf, the δ 56 Fe in the mCDW inflow (–0.70 ‰) was lower than the mCDW outflow (–0.23 ‰), whereas any change in dissolved Fe concentrations was negligible. We speculate that this shift in dissolved δ 56 Fe underneath the ice shelf is driven by a combination of enhanced preservation (and addition) of lithogenic colloidal Fe(III) and/or complexation with Fe-binding ligands, together with a differential loss of Fe 2+ . We also found distinct δ 56 Fe signatures in surface waters of the polynya, with apparent preferential uptake of isotopically light Fe in a bloom dominated by diatoms leading to a relatively heavy remnant dissolved δ 56 Fe signature of +1.06 ‰, compared to a bloom dominated by haptophytes where more modest and variable isotope ...