Fe-binding organic ligands in coastal and frontal regions of the western Antarctic Peninsula

• Published in: Biogeosciences
• Main Authors: I. Ardiningsih, K. Seyitmuhammedov, S. G. Sander, C. H. Stirling, G.-J. Reichart, K. R. Arrigo, L. J. A. Gerringa, R. Middag
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Antarctic; Antarctic Peninsula; Southern Ocean; The Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.5194/bg-18-4587-2021; https://doaj.org/article/d3ca14e1ca924842aaed67088bffb0b0

Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high-nutrient low-chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice-covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV), was applied. Our results indicated that organic ligands in the surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea ice. Organic ligands in the deeper shelf water are supplied via the resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([ L t ]) were between 1.2 and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentrations (excess ligand concentration, [ L ′ ] = 0.8–5.0 nM eq. Fe). The [ L ′ ] made up to 80 % of [ L t ], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe ( α Fe'L the product of [ L ′ ] and conditional binding strength of ligands, <math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi>K</mi><mtext>Fe'L</mtext><mtext>cond</mtext></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="28pt" height="17pt" class="svg-formula" dspmath="mathimg" ...