An increasing number of studies are considering Fe and ligand concentrations, providing data of trace element availability across the remote Southern Ocean region (Ardiningsih et al., 2021, Gerringa et al., 2020, Hassler et al., 2017, Thuroczy et al., 2012, Thuroczy et al., 2011, Caprara et al., 2016 and references therein). However, studies seldom focus on polar coastal environments which are especially sensitive to climate-induced changes. To anticipate how these changes may impact Fe availability, we must first understand the drivers of ligand supply to the Antarctic coast and offshore. The newly compiled Southern Ocean Ligand (SOLt) Collection includes all publicly available Fe complexation datasets for the Southern Ocean including dissolved Fe concentrations, Fe-binding ligand concentrations, and complexation capacities for 25 studies between 1995 - 2019.

We dissect the spokes of the ferrous wheel associated with Fe demand by quantifying the uptake rates of heterotrophic bacteria and phytoplankton in the subantarctic Southern Ocean during summer and situate these findings within a seasonal context. To do so, we conducted bioassays in which the effects of light on Fe photochemistry and uptake physiology were studied by comparing light and dark incubations, and the effects of DOC supply and competition between phytoplankton and heterotrophic bacteria were examined by isolating bacteria from the larger members of the ferrous wheel by pre-incubation size fractionation.