Abstract Samples from the upper 300 m along the 52°S band, south of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean, including a 3‐week monitoring of a persistent bloom, were analyzed to advance our understanding of iron cycling and supply to recurrent phytoplankton blooms. We measured dissolved Fe (dFe, 53 μm), while intermediate fractions were analyzed to investigate aggregation and export processes. Across all stations, dFe exhibited a consistent vertical structure, including a previously undescribed ubiquitous minimum below mixed and euphotic layers. The absence of pLFe 48h in the 0.2–3 μm fraction indicates reduced aggregation and is consistent with minimal authigenic Fe formation. Instead, pLFe 48h was concentrated in “slow” sinking particles, indicating surface entrainment. Biomass was negatively correlated with dFe but positively correlated with pLFe 48h , linking bloom development to particulate iron availability rather than dFe. Overall, rapid surface recycling of “slow” sinking pLFe 48h appeared to meet most of the daily iron demand during a prolonged diatom bloom. Near South Georgia Island, wind‐driven mobilization of iron‐rich material from the island snowpack and deposition into leeward waters likely supplied an additional iron source. By applying new protocols to characterize labile particulate iron, we reveal the elusive magnitude of the recycling dynamics of particulate iron in fecal and detrital materials sustaining Southern Ocean blooms.
Laglera et al. (Wed,) studied this question.