Seasonal depletion of the sub-surface iron reservoir in the sub-Antarctic zone of the Southern Ocean

Abstract

Iron availability in the Southern Ocean limits primary productivity with implications for the overall extent and efficiency of the biological carbon pump. Diagnosing the climate sensitivity of dissolved iron supply requires an improved understanding of the relative role of various input pathways (e.g. winter mixing, diapycnal diffusion, transient mixed layer entrainment and surface water iron recycling.. This study utilises multiple occupations of a station in the sub-Antarctic Southern Ocean, spanning winter (July. to late summer (February., to address the seasonal evolution of dissolved iron profiles, providing insight into the dominant supply mechanisms of dissolved iron to surface water production. Results highlight the seasonal decrease observed in the subsurface dissolved iron reservoir (mean euphotic depth (82 m. to maximum winter mixed layer depth (200 m., which is in excess of that which is required to support estimated surface water production. Results suggest an important vertical physical supply of dissolved iron to surface waters, over and above mixed layer remineralisation to sustain productivity through to late summer. A wind induced mixed layer deepening event in February that coincides with an increase in phytoplankton biomass is indicative of the important role of storms in supporting sub-Antarctic blooms. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.