A winter GEOTRACES study characterizing Fe-binding ligands and the physical speciation of Fe in the Southern Indian Ocean

Abstract

The Southern Ocean is of global significance to ocean biogeochemical cycling of nutrients and climate change. The trace metal Fe has been identified as a limiting nutrient to primary productivity in the Southern Ocean, thereby being classified as a High-Nutrient Low-Chlorophyll region. The cycling of Fe has been studied extensively, globally but lacking in the Southern Ocean, to determine the inputs and cycling of this crucial micronutrient. Climate change is predicted to affect the bioavailability of Fe and therefore a clearer understanding of the current Fe cycle is required to better predict future changes. Physical speciation is a major control on bioavailability of Fe to phytoplankton. The speciation of Fe in the marine environment has various controls, one dominant control is the presence of organic Fe-binding ligands. A large gap in understanding Fe cycling in the Southern Ocean lies within the lack of Fe physical speciation and seasonality data within this region. During July 2017 the IO6 Transect (30°E. was sampled, between 42°S and 58°S, for particulate and dissolved trace metals, on-board the SA Agulhas 2. Seven deep profiles were sampled along this transect. This is the first time particulate trace metal samples have been collected in the Southern Ocean during austral winter. Along with dissolved trace metal data we can start to close the gap in understanding the seasonality of Fe physical speciation. Organic Fe-binding ligand samples were also collected and the speciation of Fe can be further discussed with available organic data. Ultimately, this study aims to improve the understanding of the interactions between the size fractions of Fe and how Fe-binding ligands and seasonality affect these interactions, throughout the water column. Analysis of samples collected during the IO6 transect is currently underway. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.