Seasonal Iron speciation in the Southern Ocean, from open ocean environments to naturally fertilized sub-Antarctic Islands (Marion and Gough Islands)

Abstract

The Southern Ocean (SO) is one of the largest high-nutrient low-chlorophyll regions in the World’s Ocean, where primary productivity (PP) is limited by iron (Fe) bioavailability, thereby impacting the strength and efficiency of biological carbon pump. There are, however, exceptions with large phytoplankton blooms persistently observed downstream of the Sub-Antarctic Islands. While extensive research has focussed on Fe-biogeochemistry around Kerguelen and Crozet islands, no such studies have been conducted at Marion and Gough islands. Furthermore, while our previously funded SANAP/NRF proposal has made substantial advances toward addressing the gaps in seasonal data coverage through SCALE 2019 winter and spring cruises, there is still a paucity of dissolved Fe data in the SO, especially from autumn to late-spring. This is severely hampering our understanding of the full seasonal biogeochemical Fe cycle and its impact on PP. This project aims to continue its focus on seasonality by expanding seasonal coverage of Fe measurements to include autumn (Marion) and late-spring (Gough) cruises for more comprehensive coverage of the SO seasonal cycle, with a particular focus on quantifying biogeochemical cycling of Fe-pool around these understudied islands. To strengthen this project further, we propose to investigate temporal Fe dynamics and the drivers of naturally-fertilized regions downstream of both islands; with the aim to quantify cycling processes of Fe and organic speciation in order to improve our knowledge on Fe bioavailability. We aim to quantify (regionally and seasonally) an array of parameters that have not previously been reported during autumn or late spring in this region, including Fe (and Cu) organic speciation, particulate Fe, humic substances and Fe(II) oxidation-kinetics. In addition, we will use a state-of-the-art ocean biogeochemical model and run novel simulations within the high resolution BIOPERIANT12 configuration to complement the field work.