Processes affecting the oceanic iron cycle and their interaction with marine biology and climate

I present a model investigation on the complex marine iron (Fe) cycle. Attention is put on regional features, on the biological response to Fe availability, and on past and future climate. In a sequence of changes to the model, the main dFe features in the subtropical North Atlantic, such as a deep East-West gradient, a hydrothermal plume and a subsurface dFe minimum, could be better reproduced and explained. This was achieved by introducing scavenging on lithogenic particles and on phytoplankton, a new ligand parameterisation, a larger sinking velocity of particles and a hydrothermal source. In the Southern Ocean dFe is a limiting micro-nutrient for algee. The role of icebergs as a source of Fe was analysed, with respect to diatom and non-diatom net primary production, nutrient availability, carbon, nitrogen and silica export. The "Fe Hypothesis" suggests that the additional Fe input to the ocean contributed to lower atmospheric CO2 concentrations in the glacial. The results of a laboratory experiment indicated that high-Fe and low-pCO2 conditions (glacial ocean) were beneficial for the Southern Ocean bloom-forming diatom Pseudo-nitzschia subcurvata.