Trait–Based Adjustments: Key to Improving Model Representation of the Bloom Seasonal Cycle in the Subantarctic Zone

Abstract Southern Ocean phytoplankton have unique traits that allow them to survive extreme environmental conditions of low iron, light, and temperature. These traits are not well represented in Earth System Models and may lead to misrepresentation of the bloom seasonal cycle in this critical oceanic region. This has implications for understanding the role of the biological carbon pump in driving ocean carbon uptake and storage. We conduct a sensitivity analysis using a 1D model in the Subantarctic Zone to identify (a) the most sensitive parameters for improving representation of the seasonal cycle and its mechanisms and (b) the impact of these changes on carbon export. Lowering the phytoplankton iron quota or increasing zooplankton iron stoichiometry and both improve the seasonal cycle timing and amplitude, aligning chlorophyll and carbon seasonal cycle. However, the resulting increases in bloom amplitude translates into minimal change in carbon export due to enhanced cycling through the dissolved organic carbon pool.