Response of Southern Ocean Resource Stress in a Changing Climate

Abstract

Phytoplankton underpin ocean net primary production (NPP) and Southern Ocean phytoplankton display different ecological-biogeochemical traits, compared to temperate species. Climate models currently forecast consistent across-model NPP increases due to climate change, yet neglect specific aspects of the Southern Ocean ecological-biogeochemical system. We conducted experiments to evaluate how key regional traits, including multiple limiting nutrients, unique photophysiology and differential resource acquisition, drive changes in the projected response of resource stress, NPP and export production under a high emissions scenario. Although Southern Ocean iron limitation is widespread, it declines in the future and is replaced by growing manganese limitation, as concentrations cannot support increasing growth rates. Distinct phytoplankton traits either amplify or dampen climate-driven changes, depending on whether they are those typical of Antarctic or temperate phytoplankton, respectively. Overall, future Southern Ocean NPP trends may be more uncertain than currently assumed and future efforts should focus on accounting for regional ecological-biogeochemical differences.