Presenter: Genevieve Elsworth (University of Colorado Boulder)

Description:
Multiple studies conducted with Earth system models suggest that anthropogenic climate change will influence marine phytoplankton net primary production (NPP) over the coming century. Light limited regions are projected to become more productive and nutrient limited regions less productive. Anthropogenic climate change can influence not only the mean state, but also the variance around the mean state, yet little is known about how the variance in marine NPP will change with time. Here, we quantify the influence of anthropogenic climate change on interannual variability in marine NPP and associated biomass from 1920 to 2100 using the Community Earth System Model Large Ensemble (CESM-LE). We find a significant decrease in the interannual variance of phytoplankton carbon biomass under a business-as-usual (RCP8.5) emission scenario, with heterogeneous regional trends. Decreasing variance in biomass is most apparent in the subpolar North Atlantic, North Pacific, and Southern Oceans, where light limitation tends to dominate phytoplankton productivity in CESM. In these high-latitude regions, warming-induced stratification limits the variability in light supply and reduces the interannual variance in NPP and plankton biomass. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries) should also consider changes in phytoplankton variance driven by anthropogenic warming, particularly on regional scales.