Marine Ecosystem Changepoints Spread Under Ocean Warming in an Earth System Model. Issue 5 (16th May 2022) - Cael, B. B.
Abstract: Sudden shifts in marine plankton communities in response to environmental changes are of special concern because of their low predictability and high potential impacts on ocean ecosystems. We explored how anthropogenic climate change influences the spatial extent and frequency of changepoints in plankton populations by comparing the behavior of a plankton community in a coupled Earth system model under pre‐industrial, historical 20th century, and projected 21st century forcing. The ocean areas where surface ocean temperature, nutrient concentrations, and different plankton types exhibited changepoints expanded over time. In contrast, regional hotspots where changepoints occur frequently largely disappeared. Heterotrophy and larger organism sizes were associated with more changepoints. In the pre‐industrial and 20th century, plankton changepoints were associated with shifts in physical fronts, and more often with changepoints for iron and silicate than for nitrate and phosphate. In the 21st century, climate change disrupts these interannual‐variability‐driven changepoint patterns. Together, our results suggest anthropogenic climate change may drive less frequent but more widespread changepoints simultaneously affecting several components of pelagic food webs. Plain Language Summary: Plankton are the backbone of pelagic ocean ecosystems and play important roles in regulating Earth's climate. Plankton populations and community structure respond to climate change, but much remains unknown about how climate change will influence plankton in the future. Here, we look for rapid changes, or changepoints, in the virtual plankton communities of a global model simulating Earth's climate over the pre‐industrial era, the 20th century, and a projection of 21st century climate change. We find, for all types of plankton in the model, that the ocean area where changepoints occur expands from the pre‐industrial era into the 20th century and again from the 20th to the 21st century. At the same time, hotspot regions, where rapid changes occur at least a few times per century, tend to disappear for all plankton types, and for temperature. Large plankton are more susceptible to changepoints than small plankton, and zooplankton are more susceptible than phytoplankton. The model ecosystem response to climate change is complex and spatially variable, but suggests that rapid shifts in plankton communities may become increasingly widespread but less frequent as the climate warms. Key Points: Ocean area with changepoints in model plankton populations expands under anthropogenic climate change Hotspot regions where plankton changepoints occur frequently, corresponding to switches between alternate states, concurrently shrink Larger and/or heterotrophic plankton exhibit proportionally more changepoints