Ancient Climate Offers Clues to Ocean Productivity Under Future Warming
Researchers modeled how marine plants responded to high CO2 levels 15 million years ago, finding that warming oceans could actually boost overall carbon fixation—but with major shifts in which species thrive. The findings help resolve a critical uncertainty for policymakers betting on ocean-based carbon removal and companies planning aquaculture and fisheries investments.
Originaltitel: Modeled Changes in Marine Primary Productivity during the Middle Miocene Warming
The future of global marine primary productivity under warming conditions remains uncertain, in part because high CO2 scenario studies have been limited by the poor representation of phytoplankton ecology in fully-coupled Earth System Models. With the coupling of the Marine Biogeochemistry Library (MARBL) with the Community Earth System Model (CESM), it is now possible to explore marine carbon sequestration under varying atmospheric CO2 with greater ecological realism. Modeling past warm climates and validating results against paleo-proxy data offers an approach for inferring future trends. Here, we simulate the Miocene Climatic Optimum (MCO; ~15 Ma) using CESM-MARBL at 1° ocean resolution under 280 ppm and 560 ppm CO2 scenarios to examine global phytoplankton activity and marine primary productivity during this past warm interval. We find that elevated CO2 leads to increased global marine carbon fixation, with poleward shifts and increases of small phytoplankton and decreases in diatoms. These changes are primarily driven by stratification-altered nutrient distribution resulting from surface heating and freshwater addition. A novel model-data comparison, using MCO carbonate mass accumulation rates, shows good overall agreement. Despite modeling uncertainties, this study provides valuable insights into phytoplankton ecology and marine carbon sequestration under previous warming conditions in Earth’s history.