A New Ecosystem Model for Arctic Phytoplankton Phenology From Ice‐Covered to Open‐Water Periods:Implications for Future Sea Ice Retreat Scenarios

Abstract: To predict ecosystem change in the Arctic Ocean, understanding Arctic phytoplankton phenology is essential. We develop a marine ecosystem model focusing on phytoplankton dynamics and the competition for multiple resources based on knowledge from in situ data obtained in the Chukchi Sea. The model is designed to include the unique ecological characteristics of the Arctic Ocean. To the best of our knowledge, this is the first model successfully simulating the current paradigm for Arctic phytoplankton phenology, including both under‐ice blooms and succession of phytoplankton groups. Sensitivity experiments show that the dominance of diatoms can be sustained by lateral transport of a high‐silicate water mass (Pacific Winter Water). Experiments for future scenarios show that sea ice retreat drives a decrease in large diatoms and an increase in the other relatively small non‐diatom groups. These results suggest that dominant phytoplankton groups can be shifted from diatoms to non‐diatoms under ongoing Arctic Ocean sea ice retreat.

Plain Language Summary: Understanding the phytoplankton ecology of the Arctic Ocean is important for predicting ecosystem change as sea ice retreats. We have developed a phytoplankton ecosystem model that describes three different phytoplankton groups, each of which competes for three different nutrients. The model successfully simulates the observed characteristics of the Arctic phytoplankton ecology, such asunder‐ice blooms and the growth and decline of the various phytoplankton groups, which was not successfully simulated by previous models. Our results show that horizontal transport of waters with high silicate concentrations play a key role in sustaining silicate‐dependent phytoplankton (diatom) groups. Simulations that explore future sea ice retreat scenarios suggest that the dominant phytoplankton group can be significantly altered by the changing conditions of the Arctic Ocean.