Future Decline of Ice-Algal Primary Productivity in the Arctic Ocean: Model Intercomparison

A potential future evolution of ice-algal primary productivity (ice-PP) in the Arctic Ocean is investigated through an intercomparison of three sea ice-ocean coupled models: JAM (Japan), IOS (Canada), and UTAS (Australia). Ice-PP and related environmental variables are analyzed for three time periods: 1979–2018 (Phase 1), 2021–2060 (Phase 2), and 2061–2100 (Phase 3), assuming the high greenhouse-gas emission scenario (SSP5-8.5). All three models show pronounced regional contrasts, with higher ice-PP in shelf regions such as the Chukchi and Laptev Seas, and lower ice-PP in the central Arctic and Atlantic gateway. The JAM and UTAS models simulate ice-PP decline across regions due to reductions in sea ice and nutrients that overwhelm the enhanced light condition until Phase 2 (Phase 3) in the JAM (UTAS) model. The IOS model also simulates ice-PP decline in Atlantic-side regions, while projecting a temporary ice-PP increase in Phase 2 in Pacific–central Arctic regions, where improved light conditions temporarily dominate the impact over sea ice loss and nutrient reduction. Sensitivity experiments using the JAM model show that changing the light parameterization can reproduce ice-PP increase in Phase 2, while other changes related to ice-algal growth rate do not alter the ice-PP inter-phase pattern (decline during Phase 1–3). Results show that both decreasing nutrient availability and shrinking sea ice drive a potential future Arctic ice-PP decline, but the choices of ice-algal formulation and parameter values, especially for light conditions, produce various inter-model spreads. Observational data and laboratory experiments are needed to better parameterize ice-algal processes and constrain future projections.