Multi-model intercomparison of the pan-Arctic ice-algal productivity on seasonal, interannual, and decadal timescales

Seasonal, interannual, and decadal variations in the Arctic ice‐algal productivity for 1980–2009 are investigated using daily outputs from five sea ice‐ocean ecosystem models participating in the Forum for Arctic Modeling and Observational Synthesis project. The models show a shelf‐basin contrast in the spatial distribution of ice‐algal productivity (ice‐PP). The simulated ice‐PP substantially varies among the four subregions (Chukchi Sea, Canada Basin, Eurasian Basin, and Barents Sea) and among the five models, respectively. The simulated annual total ice‐PP has no common decadal trend at least for 1980–2009 among the five models in any of the four subregions, although the simulated snow depth and sea‐ice thickness in spring are mostly declining. The model intercomparison indicates that an appropriate balance of stable ice‐algal habitat (i.e., sea‐ice cover) and enough light availability is necessary to retain the ice‐PP. The multi‐model averages show that the ice‐algal bloom timing shifts to an earlier date and that the bloom duration shortens in the four subregions. However, both the positive and negative decadal trends in the timing and duration are simulated. This difference in trends are attributed to temporal shifts among different types of ice‐algal blooms: long‐massive, short‐massive, long‐gentle, and short‐gentle bloom. The selected value for the maximum growth rate of the ice‐algal photosynthesis term is a key source for the inter‐model spreads. Understanding the simulated uncertainties on the pan‐Arctic and decadal scales is expected to improve coupled sea ice‐ocean ecosystem models. This step will be a baseline for further modeling/field studies and future projections.