A suite of coupled ocean-sea ice simulations examining the effect of regime shift in sea-ice thickness distribution on ice–ocean interaction in the Arctic Ocean

Abstract. A major shift in Arctic sea ice occurred in 2007, transitioning from thicker, deformed ice to thinner, more uniform ice with reduced surface roughness. This abrupt change likely altered the dynamic and thermodynamic interactions between sea ice and ocean, with potential implications for nutrient and biogeochemical cycles in both sea ice and the upper ocean. In this study, we present a suite of regional coupled ocean-sea ice simulations designed to assess the potential impact of the regime shift on sea ice–ocean interactions, with a regional focus on the Atlantic sector of the Arctic Ocean. The different sea ice regimes are represented by changes in ice thickness distribution described by ice thickness classes in the sea ice model, and the effects of the different regimes are simulated through variations in the drag coefficient diagnosed from the ice thickness distribution. We emulate the two sea ice regimes by prescribing sea ice properties at the model's lateral boundaries. The results suggest a weaker dynamical coupling between sea ice and ocean in the new sea-ice regimes, leading to enhanced surface stratification, suppression of vertical mixing and momentum transfer to deeper layers. The simulation framework and the physical analyses presented here serve as a basis for ocean biogeochemical modelling studies that aim at understanding ocean ecosystem responses to changing Arctic sea ice.