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What Future States Will the Arctic Ocean Have, Using a Coupled Ice-Ocean Model with Probability Distribution Functions?

Author(s): Motoyoshi Ikeda

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Keywords: No Keywords

Abstract: As global warming proceeds, ice formation is decreasing in the Arctic Ocean. The AtlanticWater, which flows into the Arctic Ocean and is modified under ice formation in the Barents Sea, may reduce the density of the subsurface layer around 200 to 500-m depth due to the warming. A new modeling approach for simulation of the future is proposed on the base of a simple box model, with one active box for the surface layer, which interacts with the saltier box for the Greenland Sea and the lower box for the Arctic subsurface layer. Only the active box has sea ice and receives atmospheric forcing and freshwater flux. This model possesses a salinity-driven state, at which the saltier water enters the active box, is freshened, and becomes lighter, along with another solution, a convected state. The new component to the simple model is a probability distribution function (PDF) on the temperature–salinity (T–S) plane, representing horizontal heterogeneity. A T–S distribution retains only the probabilities of different water types, while their locations are discarded. The mechanisms to increase and reduce heterogeneity are represented by divergence and convergence of the PDF, respectively. The heterogeneity is generated by the intrusion of exterior water and forcing variability, and reduced by horizontal diffusion within the box. Convection with the lower box tends to concentrate the PDF to the lower box (T, S). Under the exterior condition that could produce both nonconvected and convected states in the simple model, there are two partly convected solutions in the probability model near by the two states in the simple model. As either the heterogeneity is intensified, or the subsurface layer is freshened, a convected portion increases, approaching to the nearly convected state. Thus, it is a possible consequence that the Arctic surface layer will be partly convected and have sea ice reduced significantly in the near future.


Year: 2016

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