Improvements on the upper-ocean simulation from 2007 to 2018 in the Canada Basin

The Beaufort Gyre reserves most of the freshwater in the Arctic Ocean. Observation shows that the freshwater content over 2016-2018 far exceeds the level over the plateau period 2008-2012. Modeling the vertical temperature and salinity structure and their changes in the Beaufort Gyre is a way to understand the process related to such step changes. We configured a pan-Arctic sea ice-ocean model with a southern boundary at similar to 7 degrees N in the Atlantic Ocean. The numerical simulation with sea surface salinity restoring, a latitude dependent horizontal diffusivity scaled by the squared buoyancy frequency, and a weak vertical diffusivity of 5 x 10(-7) m(2) s(-1) in the Arctic Ocean better reproduces the sea ice extent, the Pacific summer halocline water, and the freshwater variations as observed. The sea surface salinity restoring mitigates the surface desalination in the North Atlantic Ocean, therefore a weaker ocean stratification prevents the excessive warming in the intermediate Arctic Ocean. It is also found that the weak vertical background diffusivity is the major factor in our model to preserve the vertical ocean structure in the Canada Basin and also the step change of freshwater recently. In addition to resolving eddy activities in high resolution models, the success in our low resolution model suggests that tuning the vertical diffusivity serves as another approach to simulate the increasing freshwater content in the recent decade.