Observational analysis of the double-diffusive convection in the deep Canada Basin

The Canada Basin (CB) is the largest sub-basin in the Arctic, with the deepest abyssal plain of 3 850 m. The double-diffusive process is the possible passage through which the geothermal energy affects the above isolated deep waters. With the temperature-salinity-pressure observations in 2003, 500-m-thick transition layers and lower 1 000-m-thick bottom homogenous layers were found below 2 400 m in the central deep CB. Staircases with downward-increasing temperature and salinity are prominent in the transition layers, suggesting the double-diffusive convection in deep CB. The interface of the stairs is about 10 m thick with 0.001-0.002℃ temperature difference, while the thicknesses of the homogenous layers in the steps decrease upward from about 60 to 20 m. The density ratio in the deep central CB is generally smaller than 2, indicating stronger double-diffusive convection than that in the upper ocean of 200-400 m. The heat flux through the deepest staircases in the deep CB varies between 0.014 and 0.031 W/m², which is one-two orders smaller than the upper double-diffusive heat flux, but comparable to the estimates of geothermal heat flux.