Detailed survey of a large baroclinic eddy with extremely high temperatures in the Western Canada Basin

This paper presents a detailed hydrographic survey of a large anticyclone eddy (referred to as MO-eddy) that was found in early September 2010 during a Mirai Arctic cruise along the east flank of the Northwind Ridge in the southwest corner of the Canada Basin. It is ∼ 60 – 70 km in diameter, which is even larger than those found in previous studies. Moreover, it is characterized by unusually high temperatures that reach ∼ 6 ° C at the upper level of the eddy even though it is located near the southern edge of the sea-ice field. The eddy has a shape similar to that of a convex lens, which yields low potential vorticity and dynamically steers the anticyclonic circulation. Furthermore, we emphasize that the MO-eddy is tightly embedded within a strong westward jet established over the Chukchi Sea Shelf slope, which is considered to be the southern portion of the anticyclonic Beaufort Gyre. The unusually warm waters in the eddyʹs interior are likely to have been delivered by the jet flow from the Chukchi Sea Shelf through the shallow isopycnal surface of S ∼ 30.5 . In addition, a vigorous horizontal interleaving structure was identified in the vertical temperature and salinity profiles in the vicinity of the MO-eddy. Several microscale measurements reveal that such interleaving is widespread and causes a rapid dissipation of temperature variance through double diffusion, which is likely to contribute to a significant delay of ice formation during late-fall or winter.