Weddell Gyre Warm Deep Water: circulation and heat budget using Argo floats

The Weddell Gyre supplies heat towards the Antarctic ice shelves and regulates the density of water masses that feed the deepest limb of the global overturning circulation. Warm Deep Water is the primary heat source to the Weddell Gyre, which undergoes modification as it circulates the cyclonic gyre. In this study, we take advantage of a fleet of Argo floats spanning the entire Weddell Gyre from 2002 to 2016. The heat budget is diagnosed for a 1000 m thick layer encompassing the core of Warm Deep Water. The heat budget does not close at the grid cell resolution. However, the heat budget closes when integrated horizontally over large areas, within the range of uncertainty established primarily by a range of possible values of horizontal and vertical diffusivity. In the southern limb of the gyre, there is a balance between convergence due to mean horizontal advection and divergence due to horizontal turbulent diffusion, whereas in the central gyre interior, the convergence is due to horizontal turbulent diffusion, which is balanced by divergence due to mean horizontal advection. We interpret the main results as follows: Heat is brought into the gyre by (1) mean horizontal advection into the southern limb, and (2) horizontal turbulent diffusion (i.e. eddy processes) across the open northern boundary of the gyre. Heat is removed from the southern limb of the gyre, (1) northwards into the central gyre interior and (2) southwards towards the ice shelves, both by horizontal turbulent diffusion. A notable outcome of the study is that it highlights the importance of understanding the role of eddy processes in redistributing heat throughout the Weddell Gyre. This is both towards the central gyre where isopycnals dome toward the surface (i.e. heat is brought into closer contact to the surface due to upwelling), and also towards the ice shelves, where basal ice melt can contribute to rising sea levels.