Australia: The Land Where Time Began

A biography of the Australian continent 

Southern Ocean – Variability of Eddy-Induced Abyssal Mixing on Climatic Timescales

The Southern Ocean plays a pivotal role in the circulation of the global ocean and the climate (Toggweiler & Russell, 2008; Skinner et al., 2010; Rintoul & Naveira Garabato, 2013). In the Southern Ocean deep water masses of the world ocean upwell to the surface and then subsequently sink to intermediate and abyssal depths, and form 2 overturning cells that exchange substantial quantities of heat and carbon with the atmosphere (Lumpkin & Speer, 2007; Lauderdale et al., 2013). It has been relatively well established (Marshall & Speer, 2012) that the upper cell is sensitive to the climate changes in forcing. The response of the lower cell to forcing, is however, little known, in particular if small-scale mixing in the abyssal depths of the Southern Ocean, which are an important controlling process in the lower cell (Ito & Marshall, 2008; Nikurashin & Vallis, 2011), is influenced by atmospheric forcing. In this paper the authors¹ present observational evidence that relate abyssal mixing changes to oceanic eddy variability on timescales of months to decades. The study found that observational estimates of mixing rates, which had been obtained along a repeat hydrographic transect across Drake Passage, is dependent on the local oceanic eddy energy, which was derived from a moored current meter and altimetric measurements. As the westerly winds (Meredith & Hogg, 2006; Morrow, Ward, Hogg & Pasquet, 2010) of the Southern Hemisphere regulate the intensity of the regional eddy field, the findings of this study suggest the abyssal mixing and overturning in the Southern Ocean are sensitive to climatic perturbations in wind forcing.

Sources & Further reading

1. Sheen, K. L., et al. (2014). "Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales." Nature Geosci 7(8): 577-582.