Dense bottom layers in the Scotia Sea, Southern Ocean: Creation, lifespan, and destruction

• Published in: Geophysical research letters 2013-03, Vol.40 (5), p.933-936
• Main Authors: Meredith, Michael P., Brown, Peter J., Naveira Garabato, Alberto C., Jullion, Loïc, Venables, Hugh J., Messias, Marie-José
• Format: Article
• Language: English
• Subjects: Abyssal mixing; Dense bottom layers; Ocean circulation; Ocean temperature; Oceanography; Overflow; Overflows; Southern Ocean; Temperature gradients
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/grl.50260

The lower limb of the Atlantic overturning circulation is renewed by dense waters from the Southern Ocean, a substantial portion of which flow through the Scotia Sea. We report dense bottom layers here, with gradients in temperature and salinity comparable to those seen near the surface of the Southern Ocean. These are overlain by layers with much weaker stratification, and are caused by episodic overflows of dense waters across the South Scotia Ridge, and topographic trapping within deep trenches. One such layer was found to be at least 3–4 years older than the water immediately above. The estimated vertical diffusivity to which this layer was subject is substantially less than the strong basin‐average deep mixing reported previously. We conjecture that (a) vertical mixing in the Scotia Sea is strongly spatially inhomogeneous, and (b) the flushing of these layers, like their formation, is related to overflow events, and hence also strongly episodic. Key Points Scotia Sea dense water throughflow is significantly episodic Deep mixing in the Scotia Sea can be much weaker than previously reported Abyssal layers can stagnate for a number of years before being destroyed