GM01073_CH04.qxd 6/8/07 2:35 PM Page 19 A Simple Theory of the Pycnocline and Overturning Revisited

• Main Authors: Anand Gnanadesikan, Agatha M. De Boer, Bryan K. Mignone
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.143.8470; http://www.gfdl.noaa.gov/reference/bibliography/2007/a1g0703.pdf

A simple theory linking the pycnocline depth and volume transport of the thermohaline overturning to winds, eddies, surface densities and diapycnal diffusion was proposed by Gnanadesikan (Science, 283:2077-2079, 1999). This paper revisits this theory, with eye to understanding which predictions are robust, and which may be limited by the geometric simplification required to derive such a simple theory. We show that the theory works extremely well for diagnostic models, in which surface density is fixed. It thus appears that the model can be used as a diagnostic framework for understanding mechanisms behind circulation changes. The key insight of the theory that the Southern Ocean, rather than the tropics, can serve as a pathway for transformation of dense water to light water is supported by the observed distribution of radiocarbon. However, we demonstrate that changes in forcing do more than simply scale the magnitude of the circulation up and down, producing changes in pycnocline shape and circulation geometry. In particular, the roles of buoyancy forcing and stationary eddies are more complicated than would be expected from the simple theory. Such changes must be taken into account when interpreting measurements at individual locations. 1.