Vertical Heat Transport by the Ocean Circulation and the Role of Mechanical and Haline Forcing

• Published in: Journal of Physical Oceanography
• Main Authors: Zika, JD, Sijp, WP, England, MH
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Meteorological Society 2013
• Subjects: 14 Life Below Water; 13 Climate Action; anzsrc-for: 0405 Oceanography; anzsrc-for: 0911 Maritime Engineering; Antarctic; Antarc*
• Online Access: http://hdl.handle.net/1959.4/unsworks_42091; https://doi.org/10.1175/JPO-D-12-0179.1

Vertical transport of heat by the ocean circulation is investigated using a coupled-climate model and novel thermodynamic methods. Using a streamfunction in temperature-depth coordinates, cells are identified by whether they are thermally direct (flux heat upwards) or thermally indirect (flux heat downwards). These cells are then projected into geographical and other thermodynamic coordinates. Three cells are identified in the model: a thermally direct cell coincident with Antarctic Bottom Water, a thermally indirect deep cell coincident with the upper limb of the meridional overturning circulation and a shallow thermally direct cell coincident with the subtropical gyres at the surface. The mechanisms maintaining the deep thermally indirect cell are investigated. Sinking water within the deep cell is more saline than that which upwells, due to the coupling between the upper limb and the sub-tropical gyres in a broader thermohaline circulation. Despite the higher salinity of its sinking water the deep cell transports buoyancy downward requiring a source of mechanical energy. Experiments run to steady state with increasing Southern Hemisphere westerlies show an increasing thermally indirect circulation. Our results suggest that heat can be pumped downward by the upper limb of the meridional overturning circulation through a combination of salinity gain in the subtropics and the mechanical forcing provided by Southern Hemisphere westerly winds.