Closure of the meridional overturning circulation through Southern Ocean upwelling

Abstract

The meridional overturning circulation of the ocean plays a central role in climate and climate variability by storing and transporting heat, fresh water and carbon around the globe. Historically, the focus of research has been on the North Atlantic Basin, a primary site where water sinks from the surface to depth, triggered by loss of heat, and therefore buoyancy, to the atmosphere. A key part of the overturning puzzle, however, is the return path from the interior ocean to the surface through upwelling in the Southern Ocean. This return path is largely driven by winds. It has become clear over the past few years that the importance of Southern Ocean upwelling for our understanding of climate rivals that of North Atlantic downwelling, because it controls the rate at which ocean reservoirs of heat and carbon communicate with the surface.

Southern Ocean deep convection as a driver of Antarctic warming events

“…Intense cooling, sea ice production and wind-driven advection at the SO surface then return these waters to deep and intermediate depths, closing the SO overturning circulation and connecting the atmosphere with the ocean interior [Marshall and Speer, 2012]. It is estimated that ~75% of the ocean store of anthropogenic heat and ~40% of the store of anthropogenic carbon enter the ocean interior through this region [Roemmich et al, 2015;Froelicher et al, 2015].…”

Development of the Western Boundary Undercurrent at Eirik Drift related to changing climate since the early Miocene

“…The global THC is driven by deep-water formation in high latitudes due to thermohaline convection and by Southern Ocean Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsri upwelling (Marshall and Speer, 2012). Present deep-water formation is conducted in a bipolar mode in the polar regions of both the Northern and Southern Hemisphere (Van Aken, 2007).…”

“…On the Southern Hemisphere shelf ice convection is dominant and forms the densest water mass, Antarctic Bottom Water (AABW). AABW is modified by entrainment on its way north and this modified AABW is also referred to as Lower Deep Water (LDW) (Marshall and Speer, 2012;Van Aken, 2007). On the Northern Hemisphere the open ocean convection due to atmospheric cooling prevails.…”

“…The compensating counterpart is the deep ocean circulation. The surface and the deep circulation are connected via deep-water formation in high latitudes and Southern Ocean upwelling (Marshall and Speer, 2012). North Atlantic Deep Water (NADW) formation is the main driving mechanism for the North Atlantic branch of the THC (Dickson and Brown, 1994;Schmitz, 1996;Van Aken, 2007).…”

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

“…Dense waters, which form on the continental shelves through cooling and brine rejection, sink and flow away from the Southern Ocean at great depths, thereby playing a major role in the global thermohaline circulation (Sloyan and Rintoul, 2001). Wind-driven upwelling in the Southern Ocean is equally important to this global circulation as a return path from the interior ocean to the surface (Marshall and Speer, 2012).…”