Global Meridional Overturning Circulation Inferred From a Data‐Constrained Ocean & Sea‐Ice Model

Abstract

Our current understanding of the global meridional overturning circulation (GMOC) is revisited using a surface‐forced ocean model simulation constrained by global hydrographic data. The derived GMOC is qualitatively consistent with previous observation‐based studies and further provides enhanced spatial details in the sources, transformations, and transports of major global water masses including in poorly observed regions. Several important but relatively underexplored aspects of the GMOC are highlighted, including complex but vigorous heavy‐to‐light water mass transformation that occurs in the Indo‐Pacific and Southern Oceans, and the role of the equatorial Pacific upwelling in closing the GMOC circuit. These and other key aspects of the GMOC are poorly captured in a surface‐forced ocean model simulation without the temperature and salinity corrections, suggesting that current climate models do not realistically simulate the GMOC and the associated global heat, salt, and carbon balances.

Atlantic Ocean Heat Transport Enabled by Indo‐Pacific Heat Uptake and Mixing

“…The drivers of this circulation still remain under discussion, with debate centering around the proportion of water mass transformation between light and dense waters occurring in the high-latitude North Atlantic and the Southern Ocean and through diapycnal upwelling at lower latitudes (Cessi, 2019;Ferrari & Wunsch, 2009;Ferrari et al, 2017;Gnanadesikan, 1999;Talley, 2013;Lee et al, 2018;Marshall & Speer, 2012;Thompson et al, 2016;Toggweiler et al, 2019;Newsom & Thompson, 2018). The drivers of this circulation still remain under discussion, with debate centering around the proportion of water mass transformation between light and dense waters occurring in the high-latitude North Atlantic and the Southern Ocean and through diapycnal upwelling at lower latitudes (Cessi, 2019;Ferrari & Wunsch, 2009;Ferrari et al, 2017;Gnanadesikan, 1999;Talley, 2013;Lee et al, 2018;Marshall & Speer, 2012;Thompson et al, 2016;Toggweiler et al, 2019;Newsom & Thompson, 2018).…”

The Surface Pathways of the South Atlantic: Revisiting the Cold and Warm Water Routes Using Observational Data

“…Both the warm water route (Donners & Drijfhout, ; Lee et al, ; Speich et al, ; Speich et al, ; Weijer et al, ) and the cold water route (Macdonald, ; Sloyan & Rintoul, ; You, ) have found heavy favor in past studies. Two recent studies, however, suggest a more comparable role for the pathways, while still attributing a larger contribution to the warm route (Rodrigues et al, ; Rühs et al, ) The divergent estimates of the cold and warm water route contributions can be partially explained by the use of different data sets and methods, as well as the use of coarse‐resolution models (Donners & Drijfhout, ; Rühs et al, )…”

“…Interest in these competing sources stems from an expectation that the prevalence of one over the other affects the variability and stability of the AMOC because of their influence on deep water formation in the Both the warm water route (Donners & Drijfhout, 2004;Lee et al, 2019;Speich et al, 2001;Speich et al, 2007;Weijer et al, 2002) and the cold water route (Macdonald, 1998;Sloyan & Rintoul, 2001;You, 2002) have found heavy favor in past studies. Two recent studies, however, suggest a more comparable role for the pathways, while still attributing a larger contribution to the warm route (Rodrigues et al, 2010;Rühs et al, 2019) The divergent estimates of the cold and warm water route contributions can be partially explained by the use of different data sets and methods, as well as the use of coarse-resolution models (Donners & Drijfhout, 2004;Rühs et al, 2019) The majority of these past studies have addressed the contributions of the cold and warm water routes from a modeling perspective, either in the Eulerian or Lagrangian framework.…”

Regional‐scale patterns of deep seafloor biodiversity for conservation assessment

“…Although meso‐scale direction and velocity of currents at lower bathyal and abyssal depths are less well known, they form part of the thermohaline global meridional overturning circulation. Cold (~1°C) and oxygen‐rich Antarctic Bottom Water flows northwards across southern seafloors where it eventually diffuses into shallower waters to form deoxygenated but more saline Indian and Pacific Deep Waters which return southwards (~2,000 m at 40°S) to upwell in the Southern Ocean (Lee et al, ; Talley, ). Water masses in the North Atlantic have been shown to be spatially dynamic at decadal (Yasuhara et al, ) to millennial temporal scales (Yasuhara, Hunt, Cronin, & Okahashi, ).…”

“…In the Tasman Sea, the same water mass enters via two routes, from the SE as eddies and from the north as a current, where AAIW in the SW Pacific has become entrained by the East Australian Current (Davis, 2005;Ollitrault & de Verdiére, 2013). Although Deep Waters which return southwards (~2,000 m at 40°S) to upwell in the Southern Ocean (Lee et al, 2019;Talley, 2013). Water masses in the North Atlantic have been shown to be spatially dynamic at decadal (Yasuhara et al, 2019) to millennial temporal scales (Yasuhara, Hunt, Cronin, & Okahashi, 2009).…”