Abstract
The Atlantic Meridional Overturning Circulation (AMOC) is a tipping component of the climate system, with a quasi-global impact. Several numerical and observational studies emphasized two modes of AMOC variability, characterized by two distinct Atlantic sea surface temperature patterns. One is associated with centennial changes, the Trend Mode, and the other with the Atlantic Multidecadal Oscillation (AMO). The origin of the different manifestations of these modes it is not fully understood. Using observational data and an ocean general circulation model we present evidence that, whereas the Trend Mode is mainly linked with deep water formation in the Nordic Seas and with a North Atlantic AMOC cell centered at 50° N, AMO is related with deep water formation in the Labrador and Irminger Seas and with an overturning cell centered at 20° N. In combination with previous studies, these results imply that a main route of increasing atmospheric CO2 concentration influence on AMOC passes through deep water formation in the Nordic Seas and it is reflected in a subpolar North Atlantic meridional cell.
Highlights
The Atlantic Meridional Overturning Circulation (AMOC) is one of the major tipping elements of the climate system (Buckley and Marshall 2016; Lenton et al 2008)
Whereas the centennial Trend Mode (TM) is associated with NSDWF, Atlantic Multidecadal Oscillation (AMO) is essentially linked with LISDWF
While changes in NSDWF are reflected in North Atlantic through an overturning cell centered at 50° N, variations in LISDWF is linked with an AMOC cell centered at 20° N
Summary
The Atlantic Meridional Overturning Circulation (AMOC) is one of the major tipping elements of the climate system (Buckley and Marshall 2016; Lenton et al 2008). Decadal and centennial Atlantic overturning variations are thought to originate from subpolar regions, in response to time varying deep water formation (Zhang 2010) and buoyancy forcing (Yeager and Danabasoglu 2014). These processes manifest in localized regions with deep convective mixing, like the Labrador and Irminger Sea (Labrador Irminger Seas Deep Water Formation—LISDWF) (Jungclaus et al 2005; Kuhlbrodt et al 2007) and the Nordic Seas (Nordic Seas Deep Water Formation— NSDWF) (Langehaug et al 2012). Disruptions of deep convection in these regions can induce large changes of the Atlantic overturning (Zhang and Delworth 2005; Zhang et al 2011)
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