Atlantic Meridional Overturning Circulation reconstructions and instrumentally observed multidecadal climate variability: A comparison of indicators

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) has an important role in the Earth's climate system, but it remains unclear how the instrumentally observed multidecadal variability of the Earth's climate is related to the AMOC. We carried out a comprehensive evaluation of five representative indicators of the AMOC, including one atmospheric index based on the effect of accumulated atmospheric forcing on the AMOC and four oceanographic indices using surface and subsurface oceanographic variables in the North Atlantic Ocean. We compared reconstructions of the AMOC against measurement records and analysed the relationships with the multidecadal variability of the annual mean surface air temperature anomalies over the North Atlantic, Northern Hemisphere and South Atlantic. All the AMOC indicators show a weakening trend during the most recent decade, which is in good agreement with the RAPID measurement record of the AMOC. Besides, the atmospheric reconstruction shows the best agreement with the observed low-frequency variation in the AMOC since 2004. The multidecadal variability in hemispheric/ regional surface temperatures is closely related to all the AMOC reconstructions and opposite relationships are observed between the North Atlantic and South Atlantic oceans. The multidecadal surface air temperature anomalies associated with the variations in the AMOC are most pronounced for the atmospheric reconstruction index, which leads the variations in the surface air temperature by 4-5 years. Among the oceanographic indicators, the reconstructions using subsurface oceanographic variables performed best in terms of the relationship with the variations in the multidecadal surface air temperature.

Climate as a complex, self-regulating system

“…AMOC is usually seen as influencing the AMO (Marini and Frankignoul, 2014;Zhang et al, 2019) but two-way oscillatory relationships have been observed in model studies (Zhang and Wang, 2013;Kim et al, 2021). The recent changes in a range of surface variables that show a relationship between Atlantic multidecadal variability and AMOC are consistent with recent direct estimates of AMOC flow volumes (Sun et al, 2021).…”

“…If considered as part of a self-regulating complex system, this role becomes even more important. The AMO is understood to be linked to AMOC (Kim et al, 2021;Sun et al, 2021) and telecommunicates with the northern and tropical Pacific (Sun et al, 2017).…”

The Pacific Ocean heat engine

“…AMOC is generally seen as influencing the AMO (Marini and Frankignoul, 2014;Zhang et al, 2019) but two-way oscillatory relationships have been observed in model studies (Kim et al, 2021) including CMIP5 models (Zhang and Wang, 2013). The recent changes in a range of surface variables that show a relationship between Atlantic multidecadal variability and AMOC are consistent with recent direct estimates of AMOC flow volumes (Sun et al, 2021). The stability of AMOC is very much a matter of debate, but simple and intermediate models produce abrupt phase transitions (Dijkstra, 2019;Johnson et al, 2019), while more complex models produce a wide range of responses, showing high sensitivity to the background state (Johnson et al, 2019).…”

Linking AMOC Variations With the Multidecadal Seesaw in Tropical Cyclone Activity Between Eastern North Pacific and Atlantic

“…It is also suggested that the AMOC has profound influences on the multidecadal changes in the Atlantic basin and adjacent areas via anomalous ocean heat transport (Buckley & Marshall, 2016; Trenberth & Caron, 2001). It has been pointed out that the NAO forces the AMOC, transporting heat across the Atlantic basin, and eventually affects the surface air temperature and precipitation anomalies on multidecadal time scales (Sun et al., 2020; J. Zhang et al., 2021). Since the Atlantic hurricanes are favored by warm SST associated with positive ocean heat transport (R. Zhang et al., 2019), the AMOC and TC activity are thus closely related.…”