Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review

Abstract

This is a review about the Atlantic Meridional Overturning Circulation (AMOC), its mean structure, temporal variability, controlling mechanisms, and role in the coupled climate system. The AMOC plays a central role in climate through its heat and freshwater transports. Northward ocean heat transport achieved by the AMOC is responsible for the relative warmth of the Northern Hemisphere compared to the Southern Hemisphere and is thought to play a role in setting the mean position of the Intertropical Convergence Zone north of the equator. The AMOC is a key means by which heat anomalies are sequestered into the ocean's interior and thus modulates the trajectory of climate change. Fluctuations in the AMOC have been linked to low-frequency variability of Atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses. On intra-annual timescales, variability in AMOC is large and primarily reflects the response to local wind forcing; meridional coherence of anomalies is limited to that of the wind field. On interannual to decadal timescales, AMOC changes are primarily geostrophic and related to buoyancy anomalies on the western boundary. A pacemaker region for decadal AMOC changes is located in a western "transition zone" along the boundary between the subtropical and subpolar gyres. Decadal AMOC anomalies are communicated meridionally from this region. AMOC observations, as well as the expanded ocean observational network provided by the Argo array and satellite altimetry, are inspiring efforts to develop decadal predictability systems using coupled atmosphere-ocean models initialized by ocean data.

The climate of the Common Era off the Iberian Peninsula

“…Frankcombe et al (2010) propose that the AMO is dominated by two main timescales: 20-30 years associated with the AMOC (Atlantic Meridional Overturning Circulation), and so of ocean-internal origin, and 50-70 years related to the atmospheric exchange between the Atlantic and the Arctic Ocean. More recently, Buckley and Marshall (2016) revised the periodicities shown by various instrumental and proxy records and grouped them into decadal (20 years) and multidecadal (±40-70 years) and showed a statistical significance for the 70-year periodicity, supporting the notion that ocean dynamics play a significant role in the variability in European climate on multi-decadal timescales (Yamamoto and Palter, 2016;Zhang, 2007). To investigate the influence of the AMO on the weather regime over the Atlantic Iberian Peninsula, we performed wavelet analysis on our SST and [n-alk] records (Figs.…”

Development of a probabilistic ocean modelling system based on NEMO 3.5: application at eddying resolution

“…Buckley and Marshall, 2016), and is being monitored at 26.5 • N since 2004 by the RAPID array (e.g. Johns et al, 2008).…”

Historical Climate off the Atlantic Iberian Peninsula

“…More recently, (Buckley and Marshall, 2016), revise the periodicities shown by various instrumental and proxy records, group them into decadal (20 yr) and multidecadal (± 40-70 yr), and present results with statistical significance support for the 70 yr periodicity. Additionally, the authors support (Zhang, 2007 ) 15 and (Yamamoto and Palter, 2016), in that on decadal and multi-decadal time scale, ocean dynamics does play a role in the European climate variability.…”

“…Although the existence of salinity anomalies in the northern Atlantic are defended by many model 5 studies as a prerequisite for AMOC intensification (Buckley and Marshall, 2016), some modeling studies emphasize the need for a weakening of the subtropical and subpolar gyres (Häkkinen et al, 2011;Häkkinen et al, 2013), to allow for a greater penetration of warm subtropical waters into the subpolar gyre (e.g (Danabasoglu et al, 2012)). According to (Häkkinen et al, 2011), the mean gyre strength is driven by changes in the wind stress curl that in turn is associated with changes in blocking 10 between Greenland and Western Europe.…”