No Consistent Simulated Trends in the Atlantic Meridional Overturning Circulation for the Past 6,000 Years

Abstract

The Atlantic Meridional Overturning Circulation (AMOC, Rahmstorf, 2006) is a large-scale ocean circulation that helps transport heat poleward moderating the climate of Europe and eastern North America (Cherchi, 2019). Direct observations of it only became available in 21st century, and show a noticeable weakening (Smeed et al., 2018) that is not captured in full by climate models (Weijer et al., 2020), potentially because it arises from natural variability. Despite this, the IPCC Assessment Report 6 projects a further weakening in AMOC strength with high confidence (Fox-Kemper et al., 2021), although the magnitude remains uncertain. Evaluating the response of models to past variations in boundary conditions (such as orbital configuration and greenhouse gases levels, ice sheet extent) against proxy-derived reconstructions of the AMOC can potentially help constrain the uncertainty in future projections (Kageyama et al., 2018).The Holocene Epoch (roughly the past 12,000 years) saw gradual changes in the seasonal cycle of incoming solar radiation caused by changes in the orbital configuration (Braconnot et al., 2019;Otto-Bliesner et al., 2017). There were also decreasing greenhouse gases (GHG; CO 2 , CH 4 , and N 2 O) concentrations, followed by an increase that

Orbitally forced and internal changes in West African rainfall interannual-to-decadal variability for the last 6000 years

“…1 b). The AMO cooling trend is in line with a gradual weakening of the AMOC during the Holocene suggested by some studies (Thornalley et al 2018 ; Caesar et al 2021 ; Jomelli et al 2022 ), but at odds with Jiang et al ( 2023 ) who found no consistent trend in overall AMOC strength during the mid-to-late Holocene in an ensemble of nine transient simulations. Furthermore, none of the four simulations have abrupt changes in the AMO at the interannual-to-decadal timescale, although there are multi-centennial modulations in the interannual-to-decadal variability of the AMO that clearly influence WAMR variability (Fig.…”