Digital.CSIC. Repositorio Institucional del CSIC

oai:digital.csic.es:10261/360542

19 pages, 11 figures, 4 tables.-- This work is distributed under the Creative Commons Attribution 4.0 License, The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the Earth's climate. However, there are few long time series of observations of the AMOC, and the study of the mechanisms driving its variability depends mainly on numerical simulations. Here, we use four ocean circulation estimates produced by different data-driven approaches of increasing complexity to analyse the seasonal to decadal variability of the subpolar AMOC across the Greenland–Portugal OVIDE (Observatoire de la Variabilité Interannuelle à DÉcennale) line since 1993. We decompose the MOC strength variability into a velocity-driven component due to circulation changes and a volume-driven component due to changes in the depth of the overturning maximum isopycnal. We show that the variance of the time series is dominated by seasonal variability, which is due to both seasonal variability in the volume of the AMOC limbs (linked to the seasonal cycle of density in the East Greenland Current) and to seasonal variability in the transport of the Eastern Boundary Current. The decadal variability of the subpolar AMOC is mainly caused by changes in velocity, which after the mid-2000s are partly offset by changes in the volume of the AMOC limbs. This compensation means that the decadal variability of the AMOC is weaker and therefore more difficult to detect than the decadal variability of its velocity-driven and volume-driven components, which is highlighted by the formalism that we propose, This work received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 862626 (EUROSEA), the French national programme Les Enveloppes Fluides et l'Environnement (LEFE) and Ifremer. Herlé Mercier was supported by the Centre National de La Recherche Scientifique (CNRS). Fiz F. Pérez and Antón Velo were supported by the BOCATS2 (PID2019-104279GB-C21) project funded by MCIN/AEI/10.13039/501100011033 and, together with Pascale Lherminier, by the EuroGO-SHIP project (Horizon Europe #101094690). Marcos Fontela was supported by grant PTA2022-021307-I funded by MCIN/AEI/10.13039/501100011033, by European Social Fund Plus, and by the Portuguese Foundation for Science and Technology through projects UIDB/04326/2020, UIDP/04326/2020, LA/P/0101/2020, and CEECINST/00114/2018, Peer reviewed