Journal Article

Distinct sources of interannual subtropical and subpolar Atlantic overturning variability

Johnson, Helen L., Heimbach, Patrick, Holliday, N. Penny, Kostov, Yavor, Li, Feili, Pillar, Helen R., Marshall, David P., Lozier, M. Susan, Smith, Timothy, Forget, Gael

2021

Overview

The Atlantic meridional overturning circulation (AMOC) is pivotal for regional and global climate due to its key role in the uptake and redistribution of heat and carbon. Establishing the causes of historical variability in AMOC strength on different timescales can tell us how the circulation may respond to natural and anthropogenic changes at the ocean surface. However, understanding observed AMOC variability is challenging because the circulation is influenced by multiple factors that co-vary and whose overlapping impacts persist for years. Here we reconstruct and unambiguously attribute intermonthly and interannual AMOC variability at two observational arrays to the recent history of surface wind stress, temperature and salinity. We use a state-of-the-art technique that computes space- and time-varying sensitivity patterns of the AMOC strength with respect to multiple surface properties from a numerical ocean circulation model constrained by observations. While, on interannual timescales, AMOC variability at 26° N is overwhelmingly dominated by a linear response to local wind stress, overturning variability at subpolar latitudes is generated by the combined effects of wind stress and surface buoyancy anomalies. Our analysis provides a quantitative attribution of subpolar AMOC variability to temperature, salinity and wind anomalies at the ocean surface. Wind stress controls annual variations in the Atlantic meridional overturning circulation at mid-latitudes, while surface buoyancy also matters at subpolar latitudes, according to an attribution analysis using a numerical model constrained by observational array data.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/106/694/1108 / 704/106/829/2737 / Annual variations / Anomalies / Anthropogenic changes / Anthropogenic factors / Arrays / Atlantic Meridional Overturning Circulation (AMOC) / Buoyancy / Circulation / Earth and Environmental Science / Earth Sciences / Earth System Sciences / Geochemistry / Geology / Geophysics/Geodesy / Global climate / Human influences / Local winds / Mathematical analysis / Mathematical models / Numerical models / Ocean circulation / Ocean circulation models / Ocean currents / Ocean models / Ocean surface / Oceans / Regional climates / Salinity / Salinity effects / Surface properties / Surface wind / Temperature / Uptake / Variability / Water circulation / Wind effects / Wind stress