Can the boundary profiles at 26N be used to extract buoyancy-forced AMOC signals?

• Main Authors: Polo, Irene, Robson, Jon, Haines, Keith, Thomas, Christopher
• Format: Text
• Language: English
• Published: 2020
• Subjects: Nordic Seas; North Atlantic Deep Water; North Atlantic
• Online Access: https://doi.org/10.5194/os-2020-8; https://os.copernicus.org/preprints/os-2020-8/

The AMOC circulation is driven both by direct wind stresses and by the buoyancy-driven formation of North Atlantic Deep Water over the Labrador and Nordic Seas. In many models low frequency density variability down the western boundary of the Atlantic basin is linked to changes in the buoyancy forcing over the Atlantic Sub-Polar Gyre (SPG) region, and this is found to explain part of the geostrophic AMOC variability at 26N. In this study, using different experiments with an OGCM, we develop statistical methods to identify characteristic vertical density profiles at 26N at the western and eastern boundaries which relate to the buoyancy-forced AMOC. We show that density anomalies due to anomalous buoyancy forcing over the SPG propagate equatorward along the western Atlantic boundary, through 26N, and then eastward along the equator, and poleward up the eastern Atlantic boundary. The timing of the density anomalies appearing at the eastern and western boundaries at 26N reveals a propagation speed leading to ~ 2–3 years lags between boundaries with maxima along deeper levels (2600–3000 m). Time record required to capture those vertical density profiles in the model is ~ 26 years. Results suggest that depth structure, and the lagged covariances between the boundaries at 26N, may both provide useful information for detecting density anomalies of high latitude origin in more complex models, and potentially in the observational RAPID array. However, time filtering will be required together with the continuation of the RAPID program in order to extend the time period.