Abstract/Summary

The temporal variability of the Atlantic Meridional Overturning Circulation (AMOC) 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 10 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 western and eastern boundaries at 26N reveals ~2-3 years lags between boundaries 15 along deeper levels (2600-3000m). Record lengths of more than 26 years are required at the WB to allow the buoyancy forced signals to appear in as the dominant EOF mode. Results suggest that the depth structure of the signals, and the lagged covariances between the boundaries at 26N, may both provide useful information for detecting propagating signals of high latitude origin in more complex models, and potentially in the observational RAPID array. However, time filtering may be needed, together with the continuation of the RAPID program in order to extend the time period.