Sub-seasonal to seasonal variability of the Atlantic Meridional Overturning Circulation at 26.5N

KANZOW, T.; CUNNINGHAM, S.; JOHNS, W. E.; HIRSCHI, J.; MAROTZKE, J.; MEINEM, C. S.; BEAL, L. M.; ATKINSON, C.; CHIDICHIMO, M. P.; COLLINS, J.

Viena

Congreso; European Geosciences Union General Assembly 2009; 2009

A 3.5-year timeseries of the strength of the Atlantic meridional overturning circulation (AMOC) at 26.5°N is derived from the addition of four transport components: 1. Gulf Stream transports in Florida Straits inferred from cable measurements; 2. Ekman transports from wind stress measurements; 3. current meter measurements of the shallow and deep western boundary currents and; 4. mid-ocean transports inferred from mooring-based density measurements east of the Bahamas, on both flanks of the mid-Atlantic Ridge and across the African continental slope. The mean AMOC strength is 18.5 Sv, and the standard deviation of 4.9 Sv reflects substantial sub-seasonal and seasonal variability. Fluctuations in Gulf Stream, Ekman and mid-ocean transports are uncorrelated and so their variability translates directly into AMOC variability. The sub-seasonal variance (periods between 10 and 90 days) of the Ekman transport exceeds that of the Gulf Stream and the mid-ocean transport, dominating fluctuations of the AMOC. However, the seasonal variance (periods > 180 days) of both the Gulf Stream and the mid-ocean transport exceed that of the Ekman transport, dominating seasonal fluctuations of the AMOC. The amplitude of seasonal variations in the AMOC is ±4.2 Sv with maxima in early Autumn and minima in early Spring. The seasonal cycle in upper mid-ocean transport is dominated by a strong seasonal cycle in eastern boundary densities from the surface to 1000 dbar, which is a consequence of seasonal variations of the eastern boundary wind stress curl.