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

CUNNINGHAM, S. A.; KANZOW, T.; HIRSCHI, J.; JOHNS, W. E.; BARINGER, M. O.; MEINEM, C. S.; CHIDICHIMO, M. P.; ATKINSON, C.; COLLINS, J.

Edinburgo

Congreso; RAPID annual meeting 2009; 2009

Natural Environment Research Council

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 Strait 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 Ridgeand across the African continental slope. The AMOC strength is 18.5±4.9 Sv and has substantial subseasonal and seasonal variability. Fluctuations in Gulf Stream, Ekman and mid-ocean transports are independent 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 mid-ocean, dominating fluctuations of the AMOC. However, the seasonal variance (periods > 180 days) of both the Gulf Stream and mid-ocean transports exceed the Ekman transport variance, 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. A strong seasonal cycle in eastern boundary densities from the surface to 1000 dbar dominates the upper mid-ocean seasonal cycle and appears to be driven by seasonal variations of the eastern boundary wind stress curl.