Decadal Response of Global Overturning to Southern Ocean Wind Stress Perturbation

A substantial component of the deep global meridional overturning circulation appears to be driven by Westerly wind stress over the Southern Ocean. This wind stress is believed to vary over a range of timescales, including decadal oscillations and longer trends associated with global change. How is this variability likely to affect the global overturning? How quickly can overturning changes propagate away from the Southern Ocean? What spatial distribution would these changes have? Numerical experiments investigate the timescales and the spatial patterns associated with idealized wind perturbations. The experiments show that the volume transport anomaly associated with the strengthened Westerlies takes about 10 yr to reach near-full strength in the entire southern hemisphere, but continues to grow vigorously for at least 80 yr in the northern hemisphere. In steady state, the largest remote effect of the wind is thought to be in the Atlantic, but on decadal timescales, the volume transport anomaly is bigger in the Indo-Pacific. The horizontal thermocline circulation patterns associated with the overturning anomalies consist of broad flow exiting the wind perturbation belt, which feed western boundary currents over much of the Southern Hemisphere, which in turn feed cyclonic gyres in the northern North Atlantic and North Pacific. Implications of the patterns of variability for large-scale ocean observations are discussed.