There is more to heat transport in Atlantic waters than the vagaries of tropical trade winds and the Gulf Stream's warm northward flow . That's why an ambitious initiative has been instrumenting the ocen depths along the 26th parallel to measure the sum of the heat flow. That means measuring masses of water- flows so large that they are reckoned in millions of tons per second.Reviewing this research in Science this week ,Australian climate researcher John A. Church has laid another wild card on the high stakes climate policy table: the mass and heat flow is anything but steady --it varies by a factor of ~2 :
On time scales of 15 days and longer, the sum of transports into the North Atlantic should be about zero. Indeed, the observations reported by Kanzow et al. indicate that the sum varies with a root-mean-square value of only 3.4 Sverdrup (1 Sv = 106 m3/s), slightly larger than the expected measurement errors of 2.7 Sv, thus demonstrating the remarkable effectiveness of the array. The fact that the observed sum varies slightly more than the expected measurement errors presumably reflects deficiencies in the method, such as the unobserved flow deeper than the deepest part of the array and the impact of the Mid-Atlantic Ridge.
Cunningham et al. report a year-long average meridional overturning circulation of 18.7 ± 5.6 Sv (3), but with large variability ranging from 4.4 to 35.3 Sv over the course of the year.