Where do we measure?
Numerical and analytical model studies indicate that higher latitudes (32-35S) are the best location for a trans-basin MOC array for several reasons. First and foremost, higher latitudes provide larger dynamic range in the zonal density gradients, leading to improved signal-to-noise characteristics for geostrophic velocity calculations. Second, ocean model studies indicate that at higher latitudes it is possible to utilize less expensive mooring technologies, such as pressure equipped inverted echo-sounders (PIES), reducing the cost of the overall measurements. Third, measurement of the stability of the MOC, a function of the baroclinic salt flux, can best be measured at the southern boundary of the Atlantic, nominally along 34.5S. Following the community recommendation that a SAMOC monitoring array be located at 32-35S, a trans-basin array is being established along 34.5S. The array includes 20-30 deep ocean moorings, a combination of tall moorings and pressure-equipped inverted echo sounders, coupled with several shorter direct velocity moorings on the shelf on either side of the basin. Funds are also being sought to augment the trans-basin array through the addition of more moored instruments, for example to better sample transport streams by the different water masses on the western boundary continental shelf and slope.