Where is the southern Mariana Trough?

Susan and I are leaving tomorrow for our cruise to the southern Mariana Trough. This region is a back-arc spreading center - the back-arc of the Mariana Arc and the Mariana Trench, where the Pacific Plate is subducting under the Phillipine Plate. You can learn more about the geophysics in this region in a recent paper by Becker et al. (2010) Geochem. Geophys. Geosyst., 11, Q04X13, doi:10.1029/2009GC002719. The southern Mariana back-arc was recently listed as a region of "highest international priority" for hydrothermal studies by the InterRidge Working Group on Long-Range Exploration (http://www.interridge.org/WG/Exploration).