This research was supported by the National Science Foundation through grants to the Universities of Texas, Hawaii, and California at Santa Cruz. Additional support was provided by the Science and Technology Agency of Japan through the Geological Survey of Japan, Ocean Research Institute of the University of Tokyo, and Japan Marine Science and Technology Center. We thank Andy Goodliffe and Casey Moore for helpful reviews of the manuscript. Masako Sugimoto helped with the bathymetry processing. SOEST contribution number 5312; UTIG contribution number 1541.