The South Pacific Bare Zone

The South Pacific is relatively unexplored and is almost devoid of digitally-acquired seismic reflection data. While surveying for an IODP cruise on R/V Melville in February-March 2005, we identified a region of zero sediment accumulation nearly two million square kilometers in area in the Southwest Pacific Basin. This South Pacific Bare Zone is bounded approximately between the Menard Fracture Zone and the Austral Islands, or 45 and 30 degrees South latitude, and between the Adventure Trough and the Pandora Trough, or roughly 130 and 142 degrees West longitude. Seismic profiles were acquired throughout the region via 3.5 kHz echo sounder and 150 cu. in. GI airgun. This 55 million year hiatus in sedimentation marks the slowest known accumulation of sediment anywhere in the world. There is no evidence for erosion within the Bare Zone. For example, we do not typically observe sediment in basins or asymmetric sediment piles along the margins of the zone. Furthermore, the overall size of the bare region is simply too large for erosion to account for the lack of sediment. Contributing factors for low marine sedimentation rates include low biological productivity, shallow CCD/deep crustal subsidence, minimal terrigenous input, and low input of hydrogenous/hydrothermal oxides. All of these conditions coincide within the boundaries of the South Pacific Bare Zone.