University of Cambridge, United Kingdom

The global ocean is a major heat reservoir, and therefore a significant determinant of world climate. Two engine rooms drive modern ocean circulation, and thus redistribute this heat. The first is located in the North Atlantic Ocean, where dense saline surface waters sink to form south-flowing North Atlantic Deep Water (NADW). The second lies in the Southern Ocean, where the westerly wind belts force the massive seafloor-to-sea surface Antarctic Circumpolar Current (ACC), within which NADW becomes entrained. As parts of the global thermohaline ocean circulation system these engine rooms are linked by other major current flows, one of which is the Pacific Deep Western Boundary Current (DWBC). The sites drilled on ODP Leg 181 were selected to provide sediment core, and thus ocean history, from beneath the largest single input of deep, cold water into the modern global ocean, the Pacific DWBC.