Our synthesis would have been impossible without the stimulating environment aboard JOIDES Resolution provided by the frequent arrival of spectacular core and the care with which observations were made on it. The ship's officers and crew, and particularly the rig crew, ensured the former, and the scientific parties of Legs 118 and 176 provided the latter. We are also indebted to the Shipboard Scientific Parties for a great deal of the intellectual substance of our synthesis. We are especially indebted to the co-chief scientists of Leg 118, Richard Von Herzen and Paul Robinson, for their many considerations over the years. Peter Meyer, H.R. Naslund, and an anonymous reviewer commented extensively on the manuscript, to its great benefit.