CONTINENTAL RUNOFF AND EARLY CENOZOIC BOTTOM-WATER SOURCES

The dominance of warm saline bottom water during the mid-Cretaceous an d the early Cenozoic has been inferred from sea-floor sediment records , an interpretation supported by early ocean general circulation model experiments. Thermohaline circulation depends in part on upper ocean salinities; however, early ocean models neglected continental runoff, a potentially critical factor in the salinity budget of the surface oc ean. Our early Eocene ocean model sensitivity tests show that model de ep-water sources can be enhanced, diminished, or turned off by varying the treatment of continental runoff in the atmosphere-ocean moisture flux calculation, Failure to treat surface runoff adequately thus has important implications for the simulation of thermohaline flow and for mation of warm saline bottom water. Variations in runoff could have le d to rapid changes in the relative importance of high-latitude versus subtropical deep water such as may have occurred during the late Paleo cene-early Eocene boundary interval (similar to 53.6-56.2 Ma).