AGU member since 1989. Vinton Professor of Earth and Environmental Engineering (1999), professor of Earth and environmental sciences (1993), associate director and director of research, the Earth Institute at Columbia University, New York. Senior research staff member, Lamont-Doherty Earth Observatory (1993). Major interests include physical and tracer oceanography, air/sea gas exchange, transport and mixing in rivers and estuaries, dating of young groundwater, and paleoclimate. Ph.D. in physics, University of Heidelberg (1985); assistant professor, University of Heidelberg (1986–1989); associate professor, Columbia University (1989–1992). Chair, Department of Earth and Environmental Engineering (2000–2003). Member, American Geophysical Union, American Association for the Advancement of Science, the Oceanography Society, and European Geophysical Union. Past member of the steering committees of the World Ocean Circulation Experiment, the Climate Variability and Predictability Program, the Surface Ocean Lower Atmosphere Study, and the Joint Scientific Committee of the World Climate Research Program. Past member of National Academy of Science panels on the International Polar Year and the Arctic Observing Network. Past cochair of two Arctic Research Commission/NSF Working Groups on Arctic Research Support and Logistics. Present chair of the science steering committee of the Study of Environmental Arctic Change and member of the science steering group of the International Study of Arctic Change. One hundred thirty-three refereed publications, 42 in AGU journals/monographs. Editor in Chief, Journal of Geophysical Research—Oceans (1999–2002); AGU Ocean Sciences section Executive Committee member (2000–2004). AGU meeting session convener; organizer, Ewing Symposium on Tracers in the Ocean (1995). Vetleson Fellow and visiting professor, University of Washington, Seattle (1994). Elected Fellow of the AGU (2007).