1. Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA
2. Scripps Institution of Oceanography, University of California–San Diego, 9500 Gilman Drive, La Jolla, California 92037, USA
3. Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, USA
4. Institut de Ciencies del Mar, Consejo Superior de Investigaciones Cientificas, Passeig Maritim de la Barceloneta, 37-49, 08003 Barcelona, Spain