Lamont-Doherty Earth Observatory of Columbia University, 61 Rte. 9W, Palisades, NY 10964, USA
Lamont-Doherty Earth Observatory of Columbia University, 61 Rte. 9W, Palisades, NY 10964, USA; British Antarctic Survey, High Cross, Madingly Rd., Cambridge, NJ 07675 United Kingdom
Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968, USA
Department of Geophysics, University of Copenhagen, Copenhagen, NJ 07675 Denmark