Seafloor bathymetric data acquired with modern swath echo sounders provide coverage for only a small fraction of the global seabed yet are of high value for studies of the dynamic processes of seafloor volcanism, tectonics, mass wasting, and sediment transport that create and shape the undersea landscape. A new method for compilation of global seafloor bathymetry that preserves the native resolution of swath sonars is presented. The Global Multi‐Resolution Topography synthesis consists of a hierarchy of tiles with digital elevations and shaded relief imagery spanning nine magnification doublings from pole to pole (http://www.marine-geo.org/portals/gmrt). The compilation is updated and accessible as surveys are contributed, edited, and added to the tiles. Access to the bathymetry tiles is via Web services and with WMS‐enabled client applications such as GeoMapApp®, Virtual Ocean, NASA World Wind®, and Google Earth®.

[1] A time-series composed of 156 ASTER derived Digital Elevation Models (DEMs) and a radar-penetration-bias corrected version of the Shuttle Radar Topography Mission (SRTM) DEM is used to derive ice surface height and volume changes at the Southern Patagonian Ice Field (SPI) in southern South America. The observations, made between February 2000 and March 2012, indicate that the ice field is rapidly losing volume at many of the largest outlet glaciers, and in most cases thinning extends to the highest elevations of the ice field. Mass loss is occurring at a rate of À20.0 AE 1.2 Gt a À1, which, when summed with mass-loss at the adjacent Northern Patagonian Ice Field results in a combined rate of À24.4 AE 1.4 Gt a À1, equivalent to +0.067 AE 0.004 mm a À1 of sea level rise. Our decade-long mass loss rates are substantially higher than those derived during the last three decades of the 20th century, but are in good agreement with recent GRACE observations. Our volume loss estimate is sensitive to constraints applied to the amount of thickening in the accumulation zone. New field measurements and a continued DEM time-series will be required to refine our estimates. Citation: Willis, M.

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ABSTRACT. We study the evolution of the Juneau Icefield, one of the largest icefields in North America (>3700 km 2 ), using the Parallel Ice Sheet Model (PISM