A new bed elevation model for the Weddell Sea sector of the West Antarctic Ice Sheet

We present a new bed elevation digital elevation model (DEM), with a 1 km spatial resolution, for the Weddell Sea sector of the West Antarctic Ice Sheet. The DEM has a total area of ~125,000 km2 covering the Institute, Möller and Foundation ice streams and the Bungenstock ice rise. In comparison with the Bedmap2 product, our DEM includes several new aerogeophysical datasets acquired by the Center for Remote Sensing of Ice Sheets (CReSIS) through the NASA Operation IceBridge (OIB) program in 2012, 2014 and 2016. We also update bed elevation information from the single largest existing dataset in the region, collected by the British Antarctic Survey (BAS) Polarimetric Airborne Survey Instrument (PASIN) in 2010-11, as BEDMAP2 included only relatively crude ice thickness measurements determined in the field for quality control purposes. This have resulted in the deep parts of the topography not being visible in the fieldwork non-SAR processed radargrams. While the gross form of the new DEM is similar to Bedmap2, there are some notable differences. For example, the position and size of a deep trough (~ 2 km below sea level) between the ice sheet interior and the grounding line of Foundation ice stream has been redefined. From the revised DEM, we are able to better derive the expected routing of basal water at the ice-bed interface, and by comparison with that calculated using Bedmap2 we are able to assess regions where hydraulic flow is sensitive to change. Given the sensitivity of this sector of the ice sheet to ocean-induced melting at the grounding line, especially in light of improved definition of the Foundation ice stream trough, our revised DEM will be of value to ice-sheet modelling in efforts to quantify future glaciological changes in the region, and therefore the potential impact on global sea level. The new 1 km bed elevation product of the Weddell Sea sector, West Antarctica can be found in the http://doi.org/10.5281/zenodo.1035488

Evidence of an active volcanic heat source beneath the Pine Island Glacier

Tectonic landforms reveal that the West Antarctic Ice Sheet (WAIS) lies atop a major volcanic rift system. However, identifying subglacial volcanism is challenging. Here we show geochemical evidence of a volcanic heat source upstream of the fast-melting Pine Island Ice Shelf, documented by seawater helium isotope ratios at the front of the Ice Shelf cavity. The localization of mantle helium to glacial meltwater reveals that volcanic heat induces melt beneath the grounded glacier and feeds the subglacial hydrological network crossing the grounding line. The observed transport of mantle helium out of the Ice Shelf cavity indicates that volcanic heat is supplied to the grounded glacier at a rate of ~ 2500 ± 1700 MW, which is ca. half as large as the active Grimsvötn volcano on Iceland. Our finding of a substantial volcanic heat source beneath a major WAIS glacier highlights the need to understand subglacial volcanism, its hydrologic interaction with the marine margins, and its potential role in the future stability of the WAIS

Basal terraces on melting ice shelves

Ocean waters melt the margins of Antarctic and Greenland glaciers, and individual glaciers' responses and the integrity of their ice shelves are expected to depend on the spatial distribution of melt. The bases of the ice shelves associated with Pine Island Glacier (West Antarctica) and Petermann Glacier (Greenland) have similar geometries, including kilometer-wide, hundreds-of-meter high channels oriented along and across the direction of ice flow. The channels are enhanced by, and constrain, oceanic melt. New meter-scale observations of basal topography reveal peculiar glaciated landscapes. Channel flanks are not smooth, but are instead stepped, with hundreds-of-meters-wide flat terraces separated by 5-50m high walls. Melting is shown to be modulated by the geometry: constant across each terrace, changing from one terrace to the next, and greatly enhanced on the ∼45° inclined walls. Melting is therefore fundamentally heterogeneous and likely associated with stratification in the ice-ocean boundary layer, challenging current models of ice shelf-ocean interactions. Key Points Basal topography of melting ice shelves is complex Basal terraces appear ubiquitous under melting ice shelves Melting concentrates on walls between terraces © 2014. American Geophysical Union. All Rights Reserved