We present Bedmap2, a new suite of gridded products describing surface elevation, ice-thickness and the seafloor and subglacial bed elevation of the Antarctic south of 60° S. We derived these products using data from a variety of sources, including many substantial surveys completed since the original Bedmap compilation (Bedmap1) in 2001. In particular, the Bedmap2 ice thickness grid is made from 25 million measurements, over two orders of magnitude more than were used in Bedmap1. In most parts of Antarctica the subglacial landscape is visible in much greater detail than was previously available and the improved data-coverage has in many areas revealed the full scale of mountain ranges, valleys, basins and troughs, only fragments of which were previously indicated in local surveys. The derived statistics for Bedmap2 show that the volume of ice contained in the Antarctic ice sheet (27 million km³) and its potential contribution to sea-level rise (58 m) are similar to those of Bedmap1, but the mean thickness of the ice sheet is 4.6% greater, the mean depth of the bed beneath the grounded ice sheet is 72 m lower and the area of ice sheet grounded on bed below sea level is increased by 10%. The Bedmap2 compilation highlights several areas beneath the ice sheet where the bed elevation is substantially lower than the deepest bed indicated by Bedmap1. These products, along with grids of data coverage and uncertainty, provide new opportunities for detailed modelling of the past and future evolution of the Antarctic ice sheets

Digital elevation models of the Northern and Southern Patagonia Icefields of South America generated from the 2000 Shuttle Radar Topography Mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers. During the period 1968/1975–2000, these glaciers lost ice at a rate equivalent to a sea level rise of 0.042 ± 0.002 millimeters per year. In the more recent years 1995–2000, average ice thinning rates have more than doubled to an equivalent sea level rise of 0.105 ± 0.011 millimeters per year. The glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation, and their contribution to sea level per unit area is larger than that of Alaska glaciers.

Abstract:We use meteorological data from two automatic weather stations (AWS) on Juncal Norte Glacier, central Chile, to investigate the glacier-climate interaction and to test ablation models of different complexity. The semi-arid Central Andes are characterized by dry summers, with precipitation close to zero, low relative humidity and intense solar radiation. We show that katabatic forcing is dominant both on the glacier tongue and in the fore field, and that low humidity and absence of clouds cause strong radiative cooling of the glacier surface. Surface albedo is basically constant for snow and ice, because of the scarcity of solid precipitation. The energy balance of the glacier is simulated for a 2-month period in austral summer using two models of different complexity, which differ in the inclusion of the heat conduction flux into the snowpack and in the parameterization of the incoming longwave radiation. Net shortwave radiation is the dominant component of the energy balance. The sensible heat flux is always positive, while both the net longwave radiation and latent heat flux are negative. Neglecting the subsurface heat flux and corresponding variations in surface temperature leads to an overestimation of ablation of 2% over a total of 3695 mm water equivalent (w.e.) at the end of the season. Correct modelling of incoming longwave radiation is crucial, and we suggest that parameterizations based on vapour pressure and air temperature should be used rather than on computed cloud amount. We also used an enhanced temperature-index model incorporating the shortwave radiation flux, which has two empirical parameters. We apply it both with values of parameters obtained for Alpine glaciers and recalibrated on Juncal Norte. The model recalibrated against the correct energy balance simulations performs very well. The model parameters respond to the meteorological conditions typical of this climatic setting.

Recent aircraft and satellite laser altimeter surveys of the Amundsen Sea sector of West Antarctica show that local glaciers are discharging about 250 cubic kilometers of ice per year to the ocean, almost 60% more than is accumulated within their catchment basins. This discharge is sufficient to raise sea level by more than 0.2 millimeters per year. Glacier thinning rates near the coast during 2002–2003 are much larger than those observed during the 1990s. Most of these glaciers flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.

No abstract

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971-2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years

Modern geoinformatic techniques allow the automated creation of detailed glacier inventory data from glacier outlines and digital terrain models (DTMs). Once glacier entities are defined and an appropriate DTM is available, several methods exist to derive the inventory data (e.g. minimum, maximum and mean elevation; mean slope and aspect) for each glacier from digital intersection of both datasets. Compared to the former manual methods, the new grid-based statistical calculations are very fast and reproducible. The major aim of this contribution is to help in standardizing the related calculations to enhance the integrity of the Global Land Ice Monitoring from Space (GLIMS) database. The recommendations were prepared by a working group and also contribute to the European Space Agency project GlobGlacier. The document follows the former UNESCO manual for the production of the World Glacier Inventory published in 1970, identifies the potential pitfalls, and describes the differences from the former methods of compilation. The online background material for this paper (see http://www.glims.org) contains example scripts for calculation of each parameter and will be updated when required.Recommendations for the compilation of glacier inventory data from digital sources

[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.