Anja Wendt

Influence of tides and tidal current on Mertz Glacier, Antarctica

Mertz Glacier, East Antarctica, is characterized by a 140 km long, 25 km wide floating ice tongue. In this paper, we combine a large number of remotely sensed datasets, including in situ global positioning system measurements, satellite radar al- timetry, airborne radio-echo sounding and satellite synthetic aperture radar imagery and interferometry. These various datasets allow us to study the interaction of the ice tongue with the tides and currents. However, the inverse barometer effect needs to be applied to sea-level variations affecting the tongue. We find that the tide-induced currents exert a small lateral pressure on the tongue which, when integrated over the large surface of the tongue, induce a flexure of up to 2 m amplitude per day. Simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections. In addition, the along-flow velocity of the tongue does vary daily from 1.9 to 6.8 m d � 1 depending on the tidal current.When the current pushes the tongue toward the eastern boundary of the fjord, the tongue is retarded by the drag and the velocity decreases. The accumulated stress is released, allowing the tongue to flow very rapidly when the current pushes the tongue westward. These forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving.

Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

Abstract Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

Reassessment of ice mass balance at Horseshoe Valley, Antarctica

Abstract Horseshoe Valley (80°18′S, 81°22′W) is a 30 km wide glaciated valley at the south-eastern end of Ellsworth Mountains draining into the Hercules inlet, Ronne Ice Shelf. The ice at Horseshoe Valley has been considered stable; now we use Global Positioning System (GPS) measurements obtained between 1996 and 2006 to investigate ice elevation change and mass balance. Comparison of surface heights on a profile across Horseshoe Valley reveals a slight but significant elevation increase of 0.04 m a-1 ± 0.002 m a-1. The blue ice area of Patriot Hills (∼13 km2) at the mount of Horseshoe Valley shows large interannual variability in area, with a maximum extent in 1997, an exceptionally warm summer, but no clear multi-year trend, and an elevation increase of 0.05 m a-1 in eight years, which agrees with the result from Horseshoe Valley.

Recent glacier changes in southern Chile and in the Antartic Peninsula

Se presenta una sintesis de la investigacion glaciologica reciente realizada por el Centro de Estudios Cientificos, CECS, en Chile y la Peninsula Antartica mediante el uso de una variedad de metodologias modernas, con el fin de detectar las tendencias de cambio experimentadas por los glaciares en las ultimas decadas.

The Patagonian ice fields: An updated assessment of sea level contribution

Climate Change: Global Risks, Challenges and Decisions IOP Conf. Series: Earth and Environmental Science 6 (2009) 012006 IOP Publishing doi:10.1088/1755-1307/6/1/012006 S01.06 The Patagonian ice fields: an updated assessment of sea level contribution Gino Casassa(1), W Krabill(2), A Rivera(0), J Wendt(1), A Wendt(1), P Lopez(1), F Bown(1), E Rignot(0), R Thomas(0), J Yungel(6), J Sonntag(6), E Frederick(6), R Russell(6), M Linkswiler(6), A Arendt(7), K Steffen(8) (1) CECS, Valdivia, Chile (2) Code 972, NASA-GSFC/WFF, Wallops Island, Virginia, USA (3) University of Chile, Santiago, Chile (4) School of Physical Sciences, University of California, Irvine, California, USA (5) JPL, Pasadena, California, USA (6) EG&G, NASA-GSFC/WFF, Wallops Island, Virginia, USA (7) Geophysical Institute, University of Alaska, Fairbanks, Alaska, U (8) CIRES, University of Colorado, Boulder, Colorado, USA The Northern and Southern Patagonia icefields (NPI and SPI) of southern South America have a total area of approximately 17,000 km 2 , constituting the largest temperate glacier system in the southern hemisphere. Snow precipitation can exceed 10 m/y water equivalent (w.e.) due to westerly air flow, with an important east-west gradient. In the lower reaches ablation can be larger than 10 m/y w.e., with abundant calving on fjords and freshwater lakes. The vast majority of the outlet glaciers show strong retreat and thinning in the ablation areas over the past century (Rignot et al., 2003), which can be largely explained by regional atmospheric warming. However, until now the data of the accumulation areas are insufficient for deriving the mass balance in the upper plateau. Here we compare new laser altimetry data of October 2008 with earlier data of November/December 2002 collected by airborne missions performed by NASA/CECS/Armada de Chile. The laser data are supplemented by the 2000 Shuttle Radar Topography Mission (SRTM) information and by 1975 and 1995 cartographic data of Chile. The data will allow to determine if thickening is occurring in the accumulation areas, as reported for example by Moeller et al. (2007) for Gran Campo Nevado, Patagonia, and if the rate of thinning at low elevations has experienced recent increases. As a result the contribution of the Patagonian icefields to sea level rise will be reassessed. c 2009 IOP Publishing Ltd