[1] To investigate the viscosity structure of ice sheets induced by crystal orientation fabric (COF), we carried out a multipolarization plane and dual-frequency radar survey in East Antarctica. Radar surveys were done along a 670-km-long flow line from Dome Fuji toward the coast and two transverse lines of 300-km and 20-km length, respectively. The radar echoes were highly dependent on the polarization plane for ice depths between about 40 and 60% of the ice thickness in the lower reaches of the convergent ice flow sector approaching the outlet glacier. When the polarization was perpendicular to the ice flow, echoes were about 10 dB stronger than when the polarization was parallel to the ice flow. This feature was not clear in the upper part of this convergent flow sector. Farther inland, where ice flow is divergent or parallel, the radar echo varied by several decibels because of changes of the radar polarization and had maxima in two orientations. Dual-frequency data showed that the cause of the reflections was changes in COF. Multipolarization data identified anisotropic reflectivities and birefringence as causes of the anisotropic radar echoes in the lower and upper reaches, respectively. With the aid of ice-core-based studies on COF, we show that ice is composed of stacked layers of single-pole and vertical girdle fabrics in the lower reaches. In contrast, we argue that changes of single-pole clustering cause isotropic reflectivities in the upper reaches. We also discuss on the development of COF along ice flow and its implication to ice sheet dynamics.INDEX TERMS: 0669 Electromagnetics: Scattering and diffraction; 0933 Exploration Geophysics: Remote sensing; 1827 Hydrology: Glaciology (1863); 6969 Radio Science: Remote sensing; KEYWORDS: ice-penetrating radar, internal layers Citation: Matsuoka, K., T. Furukawa, S. Fujita, H. Maeno, S. Uratsuka, R. Naruse, and O. Watanabe, Crystal orientation fabrics within the Antarctic ice sheet revealed by a multipolarization plane and dual-frequency radar survey,

No abstract

No abstract

Data relating to calving dynamics in fresh water are scarce, especially for deep-water sites. A linear dependence of calving velocity (Vc) on water depth (Hw) is commonly accepted for both tidewater and fresh-water calving glaciers. Here we use recent data from temperate Patagonian glaciers to propose a revised relationship for calving in fresh water. The new ratio is derived from glaciers calving rapidly into deep water, documented using sequential satellite images and depth soundings. The main data source is a detailed remotely sensed dataset of the rapidly retreating Glaciar Upsala, complemented with global positioning system field surveys and precise ice-proximal bathymetric surveys. The area-integrated mean water depth between glacier positions in 1996 and 2000 is 490 m, with a maximum recorded depth of >700m. In the same period, image analysis reveals surface area loss of 1.37 km2 a–1 (4.8 km2) and an average calving rate of 1880ma–1. The resulting Vc/Hw ratio is of a similar order of magnitude to that recently derived for nearby Glaciar Moreno, but is well above the range of values commonly reported for lacustrine calving.

Glacier and lake variations in the Yamzhog Yumco basin in southern Tibet were studied by integrating series of spatial data from topographic maps and Landsat images at three different times: 1980, 1988/90 and 2000. The results indicate that the total glacier area has decreased from 218 km2 in 1980 to 215 km2 in 2000, a total reduction of 3 km2 (i.e. a 1.5% decrease). Glacier recession rates were clearly larger in the 1990s than the 1980s due to the warmer climate. The total lake area decreased by about 67 km2 during 1980–90 and increased by 32 km2 during 1990–2000. It is suggested that change of lake area in the basin was rapid and most likely caused primarily by the change in precipitation and evaporation in the basin, and secondarily by the increased water supply from melting glaciers.