Rodrigo Zamora

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.

Airborne radar sounder for temperate ice: initial results from Patagonia

We describe the development of a low-frequency airborne radar specifically designed for the sounding of temperate ice. The system operates at a central frequency of 1MHz and consists of an impulse transmitter with an output voltage up to 5000V and a digital receiver with a maximum gain of 80dB. The radar was deployed on board a CASA 212 aircraft, which also carries a laser altimeter, an inertial navigation system, a digital camera and a GPS receiver. A description of the radar system is provided, as well as preliminary results obtained at Glaciar Tyndall, Campo de Hielo Sur (Southern Patagonia Icefield), where an ice depth of 670m was reached.

Glaciological investigations on Union Glacier, Ellsworth Mountains, West Antarctica

Abstract Union Glacier, West Antarctica, was intensively mapped in December 2008, when an over-snow traverse was conducted by CECS and ALE, with the aim to determine the ice-dynamical characteristics of the glacier, through mapping the crevasse fields and by providing a glaciological baseline for future studies. A mean ice thickness of 1450 m was measured, confirming the presence of a deep subglacial topography (∼900 m below sea level), much deeper than previously estimated. Ice velocities were also measured at 21 stakes drilled into the ice at the narrowest gate of the glacier between December 2007 and December 2008, yielding a mean value of 22.6 m a−1. These velocities, combined with the measured ice thicknesses and a numerical model, yielded an ice flux of 0.10 ±0.03 km3 a−1 w.e. Considering the ice basin above this gate, a mean surface mass balance of 0.18 ± 0.05 m a−1 was estimated, a value consistent with a mean snow accumulation for nearby ice streams. These values indicate that the glacier is at present near equilibrium.

Glacier wastage on southern Adelaide Island, Antarctica, and its impact on snow runway operations

Abstract The variations and dynamics of the southern edge of Fuchs Ice Piedmont, Adelaide Island (67˚45’ 09’ S, 68˚55’ 04’ W), Antarctic Peninsula, are presented. The snow-covered surface of the glacier has been used since the 1960s for landing aeroplanes in support of British, and more recently Chilean, operations at nearby Teniente Carvajal station (formerly known as Adelaide T). In recent years, snow conditions in the runway area have progressively deteriorated, due to increasingly early summer melting. Radio-echo sounding, global positioning system and remotely sensed data have been analyzed for mapping the crevasse and ice velocity fields, as well as the surface and subglacial topography of the area. The results show that the runway area is located on a local ice divide surrounded by crevasses which are appearing on the glacier surface progressively earlier in the summer, presumably due to higher snowmelt and perhaps higher ice velocities, in response to regional atmospheric warming. In the near future, landing operations will be further affected as more crevasses will appear in the runway area if present warming trends persist. This situation affects all coastal areas in the Antarctic Peninsula, hence the need to search for possible new locations of crevasse-free runways at higher elevations.

Subglacial Lake CECs: Discovery and in situ survey of a privileged research site in West Antarctica

We report the discovery and on-the-ground radar mapping of a subglacial lake in Antarctica, that we have named Lake CECs (Centro de Estudios Cientificos) in honor of the institute we belong to. It is located in the central part of the West Antarctic Ice Sheet, right underneath the Institute Ice Stream and Minnesota Glacier ice divide, and has not experienced surface elevation changes during the last 10 years. The ratio between the area of the subglacial lake and that of its feeding basin is larger than those for either subglacial lakes Ellsworth or Whillans, and it has a depth comparable to that of Ellsworth and greater than that of Whillans. Its ice thickness is ∼600 m less than that over Ellsworth. The lake is very likely a system with long water residence time. The recent finding of microbial life in Lake Whillans emphasizes the potential of Subglacial Lake CECs for biological exploration.

Mapping Blue-Ice Areas and Crevasses in West Antarctica Using ASTER Images, GPS, and Radar Measurements

Before the satellite era, relatively little was known about the interior of the West Antarctic Ice Sheet (WAIS). Of special interest are the rock outcrops associated with blue-ice areas (BIAs), which have been exploited for logistical purposes as well as being the subject of scientific research. The blue ice consists of relatively snow-free glacier ice that is undergoing ablation. One of these BIAs is Patriot Hills (80°18′S, 81°22′W) where aircraft with conventional landing gear have been landing for more than 20 years. This is now the main hub supporting large terrestrial expeditions conducted by Chilean scientists within Antarctica. Kinematic GPS has been used to map BIAs since 1996, with areas delineated on ASTER images since 2001 using both manual and automated approaches. The GPS method typically delimits the largest area, and supervised classification of the images by an algorithm demarcates the smallest area due to thin patchy snow cover overlying blue ice. These areas do not display a unique spectral response when mostly snow covered, so that they can only be visually discriminated. This detailed record of BIA extent shows no significant areal change with time, but does display interannual variability, which most likely is connected to prevailing meteorological conditions. BIAs around other nunataks in the region have been mapped from ASTER imagery, with the aim of identifying other landing sites for aircraft, as well as providing a detailed map for meteorite seekers. ASTER composite images have also been used to map safe routes for terrestrial traverses through crevasse zones. High-pass filters enhanced crevasse features, but visual analysis proved to be the most reliable method of identifying all crevasses. ASTER images were superior to microwave imagery for crevasse detection, as the latter can lack sufficient contrast; however, only Radarsat imagery provided coverage of higher latitude regions. Information gleaned from visible imagery can be combined with that of field-based radio-echo sounding and ground—penetrating radar profiles through the ice to map internal layers and bedrock topography with the objective of enhancing our knowledge of this remote region.

Ice thickness surveys of the Southern Patagonian Ice Field using a low frequency ice penetrating radar system

An airborne low frequency radar system used to survey the ice thickness of the northern part of the Southern Patagonian Ice Field (SPI) is presented. The radar is an impulse system operating at a central frequency of 20 MHz. The system is controlled and operated from a helicopter cabin connected with an optical fibre cable to the antennas that are fixed to an aluminium structure weighting 350 kg that is hanging 40–50 m below the helicopter. At the antenna, there is a high-power transmitter working at a 5 kHz PRF, and a radar receiver. Also, there is a dual frequency GPS for the real-time positioning of the measurements. The survey took place in August 2015 and October 2016 while flying more than 400 kilometres of Glaciares Jorge Montt, OHiggins and the high plateau of the SPI. The system performance was adequate to survey most of the ice thicknesses, including the steep slopes and inaccessible crevassed areas. The maximum ice thickness penetration yielded 581 m of temperate ice. Several bottom reflections were obscure by englacial water and/or surface crevasses.

High resolution FM-CW radar for internal layers mapping in cold ice

A wideband ground penetrating radar was developed in order to detect internal layers in firn and shallow ice, with high resolution. Mapping of near-surface layers improves traditional snow accumulation measurements, extending the spatial and temporal coverage. This system is a frequency-modulated continuous wave (FM-CW) radar, with a transmit signal range from 203 MHz to 1019 MHz and with a power of ∼250 mW. During two over-snow field campaigns in West Antarctica plateau (January and December 2014), this radar mapped near-surface internal layers to a depth of ∼170 m, with a resolution of ∼0.15 m in ice. Future improvement includes the addition of an ultra-wideband microwave snow radar, in order to map internal layers in snow column to a depth of 10 m, with a very high resolution.