Surface velocity and mass balance of Livingston Island ice cap, Antarctica

Abstract

Abstract. The mass budget of the ice caps surrounding the Antarctica Peninsula and, in particular, the partitioning of its main components are poorly known. Here we approximate frontal ablation (i.e. the sum of mass losses by calving and submarine melt) and surface mass balance of the ice cap of Livingston Island, the second largest island in the South Shetland Islands archipelago, and analyse variations in surface velocity for the period 2007-2011. Velocities are obtained from feature tracking using 25 PALSAR-1 images, and used in conjunction with estimates of glacier ice thicknesses inferred from principles of glacier dynamics and ground-penetrating radar observations to estimate frontal ablation rates by a flux-gate approach. Glacier-wide surface mass-balance rates are approximated from in situ observations on two glaciers of the ice cap. Within the limitations of the large uncertainties mostly due to unknown ice thicknesses at the flux gates, we find that frontal ablation (−509± 263 Mt yr −1 , equivalent to −0.73 ± 0.38 m w.e. yr −1 over the ice cap area of 697 km 2 ) and surface ablation (−0.73 ± 0.10 m w.e. yr −1 ) contribute similar shares to total ablation (−1.46 ± 0.39 m w.e. yr −1 ). Total mass change (δM = −0.67 ± 0.40 m w.e. yr −1 ) is negative despite a slightly positive surface mass balance (0.06± 0.14 m w.e. yr −1 ). We find large interannual and, for some basins, pronounced seasonal variations in surface velocities at the flux gates, with higher velocities in summer than in winter. Associated variations in frontal ablation (of ∼ 237 Mt yr −1 ; −0.34 m w.e. yr −1 ) highlight the importance of taking into account the seasonality in ice velocities when computing frontal ablation with a flux-gate approach.

Geomatic methods applied to the study of the front position changes of Johnsons and Hurd Glaciers, Livingston Island, Antarctica, between 1957 and 2013

“…Typical velocities near the calving front of Johnsons Glacier are about 50 m yr −1 (Rodríguez, 2014), whereas maximum velocities in Hurd Glacier are reached in its central zone, and are typically around 5 m yr −1 (Molina, 2014), decreasing towards the terminal zones, which have been suggested to be frozen to bed on the basis of ground-penetrating radar studies, glacier velocities and geomorphological evidences Molina et al, 2007). The annual average temperature at Juan Carlos I Station (12 m a.s.l., in Hurd Peninsula) between 1988 and 2011 was −0.9 • C, with average summer (DJF) and winter (JJA) temperatures of 2.4 and −4.4 • C, respectively (Osmanoglu et al, 2014). The main glaciological studies in Hurd Peninsula include cartography of volcanic ash layers (Palà et al, 1999;Ximenis, 2001;Molina, 2014), shallow ice coring , numerical modeling of glaciers dynamics (Martín et al, 2004;Otero et al, 2010), analysis of glacier volume changes 1957-2000 (Molina et al, 2007), seismic and ground-penetrating radar surveys (Benjumea et al, 1999(Benjumea et al, , 2001(Benjumea et al, , 2003Navarro et al, 2005Navarro et al, , 2009, modeling of melting (Jonsell et al, 2012), massbalance observations Ximenis, 2001;Navarro et al, 2013) and geomorphological and glacier dynamics studies (Ximenis et al, 2000;Molina, 2014).…”

“…The main glaciological studies in Hurd Peninsula include cartography of volcanic ash layers (Palà et al, 1999;Ximenis, 2001;Molina, 2014), shallow ice coring , numerical modeling of glaciers dynamics (Martín et al, 2004;Otero et al, 2010), analysis of glacier volume changes 1957-2000 (Molina et al, 2007), seismic and ground-penetrating radar surveys (Benjumea et al, 1999(Benjumea et al, , 2001(Benjumea et al, , 2003Navarro et al, 2005Navarro et al, , 2009, modeling of melting (Jonsell et al, 2012), massbalance observations Ximenis, 2001;Navarro et al, 2013) and geomorphological and glacier dynamics studies (Ximenis et al, 2000;Molina, 2014). Glaciological studies covering the whole Livingston Island include the analysis of Livingston ice cap front position changes 1956-1996, ground-penetrating radar surveys ) and estimates of ice discharge to the ocean (Osmanoglu et al, 2014). The latter study also includes ice-cap-wide mass balance estimates and ice velocity fields determined from satellite synthetic aperture radar measurements.…”

A 14-year dataset of in situ glacier surface velocities for a tidewater and a land-terminating glacier in Livingston Island, Antarctica

“…Of course, one of the major drawbacks of the polynomial interpolation of the observed positions is that it does not allow us to represent seasonal variations in glacier velocities, which are known to occur for the glaciers in this region (e.g. Osmanoglu et al, 2014). In fact, we tried to add a sinusoidal function to the polynomial fit, and the results did not improve the fit to the observations at all.…”

“…These islands, located off the north-western tip of the Antarctic Peninsula, previously had a scarce record of in situ velocity observations, which included measurements in the late 1980s on Nelson Island (Ren Jiaven et al, 1995), earlier measurements in the late 1990s on Johnsons Glacier (Ximenis et al, 1999), and measurements in the Arctowski Icefield, the Bellingshausen Dome, and the Central Dome of King George Island between 1999and 2008/09 (Blindow et al, 2010Rückamp et al, 2010Rückamp et al, , 2011. Such in situ velocity measurements are critical for the validation of the estimates of remote-sensor-based studies of ice discharge in the region such as those by Osmanoglu et al (2013Osmanoglu et al ( , 2014 for King George and Livingston islands (the present dataset has in fact been used in the latter paper with such purposes), as well as for tuning free parameters of glacier dynamics models, as done by Martín et al (2004) and Otero et al (2010) using an earlier (and shorter) version of the dataset presented. An added interest of the presented velocity record is that it corresponds to both a tidewater glacier and a landterminating glacier, two glacier types that are typical in this region but very different in dynamical behaviour.…”

La deglaciación de las áreas libres de hielo de las islas Shetland del Sur (Antártida). Ejemplos de Byers (Livingston) y Barton (King George)

“…En este archipiélago, pequeñas variaciones en los valores medios de temperatura y/o precipitación pueden conllevar cambios significativos en los balances de masa glaciar (Navarro et al, 2013;Osmanoglu et al, 2014). Durante el Holoceno, la elevada sensibilidad climática de estas islas ha comportado numerosos avances y retrocesos glaciares en respuesta a las oscilaciones climáticas (O'Cofaigh et al, 2014).…”