Ice‐front variations and speed changes of calving glaciers in the Southern Patagonia Icefield from 1984 to 2011

Abstract

Patagonian icefields are losing volume, and their loss is due partly to rapid changes in their outlet glaciers that terminate in lakes or the ocean. Despite this key influence from outlet glaciers, relatively few of these calving glaciers have had high-frequency measurements on their frontal variations and ice speed changes. We describe here recent frontal variations and ice speed changes of all 28 major calving glaciers in the Southern Patagonia Icefield (SPI), including ice speed maps covering approximately half of the entire icefield. The analysis is based on satellite data from 1984 to 2011. Over this period, only the two termini of Glaciar Pío XI advanced. Of the remaining glacial fronts, 12 changed less than ±0.5 km, but 17 retreated at least 0.5 km. In the latter group, three glacial fronts (Glaciar Jorge Montt, HPS12, and Upsala) retreated over 6 km. Averaged over all 31 glacial fronts of the calving glaciers, the front positions retreated 1.56 km (median is 0.71 km). Along the flowline within 20 km of the front, the ice speeds up to 5900 ± 200 m a À1. Except for regions showing large acceleration or deceleration, the mean speed over the measured area decreased by 30 m a À1 from 1984 to 2011. The three most rapidly retreating glaciers showed much larger acceleration near the calving front, suggesting that ice dynamics drive their rapid retreat. Thus, we see retreat as a long-term trend for the calving glaciers in the SPI, with behavior that implies a dynamically controlled rapid recession that may explain the recently reported volume change of the SPI.

Velocidades superficiales del glaciar Upsala, Andes Patagónicos Sur, mediante el uso de correlación cruzada en imágenes satelitales: periodo 2013-2014.

“…The great depth of the Argentino Lake and the Upsala channel in particular might be related to the abundance of easily erodible rocks such as the slates of Pizarras Formation in the Upsala basin . This noticeable acceleration of glaciers at their terminus has been previously described for other outlet glaciers in Patagonia such as Jorge Montt Sakakibara and Sugiyama, 2014;Bown, 2015), where calving is driven at least in part by water depths near the front. Sakakibara and Sugiyama (2014) studied the glacier frontal variations of the outlet glaciers in the SPI.…”

“…This noticeable acceleration of glaciers at their terminus has been previously described for other outlet glaciers in Patagonia such as Jorge Montt Sakakibara and Sugiyama, 2014;Bown, 2015), where calving is driven at least in part by water depths near the front. Sakakibara and Sugiyama (2014) studied the glacier frontal variations of the outlet glaciers in the SPI. These authors reported a general recession trend for most glaciers in the area, though spatially and temporally varied.…”

“…Mouginot and Rignot (2015) In the same study authors report that between 2005 and 2010, the glacier sped up yet again by 50% before decreasing again in 2014 (3.56 md -1 ). In addition, Sakakibara and Sugiyama (2014) found velocities higher than 3,000 my 1 (8.22 md 1 ) near the calving front for 2010 year, when most freshwater glaciers in the SPI had a general deceleration trend.…”

“…On calving glaciers, surface velocities reach a maximum at the glacier front, due to the pulling effect of high calving rates (Sakakibara and Sugiyama, 2014). Upsala glacier has been in fact described as one of the most representative glaciers in this regard (Sakakibara et al, 2013).…”

“…Estimation of surface velocities studies in the Upsala catchment have been carry out by different techniques, such as aerial photogrammetry (Aniya and Skvarca, 1992), topographic surveys (Naruse and Aniya, 1992;Skvarca et al, 1995) and both optical (Skvarca et al, 2003;Sakakibara et al, 2013;Sakakibara and Sugiyama, 2014;Mouginot and Rignot, 2015) and SAR satellite images (Floricioiu et al, 2008;Floricioiu et al, 2009;Muto and Furuya, 2013;Mouginot and Rignot, 2015). These studies have estimated the evolution of glacier velocities from 1968 to 2011, considering different time scales (years or decades) and using various sensors and techniques (Table 1).…”