Ice-front variations and speed changes of calving glaciers in the Southern Patagonia Icefield from 1984 to 2013

Abstract:

Southern Patagonia Icefield (SPI) is losing volume, and the loss is due partly to rapid changes in outlet glaciers that terminate in lakes or the ocean. Despite their key influence, relatively few of these calving glaciers have had high-frequency measurements on their frontal variations and ice speed changes. We present frontal variations and ice speed changes of all glaciers having a surface area exceeding 100 km² in the SPI from 1984 to 2013. The analysis is based on satellite images acquired using Landsat 4, 5, 7, and 8. From 1984 to 2011, 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 (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: 0.71 km). Along the centerline within 20-km of the front, the ice speeds ranged from 50±40 to 5900±200 m a⁻¹. Except for regions showing large acceleration or deceleration, the mean speed over the measured area decreased by 30 m a⁻¹ from 1984 to 2011. The three most rapidly retreating glaciers showed much larger acceleration near the calving front. Except for Pío XI, the glaciers fall into one of three categories: stable front position without significant ice speed change, gradual retreat with deceleration, and rapid retreat with large acceleration. The overall retreat trend was probably due to the long-term warming trend. Nevertheless, our data demonstrated that the extraordinary large retreats in the three glaciers were not directly controlled by the warming trend, but instead driven by glacier dynamics. Such dynamically controlled rapid recession of several calving glaciers plays a key role in the recent volume decrease of the SPI.