Seasonal Variations in Terminus Position and Frontal Ablation in Glaciar Perito Moreno, a Freshwater Calving Glacier in Southern Patagonia Icefield

Patagonian icefields are characterised by numbers of calving glaciers draining into lakesand the ocean. Melting of calving front below and at the water surface plays important rolesin the mass balance of calving glaciers, but these processes are not well understood.Moreover, studies on frontal melting of freshwater calving glaciers are very few. To betterunderstand the effects of subaqueous and waterline melting on glacier changes inPatagonia, we measured the terminus position, surface velocity, lake surface and airtemperatures at Glaciar Perito Moreno, Southern Patagonia Icefield. These data were usedto calculate frontal ablation rate (calving rate plus subaqueous melt rate), a melt rate at thewaterline and quantity of calving flux and subaqueous melting. The terminus position andsurface velocity showed clear seasonal variations between 1999 and 2013. The glacierretreated from December to June, and then it advanced for the rest of the year. The meansurface velocity near the terminus was 500±100 m a-1 in winter (June-August) and590±160 m a-1 in summer (December-February). The mean frontal ablation rate alsoshowed seasonal variations with 280±130 m a-1 in winter and 770±180 m a-1 in summer.These results suggest that the seasonal terminus variations are the result of phase shiftbetween the seasonal variations in the surface velocity and the frontal ablation rate. Thefraction of the frontal ablation to the total mass loss is 31% and only 4%. However, theseasonal variations in the frontal ablation rate correlated with the lake surface temperature(R2 =0.86), suggesting the importance of waterline melting as a triggering mechanism ofcalving.