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

Abstract:

Patagonian icefields are characterised by numbers of calving glaciers draining into lakes
and the ocean. Melting of calving front below and at the water surface plays important roles
in 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 better
understand the effects of subaqueous and waterline melting on glacier changes in
Patagonia, we measured the terminus position, surface velocity, lake surface and air
temperatures at Glaciar Perito Moreno, Southern Patagonia Icefield. These data were used
to calculate frontal ablation rate (calving rate plus subaqueous melt rate), a melt rate at the
waterline and quantity of calving flux and subaqueous melting. The terminus position and
surface velocity showed clear seasonal variations between 1999 and 2013. The glacier
retreated from December to June, and then it advanced for the rest of the year. The mean
surface velocity near the terminus was 500±100 m a^-1 in winter (June–August) and
590±160 m a^-1 in summer (December–February). The mean frontal ablation rate also
showed 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 shift
between the seasonal variations in the surface velocity and the frontal ablation rate. The
fraction of the frontal ablation to the total mass loss is 31% and only 4%. However, the
seasonal 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 of
calving.