Recent spatial and temporal variations in debris cover on Patagonian glaciers

Supraglacial debris cover is an important component of glacier mass balance, especially in areas characterised by widespread glacier recession. Mapping of the spatial and temporal changes in debris cover on the surface of the receding outlet glaciers of the temperate North Patagonian Icefield (NPI) in southern South America between 1987 and 2015 shows that the total amount of debris cover has increased over time, from 168 km2 in 1987 to 307 km2 in 2015. The number of debris-covered glaciers increased from 24 in 1987, to 31 in 2001 and 32 out of 43 studied glaciers in 2015. The proportion of debris-covered area has also increased, from 4.1% in 1987 to 7.9% in 2015, with the largest proportional increases occurring east of the ice divide (where 15.2% of the glacier ice is now debris covered). Over this time, the total area of the NPI decreased from 4133 to 3887 km2. The area occupied by proglacial and ice-proximal lakes also increased from 112 to 198 km2. Between 1987 and 2015, the terminal environment of many of the outlet glaciers of the NPI changed from land-terminating to lake-calving, and these glaciers are now receding into terminal lakes. The change in the area of debris-covered ice is influenced by the loss of ice at debris-covered termini and by an increase in debris cover at higher elevations. The glaciers of the NPI remain highly dynamic as they recede and are therefore behaving very differently to high-elevation glaciers, such as those of the Himalaya, where debris cover leads to glacier stagnation at the termini.