Response of the Patagonian Glaciers to Present and Future Atmospheric Changes

Patagonia (40°S-55°S) includes two large icefields, the Northern and Southern Patagonian Icefields (NPI and SPI). Most of the glaciers within these icefields are shrinking rapidly, raising concerns about their contribution to sea-level rise and the local to regional impacts of glacier shrinking in the face of ongoing climatic change. Empirically based studies that characterize the fundamental glacier conditions are scarce in this region. Consequently, our understanding of how the glaciers are responding to changes in climate, and what the key controls are, is limited. The aim of this project was to describe, estimate and analyse key meteorological and glaciological characteristics using nine months of meteorological observations, gridded-climate products and glacier modelling in a multi-scale approach. In the north of the SPI and between October 2015 and June 2016, humid and warm on-glacier conditions prevailed to the west of the main topographic divide, whereas dry and cold conditions prevailed to the east. Air temperature lapse rates were steeper in the east (−0.0072°C m-1) compared to the west (−0.0055°C m-1). Modelled energy balance fluxes revealed that the controls of ablation differ along the west-east transect, although sensible heat and net shortwave radiation fluxes provided the main sources throughout. Melt was high on both sides of the divide, but at comparable elevations, it was greater on the western side. At glacier-wide scale, this disparity is amplified by the accumulation-area ratio, leading to the west having more melt (8.2. m w.e) than the east (2.1 m w.e.). At the Icefield scale, surface mass balance (SMB) modelling (1976-2050), forced only by climate data, revealed that the NPI is currently losing mass while the SPI is not. Ice mass loss previously detected in the SPI is attributed to frontal ablation of calving glaciers. Glaciers in balance, however, are restricted to areas where snow accumulation has increased during the period 2000–2015. Projections until 2050 suggest a mean reduction in SMB of between 1.5 and 1.9 m w.e. in the NPI and between 1.1 and 1.5 m w.e in the SPI. SMB decrease is associated with melt increase due to projected air temperature increase. SMB is still projected to be positive in the SPI, however, assuming equal frontal ablation of the recent past, both Icefields will continue losing mass and contributing to sea-level rise. Additionally, an increase in meltwater availability could act as positive feedback by affecting ice dynamics and inducing greater frontal ablation for calving glaciers. This multi-scale assessment has increased our knowledge of the meteorological and glaciological characteristics of Patagonian glaciers, and quantified the response of these glaciers to atmospheric changes.