New insights into the decadal variability in glacier volume of a tropical ice cap, Antisana (0◦290 S, 78◦090 W), explained by the morpho-topographic and climatic contex

Abstract

Abstract. We present a comprehensive study of the evolu tion of the glaciers on the Antisana ice cap (tropical An des) over the period 1956–2016. Based on geodetic ob servations of aerial photographs and high-resolution satel lite images, we explore the effects of morpho-topographic and climate variables on glacier volumes. Contrasting be haviour was observed over the whole period, with two pe riods of strong mass loss, 1956–1964 (−0.72 m w.e. yr−1 ) and 1979–1997 (−0.82 m w.e. yr−1 ), and two periods with slight mass loss, 1965–1978 (0.10 m w.e. yr−1 ) and 1998– 2016 (−0.26 m w.e. yr−1 ). There was a 42 % reduction in the total surface area of the ice cap. Individually, glacier re sponses were modulated by morpho-topographic variables (e.g. maximum and median altitude and surface area), par ticularly in the case of the small tongues located at low ele vations (Glacier 1, 5 and 16) which have been undergoing ac celerated disintegration since the 1990s and will likely disap pear in the coming years. Moreover, thanks to the availability of aerial data, a surging event was detected on the Antisana Glacier 8 (G8) in the 2009–2011 period; such an event is ex tremely rare in this region and deserves a dedicated study. Despite the effect of the complex topography, glaciers have reacted in agreement with changes in climate forcing, with a stepwise transition towards warmer and alternating wet–dry conditions since the mid s. Long-term decadal variabil-ity is consistent with the warm–cold conditions observed inthe Pacific Ocean represented by the Southern Oscillation in-dex