New evidence for an ENSO impact on low‐latitude glaciers: Antizana 15, Andes of Ecuador, 0°28′S

Abstract

[1] Continuous monthly mass balance measurements from the ablation zone of Antizana 15 glacier in the Andes of Ecuador between January 1995 and December 2002 indicate a strong dependence on El Niño-Southern Oscillation (ENSO). Over the 8-year period investigated, mass balance was negative all year round during El Niño periods but remained close to equilibrium (positive anomalies) during La Niña events. On seasonal timescales, mean ablation rates remain at a quite constant level all year round, but interannual variability shows much larger changes from year to year during the key periods February-May and September. This variability is caused by large differences that occur in the seasonal cycle during the two opposite phases of ENSO. Since ENSO is phase locked to the seasonal cycle with largest sea surface temperature anomalies around boreal winter, November-February, and the atmospheric response to ENSO is delayed by 3 months over the Ecuadorian Andes, year-to-year variations in mass balance are largest between February and May. Energy balance studies at the glacier surface indicate that high air temperature, which favors rain over snowfall, weak and sporadic snowfall, insufficient to maintain a high glacier albedo, low wind speeds, which limit the transfer of energy from melting to sublimation, and reduced cloud cover, which increases the incoming short-wave radiation, are the dominant factors related to El Niño, which tend to increase ablation. La Niña events on the other hand are characterized by colder temperatures, higher snowfall amounts, and to a lesser degree, more constant winds, factors which increase albedo and sublimation and therefore preclude melting at the glacier surface. The effects of ENSO variability are also important over the accumulation area, which represents up to 80% of the glacier surface during La Niña events (1999)(2000) and 45-60% in El Niño years. Since the accumulation rates increase during these cold periods, the specific net balance and the dynamics of the entire glacier are strongly affected. Longer mass balance records than this 8-year period are needed for conclusive answers about the dependence of the Ecuadorian glaciers on ENSO variability, but initial results suggest that the response observed on Antizana glaciers is very similar to what has been observed previously during ENSO periods on Andean glaciers in the outer tropics. The seasonal dependence on ENSO and the physical mechanisms linking ENSO with mass balance variations on Antizana, however, are different from the response observed on Andean glaciers in the outer tropics.

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“…If this is correct, it implies that there is significant interannual variability in the ELA of the MGS and, thereby, also the Carstensz Glaciers. This seems reasonable given the significant variability in the monthly mass balance of the single intensely studied tropical glacier on the eastern side of the Pacific, Antizana in Ecuador (Francou et al 2004). In the Ecuadoran case, the monthly variability translated into 290 m of variation (4 sigma) in the annual ELA between 1994 and 2005 (Haeberli et al 2007).…”

“…In the tropical Andes, Francou et al (2004) showed that the cumulative loss of ~25 m in water equivalent from Antizana Glacier in Ecuador over the eight-year period from 1995 to 2002 was due to the intensity of El Niño events in this interval. During El Niño events, glacier ablation increased because of atmospheric warming and decreased precipitation.…”

Empirical mass balance modelling of South American tropical glaciers: case study of Antisana volcano, Ecuador

“…However, other factors that could contribute to a negative mass balance such as a decrease in solar radiation absorption due to less cloud cover should not be ruled out (Sicart et al 2003, Vuille et al 2003, Francou et al 2004, Gallaire et al 2010. Furthermore, in most studies, variation in the energy balance of tropical glaciers is dominated by net shortwave radiation, which is related to albedo, one of the variables controlling melting (Wagnon et al 1999a(Wagnon et al , 1999b.…”

“…For example, during a strong El Niño event, accelerated retreat of glaciers in Ecuador has been observed with a time lag of 3-6 months (Francou et al 2004).…”

“…Favier et al (2004aFavier et al ( , 2004b, Francou et al (2004) and Vuille et al (2008a) observed that temperature and precipitation are the main factors that explain melting and the annual mass balance of Glacier 15. In addition, the almost non-existent seasonality of precipitation and of temperature implies that local variations are responsible for variations in the mass balance.…”