Climate changes in the region

Glaciers in Southern Chile and Argentina



Glaciers in Southern Chile and Argentina (36 to 46°S) have been retreating and shrinking during recent decades, presumably in response to a reduction in precipitation and upper atmosphere warming observed during the second half of the XXth century (Rivera et al., 2002; Aniya et al., 1997; Rignot et al., 2003; Carrasco et al., 2005; Villalba, 1990 and 1994; Villalba et al., 1990; Rabassa et al., 1978). Very few glacier exceptions to this trend have been observed, especially among tidewater and some freshwater Patagonian calving glaciers(Rivera et al., 1997a and 1997b; Michel and Rignot, 1999).

 

Surface temperatures in the Chilean Lake District (below 850 hPa geopotential height) showed a decreasing trend between 1933 and 1992, which was mainly explained by a strong cooling between the 1950's and 1970's(Rosenbluth et al., 1997), while upper atmosphere temperatures (between 850 and 300 hPa geopotential heights) showed a significant increase since the beginning of radiosonde measurements in 1958 (Aceituno etal., 1993). The rest of Southern Chile, especially Patagonia, has experienced a significant warming trend,registered both at the surface stations (Rosenbluth et al., 1997; Rosenbluth et al., 1995) and at higher altitude(Carrasco et al., 2002).

 

Significant negative trends in precipitation were detected in the Chilean Lake District between 1930 and 2000,with a maximum reduction at around 39°S, where a decrease of 450 mm in 70 years was measured (Quintana,2004; Bown and Rivera, 2007a). These trends could be partially explained by recurrent rainfall deficits observedat the Lake District during the maximum intensity of El Niño events in the Southern Pacific Ocean (Montecinosand Aceituno, 2003). El Niño events have been more frequent and intense after the climatic shift of 1976(Giese et al., 2002), but in contrast to a positive correlation with precipitations in Central Chile (Rutllant and Fuenzalida, 1991) which results in positive glacier mass balances (Escobar et al., 1995), a negative correlation in the Chilean Lake District, reinforced by upper atmospheric warming, is probably generating negative glaciermass balances. In Patagonia, precipitation is also showing a declining trend but this is obscure in somestations by anomalies or cycles (Rivera, 2004; Carrasco et al., 2002; Rosenbluth et al., 1995; Rivera et al.,1997) when precipitations have been well above the interannual average (before 1976) and when rainfall shave been below the average (after 1976). The 1976 shift (Giese et al., 2002) seems to have affected regional precipitations, however the temperature effects of El Niño Southern Oscillation (ENSO) phenomena in Patagonia is still unclear (Schneider and Gies, 2004).

 

Referencias

 

 

ANIYA, M., SATO, H., NARUSE, R., SKVARCA, P. & CASASSA, G. 1997. "Recent variations in the Southern Patagonia Icefield, South America". Artic and Alpine Research, 29: 1-12.

 

BOWN, F.; RIVERA, A.; ACUÑA, C. and CASASSA, G. 2007. "Recent glacier mass balance calculations at Volcán Mocho-Choshuenco 40°S Chilean Lake District" Glacier Mass Balance Changes and Meltwater Discharge, IAHS Assembly in Foz Iguaçu, Brasil. p.143-152

 

RIGNOT, E., RIVERA, A. & CASASSA, G. 2003. "Contribution of the Patagonia Icefields of South America to sea level rise". Science, 302: 434-437.

 

RIVERA, A., ARAVENA, J. & CASASSA, G. 1997a. "Recent fluctuations of glaciar Pío XI, Patagonia: Discussion of a glacial surge hiphotesis". Mountain Research and Develoment, 17 (4): 309-322.

 

RIVERA, A., LANGE, H., ARAVENA, J. & CASASSA, G. 1997b. "The 20th century advance of glacier Pío XI, Southern Patagonia Icefield". Annals of Glaciology, 24: 66-71.

 

RIVERA, A. 2004. "Mass balance investigations at Glaciar Chico, Southern Patagonia Icefiels, Chile". PhD thesis. School of Geographical Sciences, University of Bristol. UK, 324 p.