Climatology of Andean glaciers: A framework to understand glacier response to climate change
Highlights
► We systematize the climatic conditions that favor the occurrence of Andean glaciers. ► Andean glaciers occur under cold and dry, intermediate, and warm and wet conditions. ► A statistical climatic classification allows determination of seven groups of Andean glaciers. ► Our classification provides a framework to test hypothesis on spatial variability of glacier sensitivity to climate change. ► Our classification has implications for the study of glacier response to past, present and future climate changes.
Introduction
Valley glaciers are responsive systems to climate change (Dyurgerov and Meier, 2000, Lowell, 2000, Oerlemans, 2005, Rupper et al., 2009). Records of former glacial fluctuations have been used extensively to reconstruct paleoclimate at different temporal and spatial scales (e.g., Rodbell, 1992, Oerlemans, 1994, Lowell et al., 1995, Denton et al., 1999, Klein et al., 1999, Porter, 2001). However, these reconstructions typically do not account for variations in regional climate, which likely controls the magnitude of glacier response to climatic perturbations (Rupper and Roe, 2008). Here, we present a climatic classification of Andean glaciers that can serve as the basis to improve the understanding of glacier response to climatic perturbations and thus to extract the climatic signals embedded in the glacial record.
Advances in glacial and climate modeling have improved our understanding of the climate-glacier relationship (e.g., Oerlemans and Fortuin, 1992, Seltzer, 1994, Braithwaite and Zhang, 2000, Kaser, 2001, Raper and Braithwaite, 2006, Fujita, 2008a). These studies suggest that glaciers subjected to different climatic regimes could respond with different magnitudes to similar climatic perturbations (Kaser, 2001, Favier et al., 2004, Fujita, 2008b, Rupper and Roe, 2008). For example, it has been suggested that glaciers in wetter settings are more sensitive to warming than those in drier areas (Meier, 1984, Oerlemans and Fortuin, 1992, Raper and Braithwaite, 2006, Rupper and Roe, 2008). Kaser (2001) and Kaser and Osmaston (2002) proposed that glaciers located above the mean annual 0 °C isotherm (typical of arid regions) are very sensitive to changes in precipitation and insensitive to changes in temperature. Dropping temperatures will not change the rain/snow ratio of these glaciers, and hence, will not affect their net mass balance. In contrast, small changes in precipitation (i.e., accumulation) would directly increase or decrease the net mass balance (Klein et al., 1999, Rodbell et al., 2009). Recently, Fujita, 2008a, Fujita, 2008b, suggested that glaciers with summer accumulation are more sensitive to temperature than those with winter accumulation.
The above suggests that to compare glacial fluctuations in distant areas and to understand the climatic signal responsible for those fluctuations, a first step might be to identify and understand the spatial distribution of the climates that permit the presence of glaciers in those areas.
The Andes, along 9000 km of South America, span a broad range of both latitude and altitude. This dictates a large range of temperature and precipitation conditions, resulting in a mosaic of climates (Garreaud et al., 2009) (Fig. 1). In the northern portion of the Andes (12°N to 23.5°S), climate is influenced by tropical (Atlantic) circulation patterns. South of 23.5°S the tropical influence fades out and gives way to more Pacific influence. The area south of 31°S lies in the westerly circulation domain (see Rodbell et al., 2009 for a review of the climatic and glaciological conditions in each domain). This climatic diversity could be responsible for some of the variability in the response of Andean glaciers to large-scale climatic perturbations.
In this paper, we systematize, classify, and identify the spatial distribution of the climates that permit the occurrence of present-day glaciers throughout the Andes.
We suggest that our classification provides a framework to understand the spatial variability of glacier sensitivity to climate change, and has important implications for the study of past glacial fluctuations, paleoclimatic reconstructions, the climatic signals driving present-day glacier fluctuations across the Andes, and perhaps the response of these glaciers to future climate changes.
Section snippets
Methods
Based on a visual inspection of Google Earth satellite imagery, we assembled a sample of 234 small Andean glaciers (~<2 km), with simple geometry, from 12°N to 55°S. Special attention was paid in gathering a spatially distributed sample of glaciers to represent all the climatic regimes existing in the region. Whereas the World Glacier Inventory (National Snow and Ice Data Center, 1999, updated 2009) offers one of the most extensive collections of Andean glaciers in terms of sample size (N > 7000),
Results
Temperature and precipitation vary greatly in the Andes (Fig. 3). However, Fig. 4 shows that our sample of glaciers occupies distinct and non-continuous sets of temperature and precipitation conditions. Specifically, three distinctive groups are present: 1) cold and dry conditions (mean annual temperature, (MAT) -7.0 to − 1.8 °C; total annual precipitation (TAP) 120 to 620 mm/yr); 2) intermediate conditions (MAT − 1.5 to 3.6 °C; TAP 520 to 1100 mm/yr); and 3) relatively warm and wet conditions (MAT −
Discussion
Glaciers currently exist in a variety of climates along the Andes. A visual examination of the mean annual temperature and total annual precipitation suggests that our sample of glaciers (N = 234) can be divided into three groups: 1) cold and dry, 2) intermediate, and 3) relatively warm and wet. However, a more thorough statistical analysis, including a more extensive collection of climatic variables shows that Andean glaciers can be classified into seven climatic groups, each with a distinctive
Summary and final remarks
- (1)
Andean glaciers are subjected to a variety of climates. A statistical analysis of the climatic variables (temperature, precipitation and humidity) permits the classification of Andean glaciers into seven distinctive groups.
- (2)
The average climatic conditions for each group can be considered mean climate states that support the presence of Andean glaciers.
- (3)
The distinct spatial distribution of these different climate groups provides a framework to test hypotheses on spatial variability of glacier
Acknowledgments
E.A. Sagredo acknowledges support from Fulbright-Conicyt Doctoral Fellowship and expresses his thanks to the Department of Geology at the University of Cincinnati for supporting this study as part of his doctoral research. This work was supported by NSF Grant (EAR-1003072). We thank Colby A. Smith for valuable discussion and insightful comments on the manuscript. We also acknowledge Arnold I. Miller, Gary J. Motz and Anne J. Lagomarcino for their helpful advice in statistical analyses. Special
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