Deriving mass balance and calving variations from reanalysis data and sparse observations, Glaciar San Rafael, northern Patagonia, 1950–2005

Abstract

Abstract. Mass balance variations of Glaciar San Rafael, the most equatorial tidewater glacier in the North Patagonian Icefield, are reconstructed over the period 1950–2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of ice equivalent. Over that period, except for a short period of cooling from 1998–2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggest that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than changes in balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.

Rapid Surface Lowering of Benito Glacier, Northern Patagonian Icefield

“…Previous studies suggest that the general retreat and thinning of glaciers in Patagonia is a response to higher air temperatures (Rasmussen et al, 2007;Masiokas et al, 2008;Koppes et al, 2011) and/or ice flow acceleration due to the growth of proglacial lakes and increased calving rates (e.g., Harrison and Winchester, 2000;Rignot et al, 2003;Rivera et al, 2007;Willis et al, 2012). Despite Benito's proglacial lake increasing in area since 1973 (Figure 1), we discount the latter due to the lack of evidence for any significant increase in ice flow speed.…”

“…Air temperature at 850 hPa (∼1,400 m a.s.l.) was chosen because it represents both large-scale atmospheric circulation patterns and local climate at interannual timescales and is therefore a useful indicator of not only the energy fluxes received by the glacier surface but also the fraction of precipitation falling as snow (Rasmussen et al, 2007;Garreaud et al, 2011;Koppes et al, 2011).…”

“…The high accumulation rates sustain the NPI even though air temperatures are positive over much of the icefield for large parts of the year (Rasmussen et al, 2007;Koppes et al, 2011). However, the low elevation termini and rapid mass turnover rates make the west side of the NPI sensitive to air temperature, which determines not only surface melt but also the fraction of precipitation that falls as snow (Warren and Sugden, 1993;Rasmussen et al, 2007;Koppes et al, 2011).…”

“…The west side of the NPI is characterized by high accumulation rates due to a combination of moisture-laden westerlies from the Pacific Ocean and orographic precipitation over the central Andean ridge (Warren and Sugden, 1993;Harrison and Winchester, 2000;Hubbard et al, 2005). The high accumulation rates sustain the NPI even though air temperatures are positive over much of the icefield for large parts of the year (Rasmussen et al, 2007;Koppes et al, 2011). However, the low elevation termini and rapid mass turnover rates make the west side of the NPI sensitive to air temperature, which determines not only surface melt but also the fraction of precipitation that falls as snow (Warren and Sugden, 1993;Rasmussen et al, 2007;Koppes et al, 2011).…”

Distributed ice thickness and glacier volume in southern South America

“…Recent analysis of southern South America glaciers has yielded data regarding glacier area, areal and 63 volume change since the Little Ice Age (LIA) (Davies and Glasser, 2012; Glasser et al 2011), ice 64 surface velocity (Rivera et al, 2012; Jaber et al, 2013; Mouginot and Rignot, 2015), surface mass 65 balance (Koppes et al, 2011; Mernild et al, 2015; Schaefer et al, 2015; Willis et al, 2011) and 66 surface thinning and elevation changes (dh/dt) (Rivera et al, 2007; Willis et al, 2012 warming has caused a decreased in the amount of precipitation falling as snow and increased 100 ablation, exacerbating glacier recession (Rasmussen et al, 2007).…”