Late Pleistocene climate inferred from the reconstruction of the Taylor River glacier complex, southern Sawatch Range, Colorado

Abstract

Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields.Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65 F 0.05. ELAs thus derived ranged from about 3275 to 3400 m, with a mean of 3340 F 60 m. A degree-day model (DDM) was used to infer the climatic significance of the LGM ELA. With no appreciable differences in precipitation with respect to modern climate, the ELA implies that mean summer temperatures during the LGM were~7.6 8C cooler than today. The DDM was also used to determine the temperatures required to maintain steady-state mass balances for each of the reconstructed glaciers. The required reductions in summer temperature vary little about a mean of 7.1 8C. The sensitivity of these results to slight (F 25%) changes assumed for LGM precipitation are less than F 0.5 8C. Even under an LGM climate in which precipitation is assumed to be substantially different (F 50%) than the present, mean summer temperatures must be on the order of 7.0 to 8.5 8C lower to depress equilibrium lines to LGM altitudes. The greater sensitivity of the ELA to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation. D

Deglaciation of the Colorado Rocky Mountains following the Last Glacial Maximum

“…Some have used glacier equilibrium-linealtitude-(ELA-) based approaches (Meierding, 1982;Leonard, 1984Leonard, , 1989Leonard, , 2007Brugger and Goldstein, 1999;Brugger 2006Brugger , 2010Refsnider et al, 2009). Others have employed a variety of numerical-modeling approaches (Brugger, 2006(Brugger, , 2010Ward, 2009;Dühnforth and Anderson, 2011;Schweinsberg et al, 2016;Leonard et al, 2017).…”

“…The Taylor River glacier was the main outlet glacier of a small (~215 km 2 ) upland icefield, while Texas Creek glacier was an independent valley glacier. Brugger (2006Brugger ( , 2010 used a 2-D degree-day model to infer LLGM climate in the western Sawatch Range and southern Elk Mountains, but did not attempt to model deglaciation.…”

Linking glacier extent and summer temperature in NE Russia - Implications for precipitation during the global Last Glacial Maximum

“…Assuming that the annual distribution of temperatures is described by a sine curve, (Brugger, 2006;Hughes, 2008Hughes, , 2009Hughes and Braithwaite, 2008) daily temperatures at the paleo-ELA can be calculated from mean annual air temperature at the paleo-ELA as follows (eq. 2):…”

“…A glacier's ELA is defined as the altitude where net annual accumulation and ablation are in equilibrium, and is largely controlled by climate (Ohmura et al, 1992). In the DDM approach, the annual melt at the glacier's ELA is calculated from the former is based on the assumption that gLGM glaciers were temperate (with high mass-flux), and the latter on the assumption that they were of polar type (with low mass-flux).The annual sum of these daily melt values is then assumed to be equalled by accumulation (expressed in mm) at the ELA (since, at the ELA, annual accumulation = annual ablation).Assuming that the annual distribution of temperatures is described by a sine curve, (Brugger, 2006;Hughes, 2008Hughes, , 2009Hughes and Braithwaite, 2008) daily temperatures at the paleo-ELA can be calculated from mean annual air temperature at the paleo-ELA as follows (eq. 2):…”

Glaciares rocosos del sector central de la Montaña Cantábrica : indicadores paleoambientales

“…Estas temperaturas son acordes con las estimaciones recientes en Europa o las Rocosas (Brugger, 2006;Allen et al 2008). Para la fase II, el descenso térmico estimado es de 6,8ºC y para la Fase III de 6,6ºC (entre 5,8 y 7ºC).…”