New paper finds glaciers in Glacier National Park retreated up to 6 times faster during the 1930's than the past 40 years

A new paper published in Quaternary Science Reviews finds that alpine glaciers in Glacier National Park, Montana retreated up to 6 times faster during the 1930's and 1940's than over the past 40 years.  The "Multi-proxy study of sediment cores retrieved from lakes below modern glaciers supports the first detailed Neoglacial chronology for Glacier National Park (GNP)" and shows "maximum reconstructed retreat rates [in] 1930" of about 125 meters per year, compared to near zero in ~1975 and about 20 meters/year at the end of the record in ~2005.  The authors report, "Results indicate that alpine glaciers in Glacier National Park advanced and retreated numerous times during the Holocene after the onset of Neoglaciation 6,500 years before the present" and "Retreat from the Little Ice Age maximum was the most dramatic episode of ice retreat in at least the last 1000 years."

Fig. 8. Relationship between climate, retreat of the Agassiz Glacier, and flux of carbonate in core UKL-1 from AD 1750 to the present. Dashed line shows CaCO₃ flux in mg/cm²/yr. Filled gray line illustrates the reconstructed retreat rate of the Agassiz Glacier from its LIA terminal moraine, calculated from dating of trees in the glacier forefield (Carrara and McGimsey, 1981). Carbonate flux began to rise at the onset of ice retreat, and reached a peak nearly synchronous with the maximum reconstructed retreat rates ca AD 1930. Filled black line presents a tree-ring compilation (BMS Douglas Fir) sensitive to summer drought collected in the vicinity of the Agassiz Glacier (Pederson et al., 2004). Black fill (note reversed scale) denotes wetter, cooler conditions that were responsible for advance of the Agassiz Glacier to its LIA maximum position. Retreat began with the switch to below-normal precipitation.

A lacustrine-based Neoglacial record for Glacier National Park, Montana, USA

• Jeffrey S. Munroe^a, , , 
• Thomas A. Crocker^a, 
• Alena M. Giesche^a, 
• Lukas E. Rahlson^a, 
• Logan T. Duran^a, 
• Matthew F. Bigl^a, 
• Benjamin J.C. Laabs^b

• ^a Geology Department, Middlebury College, 276 Bicentennial Way, Middlebury, VT 05753, USA
• ^b Department of Geological Sciences, SUNY Geneseo, Geneseo, NY 14454, USA

• http://dx.doi.org/10.1016/j.quascirev.2012.08.005,

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Abstract

Multi-proxy study of sediment cores retrieved from lakes below modern glaciers supports the first detailed Neoglacial chronology for Glacier National Park (GNP), Montana. Analysis focused on sedimentary properties sensitive to the extent and activity of upstream glacier ice, including: water, organic matter, carbonate, and biogenic silica content; bulk density; mass accumulation rate; phosphorus fractionation; magnetic susceptibility; L*a*b* color values; and grain size distribution. Results indicate that alpine glaciers in GNP advanced and retreated numerous times during the Holocene after the onset of Neoglaciation ca 6500 BP. The two oldest phases of glacier expansion were synchronous with the well-documented Garibaldi (5600–6900 BP) and Tiedemann-Peyto (1900–3700 BP) phases in western Canada. Younger phases correspond with the First Millennium Advance in western Canada, as well as glacier with advances in the Sierra Nevada. The culminating Little Ice Age (LIA) advance was the most recent and extensive of a series of advance/retreat cycles over the past millennium. Retreat from the LIA maximum was the most dramatic episode of ice retreat in at least the last 1000 years.

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Highlights

► A high-resolution, lacustrine-based Neoglacial record. ► Neoglaciation began 6500 BP. ► Intervals of expanded glaciers were broadly synchronous within the region. ► Retreat after the Little Ice Age was the most dramatic event of the last millennium.