Variable responses of western U.S. glaciers during the last deglaciation

Abstract

Cosmogenic 10 Be exposure ages from moraines in the Wallowa Mountains, Oregon, identify two maximal late Pleistocene glaciations at 21.1 ؎ 0.4 ka and 17.0 ؎ 0.3 ka and a minor glacial event at 10.2 ؎ 0.6 ka. Our new high-resolution chronology, integrated with other well-dated glacial records from the western United States, demonstrates substantial differences in the synoptic responses of western U.S. glaciers to climate forcing associated with the global Last Glacial Maximum and subsequent millennial-scale events originating in the North Atlantic region. These variable synoptic glacier responses identify large changes in the relative contributions of regional to global controls on the climate of the western United States that accompanied the deglaciation.

New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado

“…Instead, fluctuations of western alpine glaciers have often been correlated with North Atlantic air-temperature excursions, such as those associated with Heinrich (H) events (Clark and Bartlein, 1995;Phillips et al, 1996a;Licciardi et al, 2004) and Dansgaard-Oeschger (D-O) events (Benson et al, 2003), under the assumption that these events are hemispheric or global in scale. Climate forcing of glacier advances and retreats also has been attributed to the waxing and waning of the Laurentide Ice sheet (LIS) and the repositioning of the polar jet stream (PJS), which responds to changes in size of the LIS.…”

“…Climate forcing of glacier advances and retreats also has been attributed to the waxing and waning of the Laurentide Ice sheet (LIS) and the repositioning of the polar jet stream (PJS), which responds to changes in size of the LIS. Using a 5.1 at/g/yr production rate for 10 Be at SLHL, Licciardi et al (2004) have suggested that alpine glaciers in the ''northern'' (north of $45.5 1N) 1 region of the western US reached their maximum extent prior to the last glacial maximum (LGM at 2272 calendar ka) and, during the LGM ''experienced subdued advances or retreated in response to their proximity to the LIS.'' They concluded that the glacial records they examined demonstrated substantial differences in the responses of western US glaciers to climate forcing associated with the LGM.…”

Observations: Cryosphere

“…Recent research has established the effects of the Younger Dryas as widespread at localities in the Pacific Northwest (Easterbrook, 1994a(Easterbrook, ,b, 2002(Easterbrook, , 2003aEasterbrook and Kovanen, 1998;Easterbrook, 2001, 2002), the Rocky Mountains (Licciardi et al, 2004, Gosse et al, 1995aEasterbrook et al, 2004), and California (Owen et al, 2003). Planktonic microfossil records from the Pacific Northwest and Alaska also confirm the presence of a Younger Dryas event, with alkenone estimates of sea surface temperatures west of Vancouver Island indicating a temperature drop of 3 O C (Kienast and McKay, 2001).…”

Cosmogenic 10Be chronology of the last deglaciation of western Ireland, and implications for sensitivity of the Irish Ice Sheet to climate Change

“…Additional dating is thus required to determine whether terrestrial sectors of the British-Irish Ice Sheet fl uctuated during the last deglaciation and ascertain their relation to those dated by 14 C of marine fossils. Surface exposure dating using in situ cosmogenic nuclides that are produced in glacial boulders provides such an opportunity for developing chronologies of terrestrial ice margins with millennial-scale resolution (Gosse et al, 1995;Licciardi et al, 2001Licciardi et al, , 2004Kerschner et al, 2006;Rinterknecht et al, 2006;Schaefer et al, 2006). Bowen et al (2002) reported the fi rst cosmogenic nuclide ages from glacial erratics associated with the British-Irish Ice Sheet.…”