Late Glacial and Holocene mountain glacier fluctuations in the northern hemisphere, the bipolar seesaw, and CO2

Friday, 19 December 2014: 11:40 AM
Joerg M Schaefer, Columbia University of New York, Palisades, NY, United States, Summer Rupper, Brigham Young University, Department of Geological Sciences, Provo, UT, United States, Durban G Keeler, Brigham Young University, Provo, UT, United States, Irene L. Schimmelpfennig, CEREGE, Aix-en-Provence Cedex, France, Susan Ivy-Ochs, ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland, Jostein Bakke, University of Bergen, Bergen, Norway, Hella Elisa Wittmeier, University of Bergen, Department of Earth science, Bergen, Norway, Robert C Finkel, University of California Berkeley, Berkeley, CA, United States, Naki Akcar, University of Berne, Berne, Switzerland and Christian Schluechter, Institute for Geological Sciences and Oeschger Center for Climate Change Research, University of Berne, Berne, Switzerland
Mountain Glaciers have become widely used detectors of past climate changes on a near-global scale, and knowledge of the timing, extent and underlying climate drivers have become more accurate thanks to progress in the fields of geochronology, (remote) mapping techniques, and mountain glacier modeling.

We here present new mountain glacier records from northern mid-latitudes (Swiss Alps), deposited during the Late Glacial (15-11.5 kyr ago) and Holocene (the last 11.5 kyr) periods. We used glaciological assessments to select mountain glaciers that are most sensitive to summer temperature change. We evaluate the amplitude of past advances and use a simple and robust mountain glacier model to estimate the corresponding lowering of the equilibrium line altitudes. 10Be surface exposure dating, based on recent and new local production rate calibrations, provide the chronological framework for this study.

The timing and, to a certain extent the amplitude, of the investigated Late Glacial mountain glacier culminations in northern mid- (and high-) latitudes show a high level of internal consistency, indicating regional to hemispheric summer temperature changes by a few oC as the primary driver on a regional to hemispheric scale. The consistency of the northern mountain glacier pattern during the Late Glacial period extents to the southern hemisphere, suggesting that mountain glacier fluctuations during this interval were in phase, and thus do not show a bipolar seesaw signature. In contrast, the much smaller-scale Holocene mountain glacier fluctuations show a different picture, with robust inter-hemispheric differences in the mountain glacier records. We discuss potential climate scenarios that might help to explain the observed Late Glacial and Holocene mountain glacier pattern.