The Contribution of Cosmogenic Nuclides to Unraveling Alpine Paleoclimate Histories
Moraines are non-continuous short-term records of ice marginal positions. Moraines help provide important paleo-glaciological mass balance information (e.g. glacier surface area, ice volume, terminus elevation, snowline altitudes, longitudinal ice surface gradient below the paleo-snowline) which in part controls the geometry of the glacier and the rate of advance and retreat of an ice margin. Therefore, chronologies on these ancient glacial landforms can be directly tied to local paleo-temperature and paleo-precipitation estimates for specific times during and after a glaciation. In the past two decades, the terrestrial cosmogenic nuclide (TCN) exposure dating method has made a revolutionary contribution to the study of alpine paleo-glacial histories and paleoclimatology. (i) Exposure dating of boulders on moraines provides the time since a boulder was deposited from an ice margin. It directly determines when the glacier reached a measurable mass-balance condition, whereas other chronometers, such as radiocarbon, U-series, and luminescence dating, typically provide only minimum or maximum limiting ages on ice margin positions, (ii) The method can provide a precise estimate of the timing of initial ice retreat. Timing of when an alpine glacier reaches its maximum position is not only a function of local climate but also of numerous glaciological and hydrological conditions. Initial retreat is the most discrete short-lived climate-response event in a moraine record. Unlike the timing of initial retreat, initial advance is not recorded in moraine records because glaciers override their moraines during advance (Gibbons et al. 1984).
Keywords10Be Exposure dating Glaciers Moraine Paleoclimate
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