HR: 1340h
AN: U43A-0743    [Abstracts]
TI: Timing of Holocene Glacier Recessions in the Swiss Alps
AU: * Joerin, U E
EM: ujoerin@geo.unibe.ch
AF: Institute of Geological Sciences, University of Bern Baltzerstrasse 1, Bern, 3012 Switzerland
AU: Stocker, T F
AF: Climate and Environmental Physics, Physics Institute University of Bern Sidler-strasse 5, Bern, 3012 Switzerland
AU: Schluechter, C
AF: Institute of Geological Sciences, University of Bern Baltzerstrasse 1, Bern, 3012 Switzerland
AB: Alpine glaciers are sensitive climate indicators on time scales as short as decades to centuries. Periods of cold and wet climatic conditions cause glacial advances and deposition of moraines. Subsequent change to warmer and drier conditions cause glacial recessions. Since the cold event of the Little Ice Age glaciers in the Swiss Alps have retreated substantially exposing high walls of lateral moraines which consist of a stack of overlying till units. Previous work focused on such stacked moraines and the related glacial advances. However, such paleoclimatic reconstructions based only on moraines are incomplete, in particular for periods of glacial recession. This study examines Holocene glacier recessions based on pieces of wood and peat occurring in glaciofluvial deposits of outburst flood events. These subfossil remains indicate that (i) glaciers were once smaller than present, (ii) climate conditions allowed vegetation growth and a higher treeline elevation than today, (iii) sequences of glaciofluvial gravels and lodgement tills accumulated in now glaciated basins. We focus in this study on three climaticly different re-gions: i.e. Unteraar Glacier (Central Alps), Tschierva Glacier (Eastern Alps) and Ried Glacier (South Central Alps). The conventional radiocarbon and AMS dating was used to determine the age of more than 140 samples of wood and peat fragments. The results show that glacier recessions occurred in distinct phases throughout the Holocene, synchronously in different Alpine regions. The total duration of recession phases is longer than 5500 yr or $>$ 50 $%$ of the Holocene epoch. The glacial recessions are separated by glacial advances, which occurred in time periods shorter than 400 yr. A comparison of our Holocene record of glacier length variations with the ice rafted debris events in the North Atlantic, the Be-10 record of ice cores and atmospheric $\Delta$ 14C suggest a combination of solar and North Atlantic forcing. Thus, situations of glacial recession, to the extent of smaller glaciers than present, occurred throughout the Holocene.
UR: http://mypage.bluewin.ch/eljoerin/u-page/activities.htm
DE: 3344 Paleoclimatology
DE: 2162 Solar cycle variations (7536)
DE: 1610 Atmosphere (0315, 0325)
DE: 1620 Climate dynamics (3309)
DE: 1650 Solar variability
SC: Union [U]
MN: 2004 AGU Fall Meeting