Unser Thema heute: Gletscher in Asien. Beginnen möchten wir im Karakorum. Bereits früher hatten wir an dieser Stelle berichtet, dass die Karakorum-Gletscher seit Ende der 1980er Jahre wachsen. Nun hat ein Forscherteam um Tobias Bolch versucht, die Gletschergeschichte in der Region weiter zurück zu verfolgen. Dazu untersuchten sie Gletscher im Hunza-Gebiet. Die Überraschung: Seit den 1970er Jahren sind die Gletscher hier überaus stabil. Hier die Kurzfassung der Studie, die am 9. September 2016 in The Cryosphere Discussions erschien:
Brief Communication: Glaciers in the Hunza Catchment (Karakoram) are in balance since the 1970s
Previous geodetic estimates of mass changes in the Karakoram revealed balanced budgets or a possible slight mass gain since the year ~ 2000. Indications for longer-term stability exist but no mass budget analyses are available before 2000. Here, we show that glaciers in the Hunza River basin (Central Karakoram) were on average in balance since the 1970s based on analysis of stereo Hexagon KH-9, SRTM, ASTER and Cartosat-1 data. Heterogeneous behaviour and frequent surge activities were also characteristic for the period before 2000.
Weiter gehts im Nordwest Himalaya, im Astore-Becken. Dort haben die Gletscher im Zeitraum 1973-2013 ziemlich unterschiedlich auf den Klimawandel reagiert. Laut Fahrhan et al. 2015 haben sich 28 Gletscher leicht vergrößert, 45 leicht verkleinert und die restlichen 25 waren eher stabil. Insgesamt hat sich die Gesamtfläche der Gletscher kaum verändert. Die Reduktion um 0,3% ist statistisch wenig signifikant, wenn man die Fehlerbreite der zur Verfügung stehenden Daten einbezieht. Insgesamt blieben die Gletscher im Untersuchungsgebiet also ziemlich stabil.
Schließlich noch eine Studie von Hochreuther et al. 2015 in Palaeo3 zu Tibet. Die Forscher konnten die Kleine Eiszeit in drei Vorstöße und dazwischenliegende Schmelzphasen unterteilen:
Ages of major Little Ice Age glacier fluctuations on the southeast Tibetan Plateau derived from tree-ring-based moraine dating
Advances and retreats of glaciers on the Tibetan Plateau (TP) are widely regarded as indicators for climate changes sensitive to macroclimatic forcing mechanisms like the Asian summer monsoon. However, it often remains unclear why some glaciers retreat or advance earlier than others, particularly regarding the timing of the so-called ‘Little Ice Age (LIA) maximum’. Within this study, we present newly acquired tree-ring data from four glacier forefields in the Nyainqêntanglha Range on the southeastern TP and link them to previous studies. Two of the glaciers formed a double-tongue moraine set during the LIA, with trees providing minimum ages for two different major glacier extents. In combination with evidence from a third glacier, three warm phases within the generally cold LIA can be deduced during the first half of the 16th century, and the mid-17th and 18th centuries. This implies the occurrence of three preceding major cold spells. A minor cool phase between 1790 and 1850 marks the end of the LIA on the southeast TP. Minimum ages for beginning retreat from the last major LIA glacial advance differ by only 40 years for all sampled monsoonal temperate valley glaciers in the Nyainqêntanglha Range. This implies a common forcing, whose impact on glacier dynamics is only slightly altered by topographical factors or local climatic conditions. Regression analysis suggests that the delay of the glacier retreat from the maximum extent is mainly related to glacier size, with minor influence of ablation area aspect. All moraine ages highlight intermediate LIA warm phases on the southeast TP corresponding to warm phases on the northern Hemisphere and thus prove monsoonal temperate glaciers to be highly sensitive archives for northern hemispheric climatic conditions.
