Geomorphological studies on the late Pleistocene and early Holocene glaciation in selected high mountain ranges in Taiwan

Taiwan is a subtropical mountainous island situated at the tropic of cancer in the monsoonal western Pacific region. Its high mountain ranges are not glaciated at present, but since they reach nearly 4000 m they provided favourable conditions for late Pleistocene and early Holocene glacier advances. Their isolated position may provide useful high altitude paleoclimatic information for comparison with marine and continental climate archives and other glaciated areas in the region. At the beginning of this project, only little was known about former glaciations on the island based on the work of early researchers, but detailed sedimentological or chronological information was missing. This study focuses on a detailed geomorphologic field mapping and the description and analysis of glacial landforms and deposits concerning their geometry, composition and morphostratigraphical correlation. For a chronological constrain, optically stimulated luminescence and rock surface exposure dating with in situ produced cosmogenic 10Be were applied on glacigenic sediments and glacial boulders, respectively, which allows an independent temporal correlation of different geomorphologic evidences. The central Nanhuta Shan massif in NE-Taiwan had the best preserved glacial landforms and thus studies were focused there. Comparative observations were made in Hsueh Shan and in Yushan. The main finding of this study is, that glaciers advanced repeatedly in the Taiwanese mountains during the last glacial cycle. Large scale glacio-erosional landforms indicate a last glacial equilibrium line altitude below 3000 m with a depression of about 1000 m. Although, age control is still poor for this maximum stage a correlation with the marine isotope stage (MIS) 4 is assumed. Independently derived OSL and 10Be exposure ages from different small scale glacial sediments in Nanhuta Shan yielded a reliable timeframe for a Lateglacial to early Holocene stage with two possible sub-stages at 12 - 15 ka and 9.5 ka and ELA depressions of 610 m and 510 m, respectively. These results correspond basically with the paleoclimatic proxies and other glacial records from the region and suggest a larger mountain glacier extent in East Asia during the MIS 4 than during MIS 2 and a re-advance during the Lateglacial and Holocene. Full glacial advances are interpreted in terms of an increased influence of the westerly circulation, whereas Holocene glaciations seem to be related to monsoon intensification.