The lowermost ELA in the Central Mountain Range of Taiwan during the LGM - dated with TCN

Mountain glaciers are valuable indicators for climate change in the past and present as they react sensitively by variations of their mass balance expressed by the equilibrium line altitude (ELA). The Central Mountain Range of Taiwan represents an exclusive location for palaeo-climate and palaeo-glaciation research in monsoonal East Asia as it provides high altitude terrestrial data in the western Pacific oceanic environment. The presently unglaciated mountains with about 20 mountain massifs above 3000 m altitude have been subject to repeated, multi-stage glaciations during the late Pleistocene and early Holocene. However, traces of glacial processes are only known from a limited number of mountain massifs. The until now studied glacial landforms are restricted to their highest parts (> 3000 m). Glacial deposits or landforms, which can be reliably attributed to the global Last Glacial Maximum (LGM), have not been found in Taiwan  so far. For this study we focused on a relatively low elevated mountain section in the area around the Beishi Shan massif in central Taiwan, where we mapped cirques with over-deepened floors at elevations between 2700 and 2800 m asl, facing to the east. Glacial boulders and rock surfaces of the cirques’ outlets were dated by means of paired (Be-10/ Al-26) in-situ produced cosmogenic nuclides. The derived ages represent the marine isotope stage 2 for boulders near or at the mountain crests above the cirques. Late-glacial to early Holocene ages yielded samples from the cirque outlets. From the data we reconstruct a plateau-like glaciation of this mountain section around the LGM and a subsequent back-melting that resulted in cirque glaciers persisting in favorable downwind-positions until the early Holocene. The orographic ELA was at ca. 2800 m and even lower during the LGM. This is the lowermost ever reported ELA from the Taiwanese mountain range. The east facing cirque positions also imply a great influence of the permanent westerly circulation above the shallow monsoon circulation on the precipitation regime in high altitudes in East Asia.