Cosmogenic 10Be Constraints on Deglacial Snowline Rise Since MIS 3 in the Central Himalayas, China

The geochronological dating of glacial landforms, particularly terminal and lateral moraines, is invaluable for determining the extent and timing of past glaciation and for reconstructing the magnitude and rate of past climate changes. In the central Himalayas, well-dated glacial geomorphological records have constrained the last glacial cycle around much of the Mount Everest region. However, the eastern Ama Drime Range remains comparatively less constrained.

Here, we present a detailed chronology dataset from the Marine Oxygen Isotope Stage (MIS) 3 (~29–57 ka) and subsequent deglaciation, focusing on the Zongcuo Valley and Riwu Valley in Ama Drime Range, China (28°6′N, 87°4′E). This analysis is based on 19 beryllium-10 (¹⁰Be) surface-exposure ages from terminal moraine systems within these valleys. We reconstructed the extent and thickness of Last Glacial Maximum (LGM) glaciers through geomorphological mapping and a flowline-based glacial model, PalaeoIce. Additionally, we applied the accumulation area ratio (AAR) method to estimate the equilibrium-line altitude (ELA) for each stage identified.

Our results reveal that the Zongcuo Glacier and Riwu Glacier reached their maximum extents at 39.9 ± 3.3 ka, coinciding with MIS 3. By 25.2 ± 2.9 ka, the Zongcuo Glacier had retreated slightly up-valley. This retreat is evidenced by well-preserved moraine landforms from the LGM, which greatly facilitated our reconstruction of the ancient Zongcuo Glacier. At its maximum, the glacier covered an area of 26.3 km², had a maximum thickness of 343 m, and an ELA ~560 m lower than present (~5260 m a.s.l.), which we used as a baseline for comparison.

By 15.8 ± 1.5 ka, corresponding to the Late Glacial period, the glacier had retreated ~2 km up-valley, indicating at least a ~20% reduction in glacier length relative to its LGM extent. The glacier area decreased to 19.6 km² (a ~25% reduction), with a maximum thickness of 316 m (a ~25% reduction). The ELA was ~480 m lower than present (~5350 m a.s.l.).

By 860 ± 160 years ago, during the Little Ice Age (LIA), the glacier had retreated ~7 km up-valley from its LGM position, representing at least a ~50% reduction in glacier length. The glacier area had decreased to 6.8 km² (~65% reduction), and the maximum thickness was 140 m (~59% reduction) compared to the LGM. The ELA was ~390 m lower than present (~5440 m a.s.l.).

Using a temperature lapse rate estimate, these ELA anomalies suggest that the local mean annual temperature was ~2.1°C colder than the present (1981–2010) at 860 ± 160 years ago, ~2.6°C colder at 15.8 ± 1.5 ka, and ~3.0°C colder at 25.2 ± 2.9 ka, assuming no significant change in precipitation.This study provides critical insights into the response of glaciers to climate change over the past 40 ka in the southern Tibetan Plateau.