Hydrological evolution during the last 15 kyr in the Tso Kar lake basin (Ladakh, India), derived from geomorphological, sedimentological and palynological records

摘要

The Tso Kar lake basin in Ladakh, northwestern Himalayas (33 degrees 18'N, 78 degrees E, 4527 m a.s.l.) is located close to the modern boundary of effective moisture transport from the Indian summer monsoon. In order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr, we studied the geomorphology of the basin and combined the results with multi-proxy records from Tso Kar lake sediments. Major analyses comprise geochemical data (high-resolution X-ray fluorescence, XRF), mineral composition (XRD), aquatic pollen and non-pollen palynomorphs (NPP). Although the chronological framework based on 41 C-14 AMS dates remains speculative for the Lateglacial and late Holocene periods, our results indicate major hydrological phases linked to regional climate variations and tectonic activity. The maximum glacier advance falls within the period between the global LGM and ca 15 kyr BP, while the basin remained open and may have drained along the paleo Tso Kar River. Tectonic pulses may have triggered terrace development and the closure of the lake. The estimated mean vertical displacement rate accounts for 7-9 mm/yr. Considerable summer monsoon moisture supply occurred for the periods around 12.5 kyr BP and between ca 11.5 and 8.6 kyr BP, indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora. The lake level rise about 11.8 kyr BP was due to intensified glacier melt and summer monsoon effective moisture supply. The lake reached its maximum level and extent between 8.5 and 7 kyr BP under warm-moist climate conditions. Permafrost was absent from the basin. Summer monsoon influence weakened after 8 kyr BP with a short reverse trend at ca 5-6 kyr BP. The lake shrank gradually after 7 kyr BP towards its lowest stand at about 4.2 kyr BP, with return of permafrost activity. Subsequent terrace formation was probably amplified by tectonic movement. The lake remained at a low level with minor fluctuations. The results indicate that the orbitally driven regional climate variability is well reflected in the Tso Kar basin by hydrological variations. Considerable summer monsoon moisture seems to have influenced the area only during the early Holocene. The late Quaternary evolution of the Tso Kar was controlled by the interplay of climate forces, local morphodynamics and tectonic impact.