Mass changes of Southern and Northern Inylchek Glacier, Central Tian Shan, Kyrgyzstan, during 1975 and 2007 derived from remote sensing data

Glacier melt is an essential source of freshwater for the arid regions surrounding the Tian Shan. However, the knowledge about glacier volume and mass changes over the last decades is limited. In the present study, glacier area, glacier dynamics and mass changes are investigated for the period ∼1975-2007 for Southern Inylchek Glacier (SIG) and Northern Inylchek Glacier (NIG), the largest glacier system in Central Tian Shan separated by the regularly draining Lake Merzbacher. The area of NIG increased by 2.0 ± 0.1 km2 (∼1.3%) in the period ∼1975-2007. In contrast, SIG has shrunk continuously in all investigated periods since ∼1975. Velocities of SIG in the central part of the ablation region reached ∼100-120 m ag'1 in 2002/2003, which was slightly higher than the average velocity in 2010/2011. The central part of SIG flows mainly towards Lake Merzbacher rather than towards its terminus. The measured velocities at the distal part of the terminus downstream of Lake Merzbacher were below the uncertainty, indicating very low flow with even stagnant parts. Geodetic glacier mass balances have been calculated using multioral digital elevation models from KH-9 Hexagon (representing the year 1975), SRTM3 (1999), ALOS PRISM (2006) and SPOT-5 high-resolution geometrical (HRG) data (2007). In general, a continuous mass loss for both SIG and NIG could be observed between ∼1975 and 2007. SIG lost mass at a rate of 0.43 ± 0.10 m w.e. ag'1 and NIG at a rate of 0.25 ± 0.10 m w.e. ag'1 within the period ∼1975-1999. For the period 1999-2007, the highest mass loss of 0.57 ± 0.46 m w.e. ag'1 was found for NIG, whilst SIG showed a potential moderate mass loss of 0.28 ± 0.46 m w.e. ag'1. Both glaciers showed a small retreat during this period. Between ∼1975 and 1999, we identified a thickening at the front of NIG with a maximum surface elevation increase of about 150 m as a consequence of a surge event. In contrast significant thinning (>0.5 m ag'1) and comparatively high velocities close to the dam of Lake Merzbacher were observed for SIG, indicating that Lake Merzbacher enhances glacier mass loss.