Anomaly of glacier mass balance in different vertical zones and responses to climate modes: Urumqi Glacier No. 1, China

Identifying the anomaly of glacier mass balance under climate change is vital for understanding glacier development and conservation, and the mechanism that induces spatial heterogeneity in glacier evolution. The combined effects of climate teleconnections and local atmospheric factors induce the elevation-dependent behavior of glacier mass balance. To examine elevation-dependency of glacier mass balance to climate variability, we divided Urumqi Glacier No. 1, China into seven vertical zones with equal elevation intervals of 100 m from 3700 to 4400 m above the sea level (a.s.l.). We identified anomalies of the glacier mass balance of each elevation zone using the Mann–Kendall test based on the observed data from 1970 to 2018. According to the change rate before and after an anomaly, the sensitive zone of glacier mass balance was determined to be in the middle-elevation (3800–4200 masl). A gain and loss transformation zone is found at elevation interval 4000–4200 masl, and is called the core of sensitive zone. Subsequently, the glacier mass balance response to climate variability was analyzed based on the interrelationship between the mass balance gain and loss and the warm and cold phases of different climate modes including the El Niño–Southern Oscillation, North Atlantic Oscillation and Arctic Oscillation. The La Niña and North Atlantic Oscillation-cold phases strongly affect mass balance. The former causes the mass balance loss mainly in interval 3700–4400 masl. The latter results in the gain in interval 3700–4100 masl and loss in interval 4100–4400 masl Thus, glacier mass balance distribution is vertically heterogeneous, exhibiting a hierarchical structure. In summary, glacier mass balance response to climate change depends on both elevation and climate modes.