An analysis of the ice temperature and velocity along the main flowline of Guliya Ice Cap of Western Kunlun Mountains based on glacier dynamical model

Abstract

Glacier is an important component of the hydrological cycle at different temporal scales. A major mechanism of glacier formation is ″metamorphosis″, by which snow changes into ice. The process is affected by glacier temperature, velocity and mass balance. In recent decades, glaciers in the Western Kunlun Mountains manifested differently from those in other regions. Understanding the mechanism behind their abnormal response to climate change is pressing in order to predict their future trend. However, few simulation researches of Tibetan Plateau glacier change responding to climate warming have been done due to limitation of the availability of glaciological data in situ measurements. Knowledge of present-day ice temperature and velocity is important in order to determine how fast a glacier may respond to climate change. Guliya Ice Cap is located in the Western Kunlun Mountains which lies in the northwestern part of Tibetan Plateau. It is an extremely continental-type (cold) glacier and is characterized by low temperature and precipitation. Using the few observed data for ice temperature and surface velocity, we apply a two-dimensional higher-order thermomechanical flowline dynamical model to simulate the ice temperature and velocity in steady-state along the main flowline of Guliya Ice Cap. The rare but valuable observational data are used to validate the results of numerical simulation of the model in this study. Owing to the uncertainty of parameters′ values, some diagnostic experiments have been conducted to simulate the present-day spatial distributions of ice velocity and temperature along the main flowline of the Guliya Ice Cap. Based on the sensitivity experiments described above, the appropriate parameters on which the model can best simulate the present-day ice velocity and temperature distributions of Guliya are selected. Generally, modeled and observed ice surface velocities exhibit good agreement under the parameters we adopted. Our results show that significant spatial difference of velocity field of the ice cap exists. The ice flow velocities on the terminus and the ablation zone are lower compared to those in the accumulation area. Similar to other alpine land-terminating glaciers, the mean annual horizontal ice flow speeds of Guliya are relatively low (less than 20 m/a). Several velocity extremum regions inside the ice cap can be observed from the simulation results. Along the streamline profile, the glacier surface velocity is higher than that at the bottom, especially in the glacier accumulation area. Modeled ice temperatures agree well with observed values in a borehole drilled to bottom in 1992. Temperature distribution along the glacier′s streamline profile demonstrates an increasing trend from glacier surface to the bed rock, for example −16.2–−1.65°C at a site of 6200 m above sea level (asl). We extract several vertical profiles of temperature distribution at different altitudes. We find that ice temperature near the glacier terminus remains lower than the melting point, and the temperature gradients are various in different altitudes. This phenomenon indicates that physical property of basal ice frozen to the bed constrains the low amplitude response of the temperature field and the terminus dynamics. We speculate that subsequent simulation researches can possibly consider basal sliding contributes in the future by a sensitivity test of the basal temperature under different scenarios. For a large ice cap with few data in situ observations, it is difficult to construct a suitable glacier model with both reliability and simplicity, nevertheless, we can simulate the main glacier dynamic features with much accuracy. The model suggests that the relatively small change in strain rate and low ice temperature near the glacier terminus may be the reason why the Guliya Ice Cap is the most stable glacier found in China up to now.