Ice thickness distribution and glacier bed of Hallstätter Gletscher

Hallstätter Glacier is the northernmost glacier of Austria. Appendant to the northern Limestone Alps, the glacier is located at 47°28'50'' N, 13°36'50'' E in the Dachstein-region. At the same time with its advance linked to the Little Ice Age (LIA), research on changes in size and mass of Hallstätter glacier was started in 1842 by Friedrich Simony. He observed and documented the glacier retreat related to its last maximum extension in 1856. In addition, Hallstätter Glacier is a subject to scientific research to date.
In this thesis methods and results of ongoing mass balance measurements are presented and compared to long term volume changes and meteorological observations. The current mass balance monitoring programm using the direct glaciological method was started 2006. In this context, 2009 the ice thickness was measured with ground penetrating radar. The result are used with digital elevation models reconstucted from historical maps and recent digital elevation models to calculate changes in shape and volume of Hallstätter Glacier. Based on current meteorological measurements near the glacier and longtime homogenized climate data provided by HISTALP, time series of precipitation and temperature beginning at the LIA are produced. These monthly precipitation and monthly mean temperature data are used to compare results of a simple degree day model with the volume change calculated from the difference of the digital elevation models. The two years of direct mass balance measurements are used to calibrate the degree day model. A number of possible future scenarios are produced to indicate prospective changes.
Within the 150-year-period between 1856 and 2007 the Hallstätter Glacier lost 1940 meters of its length and 2.23 km**2 in area. 37% of the initial volume of 1856 remained. This retreat came along with a change in climate. The application of a running avarage of 30 years shows an increase in precipitation of 18.5% and a warming of 1.3°C near the glacier between 1866 and 1993. The mass loss was continued in the hydrological years 2006/2007 and 2007/2008 showing mean specific mass balance of -376 mm and -700 mm, respectively. Applying a temperature correction for the different minimum elevations of the glacier, the degree day approach based on the two measured mass balances can reproduce sign and order of magnitude of the volume change of Hallstätter Glacier since 1856. Nevertheless, the relative deviation is significant. Future scenarios show, that 30% of the entire glacier volume remains after subtracting the elevation changes between the digital elevation models of 2002 and 2007 ten times from the surface of 2007.
The past and present mass changes of Hallstätter Glacier are showing a retreating glacier as a consequence of rising temperatures. Due to high precepitation, increased with previous warming, the Hallstätter Glacier can and will exist in lower elevation compared to inner alpine glaciers.

哈尔施塔特冰川（Hallstätter Glacier）是奥地利最北端的冰川。该冰川依附于北石灰岩阿尔卑斯山系，坐落于达赫斯坦（Dachstein）区域，地理坐标为北纬47°28′50″、东经13°36′50″。与此同时，其扩张过程与小冰期（Little Ice Age, LIA）紧密关联，弗里德里希·西莫尼（Friedrich Simony）于1842年启动了针对哈尔施塔特冰川规模与质量变化的研究，他观测并记录了该冰川在1856年达到末次最大扩张后发生的退缩现象。时至今日，哈尔施塔特冰川仍是持续开展科学研究的对象。

本论文呈现了当前正在进行的冰川质量平衡（mass balance）监测的方法与结果，并将其与长期体积变化及气象观测数据进行对比。当前采用直接冰川学方法的质量平衡监测项目于2006年启动。在此研究框架下，研究人员于2009年通过探地雷达（ground penetrating radar）对冰川厚度进行了测量。该测量结果与基于历史地图重建的数字高程模型（digital elevation models）以及最新数字高程模型相结合，用于计算哈尔施塔特冰川的形态与体积变化。基于冰川附近的实时气象观测数据，以及由HISTALP提供的长期均一化气候数据集，研究人员构建了可追溯至小冰期的降水与温度时间序列。这些月降水量与月均温度数据被用于将简单度日模型（degree day model）的结果与通过数字高程模型差值计算得到的体积变化进行对比。研究团队利用两年的直接质量平衡监测数据对度日模型进行校准，并构建了多种未来情景以预测冰川的潜在变化。

在1856年至2007年这150年的时段内，哈尔施塔特冰川的长度缩减了1940米，面积减少了2.23平方千米。1856年时的初始冰川体积中仅有37%得以保留。此次冰川退缩与气候变化相伴发生。通过采用30年滑动平均分析可知，1866年至1993年间，冰川附近区域的降水量增加了18.5%，气温升高了1.3℃。2006/2007与2007/2008水文年的质量损失仍在持续，其平均比质量平衡分别为-376毫米与-700毫米。针对冰川不同最低海拔进行温度校正后，基于两次实测质量平衡数据的度日模型方法能够重现1856年以来哈尔施塔特冰川体积变化的符号与量级。不过，其相对偏差仍较为显著。未来情景模拟结果显示，若将2002年与2007年数字高程模型所反映的海拔变化从2007年的冰川表面重复扣除十次，则届时仅剩余冰川总体积的30%。

哈尔施塔特冰川过去与当前的质量变化均表明，气温上升是冰川退缩的主要诱因。由于降水量较高且随前期变暖趋势有所增加，相较于阿尔卑斯内陆冰川，哈尔施塔特冰川能够且将在更低海拔区域存续。