The Upper Grindelwald Glacier as indicator for Holocene climate variability
Glaciers are useful indicators of current and past climate changes, as they allow to perceive slow changes of the climate system that otherwise would be overwhelmed by short-term variability. Old glacial moraines, for example, document past glacier states: using the appropriate methodology, this information can be converted into an envelope of possible past climate signals required to grow glaciers to a certain extent. However, one major issue with glacial moraines is that they only document the largest extents: all intermediate geomorphological evidences are wiped out by the advancing glacier.
The starting point of our research idea is a unique times series of Holocene glacier fluctuations extracted from speleothems at the Milchbach cave system (Bernese Oberland, Switzerland). The peculiarity of this published record is the uncommon setting of the cave, which has multiple entrances closing and opening with the waxing and waning of the nearby Upper Grindelwald Glacier. Each opening or closing affected the structure of the speleothems, which allowed to reconstruct the variations of the ice thickness at this point for the past ten thousand years. This time series carries a different and more detailed temporal information than paleo-moraines.
The overarching goal of our project is to extract a climate signal from this time series. For this purpose, we will calibrate and validate a numerical model of the Upper Grindelwald Glacier able to simulate the observed fluctuations of the glacier tongue during the last 150 years. We will then use the calibrated model to assess the climate conditions (temperature, precipitation) necessary to close each of the Milchbach cave entrances. This will ultimately provide a range of possible Holocene temperature and precipitation conditions at this location. The model we will use is the Open Global Glacier Model (www.oggm.org), specifically set-up and calibrated for this glacier.
At the interface between several scientific disciplines (climatology, glaciology, paleo-climatology, geology), the project will be a new contribution to the available data and knowledge about the iconic Grindelwald glaciers.