Abteilung Oberflächengewässer

Porewater salinity reveals past lake-level changes in Lake Van, the Earth’s largest soda lake

March 24, 2017
The variability of lake-levels over past millennia is an important source of climate information because it informs us about the ratio between precipitation and evaporation and hence temperature and humidity. One tool that can be used to reveal those data is mapping the ancient shore lines of lakes. This however, leads only to rather coarse estimates. On the other hand, it is difficult to reconstruct those changes from sediment cores. Recent methods to do this include measuring hydrogen isotopes on organic molecules which however is very time consuming and expensive.
Here we show that a very simple method can give accurate results: measuring the salinity in the pore water, i.e., the salt content in water that has accumulated in the pore space during sedimentation. By extracting this water and measuring the salinity over a 200 m long sediment core from Lake Van we obtained salinity data from the last 600 000 years. We observed strong changes in the salinity especially in the uppermost 100 m of the sediments in Lake Van. These salinity changes indicate major lake-level changes in the past. In line with previous studies on lake terraces and with seismic and sedimentological surveys, we identified two major transgressions (water lever rises) of up to +105 m with respect to the current lake-level at about 135 000 years and 248 000 years before today. At those times two major glacial periods ended and warm periods started. The most dramatic change occurred during the last glacial period, about 30 000 years ago, when lake level fell by about 200 m.

Salinity changes in Lake Van sediments and reconstructed lake level changes