Erosion due to climate change?

Geosciences research team discovers systematic errors in the interpretation of thermochronological data

Nanga Parbat, Western Himalayas
© Dr Rasmus C. Thiede, Kiel University

Nanga Parbat is one of the fastest-rising mountain regions of the Western Himalayas, which at the same time has the highest erosion rates world-wide. The Himalayas, as the largest and highest mountains in the world, are of great importance for the analysis of geosciences researchers.

In recent times, many geoscientists have suspected that there is a direct relationship between the climate and global degradation (erosion). However, a team led by the Potsdam-based geoscientist Taylor Schildgen has now shown that the analysis of global thermochronological records is currently not sufficiently accurate to confirm a direct relationship between erosion and climate cooling on a global scale over the last 2.6 million years of our earth's history. The research results of the team, which in addition to Taylor F. Schildgen (GFZ German Research Centre for Geosciences/University of Potsdam) also includes Pieter A. van der Beek (Université Grenoble Alpes), Hugh D. Sinclair (University of Edinburgh) and Rasmus C. Thiede (Kiel University, formerly of the University of Potsdam), have now been published in the renowned scientific journal Nature.

For several decades, geoscientists have been fascinated by the idea that the change in global erosion rates on the earth's surface could be connected with climate changes. Such connections could arise because faster erosion can lead to increased silicate weathering, and thus to a more efficient storage of organic carbon in the soil in the form of sedimentary basins. Both processes could explain the observed global cooling, through a reduction of carbon dioxide in the atmosphere. Because in the most recent period of the earth’s history, the Quaternary Period, there has been rapid switching between ice ages and warm periods. In addition, the last 2.6 million years have been characterised by a global trend of cooling. This could be an indication of the relationship between erosion and climate, since geoscientists were also able to show that the change between cold and warm periods boosts erosion.

Geoscientists previously associated the global increase in erosion rates over the last millions of years with the alternating cold and warm periods, as a worldwide increase in sedimentary deposits in the ocean basins has been measured. This data is conflicted by studies which indicated that the global erosion rates have remained stable over this period, and that the apparent increase in sedimentation in the oceans may be caused by improper conservation of sediment samples, gaps in deposition, and different measurement procedures and intervals. In recent times, geoscientists have assembled global thermochronological data sets, which show the cooling of rocks as they approach the earth's surface, for example by erosion. Recently-presented results of thermal modelling suggest a doubling of the erosion rates in high mountainous regions in the last 2.6 million years.

The team of researchers led by Taylor Schildgen examined the approach behind this thermal modelling, for 30 data sets which indicated increased erosion. Their analysis shows possible misinterpretations in 23 of these data sets, which may have been caused by spatial distortions. These distortions can arise, for example, if data from samples with different cooling histories, delineated by important geological boundaries, are combined. This can cause spatial differences to be mistakenly interpreted as thermal processes. The research team reported in Nature that in most of the 23 faulty cases, there was a combination of data from areas which should actually be assigned to different tectonic regions. In four cases, the increase in erosion rates can be explained by intensifying tectonic processes instead of climate changes, for example by faster mountain formation. Together, these 27 data sets show that the link between faster erosion and climate cannot be proven in this way, and that this thesis arose due to inadequate consideration of local geological conditions - which led to systematic errors in the analysis of large thermochronological records. Only in three of the 30 data sets could the team confirm a climatically-induced increase in erosion, which can actually be linked with the rapid cutting of glacial valleys.

The results of the team led by Taylor Schildgen suggest that the analysis of thermochronological data currently does not provide sufficient accuracy over millions of years, to investigate the possible connection between climate and erosion on a global scale. According to the researchers, there is currently no clear evidence of a direct relationship between erosion and climate cooling. Nevertheless, they recognise the potential of local thermochronological investigations to help understand the processes behind global cooling and the changes in erosion rates.

Original publication:
Taylor F. Schildgen, Pieter A. van der Beek, Hugh D. Sinclair & Rasmus C. Thiede. 2018. Spatial correlation bias in late-Cenozoic erosion histories derived from thermochronology. Nature 559, 89–93.
www.nature.com/articles/s41586-018-0260-6

Press release of the University of Potsdam (in German):
www.uni-potsdam.de/nachrichten/detail-list/article/2018-07-05-erosion-durch-klimaveraenderungen-geoforscher-entdecken-systematische-fehler-bei-der-inte.html

Contact:

Dr Rasmus C. Thiede
Petrology and Geodynamics at the Institute of Geosciences at Kiel University
+49 (0)431/880-2895
rasmus.thiede@ifg.uni-kiel.de
www.petrologie.ifg.uni-kiel.de

Professor Taylor F. Schildgen
Institute of Earth and Environmental Science
University of Potsdam
Phone: +49 (0)331/288-27507 
tschild@uni-potsdam.de 
www.geo.uni-potsdam.de

Text: Taylor Schildgen

Farah Claußen
Press, Digital and Science Communication