Section 3.4: Earth Surface Geochemistry

Head of Section: Prof. Dr. Friedhelm von Blanckenburg

The Earth's surface is always changing. Every person notices this, because rocks exposed to the elements weather, soils are washed away, vegetation grows, glaciers push moraines and rivers carry huge volumes of sediments. But, what controls Earth’s rock and soil cycling processes?

In our section, which is still being developed, we investigate these near-surface processes with new geochemical methods. We want to understand the roles that the various forces contributing to these processes play: how does the make-up of the rocks and the relief in the landscape contribute to the speed at which soil develops? How do rain and glaciers influence erosion rates and patterns? What role does the type of vegetation play? How does man influence these processes? We also ask, though, how the forces from within the Earth, such as tectonic uplift contribute to the changes at the Earth's surface.

The main tool for our investiations are atomic nuclei that have lost some of their protons or neutrons due to cosmic radiation. While these cosmogenic nuclides are very rare, they are detectable in tiny amounts in all soils, as well as in river and ocean water. The abundances give clues to the changes in and the age of a landscape. We employ highly sensitive spectrometers, to measure the very small amounts of the various nuclides in soils and sediments. Nature also gives us other geochemical clues. When a rock weathers, for example, the chemical elements which get into the groundwater are taken up as nutrients by plants. Certain subsets of these elements, the heavy or light isotopes, preferentially enter the ground water and are taken up by the plants. When we measure the ratios of these isotopes, we find the fingerprint of the chemical and biological type of material transfer on the Earth's surface.