Biota, fractures, and thresholds: Emergent self-organization in landscape evolution?

• Applicant: Professor Dr. Dirk Scherler
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry ; Physical Geography
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280525891

This proposal is a continuation of our ongoing work in EarthShape phase 1, in which we investigate the biotic controls on incision and sediment transport by rivers. Our research focuses on the combined effect of discharge variability and erosion thresholds on river incision. During phase 1, we exploit the EarthShape climate and vegetation gradient to decipher the biotic signature in discharge variability and erosional efficiency. However, results from phase 1 also indicate enormous spatial variability in river sediment size (erosion thresholds) and regolith thickness both along and across the EarthShape gradient. Within individual EarthShape study sites, observed spatial gradients in regolith thickness appear to follow gradients in fracture density. We thus hypothesize that biota, through its influence on chemical weathering, may also affect sediment grain sizes, but that this influence may be limited by fracture density. Furthermore, denudation rates in the EarthShape sites are low (~10 m/Myr). This means that the landscapes we study have been formed over time periods of up to several million years, during conditions that were likely different from the present. To unravel the biotic influence on chemical weathering, sediment size, and hence erosion thresholds, and to avoid spurious correlations, we acknowledge the potentially important influence of fracture density and the time-dependent nature of landscape evolution. Here, we propose to (1) quantify the relationship between fracture spacing, regolith thickness, and sediment size, (2) determine the sub-basin scale spatial and temporal variability in hillslope denudation rates, and (3) combine these observations in landscape evolution modeling to quantify the influence of biota on river incision. To do so, we will make extensive use of data and observations collected from all projects during phase 1 and combine these with new field measurements in a new modeling approach in which we explicitly account for hydrologic and topographic effects on chemical weathering and sediment size. Our results will provide key constraints on the comparability of the EarthShape sites, and our modeling approach will provide a new interface that helps integrating the diverse scientific approaches in the EarthShape program.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1803: EarthShape: Earth Surface Shaping by Biota
• International Connection: Chile, USA
• Cooperation Partners: Dr. Eric Deal; Professor Dr. Luca Mao
• Co-Investigator: Professor Dr. Jean Braun