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

Investigator Names and Contact Info:

• Dirk Scherler (Geology/Geochemistry).  German Research Centre for GeoSciences (GFZ) Potsdam, Germany
• Jean Braun (Geophysics / Modelling). German Research Centre for GeoSciences (GFZ) Potsdam, Germany

Chilean Collaborators Involved:

• Luca Mao (Fluvial Geomorphology). Pontificia Universidad Catolica de Chile & University of Lincoln, UK

PhD:

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

• Emma Lodes. German Research Centre for Geosciences GFZ, Potsdam & Freie Universität Berlin, Berlin,  Germany

supervisor: Jun. Prof. Dr. D. Scherler, co-supervisor: Prof. J. Braun

MSc:

Landsat-derived land surface temperatures in the Earthshape sites.

• David Scheer. German Research Centre for Geosciences GFZ, Potsdam & Freie Universität Berlin, Berlin,  Germany

supervisor: Jun. Prof. Dr. D. Scherler, co-supervisor: Prof. J. Braun

Project summary:

The proposed project is a continuation of our ongoing effort to quantify the effect of biota on bedrock river incision over geological time scales. Within the first phase of the EarthShape SPP, we hypothesized that biota, and specifically the presence of soils and vegetation, influence the process of river incision, and thus landscape evolution, primarily by modulating the magnitude-frequency distribution of flood events. We are testing this hypothesis by combining a stochastic-threshold stream power model of bedrock river incision with cosmogenic nuclide-derived denudation rates and a large dataset of daily discharge records. In the second phase, we want to extend our research towards the hillslopes and focus on how biotic and abiotic processes control discharge generation and the magnitude of erosion thresholds. The most basic and presumably important threshold in rivers is the discharge needed to mobilize the sediments that mantle most riverbeds. All else equal, mobilizing large grains requires greater discharge compared to small grains. Therefore, besides discharge distributions, both bedrock lithology and fracture spacing, which sets the initial grain size, and weathering processes, which reduce grain sizes during hillslope residence, ought to be important. We will tackle this issue by (1) quantifying spatial gradients in fracture density, regolith thickness, and sediment size using field observations, (2) quantifying the spatial variability of hillslope denudation rates using cosmogenic nuclides, and (3) testing the relative strengths of abiotic and biotic controls on landscape evolution with numerical simulations. In the modeling part, we strive to integrate existing theory with various kinds of observational data from all other EarthShape projects. We will further test the possibility of self-organization in landscape evolution that emerges through interaction and feedbacks between topography, fracture spacing, chemical weathering, and biota. The outcome of this research shall provide us with quantitative estimates of how sensitive bedrock river incision is to biota, and how we can potentially identify a biotic signature in actual landscapes.