Geologic Reconstructions of Changes in Erosion Rates and Hillslope Processes in Response to Climate Forcing
Final Report Abstract
Research within the Emmy Noether Group headed by T. Schildgen since February 2013 has resulted in important insights into landscape response to climate change, and how those responses are recorded in the geologic record. The following summary describes the main insights and their applications: 1) Our work has revealed details of landscape response to climate change in several field sites, including changes in erosion rates and erosion processes; such information is critical for understanding how future climate change may affect soil resources as well as natural hazards, particularly with respect to the incidence of landslides and debris flows. 2) We have shown that different regions, notably drainage basins of different size, are most sensitive to climate change that occurs on different timescales, suggesting that different sectors of a landscape are sensitive to different frequencies of climate forcing. With respect to ongoing anthropogenic climate change, which can be thought of as a high-magnitude, high-frequency perturbation of our climate system, this finding suggests that erosion rates and processes in small catchments and hillslopes will be more severely impacted compared to large catchments and large drainage systems. 3) We discovered that alluvial fans comprise sensitive archives to changes in precipitation, opening up a new avenue of research in the realm of geomorphic archives of paleoclimate. Specifically, we have found that alluvial fan lobes tend to be incised during periods of increased precipitation, and deposit sediment during periods of decreased precipitation. 4) We have derived an equation for the evolution of alluvial channels based on first-principles-based governing equations for flow, sediment transport, and channel morphodynamics, with parameters grounded in theory and defined through experimental data. This equation is the first that enables alluvial channels, which are the dominant type of river channel on Earth, to be interpreted in the context of their external forcing, specifically changes in water discharge, sediment discharge, and tectonic forcing. One application of this equation with respect to paleoclimate interpretations is that it allows us to discern details of how forcing has changed through time by comparing the longitudinal profiles of fluvial terraces and modern channels. 5) We found compelling evidence for how vegetation cover acts as a negative feedback on erosion rates in a dry area that experiences increased precipitation. Although similar findings had been reported for plot-scale studies and individual hillslopes, this work is among the very first to discern these effects on spatial scales of drainage basins. 6) We have illustrated that particularly at long timescales, discerning landscape response to climate change must be intimately coupled with an understanding of how other processes, including tectonics and upper mantle flow, have affected the landscape. On this topic, our work in re-examining the impact of Plio-Pleistocene climate change on global erosion rates has re-opened a topic that was previously thought to be answered. Among these insights, 2) and 3) are the main “surprises” to have emerged. Both are topics that the PI and other group members are excited to further pursue in the future through research proposals that are currently in preparation In total, this work has helped my group to establish itself among the leaders in the field in investigating landscape response to climate change. For example, I was recently recognized by Nature INDEX as being among 11 “Rising Stars” in science (https://www.nature.com/articles/d41586-018-06622-8), and both my group members and I are now regularly invited to speak both at major international conferences and at departmental seminars throughout the world on topics related to work done during the Emmy Noether project.
Publications
- 2014. Can stable isotopes ride out the storm? The role of convection for water isotopes in models, records, and paleoaltimetry studies in the central Andes. Earth and Planetary Science Letters, 407, 187-195
Rohrmann, A., Strecker, M.R., Bookhagen, B., Mulch, A., Sachse, D., Pingel, H., Alonso, R.N., Schildgen, T.F., Montero, C.
(See online at https://doi.org/10.1016/j.epsl.2014.09.021) - 2016. Climatic controls on debris-flow activity and sediment aggradation: The Del Medio fan, NW Argentina. Journal of Geophysical Research - Earth Surface, 121
Savi, S., Schildgen, T.F., Tofelde, S., Wittmann, H., Scherler, D., Mey, J., Alonso, R., Strecker, M.
(See online at https://doi.org/10.1002/2016JF003912) - 2016. Glacial isostatic uplift of the European Alps. Nature Communications, 7, 13382
Mey, J., Scherler, D., Wickert, A.D., Egholm, D., Tesauro, M., Schildgen, T.F., Strecker, M.R.
(See online at https://doi.org/10.1038/ncomms13382) - 2016. Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity. Journal of Geophysical Research - Earth Surface, 121, 392-414
Schildgen, T.F., Robinson, R.A.J., Savi, S., Phillips, W.M., Spencer, J.Q.G., Bookhagen, B., Scherler, D., Tofelde, S., Alonso, R., Kubik, P.W., Binnie, S.A., Strecker, M.R.
(See online at https://doi.org/10.1002/2015JF003607) - 2016. Tectonic control on rock uplift, exhumation, and topography above an oceanic-ridge collision - Southern Patagonian Andes (47°S), Chile. Tectonics, 35, 1317-1341
Georgieva, V., Melnick, D., Schildgen, T.F., Ehlers, T.A., Lagabrielle, Y., Enkelmann, E., Strecker, M.R.
(See online at https://doi.org/10.1002/2016TC004120) - 2017. 100 kyr fluvial cut-and-fill terrace cycles since the Middle Pleistocene in the southern Central Andes, NW Argentina. Earth and Planetary Science Letters, 473, 141-153
Tofelde, S., Schildgen, T.F., Savi, S., Pingel, H., Wickert, A., Bookhagen, B., Wittmann, H., Alonso, R., Cottle, J., Strecker, M.R.
(See online at https://doi.org/10.1016/j.epsl.2017.06.001) - 2017. Short-lived increased erosion during the African Humid Period: evidence from the northern Kenya Rift. Earth and Planetary Science Letters, 459, 58-69
Garcin, Y., Schildgen, T.F., Torres Acosta, V., Melnick, D., Guillemoteau, J., Willenbring, J., Strecker, M.R.
(See online at https://doi.org/10.1016/j.epsl.2016.11.017) - 2018. Effects of deep-seated versus shallow hillslope processes on cosmogenic 10Be concentrations in fluvial sand and gravel. Earth Surface Processes and Landforms
Tofelde, S., Düsing, W., Schildgen, T.F., Wickert, A.D., Wittmann, H., Alonso, R., Strecker, M.R.
(See online at https://doi.org/10.1002/esp.4471) - 2018. Spatial correlation bias in Late Cenozoic erosion histories derived from thermochronology. Nature, 559, 89-93
Schildgen, T.F., van der Beek, P.A., Sinclair, H.D., Thiede, R.C.
(See online at https://doi.org/10.1038/s41586-018-0260-6) - 2018. The topographic evolution of the Central Andes. Elements, 14(4), 231-236
Schildgen, T.F., Hoke, G.D.
(See online at https://doi.org/10.2138/gselements.14.4.231)
