Using a paleo perspective to decipher climate controls on erosion and landscape evolution

Abstract:

Today, topographic, erosion, and climate data are measured in abundance but the role of climate in modulating sediment production and landscape evolution remains difficult to characterize. Studies that quantify climate controls on denudation by analyzing multiple study areas with varying temperature and precipitation are hampered by site-to-site variations in topography, substrate, and vegetation, as well as uncertainty in the state of landscape adjustment. Alternatively, sedimentary records at a given location provide a means to track how climate variations influence sediment flux and weathering rates and mechanisms. Cosmogenic nuclide concentrations in well-dated sediment cores provide a means to quantify how erosion rates track climate, particularly orbital (or Milankovitch), fluctuations. Most cosmogenic analyses of erosion assume steady exhumation. By contrast, time-varying cosmogenic concentrations at a given location require a systematic inverse analysis of inheritance to decipher actual erosion rate changes that integrate in observed cosmogenic concentrations. Failure to consider transient erosion results in biased interpretations of paleo-erosion datasets. Here, we use a suite of inverse methods to constrain erosion rates through the last 50kya at our forested, steepland field site in western Oregon where Last Glacial Maximum (LGM) erosion rates are observed to be 2.5x faster than modern rates. Both paleoclimate simulations and paleovegetation data indicate colder and drier conditions during the LGM across our study domain, such that temperature, rather than precipitation, may be the dominant driver of geomorphic processes during glacial intervals in many mid-latitude regions. Other climate dependencies will apply elsewhere, but the coupling of process theory and climate reconstructions with well-characterized sedimentary records will help resolve the enigmatic role of climate fluctuations.