Earth and Planetary Science
EPS Near-Surface Geochemistry and Geobiology

Berkeley Postdoctoral Researcher Analyzes Erosion Rates and Geomorphic Processes in Western Oregon

Monday, March 27, 2017

Jill A. Marshall is first author of “Late Quaternary climatic controls on erosion rates and geomorphic processes in western Oregon, USA.” The article was first published online January 2017 in The Geological Society of America Bulletin.

Climate regulation of erosion in unglaciated landscapes remains difficult to decipher. While climate may disrupt process feedbacks that would otherwise steer landscapes toward steady erosion, sediment transport processes tend to erase past climate landforms and thus bias landscape evolution interpretations. Here, Marshall and her co-authors couple a 50 k.y. paleoenvironmental record with 24 10Be-derived paleo-erosion rates from a 63-m-thick sediment archive in the unglaciated soil-mantled Oregon Coast Range. Their results span the forested marine oxygen isotope stage (MIS) 3 (50−29 ka), the subalpine MIS 2 (29−14 ka), and the forested MIS 1 (14 ka to present). From 46 ka through 28.5 ka, erosion rates increased from 0.06 mm yr−1 to 0.23 mm yr−1, coincident with declining temperatures. Mean MIS 2 erosion rates remained at 0.21 mm yr−1 and declined with increasing MIS 1 temperatures to the modern mean rate of 0.08 mm yr−1. Paleoclimate reconstructions and a frost-weathering model suggest periglacial processes were vigorous between 35 and 17 ka. While steady erosion is often assumed, their results suggest that climate strongly modulates soil production and transport on glacial-interglacial time scales. By applying a cosmogenic paleo-erosion model to evaluate 10Be concentrations in their sedimentary archive, the authors demonstrate that the depth of soil mixing (which is climate-dependent) controls the lag time required for cosmogenic erosion rates to track actual values. Their results challenge the widely held assumption that climate has minimal impact on erosion rates in unglaciated midlatitude terrain, which invites reconsideration of the extent to which past climate regimes manifest in modern landscapes.

Jill Marshall is a postdoctoral researcher in the Berkeley Earth and Planetary Science Department.

For the full-length article please click here.