Increased Erosion Rates Following the Onset of Pleistocene Periglaciation at Bear Meadows, Pennsylvania, USA

• Published in: Geophysical research letters 2022-02, Vol.49 (4), p.n/a
• Main Authors: Del Vecchio, J., DiBiase, R. A., Corbett, L. B., Bierman, P. R., Caffee, M. W., Ivory, S. J.
• Format: Article
• Language: English
• Subjects: Bedrock; Beryllium 10; Climate change; Cold; Cold climates; Cold weather; cosmogenic; Cycles; Erosion processes; Erosion rates; Extreme cold; Extreme low temperatures; Geochemistry; geochronology; geomorphology; Glacial periods; Glaciers; Global warming; Ice ages; Interglacial periods; Isotopes; Latitude; Lithology; Meadows; Mountains; Neogene; periglacial; permaforst; Permafrost; Pleistocene; Regolith; Sediments; Signal processing; Thawing; Tracers
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096739

Direct measurements of erosional response to past climate change are scarce, but mid‐latitude landscapes can record how shifts between cold and warm periods altered erosion outside glacial margins. To study hillslope responses to periglaciation, we measured bulk geochemistry and cosmogenic 10Be and 26Al concentrations in colluvium and weathered bedrock in an 18 m regolith core from Bear Meadows, Pennsylvania, ∼100 km south of maximum glacial extent. Using core lithology, cosmogenic nuclide concentrations, and regional 10Be‐derived erosion rates, we show the onset of 100‐Kyr glacial cycles at the Mid‐Pleistocene Transition (1.2–0.7 Ma) instigated multiple periglacial episodes in central Appalachia, increasing erosion rates compared to the relatively warmer Neogene. Our results show the higher efficiency of periglacial versus temperate erosion processes and highlight a pervasive Pleistocene periglacial erosion signal preserved in the 10Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes. Plain Language Summary During ice ages in the past 2.6 million years, mid‐latitude landscapes like central Pennsylvania were shaped by extreme cold and thawing permafrost, conditions that promote fast breakdown and transport of soil. However, the effect of these cold climates and subsequent warming on erosion rates is unclear since we often lack records of hillslope erosion of warm and cold periods. We drilled 18 m through hillslope material emplaced during permafrost thaw and into the underlying weathered bedrock, and measured the concentrations of 10Be and 26Al, two isotopes that serve as tracers of burial timing and erosion rate. The ratio of 26Al/10Be in the oldest permafrost thaw unit indicates the material was deposited about one million years ago, corresponding to a switch to colder glacial periods followed by more abrupt and extreme warming. The concentrations of 10Be in bedrock below the deposits also imply slower erosion rates prior to the onset of glacial‐interglacial cycles. Our results indicate that cold climate processes are more efficient at eroding rock and transporting sediment than temperate processes and help explain patterns in erosion rates across the mid‐Atlantic region measured over different time scales. Key Points In situ 10Be and 26Al measured in 18 m regolith core from central Pennsylvania, 100 km south of Pleistocene maximum glacial extent Periglacial activity be