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

Abstract

The connection between climate and erosion is fundamental to understanding the evolution of Earth's surface, yet identifying mechanisms of climate-modulated erosion is limited by a lack of upland records of landscape change. Sediment storage time in uplands is often shorter than glacial-interglacial cycles, but landscape form integrates over timescales that include multiple climate cycles (Perron, 2017). Direct records of slope behavior are rarely preserved (Pederson et al., 2000), so reconstructions of climate-modulated hillslope processes rely on indirect evidence of changes to sediment and/or water flux preserved in river terraces, floodplains, and lake/ marine deposits, which can be obscured by the effects of sediment transport and preservation bias (Willenbring & Jerolmack, 2015).Landscapes at middle latitudes experienced wide temperature ranges before and after glacial maxima, and thus present an opportunity to study landscape response to intermittent cold (but non-glacial) periods throughout the Quaternary. Cold conditions can promote rock fracturing (Hales & Roering, 2007;Hallet et al., 1991). On hillslopes, seasonal and/or abrupt thaw of permafrost can accelerate soil flux via solifluction and slope failures

Hillslope and vegetation response to postglacial warming at Bear Meadows Bog, Pennsylvania, USA

“…To explore bog sediment provenance, we also used the handheld XRF to measure bulk geochemistry of 12 samples from an adjacent hillslope core, collected via vibratory (sonic) drilling (Del Vecchio et al, 2022) (Table S2). Five samples were from the upper 6.5 m of regolith.…”

“…To further examine geochemical trends in core S-02, we conducted two principal component analyses (PCAs) on the bulk geochemical data from S-02 and regolith from adjacent hillslopes (Del Vecchio et al, 2022; see Table S6 for additional loading data and PCAs) with the Scikit-learn Python package (Pedregosa et al, 2011). We did not analyze elements with low detection values, which we defined as a detection in fewer than 40% of the samples, to avoid skewing PCA results by including potential false negatives.…”

“…The analysis of all high-detection-threshold elements results in a biplot (Fig. 6A) with three clusters of samples: fine-grained bog sediments 0-32 cm below the peat-sediment interface (facies O-T, BG, O-M, and MA), coarse-grained bog sediments from 34 to 50 cm depth (facies BS), and nearby periglacial slope deposits (SO) and bedrock samples (BR) (Del Vecchio et al, 2022). Sediments from 0 to 32 cm depth correspond to calibrated radiocarbon ages 9510-14,720 cal yr BP, the latter date being the oldest measured date at our site.…”

“…PC2 is more positive in the deepest sediments (42-50 cm depth) as well as 28-30 cm depth (age modeled 13.3-14.0 ka) and 0-8 cm depth (age modeled 9.6-10.0 ka). We interpret the continuum of composition along PC2 among the bedrock endmember, hillslope soils comprised mainly of weathering bedrock (Del Vecchio et al, 2022), and basin sediments to imply that the most-positive values represent a geochemically local source (bedrock) and that negative values represent a source from outside the basin (i.e., dust).…”

“…Evidence for periglacial surface processes (e.g., solifluction, ice wedge polygons) is widespread from Pennsylvania to northernmost Virginia (Merritts et al, 2015; Merritts and Rahnis, 2022). Landforms and deposits from multiple Pleistocene cold periods are preserved across central Appalachian landscapes (Braun, 1989; Denn et al, 2017; Del Vecchio et al, 2018, 2022). Compared to modern processes, these relict landforms (Del Vecchio et al, 2018; Merritts and Rahnis, 2022) are interpreted to reflect a combination of high regolith production driven by frost cracking during colder glacial periods (Hales and Roering, 2007) and accelerated hillslope transport during permafrost thaw due to slope failure (Matsuoka, 2001).…”