An official website of the United States government
Abstract 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 cosmogenic10Be and26Al 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 regional10Be‐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 the10Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes.
more »
« less
This content will become publicly available on December 31, 2025
Ground-penetrating radar investigation of regolith thickness on a periglacial alpine summit flat, Uinta Mountains, Utah, USA
Summit flats are low relief, gently sloping landforms common in periglacial mountain environments. Apart from at their edges where summit flats are truncated by glacial headwalls, and at their crests where isolated tors are occasionally present, bedrock is typically mantled on a summit flat by a continuous layer of regolith. This study applied ground penetrating radar (GPR) to survey the thickness of regolith on a summit flat in the Uinta Mountains (Utah, USA). More than 500 m of GPR data were collected along transects extending from the edge of the summit flat to the crest, as well as adjacent to a deep soil pit. Results indicate that the regolith thickness is quite variable, with a mean of 91 ± 38 cm. Because the ground surface of the summit flat is notably smooth, the variability in thickness is a consequence of irregularities in the bedrock surface at depth, which is significantly rougher. Recognition that regolith thickness can vary considerably beneath an alpine summit flat has implications for soil formation, carbon storage, and the transmission and storage of shallow groundwater, as well as evolutionary models for periglacial mountain landscapes.
more »
« less
- Award ID(s):
- 2012082
- PAR ID:
- 10509544
- Publisher / Repository:
- Taylor & Francis
- Date Published:
- Journal Name:
- Arctic, Antarctic, and Alpine Research
- Volume:
- 56
- Issue:
- 1
- ISSN:
- 1523-0430
- Subject(s) / Keyword(s):
- Periglacial Summit Flat Regolith Ground Penetrating Radar Critical Zone
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Sensitivity of ecosystem productivity to climate variability is a critical component of ecosystem resilience to climate change. Variation in ecosystem sensitivity is influenced by many variables. Here we investigate the effect of bedrock lithology and weathering products on the sensitivity of ecosystem productivity to variation in climate water deficit using Bayesian statistical models. Two thirds of terrestrial ecosystems exhibit negative sensitivity, where productivity decreases with increased climate water deficit, while the other third exhibit positive sensitivity. Variation in ecosystem sensitivity is significantly affected by regolith porosity and permeability and regolith and soil thickness, indicating that lithology, through its control on water holding capacity, exerts important controls on ecosystem sensitivity. After accounting for effects of these four variables, significant differences in sensitivity remain among ecosystems on different rock types, indicating the complexity of bedrock effects. Our analysis suggests that regolith affects ecosystem sensitivity to climate change worldwide and thus their resilience.more » « less
-
Aspect influences critical zone (CZ) function, particularly in mountainous terrain where it is an ecosystem-defining geographical feature. Distinct insolation across aspects is linked to differences in water availability and flows, land cover and vegetation productivity, soil thickness and rooting depths, frost cracking, weathering rates, and solute concentrations. Relatively few studies have explored any changing influence of aspect on vegetation productivity, which governs soil water storage and runoff. We probe the hypothesis that the productivity benefit of growing on aspects with greater radiation inputs in mountain systems has been declining over the past few decades as warming has accelerated. We quantify how forest productivity varies with aspect from 1985 to 2021 across the world’s mountain ranges using a monthly-averaged, satellite-derived measure of greenness (NDVI). Globally, most montane forests exhibited increasing greenness over time. Mountainous forests ~15° to ~40° latitude N or S of the equator exhibited behavior consistent with our hypothesis by increasingly favoring shadier aspects, particularly during growing seasons when rainfall and soil moisture can be limiting to productivity. In contrast, closer to the poles where climates are coolest and aspect has an even greater influence on annual solar radiation, the benefit of a sun-facing aspect appears to be increasing across all seasons, consistent with poleward forest community migration hypotheses. We also demonstrate greater increases over time in montane forest greenness on east-facing slopes compared to west-facing slopes; north of ~40° latitude this pattern appears less robust. These observations reveal that it is increasingly disadvantageous for montane forests growing on sunnier, hotter aspects at relatively low latitudes during the hottest times of the year. Given known linkages between ecosystem productivity and CZ functions like water storage, provision, and flows, soil development, solute production, and regolith thickness, these analyses cast light on yet-underappreciated consequences of a rapidly warming climate on Earth’s montane forests and their capacity to shape CZ processes.more » « less
-
This paper presents fully kinetic particle simulations of plasma charging at lunar craters with the presence of lunar lander modules using the recently developed Parallel Immersed-Finite-Element Particle-in-Cell (PIFE-PIC) code. The computation model explicitly includes the lunar regolith layer on top of the lunar bedrock, taking into account the regolith layer thickness and permittivity as well as the lunar lander module in the simulation domain, resolving a nontrivial surface terrain or lunar lander configuration. Simulations were carried out to study the lunar surface and lunar lander module charging near craters at the lunar terminator region under mean and severe plasma environments. The lunar module’s position is also investigated to see its effect on the plasma charging relative to the craters. Differential surface charging was clearly resolved by the simulations. For the charging of a lunar lander module made of conducting materials, the results show a near-uniform potential close to that of its surrounding environment and moderate levels of local electric fields. Additionally, the risks associated with charging and discharging increase significantly under a more severe plasma charging environment as shown in the severe plasma environment cases.more » « less
-
This document details the ground-penetrating radar (GPR) collection activities carried out by I. Nesbitt in the Allan Hills during the 2019-2020 field season. This document is intended as an informal catalogue of the fild work and post-processing activities performed at the Allan Hills and later at McMurdo and elsewhere. It contains preliminary post-processing and analysis only. Any interpretation made and presented in this report based on the data herein is subject to change pending further examination. GPR was used to examine sub-ice bedrock topography and the stratigraphic relationship between two shallow ice core drill sites (CMC1 and CMC2), as well as to explore potential future drill sites. In accordance with. the project's objective to drill and analyze ancient ice at relatively shallow depths, the two main features of interest in this study are 1) bedrock topographic features in which ancient ice could be trapped, and 2) englacial stratigraphic layers, especially those which may represent large age discontinuities.more » « less
