Denudation, chemical weathering, and critical zone structure through the last glacial-interglacial transition
Abstract
Mineral dissolution rates in the critical zone depend on physical, chemical, and biotic processes, though the means by which climate variations regulate the relative importance of these processes remain ambiguous. We analyze trace element concentrations in a 50-kyr record of colluvial sedimentation at our unglaciated, mid-latitude study site to show that glacial-interglacial fluctuations generate systematic and offsetting variations in chemical weathering intensity and erosion rate. Cool and wet conditions prior to the Last Glacial (50-29 ka) coincide with a monotonic decline in chemical alteration, estimated from the chemical depletion fraction (CDF), and a progressive increase in erosion rate, estimated from in-situ 10Be analyses. During the cool and sparsely vegetated Last Glacial (LG; 29-18.5 ka), we observe consistently low CDF values (< 0.1) and high erosion rates (> 0.2 mm/yr), likely regulated by frost processes. Conversely, slower erosion rates (< 0.1 mm/yr) and higher CDF values ( 0.2) characterize the warm and densely vegetated Late Holocene (< 2.5 ka). This inverse relationship between chemical depletion and erosion rate in the LG and Late Holocene implies steady chemical weathering fluxes, despite significant variations in temperature and vegetation. Additionally, weakly altered LG sediments are chemically similar to unweathered bedrock, such that the LG-Holocene transition likely coincided with substantial alteration and deepening of the critical zone. Irrespective of hypothesized climate-weathering feedbacks, our results demonstrate how changes in the efficacy of abiotic and biotic processes modulate the vigor of critical zone processes and the flux of solutes and sediments over the last glacial-interglacial transition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP52B..08R
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 1630 Impacts of global change;
- GLOBAL CHANGEDE: 1807 Climate impacts;
- HYDROLOGYDE: 1824 Geomorphology: general;
- HYDROLOGY