EAR-PF: Controls of and connections between silicate weathering and organic carbon cycling in watersheds: A test case in the Upper Deschutes Basin, Oregon, USA

点击翻译按钮获取中文摘要

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. Evan J. Ramos has been awarded an NSF EAR Postdoctoral Fellowship to conduct research, professional development, and outreach activities at Rice University and Brown University under the mentorship of Professors Mark A. Torres and Daniel E. Ibarra, respectively. This project investigates the nature of silicate weathering, organic carbon (OC) cycling, and their potential couplings across a watershed in the Cascade Mountains of Oregon, USA. Silicate weathering and OC cycling in soils influence the transfer of CO2 between the solid Earth and Earth’s ocean and atmosphere, thereby forcing and responding to changes in climate over a range of timescales. These processes are known to influence one another, but without tools to quantitatively probe both simultaneously, our ability to understand how either silicate weathering or OC cycling have responded to past climate change or how they will respond in the future is critically limited. The goal of this project is to develop a multiproxy geochemical approach that allows for the dual analyses of silicate weathering and OC cycling over timescales spanning millennia to millions of years. Motivated by a significant inverse correlation found between published soil lithium (Li) isotope compositions (a measure of silicate weathering intensity) and soil OC concentrations in a soil age sequence in Hawaii, Dr. Ramos will test the applicability of these combined measurements by (1) measuring Li isotope compositions and OC concentrations in soil and river sediments across a watershed with environmental and geologic conditions that differ from Hawaii and (2) developing models that simulate silicate weathering and OC cycling in soils. Research and professional development will involve the training of one undergraduate at Rice and one at Brown in sample acquisition, geochemical analysis of soils, model development, and written and verbal scientific communication. Project findings will be incorporated into a virtual field experience on ecosystems and watersheds, and lesson plans related to this virtual field experience will be developed with Houston-area science educators for usage in middle and high school science classes.Silicate weathering and organic carbon (OC) cycling in soils respond to and affect climate on a range of timescales, from millennia to millions of years. While typically studied independently of one another, both silicate weathering and OC cycling are intimately tied via the budgets of nutrients, acids, and reactive surfaces in soils. The result is a complex set of positive and negative feedbacks that make it difficult to predict how either weathering or OC cycling will respond to environmental change. Moreover, the relationship(s) between weathering and OC cycling need not be the same across a landscape and may instead be modified by the physical processes operating on distinct landscape elements (e.g., mountain hillslopes, floodplains). Dr. Ramos will test the hypothesis that, over millennial timescales, silicate weathering and OC storage are positively coupled through a mutual dependence on the rate of phyllosilicate (clay) mineral formation and that, as a result, landscape elements where clay mineral formation is favored (e.g., floodplains) strongly impact the net amount of CO2 drawdown. This project will involve sampling of river sediments, soils, and bedrock and subsequent measurements of Li isotope ratios, OC contents, and radiocarbon (14C) contents across an upland to floodplain transition to further our understanding of the coupled inorganic and organic C cycles. The Upper Deschutes Basin in the Oregon Cascades offers a compelling setting to gather critical data that test our hypothesis because of its lithologic (volcanic) uniformity, geologically recent formation (6.8 kya), and its physiographic similarity to other headwater catchments in recently deglaciated terrains. Additionally, results will be used to develop a generic model to address outstanding inconsistencies in modern weathering budgets and the potential magnitude of secular C cycle variation due to changing landscape forms over geologic time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.