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Evolutionary rise of deep-rooting forests and enhanced chemical weathering: Quantitative investigations into the current paradigm (NERC grant NE/J007897/1)
The co-evolution and geographical spread of trees and deep-rooting systems is widely proposed to represent the 'Devonian engine' of global change that drove the weathering of soil minerals and biogeochemical cycling of elements to exert a major influence on the Earth's atmospheric CO2 history. If correct, this paradigm suggests the evolutionary appearance of forested ecosystems through the Devonian (418-360 Myr ago) constitutes the single most important biotic feedback on the geochemical carbon cycle to emerge during the entire 540 Myr duration of the Phanaerozoic. Crucially, no link has yet been established between the evolutionary advance of trees and their geochemical impacts on palaeosols. Direct evidence that one has affected the other is still awaited, largely because of the lack of cross-disciplinary investigations to date. Our proposal addresses this high level 'earth system science' challenge. The overarching objective is to provide a mechanistic understanding of how the evolutionary rise of deep-rotting forests intensified weathering and pedogenesis that constitute the primary biotic feedbacks on the long-term C-cycle. Our central hypothesis is that the evolutionary advance of trees left geochemical effects detectable in palaeosols as forested ecosystems increased the quantity and depth of chemical energy transported into the soil through roots, mycorrhizal fungi and litter. This intensified soil acidification, increased the strength of isotopic and elemental enrichment in surface soil horizons, enhanced the weathering of Ca-Si and Ca-P minerals, and the formation of pedogenic clays, leading to long-term sequestration of atmospheric CO2 through the formation of marine carbonates with the liberated terrestrial Ca. We will investigate this research hypothesis by obtaining and analysing well-preserved palaeosol profiles from a time sequence of localities in the eastern North America through the critical Silurian-Devonian interval that represents Earth's transition to a forested planet. These palaeosol sequences will then be subjected to targeted geochemical, clay mineralogical and palaeontological analyses. This will allow, for the first time, the rooting structures of mixed and monospecific Mid-Devonian forests to be directly linked to palaeosol weathering profiles obtained by drilling replicate unweathered profiles. Weathering by these forests will be compared with the 'control case' - weathering by pre-forest, early vascular land plants with diminutive/shallow rooting systems from Silurian and lower Devonian localities. These sites afford us the previously unexploited ability to characterize the evolution of plant-root-soil relationships during the critical Silurian-Devonian interval, whilst at the same time controlling for the effects of palaeogeography and provenance on palaeosol development. Applying geochemical analyses targeted at elements and isotopes that are strongly concentrated by trees at the surface of contemporary soils, and which show major changes in abundance through mineral weathering under forests, provides a powerful new strategy to resolve and reconstruct the intensity and depth of weathering and pedogenesis at different stages in the evolution of forested ecosystems. The project is tightly focused on "improving current knowledge of the interaction between the evolution of life and the Earth", which represents one of the three high level challenges within NERC's Earth System Science Theme.
Cation, anion and Sr isotope data from Nepalese river water. Suspended sediment concentration, suspended sediment chemistry presented as wt% oxides from Nepalese rivers. Both the waters and sediments were collected following the 2015 earthquakes.
Carbon dioxide flux and isotopic composition from sedimentary rock weathering, Draix-Bleone Critical Zone Observatory, France
The measurements and data were obtained to study the release of carbon dioxide during the chemical weathering of sedimentary rocks, and how these CO2 fluxes were related to environmental parameters (temperature, hydrology). Weathering of sedimentary rocks can result in CO2 release from the oxidation of rock organic carbon oxidation, but also due to the oxidation of sulfide minerals, production of sulfuric acid and subsequent release of CO2 from carbonate minerals. The rock-derived carbon sources are understudied, and form an important part of the geological carbon cycle. The CO2 flux measurements were made on 5 rock chambers (H4, H6, H7, H8 and H13) installed in the Draix-Bleone Critical Zone Observatory, France, on outcrops of Jurassic marls. Measurements and data were collected from December 2016 to May 2019. Regular visits to the site (~4 per year) returned data on total CO2 flux (Total-CO2-flux.csv). This was explored as a function of temperature and ambient hydroclimate (precipitation). The datasets include the total CO2 flux measured at each visit to a chamber, and measurements of the internal chamber temperature. To determine the source of CO2 measured in the chambers, we trapped the CO2 using zeolite sieves and recovered it in the laboratory. The radiocarbon activity (reported as fraction modern, F14C) and its stable isotope composition (d13C) were measured from CO2 collected from chambers H4 and H6 over the sampling period (Radiocarbon-data.csv). These were used in a mixing analysis to partition the source of CO2 using a mixing model approach (Partitioned-CO2-fluxes.csv) as explained in full in the published paper Soulet et al., 2021, Nature Geoscience. We also measured the geochemical characteristics of the bedrocks being measured (rock-geochemical-composition.csv), including the organic carbon concentration, inorganic carbon concentration and their isotopic composition. Finally, we measured environmental variables of interest - the chamber temperature and the air temperature at the Draix-Bleone observatory (chamber-temperature.csv and Air-temperature-at-laval-le-plateau-weather-station.csv, respectively). This research was funded by a European Research Council Starting Grant to Robert Hilton (ROC-CO2 project, grant 678779) and radiocarbon and stable isotope measurements were funded by the Natural Environment Research Council (NERC), UK, (NERC Environmental Isotope Facility NEIF Radiocarbon Allocation 2074.1017) to Guillaume Soulet, Robert Hilton and Mark Garnett. Full details of data analysis and interpretation can be found in Soulet et al., 2021, Temperature control on CO2 emissions from the weathering of sedimentary rocks, Nature Geoscience
Dissolved rhenium and other dissolved ions in Alpine catchments of the Erlenbach and Vogelbach (Switzerland) and the East River (Colorado, USA) (NERC Grant NE/I001719/1)
The measurements and data contained here were obtained to study the chemical weathering of sedimentary rocks, and more specifically the oxidation of rock organic carbon and the associated release of CO2. The primary aim was to better understand the production and mobility of the trace element rhenium during weathering, because this element has been proposed as a proxy for rock organic carbon oxidation. The study focused on three Alpine catchments that drain sedimentary rocks, which all experience moderate to high erosion rates where oxidative weathering rates are thought to operate faster. Two catchments were located in Switzerland - the Erlenbach and Vogelbach, and one catchment in Colorado, USA - the East River. To study chemical weathering and the production and mobility of rhenium, a suite of samples were collected to capture the source and products of weathering reactions. These focused on stream and river water, river sediments and weathering profiles collected on sedimentary rocks. The Swiss catchments, water samples were collected from 2011 and 2012 to capture changes in river flow and seasonal changes in hydro-climate. Samples were collected from a gauging station operated by the Swiss Federal Institute for Forest, Snow and Landscape Research - WSL. In the East River, samples were collected from the gauging station operated by the Lawrence Berkeley National Laboratory Watershed Function Scientific Focus Area from 2015 and 2016. Additional samples included snow samples collected from the Erlenbach. All water samples were analysed for their major dissolved ion content by Ion Chromatography. Dissolved rhenium concentrations were determined by High Resolution and Quadrupole Inductively Coupled Plasma Mass Spectrometry. Solid samples were digested and analysed for Re content by ICP-MS. These geochemical measurements were paired with water discharge data to quantify the flux of dissolved elements, using rating curves and flux-weighted average methods, and interpret the hydrological context of ion production and mobility through the landscape. This new data acquisition was funded by a European Research Council Starting Grant to Robert Hilton (ROC-CO2 project, grant 678779) and a Natural Environment Research Council (NERC), UK, Standard Grant (NE/I001719/1). Further details of subsequent data analysis and interpretation can be found in Hilton, R.G., et al., 2021, Concentration-discharge relationships of dissolved rhenium in Alpine catchments reveal its use as a tracer of oxidative weathering, Water Resources Research