scholarly journals Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

2019 ◽  
Vol 245 ◽  
pp. 154-171 ◽  
Author(s):  
Melissa J. Murphy ◽  
Don Porcelli ◽  
Philip A.E. Pogge von Strandmann ◽  
Catherine A. Hirst ◽  
Liselott Kutscher ◽  
...  
Keyword(s):  
Silicate Weathering ◽  
Lithium Isotopes ◽  
Lena River ◽  
River Watershed ◽  
Weathering Processes

Lithium isotopes tracing weathering processes in a time series through soil porewaters

2020 ◽  
Author(s):  
David Wilson ◽  
Philip Pogge von Strandmann ◽  
Gary Tarbuck ◽  
Jo White ◽  
Tim Atkinson ◽  
...  
Keyword(s):  
Time Series ◽  
Chemical Weathering ◽  
Silicate Weathering ◽  
Lithium Isotope ◽  
Lithium Isotopes ◽  
Drip Water ◽  
Weathering Processes ◽  
Li Isotope ◽  
Clay Formation ◽  
Isotope Measurements

<p>Chemical weathering is a key process that controls Earth’s geochemical cycles and global climate, yet at present the climate-weathering feedback is poorly understood. Lithium (Li) isotopes are sensitive to silicate weathering processes [1] and can be applied in a range of settings to improve our understanding of weathering mechanisms and timescales, and hence to quantify the role of weathering in the global carbon cycle. While marine carbonates [2] and speleothems [3] are suitable for recording changes over million year and thousand year timescales, respectively, it is equally important to assess how weathering operates over seasonal [4] and shorter [5] timescales.</p><p>In order to explore seasonal variability in a natural system, we analysed Li isotopes and major/trace elements in a time series of cave drip-water samples from Ease Gill and White Scar caves (Yorkshire Dales, U.K.). Since the drip-waters are sourced from the overlying soil porewaters, these measurements provide a record of the evolving weathering fluid chemistry at approximately monthly intervals. Our data reveal striking temporal variations in ∂<sup>7</sup>Li of 4 to 8 permil, hinting at rapid changes in weathering processes over monthly to seasonal timescales. We assess the sources of Li using isotope measurements on local rocks and soils, which enables a first order quantification of the temporal changes in Li removal by clay formation. Comparison to records of temperature, precipitation, drip rates, and drip-water chemistry allows the local controls on weathering to be assessed and indicates that a dominant control is exerted by the fluid residence time.</p><p>These data are further complemented by batch reactor experiments, which were conducted to replicate rock weathering over timescales of hours to weeks. In combination, the time series and experiments contribute to a better understanding of weathering changes over short timescales and their influence on Li isotopes. In addition, results from the drip-waters provide key ground-truthing for interpreting our ongoing Li isotope measurements on speleothems, which will provide new records of weathering changes over longer timescales in response to regional climate forcing.</p><p>[1] Pogge von Strandmann, P.A.E., Frings, P.J., Murphy, M.J. (2017) Lithium isotope behaviour during weathering in the Ganges Alluvial Plain. GCA 198, 17-31.</p><p>[2] Misra, S. & Froelich, P.N. (2012) Lithium isotope history of Cenozoic seawater: changes in silicate weathering and reverse weathering. Science 335, 818-823.</p><p>[3] Pogge von Strandmann, P.A.E., Vaks, A., Bar-Matthews, M., Ayalon, A., Jacob, E., Henderson, G.M. (2017) Lithium isotopes in speleothems: Temperature-controlled variation in silicate weathering during glacial cycles. EPSL 469, 64-74.</p><p>[4] Liu, X.-M., Wanner, C., Rudnick, R.L., McDonough, W.F. (2015) Processes controlling δ<sup>7</sup>Li in rivers illuminated by study of streams and groundwaters draining basalts. EPSL 409, 212-224.</p><p>[5] Pogge von Strandmann, P.A.E., Fraser, W.T., Hammond, S.J., Tarbuck, G., Wood, I.G., Oelkers, E.H., Murphy, M.J. (2019) Experimental determination of Li isotope behaviour during basalt weathering. Chemical Geology 517, 34-43.</p>

scholarly journals Lithium and Lithium Isotopes in Earth’s Surface Cycles

Elements ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 253-258 ◽  
Author(s):  
Philip A.E. Pogge von Strandmann ◽  
Simone A. Kasemann ◽  
Josh B. Wimpenny
Keyword(s):  
Climate Change ◽  
Atmospheric Co2 ◽  
Silicate Weathering ◽  
Lithium Isotope ◽  
Climatic Warming ◽  
Pore Waters ◽  
Lithium Isotopes ◽  
Weathering Processes ◽  
Isotope Evidence ◽  
Clay Formation

Lithium and its isotopes can provide information on continental silicate weathering, which is the primary natural drawdown process of atmospheric CO2 and a major control on climate. Lithium isotopes themselves can help our understanding of weathering, via globally important processes such as clay formation and cation retention. Both these processes occur as part of weathering in modern surface environments, such as rivers, soil pore waters, and groundwaters, but Li isotopes can also be used to track weathering changes across major climate-change events. Lithium isotope evidence from several past climatic warming and cooling episodes shows that weathering processes respond rapidly to changes in temperature, meaning that weathering is capable of bringing climate back under control within a few tens of thousands of years.

Geochemistry of Carbon Cycles on Rocky Exoplanets

2020 ◽  
Author(s):  
Kaustubh Hakim
Keyword(s):  
Carbon Dioxide ◽  
Carbon Cycle ◽  
Atmospheric Carbon Dioxide ◽  
Surface Composition ◽  
Deep Ocean ◽  
Silicate Weathering ◽  
Rock Composition ◽  
Weathering Processes ◽  
Rock Types ◽  
Strong Control

<p>The atmospheres of rocky exoplanets are secondary and regulated by geochemical volatile cycles. Earth scientists have studied in detail the long-term inorganic carbon cycle (also known as the carbonate-silicate cycle) acting on timescales of hundreds of thousands of years. This cycle provides essential negative feedback to maintain temperate climates on Earth. With the discovery of about a thousand rocky exoplanets and ongoing hunts for an Earth-twin, it is imperative to understand the factors affecting the stability of the carbon cycle. These factors could be dependent on the orbital and stellar parameters such as stellar radiation as well as planet-specific properties such as rock composition, land and ocean fractions. On Earth, continental silicate weathering and seafloor basalt weathering act as sinks for the atmospheric carbon dioxide. In this study, we develop a novel framework to unify both weathering processes. This is done by incorporating a set of silicate weathering reactions leading to the formation of carbonates. We focus on modeling the chemistry of rock-water interaction for different rock types (depending on the planet’s surface composition), as well as pH, temperature and partial pressure of carbon dioxide. We quantify the effects of fresh rock availability for the continental weathering and landmass fractions and shallow and deep ocean fractions for the seafloor weathering. Other components of the carbon cycle such as subduction, ridge and arc volcanism are parameterized based on previous studies. The effects of planet size, redox states, and tidal locking are also investigated. Our study gives a strong control over the connection between atmospheric observables and the carbon cycle. The ultimate goal is to provide an abiotic library of geological false positives of biosignatures.</p>

scholarly journals Tracing Silicate Weathering Dynamics in a Shale-Dominated Hillslope Using Lithium Isotopes in a Reactive Transport Framework

2020 ◽  
Author(s):  
Jon Golla ◽  
Marie Kuessner ◽  
Julien Bouchez ◽  
Daniella Rempe ◽  
Jennifer Druhan
Keyword(s):  
Reactive Transport ◽  
Silicate Weathering ◽  
Lithium Isotopes

scholarly journals The hydrochemical signature of incongruent weathering in Iceland

2021 ◽  
Author(s):  
Trevor Cole ◽  
Mark Torres ◽  
Preston Kemeny
Keyword(s):  
Geochemical Data ◽  
Silicate Weathering ◽  
Carbonate Dissolution ◽  
Weathering Processes ◽  
Mineral Phases ◽  
Inverse Models ◽  
Wide Range ◽  
Basalt Weathering ◽  
Clay Formation ◽  
End Members

Basaltic watersheds such as those found in Iceland are thought to be important sites of CO₂ sequestration via silicate weathering. However, determining the magnitude of CO₂ uptake depends on accurately interpreting river chemistry. Here, we compile geochemical data from Iceland and use them to constrain weathering processes. Specifically, we use a newly developed inverse model to quantify solute supply from rain and hydrothermal fluids as well as allow for different mineral phases within basalts to react at different rates, solutes to be removed via clay formation, and some Ca to be sourced from carbonate dissolution. While some of these processes have been considered previously, they have not been considered together allowing us to newly determine their relative contributions.We find that weathering in Iceland is incongruent in two ways. Firstly, solute release from primary silicates is characterized by a higher proportion of Na than would be expected from bulk basalts, which may reflect preferential weathering or some contribution from rhyolites. This Na enrichment is further enhanced by preferential Mg and K uptake by clays. No samples in our dataset (n=537) require carbonate dissolution even if isotopic data (δ26Mg, δ30Si, δ44Ca, and/or 87Sr/86Sr) are included. While some carbonate weathering is allowable, silicate weathering likely dominates. The complexity we observe in Iceland underscores the need for inverse models to account for a wide range of processes and end-members. Given that riverine fluxes from Iceland are more Na-rich than expected for congruent basalt weathering, the characteristic timescale of CO₂ drawdown is likely affected.

scholarly journals The effect of hydrothermal spring weathering processes and primary productivity on lithium isotopes: Lake Myvatn, Iceland

2016 ◽  
Vol 445 ◽  
pp. 4-13 ◽  
Author(s):  
Philip A.E. Pogge von Strandmann ◽  
Kevin W. Burton ◽  
Sophie Opfergelt ◽  
Eydís S. Eiríksdóttir ◽  
Melissa J. Murphy ◽  
...  
Keyword(s):  
Primary Productivity ◽  
Lithium Isotopes ◽  
Weathering Processes ◽  
Hydrothermal Spring ◽  
Lake Mývatn

Long-term weathering of silicates in a sandy soil at Nordmoen, southern Norway

Clay Minerals ◽  
1990 ◽  
Vol 25 (4) ◽  
pp. 447-465 ◽  
Author(s):  
S. Teveldal ◽  
P. Jørgensen ◽  
A. O. Stuanes
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Internal Standard ◽  
Silicate Weathering ◽  
Rock Fragments ◽  
Weathering Processes ◽  
Dioctahedral Mica ◽  
Southern Norway ◽  
Interstratified Mineral

AbstractWeathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3·2 g/m2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m2.

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