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Reconstructing weathering environments using clay triple-oxygen isotopes (ClayOx)

Applicant Hemingway Jordon
Number 207786
Funding scheme Project funding
Research institution Geologisches Institut ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.04.2022 - 31.03.2026
Approved amount 566'144.00
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All Disciplines (4)

Hydrology, Limnology, Glaciology

Keywords (10)

triple-oxygen isotopes; silicate weathering; paleohydrology; pedogenesis; paleotemperature; clay minerals; hydrology; climate proxies; carbon cycle; isotope ratio mass spectrometry

Lay Summary (German)

Durch die chemische Zersetzung von Gesteinen an Land und im Meer wird der Atmosphäre Kohlendioxid durch einen Prozess entzogen, der als "Silikatgestein-Verwitterung" bekannt ist und der dazu beiträgt, Veränderungen des Kohlendioxidgehalts über Zeiträume von Millionen Jahren auszugleichen. Außerdem setzt diese Verwitterung an Land Nährstoffe an die Umwelt frei und bildet Tonminerale, die für die Entwicklung gesunder Böden entscheidend sind. Obwohl die Silikatverwitterung ein wichtiger Prozess ist, der das Klima auf der Erde bewohnbar hält, ist wenig darüber bekannt, wie sich das Ausmass der Verwitterung im Laufe der Zeit verändert hat und wie sich diese in Zukunft als Reaktion auf anthropogene Aktivitäten ändern könnte.
Lay summary
Inhalt und Ziele des Forschungsprojekts

Unser übergeordnetes Ziel ist die Entwicklung einer neuen "Proxy"-Methode zur Quantifizierung der Silikatverwitterung in der geologischen Vergangenheit. Dies erreichen wir durch Messen der Isotopenzusammensetzung von Sauerstoffatomen in Tonmineralen, die Aufschluss über das Klima gibt, das zum Zeitpunkt der Verwitterungsreaktion herrschte. Konkret werden wir (i) aktualisierte theoretische Isotopenmodelle, (ii) neue Laborsyntheseversuche und (iii) die Analyse moderner Bodenproben aus verschiedenen Klimazonen zur Kalibrierung dieses Proxy kombinieren. Diese Informationen werden es uns ermöglichen, zu bestimmen, wie sich die Verwitterung als Reaktion auf den Klimawandel verändert, mit dem langfristigen Ziel, diesen Prozess in der erdgeschichtlichen Vergangenheit zu rekonstruieren/die Rolle dieses Prozesses in der Erdgeschichte zu rekonstruieren)  

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts

Unsere Arbeit wird neue Erkenntnisse über die natürlichen Prozesse liefern, die das Klima und die Bewohnbarkeit der Erde über lange Zeiträume hinweg regulieren. Dies wird unser kollektives Verständnis des langfristigen Klimawandels aktualisieren und dazu beitragen, die laufenden anthropogenen Klimaveränderungen in einen Kontext zu stellen.
Direct link to Lay Summary Last update: 29.03.2022

Lay Summary (English)

The chemical breakdown of rocks on land and under the ocean removes carbon dioxide from the atmosphere through a process known as "silicate rock weathering," which acts to counter-balance any changes to carbon dioxide levels over million-year timescales. Additionally, weathering on land releases nutrients to the environment and forms clay minerals that are crucial for the development of healthy soils. Although silicate weathering is an important process that keeps Earth’s climate habitable, little is known about how the amount of weathering has changed through time and how this might change in the future in response to anthropogenic activity.
Lay summary
Contents and goals of the research project

Our overarching goal is to build a new "proxy" method to quantify silicate rock weathering in the geologic past. We will achieve this by measuring the isotope composition of oxygen atoms in clay minerals, which record information about the climate that was experienced when the weathering reaction occurred. Specifically, we will combine (i) updated theoretical isotope models, (ii) new laboratory synthesis experiments, and (iii) analysis of soil modern samples from different climates to calibrate this proxy. This information will allow us to determine how weathering changes in response to changing climate, with the long-term goal of reconstructing this process through time.

Scientific and societal context of the research project

Our work will provide new insights into the natural processes that regulate Earth’s climate and habitability over long timescales. This will update our collective understanding of long-term climate change and help to contextualize ongoing anthropogenic climate changes.
Direct link to Lay Summary Last update: 29.03.2022

Responsible applicant and co-applicants


Project partner

Associated projects

Number Title Start Funding scheme
205998 Tropical Soil Erosion Dynamics (TropSEDs): Unraveling the roles of climate and land-use on the erosional transfer of carbon from source to sink through time in the Kasai Basin 01.03.2022 Sinergia


The long-term evolution of climate and atmospheric carbon dioxide levels (pCO2) is governed by a suite of mechanisms that exchange carbon between the biosphere and the solid Earth. Silicate rock weathering is of particular interest since this process leads to the precipitation and burial of carbonate in marine sediments, thus constituting a long-term CO2 sink. Furthermore, because weathering rates increase with temperature-which is itself a function of pCO2-silicate weathering constitutes a negative feedback that dampens climate and carbon-cycle perturbations. This “silicate weathering thermostat” is thought to be the primary driver of global climate stability over multi-million year timescales.Despite this importance, three key limitations hinder our ability to quantitatively and mechanistically reconstruct silicate weathering, including its response to climate and carbon-cycle perturbations: (i) Confounding controls on existing global weathering flux proxies. Trace-metal proxy records are subject to lithology source variability and secondary overprinting effects and thus cannot be treated as direct tracers of silicate weathering flux. (ii) No suitable paleohydrology proxies. Despite the known importance of hydrology in regulating silicate weathering flux, the hydrologic conditions of past weathering environments remain largely unconstrained. (iii) Model uncertainty. Carbon-cycle models employ empirical weathering parameterizations that are validated at modern or near-modern environmental conditions, leading to large uncertainty in model-predicted weathering fluxes at elevated pCO2. Importantly, each of these limitations is driven by a lack of direct observations about the environmental conditions in which silicate weathering occurs, both in modern environments and in the geologic past.To provide new insight, the ClayOx project will refine and apply a recently developed paleotemperature and paleohydrology proxy: the site-specific triple-oxygen isotope composition (17O/16O and 18O/16O) of clay minerals. Pedogenic clays such as kaolinite and smectite are formed during silicate weathering and exhibit temperature-dependent equilibrium isotope offsets from soil pore waters; their oxygen isotope compositions directly track temperature and hydrology during weathering. Furthermore, clays contain two isotopically unique oxygen sites: (i) structural oxygen, here termed Si-O-Si, and (ii) hydroxyl, here termed Al-OH. By separating and independently measuring Si-O-Si and Al-OH isotope compositions, this project will refine a recent isotope proxy system and will serve to unambiguously constrain paleotemperature and paleohydrology. We specifically seek to answer the following questions: (i) What are the site-specific, temperature-dependent, triple-oxygen isotope fractionation factors for common clay minerals? Studies to date provide promising results, but further application of this isotope framework requires accurate and precise fractionation-factor constraints. (ii) How do temperature and hydrology regulate the isotope composition of clays in modern soils and recent sediments? By studying modern systems, we will elucidate mechanistic insight into the conditions under which silicate weathering occurs; this is a critical step to ensure accurate application of the clay oxygen isotope proxy to geologic reconstructions.We will answer these questions by executing two work packages that progressively build from theoretical predictions to experimental calibrations and modern field studies. These activities will refine a state-of- the-art tool to assess silicate weathering throughout Earth history. The isotope systematics developed here will additionally provide a foundation for understanding silicate mineral transformations in other environments, particularly high-temperature alteration of oceanic crust and “reverse” weathering during authigenic clay formation in marine sediments.