ISO-THERM: Isotopic testing of Earth's weathering thermostat
Lead Research Organisation:
University College London
Department Name: Earth Sciences
Abstract
Weathering is a chemical reaction which dissolves rocks in rainwater and over long timescales removes carbon dioxide (CO2) from the atmosphere. Both theories and experiments predict that rocks will dissolve faster with warmer temperatures, potentially making chemical weathering the key process that has stabilised Earth's climate over millions of years. Conceptually, if atmospheric CO2 levels increase, the greenhouse effect would lead to warmer temperatures and more weathering, thereby removing CO2 and cooling climate. Hence, weathering can provide a climate "thermostat", preventing big swings in climate and maintaining a habitable planet.
However, weathering in the real world is more complex than in the laboratory, and evidence for how this climate "thermostat" operates is lacking. We simply do not know how sensitive weathering is to climate, either locally or globally, and therefore we do not know how well this thermostat works. Indeed, we do not even know if weathering is the most important control on the earth's climate, as some scientists have proposed alternative controls such as seafloor alteration, biological carbon cycling, and sulphuric acid weathering of limestone. Our poor understanding of weathering represents a major gap in our understanding of the global carbon cycle, and a significant challenge for modelling past and future climate change.
To test the weathering "thermostat" on Earth, this project will reconstruct how weathering has changed in the past using a programme of geological detective work. Although there have been interesting clues to date, the evidence has been circumstantial and often unreliable. The problem is that records of past ocean chemistry have indicated weathering changes, but we have not had reliable forensics to tie these changes to the continental regions where the weathering occurred.
Fortunately, two discoveries from my previous investigations lead to a way forward in this case. First, the distinct composition of the lead (Pb) atoms in continental rocks provides a geological "fingerprint" that is transferred by chemical weathering via rivers into the ocean. Second, sediments formed in the ocean are witnesses to this "fossil seawater" composition. Therefore, by analysing ocean sediments of different ages, a detailed timeline of weathering changes will be reconstructed, and comparison to those continental Pb fingerprints will reveal the weathering culprits. Measuring another element, lithium (Li), will provide corroborating evidence on the weathering environment, revealing how the weathering was carried out and what controlled it.
Together, this new evidence will reveal the controls of climate and mountain uplift on the weathering of different rock types in different regions. Computer modelling will then be used, in combination with evidence of past changes in climate and CO2, to determine the strength of the weathering "thermostat". This result is crucial for addressing the question of how a habitable climate is maintained on Earth. Furthermore, this information will improve climate models, because predicting Earth's future climate evolution in response to anthropogenic carbon emissions relies on an understanding of how, and how quickly, weathering will respond to these changes.
However, weathering in the real world is more complex than in the laboratory, and evidence for how this climate "thermostat" operates is lacking. We simply do not know how sensitive weathering is to climate, either locally or globally, and therefore we do not know how well this thermostat works. Indeed, we do not even know if weathering is the most important control on the earth's climate, as some scientists have proposed alternative controls such as seafloor alteration, biological carbon cycling, and sulphuric acid weathering of limestone. Our poor understanding of weathering represents a major gap in our understanding of the global carbon cycle, and a significant challenge for modelling past and future climate change.
To test the weathering "thermostat" on Earth, this project will reconstruct how weathering has changed in the past using a programme of geological detective work. Although there have been interesting clues to date, the evidence has been circumstantial and often unreliable. The problem is that records of past ocean chemistry have indicated weathering changes, but we have not had reliable forensics to tie these changes to the continental regions where the weathering occurred.
Fortunately, two discoveries from my previous investigations lead to a way forward in this case. First, the distinct composition of the lead (Pb) atoms in continental rocks provides a geological "fingerprint" that is transferred by chemical weathering via rivers into the ocean. Second, sediments formed in the ocean are witnesses to this "fossil seawater" composition. Therefore, by analysing ocean sediments of different ages, a detailed timeline of weathering changes will be reconstructed, and comparison to those continental Pb fingerprints will reveal the weathering culprits. Measuring another element, lithium (Li), will provide corroborating evidence on the weathering environment, revealing how the weathering was carried out and what controlled it.
Together, this new evidence will reveal the controls of climate and mountain uplift on the weathering of different rock types in different regions. Computer modelling will then be used, in combination with evidence of past changes in climate and CO2, to determine the strength of the weathering "thermostat". This result is crucial for addressing the question of how a habitable climate is maintained on Earth. Furthermore, this information will improve climate models, because predicting Earth's future climate evolution in response to anthropogenic carbon emissions relies on an understanding of how, and how quickly, weathering will respond to these changes.
Planned Impact
This project is addressing fundamental science relating to the evolution of the Earth's carbon cycle, and especially the operation of feedbacks between tectonics, weathering and climate. Such research is of global significance for both establishing natural processes of climate variability and for predicting future changes. In particular, continental weathering will represent the ultimate major sink for anthropogenic carbon emissions, and how quickly weathering responds to a changing climate will affect our future climate evolution. It is therefore important to constrain the sensitivity of weathering to climate, which is at present poorly known.
Enhanced weathering reactions may also represent a viable means for future geoengineering to accelerate carbon dioxide removal from the atmosphere for human benefit. Therefore, understanding the timescales of weathering-related carbon dioxide drawdown, and how to accelerate these, could be of major societal relevance. In addition, nutrient supply changes related to future weathering fluxes will impact upon marine and terrestrial ecosystems, biological productivity and diversity.
More broadly, the question of how and why climate has changed in the past has puzzled scientists for decades and represents a fascinating detective story. My research aims to provide the most direct evidence yet to solve this question. There is an excellent opportunity for outreach activities to highlight research on global change, including explaining the carbon cycle, and comparing and contrasting mechanisms and rates of change for perturbations of natural and anthropogenic origin. An interesting analogy (albeit with some differences) can be drawn between weathering changes in geological history and the future response to our anthropogenic carbon release experiment.
School children: For junior school age groups, the broad topics of the formation of mountains, global climate changes and the history of ice sheets can be explained, and also readily demonstrated with models and visualisations. For secondary school age groups, a detective story starting from the idea of the Himalayan "uplift hypothesis" will be a good way to introduce students not only to climate science, but also to geology and isotope chemistry, and to STEM subjects more generally.
Wider public: The public stands to benefit by gaining an awareness of earth systems, climate and global change. In part, this can be achieved through the narrative of the role of the Himalayas in our natural climate evolution, and by contrasting that with current and future scenarios.
Wider geoscience community: Educating colleagues and practitioners with a geoscience background, but who lack a specialised understanding of climate change, paleoclimate and geochemistry, may be readily achieved through this project, given its interdisciplinary nature (e.g. links with earth surface processes, sedimentology, solid earth processes, modelling).
Politicians and decision-makers: The scientific concepts involved in this project are highly relevant to political decisions relating to climatic and global change. There is an interesting analogy between past climate and weathering changes, and the Earth's future response to anthropogenic emissions, including potential mitigation. Constraining the nature of the climate-weathering feedback has specific relevance for predicting our climatic future.
Enhanced weathering reactions may also represent a viable means for future geoengineering to accelerate carbon dioxide removal from the atmosphere for human benefit. Therefore, understanding the timescales of weathering-related carbon dioxide drawdown, and how to accelerate these, could be of major societal relevance. In addition, nutrient supply changes related to future weathering fluxes will impact upon marine and terrestrial ecosystems, biological productivity and diversity.
More broadly, the question of how and why climate has changed in the past has puzzled scientists for decades and represents a fascinating detective story. My research aims to provide the most direct evidence yet to solve this question. There is an excellent opportunity for outreach activities to highlight research on global change, including explaining the carbon cycle, and comparing and contrasting mechanisms and rates of change for perturbations of natural and anthropogenic origin. An interesting analogy (albeit with some differences) can be drawn between weathering changes in geological history and the future response to our anthropogenic carbon release experiment.
School children: For junior school age groups, the broad topics of the formation of mountains, global climate changes and the history of ice sheets can be explained, and also readily demonstrated with models and visualisations. For secondary school age groups, a detective story starting from the idea of the Himalayan "uplift hypothesis" will be a good way to introduce students not only to climate science, but also to geology and isotope chemistry, and to STEM subjects more generally.
Wider public: The public stands to benefit by gaining an awareness of earth systems, climate and global change. In part, this can be achieved through the narrative of the role of the Himalayas in our natural climate evolution, and by contrasting that with current and future scenarios.
Wider geoscience community: Educating colleagues and practitioners with a geoscience background, but who lack a specialised understanding of climate change, paleoclimate and geochemistry, may be readily achieved through this project, given its interdisciplinary nature (e.g. links with earth surface processes, sedimentology, solid earth processes, modelling).
Politicians and decision-makers: The scientific concepts involved in this project are highly relevant to political decisions relating to climatic and global change. There is an interesting analogy between past climate and weathering changes, and the Earth's future response to anthropogenic emissions, including potential mitigation. Constraining the nature of the climate-weathering feedback has specific relevance for predicting our climatic future.
People |
ORCID iD |
David Wilson (Principal Investigator / Fellow) |
Publications
Struve T
(2022)
A deep Tasman outflow of Pacific waters during the last glacial period.
in Nature communications
Wilson D
(2022)
Antarctic Climate Evolution
Colleoni F
(2022)
Antarctic Climate Evolution
Pogge Von Strandmann P
(2023)
Assessing hydrological controls on the lithium isotope weathering tracer
in Chemical Geology
Crotti I
(2022)
Author Correction: Wilkes subglacial basin ice sheet response to Southern Ocean warming during late Pleistocene interglacials.
in Nature communications
Chen B
(2023)
Behaviour of Sr, Ca, and Mg isotopes under variable hydrological conditions in high-relief large river systems
in Geochimica et Cosmochimica Acta
Chen BB
(2022)
Calcium isotopes tracing secondary mineral formation in the high-relief Yalong River Basin, Southeast Tibetan Plateau.
in The Science of the total environment
Little S
(2021)
Cold-water corals as archives of seawater Zn and Cu isotopes
in Chemical Geology
Zhong Y
(2021)
Contrasting Sensitivity of Weathering Proxies to Quaternary Climate and Sea-Level Fluctuations on the Southern Slope of the South China Sea
in Geophysical Research Letters
Charrieau L
(2023)
Controls on Lithium Incorporation and Isotopic Fractionation in Large Benthic Foraminifera
in Minerals
Description | Citations in IPCC AR6 Climate Change 2021 report |
Geographic Reach | Multiple continents/international |
Policy Influence Type | Citation in systematic reviews |
URL | https://www.ipcc.ch/report/ar6/wg1/ |
Description | Convenor of London Paleoclimate Network |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Professional Practitioners |
Results and Impact | I organise and convene the London Paleoclimate Network, which holds monthly talks and discussions to facilitate interaction between students and researchers in paleoclimate and climate change at multiple institutes across London. A strong focus is placed on early career researchers, while particular attention is paid to ensure the diversity of speakers. We also engage with policy-relevant topics, including for example a session in 2021 in relation to the IPCC AR6 report. |
Year(s) Of Engagement Activity | 2021,2022 |
Description | Invited talk at University of Mainz |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Invited talk at University of Mainz |
Year(s) Of Engagement Activity | 2021 |
Description | Invited talk for The Paleoclimate Society |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | This invited talk was targeted at a broad audience and the video is available to the general public as well as to policymakers and other scientists on YouTube. |
Year(s) Of Engagement Activity | 2021 |
Description | Online talk at GGRIP 2021 meeting |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Online presentation on chemical weathering at UK Geochemistry Group RIP meeting |
Year(s) Of Engagement Activity | 2021 |
Description | Online talk at Goldschmidt 2021 meeting |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Online talk on chemical weathering at Goldschmidt 2021 meeting |
Year(s) Of Engagement Activity | 2021 |
Description | Outreach talk at Gilbert White's House and Gardens |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | A public outreach talk on climate change delivered to around 40 members of the public from a wide range of backgrounds, followed by a Q+A session and subsequent discussions with individuals |
Year(s) Of Engagement Activity | 2023 |