Testing the control of weathering on CO2 - evidence from extreme climate events

How does the Earth's climate recover from events of rapid and extreme global warming or cooling? Why have the huge fluctuations in atmospheric CO2 in the geological past not caused runaway climate effects, making the Earth become Venus- or Mars-like? Silicate weathering of the continents is the main CO2 removal process, and therefore a dominant long-term climate control mechanism. However the debate on what controls silicate weathering, and therefore atmospheric CO2, is still contentious and ongoing.
A correct understanding of the controls on weathering, and its link to atmospheric CO2 levels is critical, because 1) it is possible that weathering is the process that has kept Earth's climate in the relatively narrow bounds required for life over the past several hundred million years; 2) it is impossible to decipher the causes and consequences of long-term climate variations through Earth's history without accurate weathering data, which in turn impacts on our understanding of current climate; 3) comprehension of climate systems leads to more accurate modelling of future climate change; 4) rapid global climate change inevitably leads to large mass extinctions. Therefore it is important to unravel the link between extinctions and the Earth's climate systems, including CO2 control.
Lithium isotopes have gained much interest over the past few years because large variations in the Li isotope ratio in rivers and clays are caused by silicate weathering processes. Furthermore, unlike tracers of weathering used previously, Li isotopes also respond to the intensity of weathering, and therefore can be linked directly to weathering rates. This is critical, because for the first time is gives us a window into the variation of weathering rates through time, which in turn means we can use the Earth's past climate variations as a natural laboratory.
Three of the largest climate fluctuations and mass extinctions in Earth's history will be examined and modelled, primarily using Li isotopes, but also several other tracers, which will serve to reveal information on marine and volcanic conditions at the time. These geological periods (the end-Ordovician glaciation (450 Ma (million years ago)), the Permo-Triassic event (251 Ma) and the Cenomanian-Turonian Ocean Anoxic Event (94 Ma)), represent times when rapid warming or cooling of Earth's climate occurred, resulting in the extinction of up to 90% of life on Earth.
Samples from these time periods exist in the form of marine calcium carbonate. This was precipitated (either inorganically, or via various life forms) in the oceans at the time, and provides a record of ocean chemistry, which in turn is directly linked to the atmospheric conditions. Analysing Li isotopes is a complex procedure, and will be undertaken at Oxford University. Collaborations will exist with Prof. Jan Veizer (Ottawa University) and Dr. Christoph Korte (Copenhagen University), who are specialists in the studied time periods, with Prof. Andy Ridgwell (Bristol University), who is an expert climate modeller, and with Prof. David Harper, who is an expert in mass extinctions.
By understanding weathering and climatic responses to periods of rapid global warming and cooling we will gain critical information on Earth's climate feedbacks, and on processes that led to the extinction of vast proportions of the biosphere.

This project aims to provide increased understanding of the processes that control silicate weathering, which is the Earth's dominant natural CO2 removal process. In addition, silicate weathering also affects the short-term ability of the oceans to take-up and store CO2, by influencing the oceans' carbonate saturation state. As such, weathering represents a process that not only needs to be understood in order to accurately predict the effects of anthropogenic climate change and ocean acidification, but also experiments are underway to use forms of silicate weathering to artificially sequester carbon.

Therefore academic beneficiaries of the proposed research not only include isotope geochemists, but also, from the interdisciplinary perspective, palaeontologists, palaeoclimatologists and climate system modellers.
The wider group of beneficiaries of this project include policy-makers (both national and international), the budding carbon sequestration industry (and research in that area) and to a certain extent the wider public.

Climate change
Sections on silicate weathering are already featured in the most recent IPCC (International Panel on Climate Change) report sections on natural climate control. Further insights into the controls on weathering may enhance the accuracy of climate system model predictions, directly impacting on future policy forming bodies, such as international and national governmental environment and climate change departments, as well as international bodies and NGOs (e.g. IPCC, environmental and fisheries charities (who rely on ocean carbonate saturation and therefore acidification data) and pressure groups).

Industry
Research is currently being conducted by the University of Iceland in collaboration with Oxford University (among other institutions) into the use of silicate weathering in carbon sequestration, by pumping components such as bicarbonate into basalt. It is thought that this eventually can be scaled-up by using the mid-ocean ridge systems. This research is part of international consortiums, linked to industry such as the Icelandic National Energy Authority. The more we understand on the controls on silicate weathering, the more efficient carbon sequestration can become. This technology is currently only in the research stage, but it can confidently be predicted that it will become a major industry in the very near future. As such, it is important that UK research is directly involved.

Public
The results of this proposed project can also affect the greater public, and nurture its interest in ancient life. The public's interest in mass extinction events is typified by the BBC's Horizon Programme's episodes on such events. For example, in March 2004, Horizon aired a programme on the Permo-Triassic mass extinction called "The Day The Earth Nearly Died". Part of this episode dealt with the threat of methane hydrates and rapid global warming, which is a process this proposal will directly address. Further, the K-T boundary and its associated with the extinction of the dinosaurs is a topic that is frequently addressed by the media. This project aims to discover how weathering and climate varied across these mass extinction boundaries, and this directly benefits the large section of the public that shows interest in mass extinctions and past climate.
While the benefits to the carbon sequestration industry will take several years to realise, the cultural benefit to the UK's public will occur shortly after publication. The fellow of this proposed project has direct links to BBC Science, as evidenced by his trip to Nepal with the BBC in September 2010 to be interviewed as a scientific expert in the "Wonders of the Universe" series. This link to the BBC will greatly assist exciting new scientific finds being brought to the public's attention.