Evolution of Carbon Cycle Dynamics (eCCD)

Lead Research Organisation: University of Bristol
Department Name: Geographical Sciences

Abstract

The global carbon cycle - how much carbon is stored in its interconnected reservoirs (ocean, atmosphere, plants and soils on land, sediments in the deep sea) as well as the fluxes between them, is not set in stone. We know from the geological record that the concentration of CO2 in the atmosphere has varied enormously over the last few hundred million years. The chemistry of the oceans also gradually changes with time and the organisms living within it adjust and evolve. As a result, how the carbon cycle 'works', and particularly, how well (or not) atmospheric CO2 (and hence climate) is regulated in the face of disruption, also changes on geological time-scales. This creates challenges to understanding the causes and consequences of past global warming like events and how such events can be related to potential future changes. Sediments slowly accumulating in the deep ocean reflect what goes on around and above them, both chemically and biologically. Of particular interest to us is the mineral calcium carbonate (CaCO3), which can be found in the form of chalk and limestone rocks today. CaCO3 is used by certain marine organisms for constructing shells and skeletons. Hence, the amount of CaCO3 that in buried in sediments tells us something about ancient organisms and ecosystems. In addition, CaCO3 will start dissolving in seawater if the conditions too are acidic or the depth (and thus pressure) too great. How much CaCO3 originally created by organisms at the surface that escapes dissolution in sediments below to be buried and preserved in the geological record can thus tell us something about the chemistry, depth, and when data from many locations is available, the circulation of the ocean in the past. Looking for subtle changes in the composition of ancient mud in the hundreds and hundreds of meters of sediment core recovered from the ocean floor by drill ship would be a little like looking for a needle in a haystack. However, Nature has been kind to us and the transition from white-colored sediments rich in the carbonate shells of dead marine organisms to clays devoid of carbonate is easy to spot. This point represents a fine balance between the amount of shell material being deposited to the sediments and the rate of dissolution of these shells. Hence, this reflects a certain relationship between surface ocean biological processes and deep ocean chemistry and circulation. Any change in these factors will drive sediments rich in CaCO3 or devoid of any trace of carbonate secreting organisms. In this project we will compile the records from many hundreds of different sediment cores that have been recovered since the 1960s. Will identify the 'balance point' in these cores (if one exists) and combine all the confirmation to reconstruct how this balance point has changed in depth and time in the different ocean basins. Because the age of the sediments in some cores extends back to well before the white cliffs of Dover were deposited, we will start our record there. The interpretation of our curve will not be entirely straightforward, because multiple environmental influences all push and pull the balance point in different directions and with different strengths. We will therefore also use a computer model representation of the Earth's climate and oceans, its carbon cycle, ocean chemistry, and the composition of sediments in the deep sea. We will use this model to explore how the different aspects of the global carbon cycle affect the balance point, and by comparing model predictions to our new curve, interpret how the carbon cycling and the sensitivity of atmospheric pCO2 (and hence climate) to being perturbed by massive greenhouse gas release, has changed over the past 150 million years. Hence we will not only be able to answer the question: do we live in a particularly 'lucky' or 'unlucky' time in terms of how sensitive our global environment is burning fossil fuels, but we will know why.

Publications

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Description This project help lead to the conclusion that current rates of ocean acidification are unparalleled in Earth's history.

The study is based on computer modelling carried out as part of the project, as well as an expert workshop led by Columbia University's Lamont-Doherty Earth Observatory and the University of Bristol during which a number of climate change events in the planet's history were assessed in detail, including the asteroid impact that made the dinosaurs go extinct and the Permian mass-extinction which wiped out around 95 per cent of all life on Earth. The findings were reported in a paper in Science.

Oceans are currently absorbing about a quarter of the CO2 released into the atmosphere, lowering the pH of the surface ocean. As atmospheric CO2 increases, so does the rate at which it will dissolve in seawater, forcing surface ocean pH lower and lower - a process called ocean acidification.

Laboratory experiments suggest that if the pH continues to fall, we may start to see impacts on marine organisms such as slower growth, fewer offspring, muscle wastage, dwarfism, reduced activity and the dissolution of their carbonate shells - with knock-on effects throughout the marine ecosystem. However, as a large number of processes are involved, it is hard to predict what ecosystems in the oceans will look like in future and what services for humankind they will be able to support.

In order to learn about the future, the researchers looked to the past, reviewing climate events over the past 300 million years that showed evidence of elevated atmospheric CO2, global warming and ocean acidification.

Dr Daniela Schmidt, a Royal Society Research Fellow in Bristol University's School of Earth Sciences, was one of the organizers of the workshop which gathered all the experts and compiled the evidence. She said: "Laboratory experiments can tell us about how individual marine organisms react, but the geological record is a real time experiment involving the entire ocean."

Professor Andy Ridgwell added: "The geological record suggests that the current acidification is potentially unparalleled in at least the last 300 million years of Earth history, and raises the possibility that we are entering an unknown territory of marine ecosystem change.
"Although similarities exist, nothing in the last 300 million years parallels rates of future projections in terms of the disrupting of ocean carbonate chemistry - a consequence of the unprecedented rapidity of CO2 release currently taking place."
Exploitation Route In providing a sound and quantitative geological perspective on one of the great global environmental challenges facing us -- ocean acidification.
Sectors Education

 
Description ERC 'Consolidator' scheme
Amount € 2,000,000 (EUR)
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 05/2014 
End 04/2019
 
Description n/a
Amount $1,000,000 (USD)
Organisation Heising-Simons Foundation 
Sector Charity/Non Profit
Country United States
Start 04/2016 
End 03/2020