Geological History of CO2: Carbon Cycle and Natural Sequestration of CO2

Course Description

With respect to the current genuine public concern regarding the anthropogenic increase of Green-House gases, intensive research and technology development focus on the capture and underground storage of industrial quantities of CO₂ concentrated in emissions from combustion sources. At the global scale, the withdrawal of the CO₂ diluted in the atmosphere relies essentially on natural bio-geological processes. As a complement to the study of the involved factors in the modern terrestrial eco-system, the geological perspective provides the opportunity to investigate these processes and their consequences at different time scales.

During Earth’s history the atmospheric CO₂ has been subjected to extensive changes in term of absolute quantity and relative concentration. From a geological perspective, the current anthropogenic driven alteration of the Earth’s atmosphere actually occurs during a period of low atmospheric CO₂ (Ice-House). A large part of the remaining time intervals of the Phanerozoic were apparently dominated by Green-House conditions. The latter situation resulting from the high concentration of atmospheric CO ₂, due to volcanic and metamorphic degassing associated with the long term tectonic activity of Phanerozoic megacycles. The subsequent decrease of atmospheric CO₂ at the end of the megacycles is interpreted by a negative feedback involving the CO2 driven silicate weathering which consumes CO₂. Based on the CO₂ sourcing (tectonic degassing) and CO₂ sinking (sedimentation of carbonates and organic matter), the most popular model depicting the change of atmospheric CO₂ during the Phanerozoic are based on the Berner’s GEOCARBSULF approach. The resulting curve which exhibits the long-term change is, to some extent, comforted by the comparison with the estimates of past PCO₂ values provided by different indicative proxies.

However some available data depart from the model and high resolution series of proxies suggest that high amplitude and high frequency changes in atmospheric CO₂ were occurring at a much lower time scale. Implications include the possibility to better explain short term climatic events such as the Late Ordovician continental-wide glaciation, to reconsider the significance of brutal events of injection of CO₂ in the atmosphere as a result of intra-plate volcanism and their environmental responses and geochemical record in oceanic sediments (e.g.the Permo-Trias Siberian traps), to revisit the so-called climatic optima such as the Late Palaeocene and Early Eocene, and the necessity to improve our assessment of the kinetics of the retroaction loops controlling the level of CO2 in the atmosphere.

The main reservoir of carbon is the Mantle. It is the likely repository of a large part of the CO₂ which was initially present in the primitive atmosphere of the Earth, following accretion and degassing, and from which it was probably progressively withdrawn through the process of subduction. The two other major reservoirs of carbon are the sedimentary carbonates and organic matter. The progressive build up of these reservoirs correspond to a long-term sink for around 80 bar of atmospheric CO₂. It should be noted that for both of them the processes involved in the transformation of CO₂ into carbonates and kerogen are biologically driven and that the efficiency of these processes tends to increase as biological evolution proceeds

Course Objectives

Upon completion of the course, participants will be able to:

• Place the current atmospheric CO₂ concentration in a geological perspective;
• Provide an overview of the methods used to approach the value of the past atmospheric CO₂ content;
• Review the change in the carbon cycle throughout geological time: Evolution of source and sink.

Course Outline

• Tools for monitoring changes in atmospheric CO₂ throughout time.
• The carbon cycle.
• Processes of natural sequestration of atmospheric CO₂: the carbon sinks.
• Atmospheric CO₂ change on planet Earth:
• from Precambrian to Phanerozoic;
• the Cenozoic;
• the Pleistocene ice house an inaccurate analogue for the current CO₂ departure from natural values.
• Evolution of carbon sinks, the instrumental role of biology.

Participants’ Profile

Anyone interested in the current atmospheric CO₂ concern and the evolution of the biogeochemistry of the Earth’s system.

Prerequisites

Basics geology and chemistry (biology).

About the Instructor

Alain-Yves Huc
PhD Strasbourg University, France (1978)
Post doc Woods Hole Oceanographic Institution, USA (1978-1979)
Research Associate at the Applied Geology Department, Orleans University (1979-1981) then at IFP New Energies
Head of the Geochemistry Department, IFP New energies, France (1990-2000)
Director of the Exploration Department at IFP School (2000-2004)
Expert Director at IFP New energies (2004-2013)
Research Director Emeritus at UPMC (2013-)