CENTA NERC - Climatic consequences of geologically realistic methane emissions from large igneous provinces

Large Igneous Provinces (LIPs) are often associated with global climate change. The best studied example is the association between the Paleocene-Eocene Thermal Maximum (PETM) and the North Atlantic Igneous Province (NAIP). Thermogenic methane is a leading candidate to explain the association. This methane is formed when igneous sills intrude sedimentary rock with an organic component, and is then released to the atmosphere where it forces greenhouse warming. Knowing the rate of methane emission is of critical importance in judging between this and other mechanisms of climate change; methane is a potent greenhouse gas, but on entering the atmosphere it is rapidly oxidised and removed, so that sustained high methane emission rates are required to force significant climate warming.
Existing studies of the LIP thermogenic methane source provide good estimates of the total mass of thermogenic methane released, but the temporal fluctuations in emission rate remain unclear. On the other hand, climate modelling studies have placed bounds on methane emission rates that would be required to match observed warming, but they cannot judge whether such rates could feasibly be delivered by geological processes.
This project will build on work recently completed at the University of Birmingham to determine geologically reasonable methane emission rate scenarios for LIPs. The new framework has four key components. First, the rate of break-down of organic material into methane within thermal aureoles of individual sills is determined, using chemical kinetic maturation modelling tried and tested by the oil-industry. Next, the proportion of generated methane that escapes the solid earth to the atmosphere is estimated, based on established principles of reservoir engineering and also on palaeogeographic modelling. Thirdly, a database of sill dimensions, compiled using 2D and 3D seismic mapping, specifies the range of emission rate histories across the population of individual sills. Finally, a new technique is used to combine emissions from the sill population, to yield the methane emission rate history for the entire LIP. Importantly, this framework allows sill and host-rock statistics measured in well-explored parts of the LIP to be projected across unexplored regions, in order to quantify uncertainty in predicted methane emission rate histories.

The project will use climate modelling to link the new, realistic methane emission histories to observations of climate warming and environmental change. A global climate model of intermediate complexity that explicitly includes carbon cycling will be used to investigate how the estimated range of methane emission scenarios translates in sea surface and deep sea temperature, magnitude and duration of the carbon isotope excursion, difference between marine and terrestrial carbon isotope records, and changes in lysocline depth. Emphasis will be placed on thoroughly exploring how the range of plausible methane emission scenarios maps into model predictions. Modelling predictions will be compared with observations to assess the role of LIP thermogenic methane in forcing various climate change events, beginning with the PETM-NAIP association, then widening in scope to other cases.