Ancient British Bog Provides Clue to Global Warming
28 Sep, 2007 12:02 pm
A group of interdisciplinary scientists have used the chemical signatures of microbial molecules preserved in ancient bog to learn how the Earth responded to a global warming event 55 million years. In response to 5C warming and associated climate changes, more methane was generated in and likely released from the bog. If the same changes occurred in other bogs at this time, then this ecosystem response to global warming could have amplified the climate changes occurring at this time.
In order to learn more about this event, our team, funded by the Leverhulme Trust and comprising scientists from the University of Bristol, Royal Holloway University of London, the Natural History Museum in London and The Field Museum in Chicago, examined the Cobham lignite, bog sediments deposited in SE England. The section, only fortuitously found during excavation of a rail line linking London to the Channel Tunnel, represents the rare opportunity to examine how a wetland ecosystem responded to ancient global warming. Initially, Professors Margaret Collinson and Andrew Scott and Dr. David Steart of Royal Holloway used this unique section to show that the climate actually became wetter as a response to the warming. In the most recent work, we turned our attention to the microorganisms living in the bog.
We showed that hopanoids, compounds made by bacteria, are abundant in the bog, consistent with the presence of a vibrant microbial community. However, to learn what the organisms were doing, we determined these compounds’ carbon isotopic compositions. This chemical signature, which is carried by all living organisms, can be used to study the source of the carbon being consumed by the bacteria. In the Cobham section, the hopanoids carbon isotopic compositions suddenly decrease in a manner that can only be explained by switching to a diet of methane. More methane in the bacterial diet suggests that there was more methane being generated – probably by other microorganisms – deeper in the sediment.
Methane is a very powerful greenhouse gas. Therefore, if the processes occurring at Cobham were widespread, then the increase in methane emissions could have caused further warming, amplifying the climate change at this time. This suggests that comparable processes could occur as the Earth warms in the next century, exacerbating the effect of greenhouse gases added directly by human activity. However, the analogy with current climate change must be applied cautiously; the climate 55 million years ago was much warmer than that of today, and the response of wetlands to current global warming could be rather different. Nonetheless, the work illustrates the complexity of the Earth’s linked geological, biological and chemical processes, such that the knock-on effects of human activity could be far-reaching and difficult to predict.
Pancost D.R., et al., Increased terrestrial methane cycling at the Palaeocene-Eocene thermal maximum. Nature 449, 332-335 (20 September 2007)