| Summary
The chemistry of the ancient atmosphere is strongly regulated
by emissions of extremely reactive volatile organic compounds
(VOCs) and other trace gases (e.g. CH4 and NOx) from terrestrial
ecosystems. Stratospheric ozone - needed to shield us from
harmful UV radiation - is affected by atmospheric O2
concentration. Past changes in atmospheric O2,
and the distribution and productivity of terrestrial ecosystems,
will therefore have repercussions for the chemistry of the
atmosphere which in turn will exert a direct feedback on climate.
This realization leads to an urgent need to answer some basic
questions concerning the nature of plant-climate-atmosphere-chemistry
feedbacks. Our multidisciplinary research addresses the problem
with the development of a new interdisciplinary subject area
in the Earth Sciences 'palaeoatmospheric chemistry'. The approach
utilises modelling and experimental approaches, and geochemical
analyses of fossil plants. We have begun our numerical simulations
by focusing on recent atmospheric CH4 changes (1980-1990),
and two intervals in the late Quaternary, the Holocene (past
10kyr) and last ice age (21kyr ago). The late Quaternary is
an ideal time interval for study the behaviour of the atmosphere
under conditions different from now because ice cores provide
us with a wealth of critical information on its chemical state
which can be used to examine the accuracy and validity of
our simulations.
From the 'recent past' studies, we have begun to move further
back in time, focusing in particular on the ancient 'greenhouse'
world of the Eocene, 50 million years ago. Fossil sediments
indicate wetlands and tropical forests were much more widespread
than now. Since wetlands are a major source of CH4, and tropical
forest emit VOCs, it follows that the atmospheric chemistry
was probably rather different at that time. These differences
could be the key to explaining the global warmth seen in marine
oxygen isotope records, because atmospheric CH4 is a potent
greenhouse gas. On-going work aims to quantify the feedback
of these changes in atmospheric composition on climate and
vegetation primary production.
Check out our latest research findings in the paper below:
Valdes, P.J., Beerling, D.J. &
Johnson, C.E. (In revision) An Earth systems approach closes
the ice-age global methane budget. Nature.
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