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Dynamics of the terrestrial biota and its role on the global carbon cycle during the last 125,000 years

The natural greenhouse effect of trace gas (as carbon dioxide and methane) is a well known component of the global climate of the Earth. But the effect of the anthropogenic increase of these trace gas cannot yet be predicted with sufficient precision because the timing between "cause" and "effect" is unclear and because of unknown missing sink for CO2.

It is only in the last ten years that ice cores studies at Vostok, led by a French-Russian team has demonstrated the clear quasi-parallelism between CO2, CH4 and temperature in the atmosphere at the glacial/interglacial time-scale. Still the cause of this co-variation (with time lag and lead between trace gas and temperature) cannot be explained by present day models. The ocean could be the necessary source or sink for CO2 but the models require an even larger "missing sink" or "missing source".

To understand the global carbon cycle we lack knowledge of a global view of the terrestrial component. The results obtained by the INTAS project 93/2037 and the associated international group based on the activities on the INTAS members contributed strongly to increase our knowledge of the continental dynamics of the carbon cycle. A main fact now demonstrated is the great variability of the terrestrial carbon reservoir.

At the time scale of the glacial cycle the global stress of temperature changes, amplified by the global water budget modifications, has a strong effect on vegetation and soil carbon: continental carbon reservoir varies globally in phase with the atmosphere reservoir. The more vegetation and soils expand (peat included) the more CO2 (and possibly CH4) there is in the atmosphere. The atmosphere changes are of 20 per cent above or under a mean of about 500 GT C, but the terrestrial changes could be (in several wide areas studied: Eastern Europe, Siberia, Sahara arid belt) an increase of 3 to 5 times more carbon during warm-wet Holocene than at the last cold-dry glacial maximum (L.G.M.). Some test areas studied by the INTAS team show an even greater change in their carbon storage during the two last climatic cycles.

Still more work has to be done on the wet tropics, but the global calculations of the INTAS team shows that very probably in the natural system the terrestrial carbon sink can double (and maybe triple) its content of carbon during the climatic cycle.

This unexpected result has to be introduced in new models of the carbon cycle. With future investigations on the isotopic carbon cycle, on peat and on past methane production, the complete terrestrial domain (including the underground water) shall allow to reconstruct the past and the future carbon cycle. This is a preliminary to a better prediction of a possible global warming. The dynamics of the past carbon cycle can improve our prediction of future evolution.

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H FAURE
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Record Number: 24281 / Last updated on: 2000-03-28
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Collaboration sought: Further research or development support, Information exchange/Training
Stage of development: Other,
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