News - INQUA Commission on Carbon

CALL FOR ABSTRACTS

INQUA COMMISSION ON CARBON (RENO CONGRESS july 2003)

SYMPOSIUM and Associated POSTER SYMPOSIUM

REGIONAL TO GLOBAL CARBON CYCLE CHANGES

A specific scientific problem concerns the Quaternary, particularly the change that appears in the Carbon Cycle during glacial-interglacial oscillations. The mechanisms behind the climatic fluctuations that have occurred during the Quaternary are a subject of key interest not only in themselves, but for the clues which they indirectly yield for predicting future anthropogenic effects on the biosphere. A great deal of attention has been focused on the observation that the concentration of carbon dioxide and methane in ice cores from the late Quaternary strongly parallel global temperatures and ice volumes. The Vostok ice core record (Barnola et al., 1987; Petit et al., 1999) indicate that the concentration of atmospheric CO₂ has fluctuated widely over the last four glacial-interglacial cycles. The amplitude of the recorded signal is 80-100 ppmv. The reason for this CO₂ fluctuation has remained an unsolved question over the last two decades. Understanding these atmospheric CO₂ fluctuations and the associated changes in the global carbon cycle is, however, critical for our knowledge of the mechanisms which drive the climate system from a glacial to an interglacial state and vice-versa.

The greenhouse gases have been suggested as key components in the system of climate feedbacks by which glaciations begin and end. Although the observation that CO₂ levels showed large variations during the Quaternary is accepted as being of key importance, there is little genuine understanding of exactly why the gas concentration varied, and what the key controls on the amplitude of the variation actually were. Whilst there can be little doubt that the oceans were primarily responsible for 'dragging down' CO₂ levels during glacial phases, there is confusion over how exactly this could have occurred. Furthermore, the changing distribution of a very large labile reservoir of carbon on land, in organic and inorganic forms in soils and vegetation, has essentially been ignored by previous models which attempt to reconstruct the changing carbon cycle during the key phase of deglaciation. This is a major omission, for the amount of carbon on land at present is much greater than the total amount in the atmosphere, and variations in the size of this reservoir may well have had an important effect on both the total amplitude of fluctuation and the detailed dynamics of changes in CO₂ levels during the Quaternary. This, in turn, may have implications for interpreting the strength and mode of operation of oceanic 'pumps'.

There have been various attempts to estimate carbon storage changes between glacial and interglacial conditions. Oceanic isotope shifts have been used by various authors, but from detailed consideration of the assumptions involved in such work there are serious reservations about the use of these. Similarly, GCM simulations have been used to simulate vegetation distribution and hence carbon storage for the last glacial maximum. However, checking against those areas in which good palaeoevidence is available suggests that progress is still necessary to validate model with data.

A more direct, and possibly more reliable, method of estimating the carbon storage shift between glacial and interglacial conditions were to map palaeovegetation from the range of best available environmental indicators, and deduce bulk carbon storage in this way. This method was initially attempted in a preliminary form in 1990 and developed during the execution of the IGCP n°404 (1996-2000) and within the framework of the INQUA Carbon Commission/Working group QEN. All three methods (ocean isotopes, GCMs & palaeoevidence) seem to be converging on a significant (at least hundreds of gigatons) increase in carbon storage from the LGM to the early/mid Holocene.

However, there is still disagreement, and it is important to narrow down the uncertainty as much as possible to improve understanding of the global system. The palaeoevidence method gives a substantially greater carbon storage shift than either of the other two methods (1350 Gt as opposed to around 500 Gt), a difference which would in itself have important implications for understanding the global carbon cycle. In addition, it is necessary to use palaeoevidence in order to consider the ways in which other sources and sinks of carbon (such as rock weathering) shifted in relation to glacial-to-interglacial climate changes. The role of weathering processes has been almost completely neglected in consideration of the late Quaternary carbon cycle. Recent estimates made during the execution of IGCP n° 404 show that soil erosion and the subsequent river flux of organic carbon were at least 10% lower at the LGM than today (Ludwig and Probst, 1999). But it could be more reduced if we could take into account the spatial distribution of carbon storage reduction in the soil during LGM. In the same way, the atmospheric/soil CO₂ consumed by chemical weathering of silicate rock and the subsequent river alkalinity transport to the oceans were reduced by about 10% at the LGM (Ludwig et al., 1999). Nevertheless several uncertainties remain for the LGM on the lithology and climatology of continental emerging shelves, on the chemical weathering under ice sheets, on the runoff modelling, on the role of lateritic covers, on the modelling of weathering processes, on the fate of river carbon entering in the oceanic system…

This Symposium aims at giving a general view of results concerning the changes that affect the carbon cycle at different Quaternary time-scales. State of the art presentations are expected in progress on the behaviour of the carbon in various environments and reservoirs as ocean, atmosphere, cryosphere, continents and their biota, soils, peats, surface and underground waters, etc). Field evidences may include example from different space scales. Models may reach the continent or the global scale and when possible include data from the field. The Glacial-Interglacial climatic extreme may be the more appropriate examples to illustrate changes in the carbon cycle.

To cover such a broad variety of environments and time frame, the aim of the Symposium is to gather scientists from different disciplines and to arrange a meeting between the modellers and the field data community.

The purpose of the Symposium will be also to highlight new horizons in the study of the glacial/interglacial carbon cycle and to point out lack of data and potential weakness in our models. The Symposium will also look forward, considering promising new techniques and areas of research which may yield new clues about the workings of the glacial/interglacial carbon cycle.

Convenor : Jean-Luc PROBST and a team of co-convenors including :

Jonathan Adams, Louis Francois, Giuseppe Etiope, Andy Watson, Ed Boyle, Jean-Marc Barnola, Eric Steig, Joel Guiot, Alayne Street-Perrott, Hugues Faure, Andrei A. Velichko.

Sponsors: Commission on Carbon of INQUA, IGCP459 (and ex-404), in cooperation with CHANGES, an IUGS sponsored Project

This information has been provided by M. Telfer and P. Bragg
© CHANGES. Last updated: 2 July 2002

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