Carbon is an essential element for life, food and energy. It is also a key component of greenhouse gases and, thus, plays an important role in past and present climatic changes

Faure, Hugues

François, Louis

Probst, Jean-Luc

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The global carbon cycle and its changes over glacial interglacial cycles

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Faure, H.

Probst, J. L.

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Global and Planetary Change

The global carbon cycle and its changes over glacial-interglacial cycles - Preface

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 Any correspondence concerning this service should be sent to the repository administrator:staff-oatao@inp-toulouse.fr  Open Archive Toulouse Archive Ouverte (OATAO)  OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.  This is an author -deposited version published in: http://oatao.univ-toulouse.fr/  Eprints ID: 3448 To link to this article: DOI:10.1016/S0921-8181(02)00056-5 URL: http://dx.doi.org/10.1016/S0921-8181(02)00056-5 François, Louis and Faure, Hugues and Probst, Jean-Luc ( 2002) The global carbon cycle and its changes over glacial–interglacial cycles. Global and Planetary Change, vol. 33 (n° 1-2). VII-VIII. ISSN 0921-8181 The global carbon cycle and its changes overglacial–interglacial cyclesCarbon is an essential element for life, food andenergy. It is also a key component of greenhouse gasesand, thus, plays an important role in past and presentclimatic changes. The concentration of greenhousegases, mostly CO2 and CH4, in the atmosphere isincreasing rapidly. This trend will continue in the futureand, according to scenarios recently established by theIPCC working group I (Houghton et al., 2001), willeven be reinforced at least until the second half of the21st century. As a result of this change in the radiativeforcing of the planet, the global mean surface airtemperature has increased by approximately 0.6 jCover the 20th century and is projected to rise by 1.4 to5.8 jC between 1990 and 2100. Important changes inprecipitation and extreme events are also expected.Precipitation will increase globally, but regionallysubstantial reductions are forecasted in some areas,as in the Mediterranean basin. These climate changeswill impact the carbon cycle, including terrestrialvegetation and marine biology, possibly leading tounexpected feedback on the carbon and, hence, green-house gas budgets of the atmosphere. Consequently,the reliability of future climate projections heavilydepends on our understanding of the carbon cycleand its two-way interaction with the climate system.This understanding is still limited, especially regardingbiological subsystems or side processes which havebeen disregarded up to now, because they are thoughtto operate at longer timescales. The models currentlyused for future projections are calibrated on thepresent-day system and validated at most on the periodfor which we have instrumental climatic data, mostlythe 20th century. This means that we are actuallyextrapolating climate from two know points (the endof the 19th and 20th centuries) which are very closefrom each other in the climatic space, especially inregard to the projected future changes. It is urgent thatwe acquire a four-dimensional understanding of thecarbon cycle and climate systems, i.e., both in spaceand time. The Pleistocene is the most recent period ofthe Earth’s history, where the climate underwent bothrapid and longer-term fluctuations comparable in mag-nitude to the changes forecasted for the future,although the forcing factors were different. The Pleis-tocene and, more generally, the Quaternary as well asearlier periods of the Earth’s history, such as thePliocene and the Miocene, provide a laboratory forimproving our understanding of the coupled carboncycle–climate system and for testing our models.This special issue of Global and Planetary Changepresents a series of papers dealing with the globalcarbon cycle and its changes over the Quaternary. Thispublication is organised by the Carbon Commission ofthe International Union for Quaternary Research(INQUA). The Carbon Commission was created in1995 at the XV INQUA Congress held in Berlin. Itsobjective is to gain a better understanding of the globalcarbon cycle by establishing the carbon budget of itssurface components during the Pleistocene and Holo-cene epochs. It focuses mainly on land reservoirs, suchas vegetation, soils, peats, rivers, underground waters,and includes the continental shelf. The aim is toquantify the contribution of these continental reservoirsto the glacial– interglacial changes of ocean and atmos-phere carbon budgets. The commission involves aseries of working groups dealing with the variousreservoirs and/or processes as well as with modelling.This volume results from two symposia organised bythe Carbon Commission in 1999 during the EuropeanUnion of Geosciences 10th meeting (EUG 10) held inStrasbourg, France, and the XVI INQUA Congressheld in Durban, South Africa.Most papers in the volume deal with the past carboncycle both in the marine and terrestrial environments.However, a few papers do not analyse past changes, butattempt to describe some specific features of themoderncarbon cycle, which are today still poorly knownquantitatively, such as karst dissolution, tropical soilcarbon, the isotopic budget of methane-producing lakesediments and carbon degassing from the lithosphere.Consistently, with the overall structure of the INQUACarbon Commission, the papers are organised on areservoir basis. The volume starts with a global studyin which the carbon exchange fluxes between theatmosphere, the ocean and the biosphere over the lastthree glacial–interglacial cycles are reconstructed witha model on the basis of marine isotopic data (Ikeda etal.). It then focuses on specific reservoirs. Two studiesrelate to the ocean including the pelagic environmentwith an investigation of carbonate preservation in theNordic Seas during the last five glacial– interglacialcycles (Helmke and Bauch) and the continental shelfwith a study of the carbon flux in the South China Seaoff Hong Kong (Yim et al.). The next paper by Faure etal. analyses the possibility that groundwater dis-charged to the ocean may have been higher at times oflowered sea level, leading to abundant springs (coastaloasis) on the emerged continental shelf during ice ages.Coastal oases may have affected the glacial carbonbudget through the release of groundwater carbon inthe ocean and the presence ofmore abundant vegetationon the emerged shelf. This is followed by an analyticaland modelling study of early diagenesis and carbonisotopic composition of a lake sediment (Ogrinc et al.).The next study by Bird and Cali presents a revised highresolution oxygen-isotope chronology and discusses itsimportance for biomass burning in Africa. The nexttwo papers relate to soils, with amapping of total carbonin the soils of the Congo (Schwartz and Namri) and thecarbon isotopic composition of charcoal and soils of theSa˜o Paulo state of Brazil and its implications forpaleovegetation (Gouveia et al.). Afterwards, comesome analyses of vegetation changes from the lastglacialmaximum (LGM) to theHoloceneor the present:H. Behling estimates the increase of carbon storage inSouth American tropical forest ecosystems during thelast deglaciation, while Otto et al. present LGM vege-tation reconstructions made with a global vegetationmodel. The remaining papers deal with rock/litho-spheric processes. Jones et al. and Munhoven addressthe question of the importance of rock chemical weath-ering for the carbon and alkalinity budget of the oceanand the atmospheric CO2 changes over the glacial–interglacial cycles. Ph. Gombert analyses the role ofkarst dissolution in the present-day global carbonbudget. Finally, Mo¨rner and Etiope provide a literaturereview of lithospheric carbon degassing estimates andsuggest that a significant disequilibrium exists todaybetween CO2 degassing and silicate weathering.It is really a success for us that this special issue dealswith essentially all components of the carbon cycle andencompasses all timescales relevant to its Quaternaryhistory. It points to the need for a multi-timescales andmulti-reservoirs analysis of global changes.ReferencesHoughton, J.T., Ding, Y., Griggs, D.J., Noguer, M., Van der Linden,P.J., Xiaosu, D. (Eds.), 2001. Climate Change 2001: The Scien-tific Basis. Contribution of Working Group I to the Third As-sessment Report of the Intergovernmental Panel on ClimateChange (IPCC). Cambridge Univ. Press, United Kingdom.Louis Francois*Laboratoire de PhysiqueAtmosphe´rique et Plane´taire,Universite´ de Lie`ge, Baˆt. Bsc, 17 Alle´e du 6 Aouˆt,B-4000 Lie`ge, BelgiumE-mail address: francois@astro.ulg.ac.beHugues FaureINQUA Commission on Carbon,Faculte´ des Sciences,Universite´ de la Me´diterrane´e, P.B. 106,F-13406 Marseille cedex 09, FranceJean-Luc ProbstLaboratoire des Me´canismes deTransfert en Ge´ologie,CNRS UMR 5563, Universite´ Paul Sabatier,38 rue des Trente-Six Ponts,F-31400 Toulouse, France* Corresponding author. Tel.: +32-4-3669776; fax: +32-4-3669711.

The global carbon cycle and its changes over glacial–interglacial cycles

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The global carbon cycle and its changes over glacial–interglacial cycles

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