//FS/ELS/PAGINATION/ELSEVIER AMS/STPS/3B2/CH40-N2955.3D – 595 – [595–614/20] 30.10.2006 7:12PM 40. Chronology and Climate Forcing of the Last Four Interglacials Frank Sirocko, Martin Claussen, Thomas Litt, Maria Fernanda Sa´nchez Gon˜i, Andre´ Berger, Tatjana Boettger, Markus Diehl, Ste´phanie Desprat, Barbara Delmonte, Detlev Degering, Manfred Frechen, Mebus A. Geyh, Matthias Groeger, Masa Kageyama, Frank Kaspar, Norbert Ku¨ hl, Claudia Kubatzki, Gerrit Lohmann, Marie-France Loutre, Ulrich Mu¨ ller, Bert Rein, Wilfried Rosendahl, Katy Roucoux, Denis-Didier Rousseau, Klemens Seelos, Mark Siddall, Denis Scholz, Christoph Spo¨tl, Brigitte Urban, Maryline Vautravers, Andrei Velichko, Stefan Wenzel, Martin Widmann and Bernd Wu¨ nnemann The last four interglacials (intervals during suggestions for future research themes, which global ice volume was similar to, or which will need to be answered soon if the less than, that of our current warm stage) climate of the past is to be of use for the correspond to the warmest parts of the mar- prediction of climatic and environmental ine oxygen isotope stages MIS 5, 7, 9, 11. evolution in the future when the natural These interglacials followed the 100-kyr forcing of climate has to interact with the rhythm of eccentricity, but each had different human influence on the atmosphere and insolation regimes, different durations, dif- land surface. ferent ice volumes and different sea-level heights, but atmospheric greenhouse gas concentrations were similar and reached STATEMENTS BY FIRST AUTHORS values which, by and large, were close to OF RESEARCH ARTICLES those of the current interglacial (Holocene or MIS 1) before the industrial revolution Martin Claussen, University Hamburg and led to the artificial enrichment of the atmo- Max Planck Institute for Meteorology, Hamburg, sphere’s greenhouse gas concentrations via Germany the burning of fossil fuels. The Holocene is addressed in a few papers, but an intercom- (1. Introduction to Climate Forcing and Cli- parison of the ongoing interglacial with the mate Feedbacks) past interglacials is not the focus of this book. This final paper of the book will summar- 1. Commonly, climate is defined as statis- ize the evidence presented and discussed in tics (mean, variance, ...) of the atmo- the research articles. It is intended to be sphere. In climate physics, however, a comprehensible to the lay reader and thus wider definition has proven to be useful does not go into detail. Every paper is repre- in which climate is viewed as the state sented by a list of three statements which and statistics of the climate system which sum up the key findings. This is followed by encompasses the atmosphere, the ocean, a synthesis of the current state of knowledge the ice and the land including the living on each of the climatic warm intervals dis- world, i.e. the marine and terrestrial bio- cussed in the book. There is almost complete sphere as well as carbon and nutrient agreement on several themes, in particular cycles. on the subject of insolation forcing, while 2. Climate varies on all timescales, not only other topics, such as the correlation of because of changes in climate forcing, but sequences dated by different techniques, also because of internal dynamics and will need to be discussed and evaluated feedbacks between the components of further before a consensus is reached. At the climate system which are seemingly the end of this paper, we make some unrelated to variations in forcing. //FS/ELS/PAGINATION/ELSEVIER AMS/STPS/3B2/CH40-N2955.3D – 595 – [595–614/20] 30.10.2006 7:12PM 598 Frank Sirocko et al. 3. Not all climate variations on timescales 3. It is likely that changes in insolation longer than 30 years are directly driven caused by changes in orbital parameters by oscillation forcing; some of these varia- trigger fast internal feedbacks such as the tions could arise because of the sluggish water vapour–temperature feedback and dynamics of the deep ocean or the ice the snow–albedo feedback. Some feed- sheets or because of a strongly nonlinear, backs, like the snow–albedo feedback, disproportional response of the climate amplify climate changes very rapidly system to subtle variations in forcing. once a certain threshold in the system is crossed. Initial changes are then further Andre´ Berger, Universite´ catholique de amplified by slower feedbacks such as Louvain, Belgium biogeochemical and biogeophysical feed- backs and finally, the isostatic response (2. Insolation During Interglacials) of the lithosphere to icesheet loading. 1. The spectrum of the long-term variations Andre´ Berger, Universite´ catholique de of daily insolation is dominated by pre- Louvain, Belgium cession everywhere over the Earth and for any day except close to the polar night. (4. Modelling the 100-kyr Cycle – An Exam- 2. The energy received by the Earth over a ple From LLN EMICs) given time slice during the year defined in terms of the longitude of the Sun (an 1. The LLN model is a model of intermedi- astronomical season for example) is a ate complexity which takes into account, function of obliquity only, the length of in a simplified way, the atmosphere, the such astronomical seasons being a func- hydrosphere, the cryosphere, the bio- tion of precession only. sphere, the lithosphere, their mutual 3. The amplitude of the variations of insola- interactions and internal feedbacks. tion (in particular during the intergla- Under the forcing of insolation and a cials) is a function of the amplitude of progressively decreasing atmospheric the variations of precession. CO2 concentration, it simulates the tran- sition between the 41-kyr and the 100-kyr Martin Claussen, University Hamburg, and worlds around 850 kyr. Max Planck Institute for Meteorology, Ham- 2. The model also simulates the spectrum of burg, Germany the northern hemisphere ice volume over the last 450 kyr, with the strongest period (3. A Survey of Hypotheses for the 100-kyr at 100 kyr. Cycle) 3. It fails to reproduce the reduced ampli- tude of the 100-kyr cycles before 450 kyr 1. Even some 160 years after first geological with cool interglacials and cold glacials. evidence, the ice-age riddle is not yet fully solved. However, we have some clues on Frank Sirocko, University of Mainz, Germany which elements should constitute a theory of Quaternary Earth system dynamics, (5. Introduction: Palaeoclimate Reconstruc- regarding concepts and model structure. tions and Dating) 2. It is certain that the ice-age riddle cannot be explained in terms of a single domi- 1. The beginning, end and duration of the nating process. Instead, a systems past interglacials do not appear to be approach involving a number of feed- synchronous all over the world, i.e. back processes and the nonlinear nature parts of the climate system have been of the climate system is expected to lead in an interglacial state for longer than to a solution. others. //FS/ELS/PAGINATION/ELSEVIER AMS/STPS/3B2/CH40-N2955.3D – 595 – [595–614/20] 30.10.2006 7:12PM Chronology and Climate Forcing 599 2. Beginning and end of interglacials in the 1. The last nine interglacial periods differ low latitudes and in the Antarctic lead to not only in height and variability of sea respective changes on the northern level, but also in timing relative to north- hemisphere. ern summer insolation peaks. 3. Time-transgressive climate shifts are also 2. Sea levels during MIS 5e, 9c and 11 were strong over Europe, where the sea-surface close to or slightly higher than modern sea temperature (SST) changes of the North level but sea level during MIS 7 may have Atlantic drift were associated with a step- been slightly lower than present day. wise shift of the vegetation zones, at least 3. Some interglacials have a single peak at the end of the past interglacial, with close to modern sea level (MIS 5e, 9c) interglacial conditions persisting for and others have several (MIS 7), while longer in southern Europe than in the MIS 11 persisted with little variation for north. at least 30 kyr. Barbara Delmonte, DISAT, University Manfred Frechen, Leibniz Institute for Milano-Bicocca, Milano, Italy. Applied Geosciences (GGA-Institut) Hannover, Germany (6. Late Quaternary Interglacials in East Antarctica from Ice-Core Dust Records) (8. Uranium-Series Dating of Peat from Cen- tral and Northern Europe) 1. Aeolian dust records from deep East Ant- arctic ice cores preserve evidence for 1. Fen peat is suitable for uranium-series extremely low dust fluxes during the last dating under the asumption of complete five interglacials (10 to 25 times lower fractionation of uranium and thorium than in glacial periods). This is related during formation and no gain or loss of to reduced primary production and U and Th since the time of formation. mobilization of dust on the Southern 2. Uranium-series dating provides more Hemisphere continents, and to changes reliable and precise absolute dates of in atmospheric transport and the hydro- interstadial and interglacial peat layers logical cycle. The data show no evidence in Central Europe. Examples of uranium for pronounced cold events within the dates for MIS 5, 7 and 9 are: 91 2 kyr for last five interglacials (back to MIS 11.3). lignite (MIS 5c) from Zell in Switzerland,Æ 2. The Sr–Nd isotope fingerprint of aeolian 106 11 kyr for the fen peat (MIS 5e) dust in Antarctica suggests a dominant fromÆ Allt Odhar in Scotland, 214 8 kyr southern South American provenance for peat (MIS 7) from Groß-RohrheimÆ during Quaternary glacial times, but the in Germany and 317 14 kyr for fen first geochemical data for stage 5.5 and peat from Tottenhill QuarryÆ in Norfolk, the Holocene show significant differ- England. ences and opens up the possibility for 3.