Exploring Late Pleistocene climate variations M. Sarnthein, J. Kennett, J. Chappell, T. Crowley, W. Curry, J.C. Duplessy, P. Grootes, I. Hendy, C. Laj, J. Negendank, et al.

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M. Sarnthein, J. Kennett, J. Chappell, T. Crowley, W. Curry, et al.. Exploring Late Pleistocene climate variations. Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), 2000, 81 (51), pp.625. ￿10.1029/EO081i051p00625-01￿. ￿hal-03245041￿

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HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Copyright Eos, Vol. 81, No. 51, December 19, 2000

EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION

VOLUME 81 NUMBER 51

DECEMBER 19, 2000

PAGES 625-640

Earth's system in this manner. For example, Exploring Late Pleistocene there is mounting evidence that changes in the system were associated with abrupt switches in the strength of the North Atlantic Climate Variations thermohaline circulation and "The Great Ocean Conveyor" [van Kreveldet a/., 2000, PAGES 625,629-630 record of this unexpected climatic behavior and references therein]. Recent evidence has been found in many regions (Figure 1), has emerged that perhaps even the source The origin of much of the variability in late including polar ice sheets; marine sediments of oceanic shallow intermediate waters has Quaternary climate remains a major question of the Atlantic, Pacific, and Indian Oceans; likewise oscillated in close concert with these in the understanding of processes of past and and in terrestrial lakes and bogs. DO cycles climate changes [Kennett et al, 2000]. Distinc­ future climate change.The origin of major are recorded, for example, by changes in oxygen tive patterns have emerged.There appears to rapid, decadal climate change during the latest isotopes(d'sO) of polar ice; in sea surface tem­ be a vague -7200-year oscillation, with each Quaternary remains an enigma.These issues peratures and dsO of sea water recorded in episode consisting of several DO cycles are critical for understanding global change. foraminiferal shells in marine sediments; and [Bond et al, 1993, cited in van Kreveld et al, Although major progress continues to be in climate curves of pollen assemblages from 2000],where both the first warm interstadial made, a general consensus has developed lake sediments (Figure 2).These climate fluc­ and the last cold stadial were of longest dura­ that limitations in knowledge of the chronology tuations are also recorded by significant oscil­ tion. The cycle climaxes with a severely cold of millennial-scale climate variability are lations in atmospheric trace gases (such as Heinrich event. A saw-tooth pattern of change

impeding further progress. CH4) in the ice cores and in large changes in at the millennial scale is evident in certain However, a suite of valuable techniques, the marine and terrestrial biosphere. Clearly, records, much like the well-known saw-tooth approaches, and potential new site locations much recent evidence suggests that the Earth pattern at the Milankovitch or orbital time can improve our understanding of the chronol­ system as a whole experienced this unstable scale that is expressed, for example, in the 100 ogy of rapid climate change.The idea of creating behavior during the last glacial cycle. k.y cycle that marks the late Quaternary. a joint global time scale of decadal-to-millennial- The origin of this climatic behavior largely Much has been accomplished toward under­ scale climate oscillations was discussed by more remains a mystery, although certain associa­ standing the extent and magnitude of this than 50 scientists from various disciplines at the tions have emerged that clearly are critical in behavior in the Earth's system. However, SCOR-IMAGES (Scientific Commission of Ocean the assessment of processes that drive the further progress requires studies of climatic Research-Trie International Marine Past Global Change Study) Workshop in Trins, Austria, Febru­ ary 16-19,2000.Their recommendations are reported at the end of this article.

New Millennial-Scale Climate Variability

The Late Quaternary climate was highly unstable and prone to large, rapid changes that could be as short as a few decades. Curiously, this instability was particularly pronounced during the last ice age, when ice sheets covered northern high-latitude conti­ nents, which led to exposure of the continen­ tal shelves. First identified in ice cores drilled through the Greenland ice sheet, a series of «3

(a) Air Temperature Calendar Year Chronologies (c) Pakistani Margin (h) Lago Grande di Monticchio over Greenland for the Last 80 k.y. 18 Total Organic Carbon Forest Pollen (GISP2 0) Weak ^ Strong Less More Techniques that can be employed to help Precipitation Precipitation^ Q Cooler*-*-Warmer ^Upwelling^Upwelling ( ) Iceland Sea e establish calendar year chronologies for strati- graphic records representing the last 80 k.y fall into three categories: incremental dating, radiometric dating, and correlation/ matching procedures. 10 Incremental dating techniques provide con­ tinuous and independent calendar year chronologies. Dendrochronology—annual rings laid down by long-lived trees in temper­ ate regions of the world—provides one of the 20 best annual records. Ring-width variations can be cross-matched between trees and a com­ posite calendar year time scale can be con­ structed. A continuous dendrochronology now extends to 11,800 calendar years B.P -30- Older "floating" sections of dendrochronologi- cal records have yet to be tied to the continu­ ous record; once this is achieved, a detailed o calibration curve will extend to -40 k.y B.P However, it is rarely possible to apply dendro- chronological dates to other records without < 40- cross-matching between tree ring measure­ ments and other proxies. Ice cores from polar ice sheets yield extremely valuable paleoclimatic archives. Major strengths of these records are their very 50- high stratigraphic resolution (sub-annual in upper parts) and the many paleoenvironmen- tal proxies represented. Changes in many of these proxies can be directly compared with each other with no phase uncertainty, 60 J ice core [see Stuiver and Grootes in Hammer et al, 1997]; (b) N. published simultaneously [Hammer et al, pachyderma dextral to sinistral coiling ratio from ODP Hole 893A, Santa Barbara Basin [Hendy 1997], However, several different time scales and Kennett, 2000];(c) total organic carbon record from core SO90-136KL, Pakistani Margin now exist for each ice core and an integrated, 8 [Schulz et al, 1998]; (d) benthic d' 0 record of Faeroe Drift deposits [Rasmussen et al, 1996]; optimal time scale has yet to be established (e) ice-rafted detritus accumulation for core PS2644, Western Iceland Sea [see Voelker in van using both cores. Kreveld et al, 2000]; (f) sea surface temperature based on fauna I assemblages for core S082-5, Irminger Sea [van Kreveld et al, 2000]; (g) magnetic susceptibility for core MD95-2010, Norwe­ The GISP2 time scale was derived by contin­ gian Sea [see Kissel et al, 1999, cited in Laj et al, 2000]; and (h) woody taxa pollen abundance uous counting of several properties exhibiting a for Largo Grande di Monticchio [Allen et al, in Zolitschka, 1999]. seasonal cycle; conservatively estimated errors range from 2% over the last 40 k.y. to about 20% at 110 k.y. B.P Older than about 50 k.y. B.P, the widely used GISP2 time scale uses records at very high decadal resolution, mechanisms must have played a central role a comparison of <5180 of oxygen in trapped air because the extremely rapid changes in the in creating abrupt change over only a few with that in the Vostok, record and is consis­ Earth system have global responses, some of decades, it is crucial to understand and date tent with the marine SPECMAP project time which appear synchroneous when transmitted leads and lags between different global envi­ scale.This provides a time scale with probably through the atmosphere, and others sometimes ronmental systems.This requires the develop­ somewhat smaller uncertainties at 100 k.y B.P appear diachroneous when transmitted ment of high-resolution stratigraphic records The GRIP time scale back to ~7 k.y.a. is through the ocean. Climate changes appear for the late Quaternary with accurate calendar based on correlation with the counted Dye-3 synchroneous between Greenland, California year chronologies. Creation of a global time record using volcanic acidity layers as data. margin waters, and the Cariaco Basin (tropical scale of decadal-to-millennial-scale climate Continuous layer counting in GRIP was used Venezuela), and anti-phased between the oscillations has become a pressing issue. between 7 k.y.B.Pand the Oldest Dryas/ north and south Atlantic basins, and between Significant progress can be gained by estab­ Boiling transition at -14.5 k.y.a. Ice flow mod­ Greenland and parts of Antarctica. lishing calendar year chronologies in terrestrial eling, incorporating smoothly varying Poor understanding of temporal relations and marine records for the last 80 k.y,testing accumulation estimates based on the d]S0 between climate changes around the Earth hypotheses for late Quaternary climate behav­ record, and using age control points at the hinders understanding of the processes that ior by acquiring critical new records, and ana­ Younger Dryas/Pre-boreal transition (11.5 k.y caused past climatic instability and rapid lyzing new and existing records using multiple ago), and MIS 5d (110 k.y. ago), was used to climate change. Since climatic feedback approaches at higher temporal resolution. construct the remainder of the GRIP"ss08 Eos, Vol. 81, No. 51, December 19, 2000 time scale." An independent time scale for this technique is that there has been no loss (NAPIS-75) of late Quaternary age (75-10 k.y. GRIP back to -60 k.y. B.P is based on counts or gain of nuclides since deposition; that is, B.P; Lay et al., 2000).The stacked record has of annual dust layers [Hammer et al, 1997]. the system must be closed. Unlike 14C,the for­ been dated by correlation of one of the cores Annual laminations or varves can be mation of these nuclides does not depend on to the GISP2 ice core via d]80 meltwater signals preserved in both marine and lacustrine sedi­ variations in solar activity or reorganizations [van Kreveld et al.,2000]. Refined techniques ments. Marine varved chronologies usually in the global carbon cycle. When correcting are necessary for precise and objective correla­ only represent fragments of the last 80 k.y (for for various sources of error,such as inherited tions using the entire character of the paleo- example, 9-15 k.y. ago) in the Cariaco Basin Th,this technique provides calendar year intensity records.This should soon enable [Hughen et al, 1998].Lacustrine environ­ chronologies. global correlations with an uncertainty of less ments [Zolitschka, 1999] can provide ideal Radiocarbon dating is widely used for dat­ than 2-5 k.y conditions for the development of varved sed­ ing materials up to - 50 k.y. B.P Carbon 14 dat­ Volcanic ash layers, when described in iment sequences for the length of the life of ing by decay counting or accelerator mass terms of their geochemical and mineralogical the lake. Examples include Lake Gosciaz in spectrometry (AMS) has an age uncertainty properties, can also be utilized as event markers Poland, Lake Holzmaar and Meerfelder Maar ranging from about ±20-30 years for samples (datums) to correlate ice and sediment cores. in Germany, Lake Monticchio in Italy, Elk Lake back to 10.5 k.y. ago, up to ±100 years back to Furthermore, such events are suitable for in the United States, and possibly Lake Suiget- 20 k.y ago, and up to >±1000 years forages 39Ar/40Ar dating with an error of 2 k.y or less su in Japan; but none completely covers the close to the limits of counting statistics for the last 80 k.y last glacial cycle. depending on the age and size of a sample. Changes of sea level directly express Corals and speleothems may exhibit annual Radiocarbon ages require calibration changes in the volume of continental ice growth bands, thus providing a calendar year because the atmospheric ,4C/12C ratio was not sheets. Such changes can be determined from 14 chronology. However, these records are usually constant in the past due to changes in the C study of coral reef deposits dated by ,4C or limited to the last few centuries. Fossil corals production rate and the oceanic carbon system. ^U/^Th methods. Coral terraces at sites with can provide records representing older time Calibration is necessary for comparing ,4C- high tectonic uplift provide detailed records windows.These provide "floating" chronologies dated records to other calendar year records, of past sea level changes. However, the use of that require dating using other approaches and this increases error.The problem is exac­ sea level stands as global chronological markers such as 14C and U-series dating. Speleothem erbated by plateaux in the calibration curves are often problematic because of the compli­ dating is often limited by progressive fading resulting from large temporal variations in cating effects of local tectonics, storms, and of the growth bands, which thus tend to lose atmospheric 14C content. Back to 11.8 k.y. B.P tsunamis. their annual resolution. the calibration uses 14C dating of dendro- chronologically dated tree rings.This will be Testing Explanations for Millennial- extended into the late glacial episode when Comparing Incremental Scale Climate Variability floating dendrochronologies of this age are Dating Techniques tied to the Holocene master record. Beyond Many records of varying chronological reso­ The time scales developed for the these limits back to about 55 k.y. B.P, attempts lution now exist that clearly exhibit rapid Greenland ice cores have special value to extend the calibration curve are based on: oscillatory behavior in climate at centennial- extending far beyond that of ice core studies 230U/234Th ages of corals; annually laminated through-millennial time scales, much like the for several reasons.They certainly provide the sediments from marine [Hughen et al., 1998] DO cycles recorded in the Greenland ice. longest archives for studies of features such as and lacustrine sediment sequences; and indi­ Examples of some particularly high-resolution the 11-year sunspot cycle. Some hypotheses rect calibration by measuring at high resolu­ time series are shown in Figure 2.These records for explaining climatic variability rely on time- tion the ,4C ages on well established climatic describe variability in the atmosphere-ocean series analyses, which are critically dependent time series, thus allowing detailed cross­ system through proxies reflecting changes; for on the integrity of the time scale. Paleoceano- matching with well-dated climate records; for example, in polar and sea surface temperature. graphic records can only obtain a precise example, Greenland ice cores [van Kreveld et Several hypotheses have been proposed time scale sufficient for time-series analysis by a/.,2000 and references contained therein]. [van Kreveld et al., 2000] to explain such phe­ correlation with the Greenland ice core In addition, dates of marine sediments may nomena, at least in part.The most prominent record. Correlation to Greenland obviously be affected by the local l4C reservoir of the is variations of the Global Conveyor and low- provides an essential link for ensuring accura­ ocean.This local effect may vary by the same frequency variability in the eastern equatorial cy of Antarctic ice core chronologies.The magnitude as potential leads and lags Pacific upwelling system. Different mecha­ accuracy of time scales based on annual layer between various climate signals of DO cycles nisms may have triggered such variability Vari­ counting in lake sediments and tree rings can and thus add uncertainties to the interpreta­ ability in conveyor strength may have been ultimately be checked only by comparison tion of marine paleoenvironmental records. produced by meltwater pulses in the northern with other annually resolved time scales.The To overcome these calibration problems, 14C North Atlantic linked to internal ice sheet insta­ Greenland records should remain an ultimate ages must be measured at high resolution in bilities, by variations in surface water circula­ means for such checking. Increasingly impor­ more annually laminated records that have tion in the tropical Atlantic, or by changes in tant paleoclimatic time series are based on independent calendar-year chronologies and solar irradiance. In the equatorial Pacific, circu­ "floating" annually resolved time scales.These finally, to assemble a single 14C calibration lation changes might represent a resonant time include stalagmite sections, pieces of wood, curve from these records for the past 50 k.y scale for the Pacific Basin as a whole, and thus and lake sediment records that do not extend climate change of global magnitude. The two to the present.Their value is enhanced when mechanisms may be interdependent, with Correlation Techniques they are calibrated with the continuous variations in equatorial Pacific climate affect­ Greenland ice core time scale. Certain correlation techniques enable syn­ ing the North American and Greenland ice chronous cross-matching of proxies for trans­ sheets and, in turn, conveyor circulation. Con­ fer of chronology from a dated to an undated versely, changes in the conveyor may trigger Radiometric Techniques climate record. trade wind changes in the eastern equatorial Radiometric techniques provide discrete Geomagnetic paleo-intensity is a synchronous Pacific, or changes in the strength of the Siber­ dates and continuous chronology Uranium- signal that is employed for global correlation ian high may influence westerly wind bursts Thorium (230U/234Th) dating using thermal-ion- of many geological records. Geomagnetic in the western equatorial Pacific or changes ization mass spectrometry (TIMS) can be excursions and events are used as master tie in upwelling of cold deepwater in the north­ used to date materials from speleothems, points between separate records. An example western-most Pacific. corals, carbonate deposits, peat, and bones is the new high-resolution paleo-intensity Each mechanism above has a different "fin­ from 350 to 5 k.y a. The crucial prerequisite for record from North Atlantic marine sediments gerprint" in the time and space domains.Thus, Eos,Vol. 81, No. 51, December 19,2000 regions on land and in the ocean that appear Obtaining new sequences in the equatorial various episodes, including meltwater pulses to have played a key role in rapid, millennial- Pacific would provide records of: warming and equatorial Pacific climatic oscillations. scale climate variability need to be targeted for episodes in the eastern equatorial Pacific; future high-resolution climate studies to test dif­ aridity in Australia (as detectable using pollen ferent mechanisms of climate change. Never­ records);sea-surface temperature increases Acknowledgments theless, because understanding of such along the west coast of North America; precipi­ The Trins Workshop was supported by processes is at an early stage, a delicate tation in the American southwest; upwelling SCOR,IMAGES,Volkswagen,and the U.S. balance needs to be struck between targeted along the Peru/Chile margin; and potential National Science Foundation.This article was sites and those of serendipity "Incomplete" climatic links with central Canada. prepared by members of the Trins workshop. high-resolution records of climate change, Studies of the potential role of low-frequency including varved sequences and speleothems, solar irradiance changes in millennial-scale should also be targeted for the last 80,000 climate variability would also be valuable. Authors years, since this information is often valuable. Studies of Holocene records provide some support for the role of low-frequency solar irra­ M. Sarnthein, J. PKennett, 1 Chappell, T. Crowley, W. Curry, J. C Duplessy PGrootes, I. Hendy Recommendations of SCOR-IMAGES diance changes in contributing to decadal-to- millennial-scale climate variability. If so, such C. Laj, J. Negendank, M. Schulz, N. J. Shackleton, Workshop variability may also be detected in ice age A. Voelker, B. Zolitschka and the other Trins Participants reached a consensus about records. Better testing of the solar hypothesis workshop participants many recommendations. First, a significant requires the production of more ,0Be and 36C1 For additional information, contact coordinated effort should be made to devel­ data to assist with the separation of the cosmo- M. Sarnthein, Institut fur Geowissenschaften, op a new calendar time scale for the Green­ genic effect from the 14C record, the latter of University of Kiel.D-24098 Kiel, Germany; land GISP2 and GRIP ice core records. This which is also influenced by changes in ther- E-mail: [email protected] highly detailed record should be upgraded as mohaline circulation. new information becomes available. High-resolution records of continental climate Joint research efforts should be initiated change need to be developed with improved References across various disciplines to improve the glob­ age control, particularly in the Southern Hemi­ Eos limitation on the numbers of references pre­ al time scale of millennial climate oscillations. sphere. Models suggest that the solar signal is cludes a balanced listing of all relevant publications. This should establish a common 14C-time scale stronger over land, with the same sign of based on existing annually laminated sedi­ response in both hemispheres. New and exist­ Hammer, C, PA. Mayewski, D. Feel, and M. Stuiver (eds.), ment and ice records and to locate additional ing records should be analyzed to test mecha­ Greenland summit ice cores.i Geophys. Res., 102, laminated lacustrine and marine records, nisms of climate change. A number of C12.1997. calibrate the common 14C-time scale back complementary and overlapping approaches Hendy I. L and J. PKennett, Dansgaard-Oeschger cycles to 55 k.y. B.P, define variations in the 14C may lead to better understanding of centenni­ and the California Current System: Planktonic foraminiferal response to rapid climate change in reservoir effect in various ocean basins, al/millennial-scale climatic change, two of Santa Barbara Basin, Ocean Drilling Program hole validate and promote the geomagnetic which are "zereo'th order" best-fit correlations S93A,Fbleoceanogr., 75,30-42,2000. palaeo-intensity record as a dating tool, and between different time series and the standard Hughen, K. A., J.T. Overpeck, S. J. Lehman, M. Kashgarian, establish a set of global time markers. Greenland ice core records.Time slice studies J. Southon, R. Alley and D. M. Sigman, Deglacial New records should be obtained to test vari­ of selected DO oscillations should document changes in ocean circulation from an extended ous components of the conveyor hypothesis. the spatial evolution of oceanic and atmospher­ radiocarbon calibration, Ataure, 397,65-68,1998. These include north and tropical Atlantic cores ic patterns. Other pressing research needs Kennett, J. P, K. G. Cannariato, I. L Hendy and R. J. Behl, to examine phase relations between deep- and include the effect of millennial-scale climate Carbon isotopic evidence for methane hydrate insta­ bility during Quaternary m\.erstad\a\s, Science, 288, surface-water hydrography and their origin, ice- changes on methane and carbon dioxide 128^133,2000. rafting events, meltwater and brine pulses, and variations of the atmosphere and potential Laj, C, C. Kissel, A. Mazaud, J. E.T. Channell, and J. Beer, feedbacks of atmospheric trace gas changes on indications of tropical humidity changes; south North Atlantic paleointensity stack since 75 k.a. Atlantic sites where the Atlantic seesaw would centennial-to-millennial-scale oscillations; inten­ (NAPIS-75) and the duration of the Laschamp event, predict increased sea surface temperatures and sive statistical examination of the 1500-year Phil. Trans. R. Soc. London A, 358,1009-1025,2000. southern African precipitation during DO stadi- cycle to determine its robustness, bandwidth, Martinson, D. G., et d\.,Natural Climate Variability on als; and regions affected by meltwater-induced and coherence and phase relationships Decade-to-Century Time Scales, 630 pp., National Acad­ changes in the strength of the Siberian high and between different regions; and an examination emy Press, Washington, D.C., 1995. its effect on the south and east Asian monsoons. of periodicities of the DO band other than the Rasmussen.T. L, E.Thomsen, L. Labeyrie, and T. C. E. Such sites would be useful in testing whether 150Oyear cycle. van Weering, Circulation changes in the Faeroe- Shetland Channel correlating with cold events sub-polar north Pacific sea surface temperature Centennial/millennial-scale fluctuations in during the last glacial period (58-10 k.a.), Geology, is controlled by coeval atmospheric forcing or non-glacial sections also deserve analysis. 24,937-940,1996. rather by thermocline ventilation at the terminus Even though such oscillations are of lower Schulz, H., U. von Rad, and H. Erlenkeuser, Correlation of the "global conveyor" in anti-phase with north amplitude than their glacial cousins [Martin­ between Arabian Sea and Greenland climate oscilla­ Atlantic changes. son et al., 1995],the removal of the greatly tions of the past 110,000 years, Nature, 393,54-57, New records should also be obtained in the complicating effect of most of the Northern 1998. high latitudes of the Southern Ocean and Hemisphere ice sheets may enable isolation van Kreveld, S., M. Sarnthein, H. Erlenkeuser, PGrootes, Antarctica.These might record anti-phase of the relative importance of other sources of S. Jung, M. J. Nadeau, U Pflaumann, and A.Voelker, Fbtential links between surging ice sheets, circulation behavior between the Northern and Southern forcing, especially during the last 1000 years, changes, and the Dansgaard-Oeschger cycles in the where time and space control of samples is Hemispheres. Since the conveyor also predicts Irminger Sea, 60-18 kyr, Fuleoceanogr., 15,425-442, a west-east seesaw in Antarctic Circumpolar very good. Finally, intercomparisons of climate 2000. flow, cooling in the Ross Sea may be in-phase models will allow assessment of the Zolitschka, B., (ed.), High-resolution records from with North Atlantic cooling. robustness of model-predicted responses to European Lakes, Quat. Set Rev., 18,7,1999.