Evidence for last interglacial chronology andenvironmental change from Southern EuropeAchim Brauer*, Judy R. M. Allen†, Jens Mingram*, Peter Dulski*, Sabine Wulf*, and Brian Huntley†‡

*GeoForschungsZentrum Potsdam, Section 3.3, Telegrafenberg, D-14473 Potsdam, Germany; and †Institute of Ecosystem Science, School ofBiological and Biomedical Sciences, University of Durham, Durham DH1 3LE, United Kingdom

Edited by James P. Kennett, University of California, Santa Barbara, CA, and approved November 9, 2006 (received for review April 24, 2006)

Establishing phase relationships between earth-system compo-nents during periods of rapid global change is vital to understand-ing the underlying processes. It requires records of each compo-nent with independent and accurate chronologies. Until now, nocontinental record extending from the present to the penultimateglacial had such a chronology to our knowledge. Here, we presentsuch a record from the annually laminated sediments of LagoGrande di Monticchio, southern Italy. Using this record we deter-mine the duration (17.70 � 0.20 ka) and age of onset(127.20 � 1.60 ka B.P.) of the last interglacial, as reflected byterrestrial ecosystems. This record also reveals that the transitionsat the beginning and end of the interglacial spanned only �100 and150 years, respectively. Comparison with records of other earth-system components reveals complex leads and lags. During thepenultimate deglaciation phase relationships are similar to thoseduring the most recent deglaciation, peaks in Antarctic warmingand atmospheric methane both leading Northern Hemisphereterrestrial warming. It is notable, however, that there is no evi-dence at Monticchio of a Younger Dryas-like oscillation during thepenultimate deglaciation. Warming into the first major interstadialevent after the last interglacial is characterized by markedly dif-ferent phase relationships to those of the deglaciations, warmingat Monticchio coinciding with Antarctic warming and leading theatmospheric methane increase. Diachroneity is seen at the end ofthe interglacial; several global proxies indicate progressive coolingafter �115 ka B.P., whereas the main terrestrial response in theMediterranean region is abrupt and occurs at 109.50 � 1.40 ka B.P.

Eemian � phase relationships � pollen � varves

Reconstructing the phase relationships between major earth-system components relies on precise, accurate, and inde-

pendent chronologies. However, absolute dating of geologicalrecords beyond the range of radiocarbon (more than �50 kaB.P.) is problematic, and age estimates for records of the lastinterglacial (LI) commonly rely on indirect dating approaches(1–4), often either by tuning to the time scale of orbitalvariations (2) or ‘‘wiggle-matching’’ to another record andapplying its chronology (3, 4). Until now no continuous conti-nental record extending from the present through the LI to thepenultimate glacial had its own internal chronology to ourknowledge. Thus timing and duration of the LI, as reflected incontinental, marine, and ice-core records, and the phase rela-tionships between these major earth-system components duringmarine oxygen isotope stage (MIS) 6–4, have been the subjectof much debate (1, 5–9). Shackleton (9) first proposed corre-spondence between the LI and MIS 5e, whereas Woillard (10)subsequently demonstrated such apparent correspondence in acontinental record. More recently, however, pollen, alkenone,and �18O analyses of marine cores from locations close to theIberian peninsula have shown asynchrony between changes interrestrial vegetation, sea surface temperature (SST), and globalice volume during MIS 5 (6, 11). Using a chronology with five agecontrol points (at 82.9, 116.1, 129.1, 128, and 132 ka B.P.), basedon correlation of plateaux in the �18O record of global ice volumewith radiometrically dated records of sea-level stillstands from

corals, the duration of the continental LI, as recorded in thesame marine cores, has been estimated at �16 ka (11). Otherattempts to relate continental and marine LI records have basedtheir chronology on an orbitally tuned time scale (2), makingimplicit assumptions about phase relationships between insola-tion and the palaeovegetation record, and using as few as threeage control points (1).

Previous studies of the sediments of Lago Grande di Montic-chio, a maar lake in southern Italy (40° 56� north, 15° 35� east,656 m above sea level), spanning the period from the present dayback to �100 ka, demonstrated the presence of long varvedintervals (12, 13), providing the basis for well dated palaeoen-vironmental reconstructions (14). Here, we present data fromcores collected in 2000 that extend the record by �30 m, thusproviding an overall record spanning 102.3 m and comprising acomplete sediment sequence extending from the present back tothe penultimate glacial stage. The upper 72.5 m of the 2000 coresequence correlates perfectly at the level of microscopic featureswith previous cores. The additional sediments recovered in thecores were subjected to lithological examination in thin section,using a petrographic microscope. This process showed annuallaminations to be present throughout the LI and during thetransitions into and out of the interglacial; it also provided varvemicrofacies data and varve counts. Varve microfacies changeshave been used as proxies for autochthonous deposition (lakeproductivity) and detrital sediment fluxes from the catchment,contributing to the characterization of the dynamics of environ-mental changes. Varve counting has provided a continuousincrement chronology for the LI.

To assess uncertainty in this varve chronology, it must beconsidered in three parts. First, the Holocene and most of theglacial part of the record include both varve-counted intervalsand nonvarved intervals for which sedimentation rates have beencalculated on the basis of sedimentological features (12, 13). Theresulting chronology is, however, corroborated by 26 indepen-dently dated volcanic ash layers that have been clearly correlatedto tephra layers in the Monticchio record by means of theirgeochemical and mineralogical composition (15). A furtherprominent tephra layer located in the core sequence at a depthof �78 m, within the sediments of the Melisey I stadial, matchesgeochemically tephra X6 deposited during MIS 5d in Mediter-ranean marine sediments and dated there to 107 � 2 ka B.P. (16).This layer is dated to 108.33 ka B.P. by the Monticchio chro-nology, the excellent agreement between the Monticchio varveage and the age from marine sediments adding to confidence inour chronology and suggesting that the uncertainty in the latteris �1.3%. Thus we estimate the uncertainty in our assessment of

Author contributions: A.B. and B.H. designed research; A.B., J.R.M.A., J.M., P.D., and S.W.performed research; J.R.M.A. and J.M. analyzed data; and A.B. and B.H. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS direct submission.

Abbreviations: LI, last interglacial; MIS, marine oxygen isotope stage; SST, sea surfacetemperature; ppmv, ppm by volume.

‡To whom correspondence should be addressed. E-mail: brian.huntley@durham.ac.uk.

© 2007 by The National Academy of Sciences of the USA

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the absolute age for the end of the LI as �1,400 years. Second,the �14 m of sediment (depth �78–92 m) underlying this tephralayer form a continuously varved interval spanning the entire LIand extending to the penultimate glacial; a total of 22,600 varveshas been counted from this interval. Apart from those depositedduring a short period within the Melisey I stadial, these varvesare particularly well preserved and easily recognized, minimizingcounting errors. It has been reported previously that fading outof single varves may result in underestimation, by up to �1.5%,of the period spanned if only a single composite profile iscounted (17); duplicate counts of sections of the Monticchio LIsediments, however, indicate uncertainty of �1% in assessmentsof the duration of intervals within the LI. We therefore estimatethe uncertainty in the absolute age for the onset of the LI as�1,600 years. Third, frequent intercalation of turbidites, up toseveral centimeters thick, deposited during the initial develop-ment of the lake, and that are potentially erosive in origin, leadsto increased uncertainty in the basal part of the chronology

(�131 ka B.P.). Assessing the uncertainty for this interval is verydifficult, but an underestimation of the interval spanned by 10%or more is not unlikely. Therefore, we can state only that ourvarve chronology places the onset of sedimentation at Montic-chio before 132.9 ka B.P. This age is in agreement with theestimated eruption time of the Monticchio maar lakes of 132 �12 ka B.P. (18).

The material now available provides a continuous detailed andindependently dated palaeoenvironmental record extendingfrom the present to MIS 6 (Fig. 1). During MIS 2, 4, and 6, andmost MIS 3 and 5 stadials, regional vegetation was dominated byherbaceous taxa, with a substantial steppic element. The onlyexception is Melisey I during which steppic taxa are limited,whereas Betula abundance is relatively high, indicating that,although cold, this period had greater moisture availability thanother cold periods. Mesic woody taxa reached moderate abun-dance during many MIS 3 interstadials, but dominated onlyduring the Holocene, St. Germain I and II, and the LI. During

Fig. 1. Lago Grande di Monticchio: Overview and correlation with marine records. The overall record extends from MIS 6 to the present. It shows thecharacteristic sequence of palaeoenvironmental fluctuations that denote the substages of MIS 5 and numerous shorter environmental fluctuations and eventsthat can be correlated with those seen in marine and ice-core records (14). Proposed correlations with marine events (C21–C25) during MIS 5 substages areindicated; ages for these events in the marine record follow aLehman et al. (19) and bSanchez-Goni et al. (20).

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the first 2.65 ka of the latter, however, they only reached levelscomparable to those during the Weichselian late-glacial inter-stadial and the most strongly expressed MIS 3 interstadials; asduring those intervals, grasses and other herbaceous taxa ac-counted for �30% of the pollen. Whereas the periods dominatedby mesic woody taxa had a climate without any marked seasonalmoisture shortage, these periods of intermediate abundancewere times of moderate seasonal moisture deficiency. Mediter-ranean woody taxa (sclerophyllous trees and shrubs tolerant ofsummer drought but intolerant of cold winter conditions)reached greatest abundance during the LI, otherwise beingpresent only during the Holocene and St. Germain I before theMontaigu event. Even considering only these aggregated taxa,the distinct character of the palaeoenvironment during individ-ual ‘‘warm’’ and ‘‘cold’’ (sub-)stages is apparent.

DiscussionThe Monticchio varve chronology enables the timing and dura-tion of MIS 5 substages and intercalated brief oscillations to beestablished independently in a lacustrine record (Table 1). Inturn, this independence enables phase relationships betweenearth-system components to be investigated, within the limita-tions of their inherent dating uncertainties, by comparing therecord from Monticchio with proxy records from marine sedi-ments and ice cores and other continental records (Fig. 2).

The lowermost part of the record corresponds to the end ofthe MIS 6 glaciation. The predominance of nonarboreal pollen,especially Artemisia and Chenopodiaceae, indicates steppe veg-etation and a climate with severe seasonal moisture deficiencyand marked temperature seasonality. Transition from glacialconditions began 130.55 ka B.P., with varve thickness decreasingand water content and Quercus pollen abundance both increas-ing. A 250-year reduction in tree pollen abundance (128.15–127.90 ka B.P.) that interrupts this transition may correspond tothe �18O plateau shortly preceding MIS 5e in MD95-2042 (11).Persistent dominance of steppe taxa indicates seasonal moisturedeficiency, which was most severe 130.00–127.20 ka B.P. whensummer sublayers were formed by aragonite (Fig. 3a); formationof this carbonate mineral in lakes requires high Mg/Ca ratios,indicating a strongly evaporative environment (27).

The beginning of the LI at 127.20 ka B.P. is marked by furtherrapid increases in water content and relative abundance ofQuercus, corresponding decreases in Artemisia and especiallyChenopodiaceae, and an abrupt end to aragonite precipitation(Fig. 3a). The LI spans an interval of 17.70 ka, ending at 109.50ka B.P. when forest vegetation rapidly opened up and mesic trees

all decreased in abundance, although trees characteristic ofcooler climates, notably Betula, maintained their abundance.The primarily organic interglacial sediments were replaced atthis time by sediments with greater minerogenic detritus content,as indicated by a sharp rise in Ti content and fall in Si/Al ratio(Fig. 3b).

Three principal phases can be distinguished within the LI onthe basis of coincident major lithological and vegetation changes.The first phase LI1 (127.20–124.55 ka B.P.), characterized by50–60% Quercus pollen and abundant pollen of Mediterraneanwoody taxa, is interpreted as an interval of hot summers andseasonal moisture deficiency. Relative abundance of Pteridiumspores may indicate high fire frequency. Correspondence be-tween this interval and peak summer insolation (Fig. 2g) mayaccount for the hot dry summers. Evidence from the Vostok icecore (21) shows atmospheric carbon dioxide (CO2) levels reach-ing their maximum value [�280–290 ppm by volume (ppmv)]already by �129 ka B.P. (Fig. 2a), ruling out physiological effectsof lower atmospheric CO2 concentrations as an alternativeexplanation for apparent moisture deficiency during this inter-val. Phase LI1 at Monticchio probably correlates with the earlyEemian period of northwest Europe characterized by occur-rences as far north as Great Britain of warmth-demandingspecies (28, 29), and for which warmer than present summertemperatures are reconstructed and modeled for northern Eu-rope (29, 30). Its duration (2.7 ka) also corresponds well to thatestimated for the early MIS 5e interval of warmer than presentNorwegian Sea SSTs (31). This phase of the interglacial culmi-nated with a 450-year interval (124.55–124.10 ka B.P.) whenQuercus pollen abundance fell to �40% and Gramineae in-creased to �30%. Correspondence between this dry interval andcold Norwegian Sea SSTs (31) may implicate changed oceancirculation as the cause of this climatic fluctuation.

After this dry interval, woody taxa abundance increased tomaximum values (�90%) within 1.2 ka; thereafter, forest coverdominated during the second phase of the interglacial (LI2) thatended 115.80 ka B.P. Quercus and Mediterranean woody taxaremained abundant, whereas various other mesic woody taxaincreased in abundance. This was a period of mild winters andwarm summers, with less marked seasonal moisture deficiencythan previously. Very uniform sedimentation of organic diatomvarves without a major clastic component indicates a biologicallyproductive lake and stable environment. A pronounced shift inforest composition marked the end of this phase. Abies and Alnusbecame prominent forest components and Betula increased inabundance, whereas Mediterranean woody taxa decreased. For-

Table 1. Lago Grande di Monticchio varve chronology for MIS 6–4 stage boundaries andevents

Terrestrial correlates, principalstages and substages

Monticchio varve chronology, ka

Marine correlatesLower boundary Upper boundary Duration

Last glacial 82.73 — —St. Germain 2 87.98 82.73 5.25Melisey 2 90.65 87.98 2.67 C21

94.41 93.32 1.09 C22Montaigu Event 105.57 102.78 2.79 C23

St. Germain1 107.60 90.65 16.95Melisey1 109.50 107.60 1.90 C24

Woillard Event 110.53 110.21 0.32 C25LI Phase 3 115.80 109.50 6.30LI Phase 2 124.55 115.80 8.75LI Phase 1 127.20 124.55 2.65

Last interglacial 127.20 109.50 17.70Glacial–interglacial transition 130.55 127.20 3.35Penultimate glacial — 127.20 —

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est nonetheless also dominated during the final phase of theinterglacial (115.80–109.50 ka B.P.), although varve thicknessgradually decreased, mainly as a result of weaker diatom blooms.Seasonal moisture deficiency was minimal during this phase;although winters were not severe, summer warmth was reduced.The marked shift toward cooler conditions at 115.80 ka B.P.occurs at about the same time as marine event C26 (32).However, an event-like structure is not seen in the Monticchiorecord, indicating that the short-term effect was not very strongin the Mediterranean region. Toward the end of the final phaseof the interglacial short intervals (decades–centuries) of in-creased minerogenic deposition occurred, indicating cooler andprobably wetter conditions; the most prominent, 110.53–110.21ka B.P., correlates with the Woillard Event at Grand Pile andmarine event C25 (33) and is manifested at Monticchio also asa decrease in the abundance of pollen of trees, especially Abiesand Alnus.

The 17.70 ka duration of the LI at Monticchio is 1–2 ka morethan recent estimates from Iberia (11) and Greece (1), althoughless than earlier estimates (8, 33). Given the location of Mon-ticchio between the Iberian and Greek records, it is implausiblethat the LI would differ in duration by this much. We also canrule out overestimation of varve counts because of the excel-lently preserved organic varves; indeed it is more likely that theduration has been underestimated by not more than �1% as aresult of missed varves in the single main profile counted.Although onset of the LI lagged by 3–4 ka the onset of global icevolume decrease (26) and atmospheric CO2 and methane (CH4)increases (7, 33), the beginning of the first rapid increase inQuercus pollen abundance at 128.85 ka B.P. was almost con-temporaneous with the most rapid large increase in CH4 and

CO2 concentration first exceeding 270 ppmv, and with the rapidincrease in strength of the Asian monsoon inferred from the�18O records in stalagmites from the Dongge Cave in China (Fig.2e) (24, 25). However, by the time of the second rapid increasein Quercus at Monticchio 1.6 ka later, that coincided with theabrupt end of aragonite precipitation and marked the onset ofthe LI, CH4 probably already had fallen from its peak values andCO2 concentration fallen back to �260 ppmv. The most rapidSST increase in the Alboran Sea (ODP 977; Fig. 2c) (23),however, closely corresponded with the onset of the LI atMonticchio. Changes in earth-system components at the end ofthe LI also showed diachroneity. In particular, as in marinerecords west of Iberia (Fig. 2b) (20), the end of the LI atMonticchio lagged by 6–7 ka the onset of global ice volumeincrease and hence the MIS 5e/5d boundary, the latter insteadcoinciding closely with the environmental change at 115.80 kaB.P. Although the apparent �1.5 ka lag between the end of theLI and the fall of CO2 concentration to �270 ppmv (21) is closeto the uncertainty for the Monticchio time scale, this is not thecase for the �3.5 ka lag between the end of the LI and the fallof CH4 to a minimum that extends also through the Melisey Isubstage. Similar diachroneity is seen at the transition betweenMelisey I and St. Germain I at 107.60 ka B.P. On this occasionthe rapid increase in tree pollen abundance marking the tran-sition occurred �1.5 ka before the sharp increase in CH4 and ata time when CO2 concentration had fallen to �240 ppmv and wascontinuing to fall. Although this discrepancy in timing is close inmagnitude to the uncertainty in the Monticchio time scale, therapid increase in tree pollen abundance coincided with a rapidincrease in �D at Vostok. This finding contrasts with thewarming at the onset of the LI when the peak in �D preceded

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Fig. 2. MIS 6–5c at Monticchio compared with other records of the same interval. (a) Vostok ice core (21, 22): �D; CO2; CH4. (b) Portuguese coast record(MD95-2042) (6, 11): planktonic foraminifera �18O; benthic foraminifera �18O; pollen record (selected taxa); positions of cold events C23–C25 are indicated. (c)Alboran sea core record (ODP 977) (23): SST estimate based on alkenones; �18O vs. Pee Dee Belemnite (of Globigerina bulloides). (d) MIS boundaries (2). (e) �18Oof carbonate from stalagmites in the Dongge Cave, China (24, 25). ( f) Pollen record from Monticchio (selected taxa). (g) Lithological proxies from Monticchio:water content; 100-year means of varve thickness (expressed as mm�yr�1). Positions of tephra X6 and Monticchio zone boundaries are indicated: G1, St. Germain1; M1, Melisey 1, LI1, LI2, LI3, LI subzones; S, Saalian Glacial. (h) January and July insolation (percent anomaly from present) at 41°N (26).

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the onset of the LI, corresponding instead to the final substageof the Saalian glacial; �D values already were falling at the onsetof the LI. The transition from Melisey I to St. Germain I atMonticchio coincided closely with a rapid decrease in planktonic�18O in MD95-2042, indicating a common trigger for thesechanges. In contrast, a marked SST shift and a decrease in �18Oof Globigerina bulloides in ODP977 appear to occur �2,000 yearsearlier than the environmental changes at Monticchio and incore MD95-2042. Diachroneity of this magnitude in such apronounced change is unlikely among records from the sameregion; we therefore suggest that uncertainties in the orbitallytuned time scale of core ODP977 may account for the apparentage difference.

These phase differences between terrestrial ecosystems andother earth-system components cannot be explained by ecosys-tem ‘‘inertia’’ (34) or migrational lag (35) and have importantimplications for understanding the mechanisms underlying past,and also future, rapid global changes. Whereas the global signalsof decreasing ice volume and increasing CH4 and CO2 concen-tration during termination 2 closely paralleled the increase inJuly insolation and began to change from their glacial statesalready �135 ka B.P., there was relatively close synchrony

between the increase in SST in the Mediterranean, the decreasein �18O of planktonic foraminifera in the Atlantic west of Iberia,and the lithological and vegetation changes marking the onset ofthe LI at Monticchio at 127.20 ka B.P. The lag between the onsetof global change and the onset of the LI, plus the much morerapid changes that characterized the latter, indicate a nonlinearresponse in the northern hemisphere that most probably wasassociated with mode switching by the ocean thermohalinecirculation (36) and associated reorganization of atmosphericcirculation. Furthermore, the lag of the onset of the LI behindthe peak in �D at Vostok supports the notion that, as during thelast glacial stage and termination 1 (37), there was hemisphericasynchrony, peak Antarctic warming during termination 2 ap-parently leading by �3 ka the rapid Northern Hemispherewarming. The lag of �2 ka between the peak CH4 value and thevegetation and lithological evidence for the onset of the LI atMonticchio indicates that, as during termination 1 (38), themajor sources of CH4, probably especially in the SouthernHemisphere tropics (25, 39), exhibited a strong response severalmillennia before the onset of interglacial conditions. In strikingcontrast to termination 1, however, there is no clear evidence atMonticchio of a Younger Dryas-like cold oscillation interruptingthe overall deglacial warming; in this respect Monticchio paral-lels records such as those of �D and CH4 from Vostok and �18Ofrom stalagmites in the Dongge (24, 25) and Hulu (39) caves inChina (Fig. 2e). Although previous studies (20, 40, 41) havereported evidence of such an oscillation, the extent to which anyglobal oscillation occurred must remain in doubt. The onlycandidate event at Monticchio is the fluctuation in tree pollenabundance between 128.15 and 127.90 ka B.P.. The shortduration of this event (�250 years), however, contrasts with thatof the Younger Dryas (1,090 years; see ref. 42), perhaps ac-counting for the lack of an obvious correlate in the Vostokrecords.

Strikingly and importantly, the phase relationships betweenthe various signals were quite different during the warming thatmarked the transition from Melisey I to St. Germain I. At thattime there appears to have been synchrony between Antarcticwarming, SST increase in the Atlantic west of Iberia and onsetof the interstadial at Monticchio at 107.60 ka B.P., whereas themarked rise in CH4 recorded in the same Antarctic ice core asthe �D record of warming, lagged this event by �1.5 ka. Thisdifference in phase relationships implies a pattern of interactionsbetween earth-system components quite distinct from that dur-ing glacial terminations, perhaps primarily as a consequence ofthe very different state of the global system before the warming.In particular, maximum global ice volume was substantially lessduring Melisey I than during the latter part of the Saalianglaciation that preceded the glacial termination.

Finally, the very abrupt end of the LI, that occurred within nomore than 0.15 ka (Fig. 3b), but that lagged by �6.3 ka the onsetof long-term decreases in SST, Vostok �D and CH4 and increasein global ice volume, once again indicates a nonlinear responseand suggests important threshold processes.

The Monticchio record, with its independent chronology,enables detailed and critical examination of the phase relation-ships between terrestrial vegetation and other earth-systemcomponents during the LI. It is only through improved knowl-edge of these relationships, and especially the nonlinear dynam-ics during times of rapid global change that are revealed by suchcritical examination, that we can hope to gain improved under-standing of the processes underlying rapid global changes andthus provide more robust assessments of likely future changes.

MethodsElement abundance data were obtained by � x-ray f luores-cence (�-XRF) analysis of 10-cm-long impregnated sedimentblocks. Thin sections were prepared from the same blocks,

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Fig. 3. Rapid onset and end of the LI at Lago Grande di Monticchio. (a) Onsetof the LI: aragonite sublayer thickness (mm), calcite sublayer thickness (mm),100-year means of varve thickness (expressed as mm�yr�1), and pollen (woodytaxa percent). Gray bar indicates the transition as it appears in microfacieschange. Plates show microscopic images of thin sections and illustrate varvesbefore (Plate 1) and after (Plate 2) the rapid onset of the LI. Plate 1 (polarizedlight) shows regular light-grayish aragonite layers. Plate 2 (partly polarizedlight) shows thin bright layers of calcite included in some of the varves. (b) Endof LI: titanium (counts), silica/aluminium ratio, 100-year means of varve thick-ness (expressed as mm�yr�1), and pollen (woody taxa percent). For furtherexplanation of the unit counts see Methods. Gray bar indicates the transitionas it appears in microfacies change. Plates show microscopic images of thinsections and illustrate varves before (Plate 3) and after (Plate 4) the abrupt endof the LI. Plate 3 shows regular, very thin organic-diatomaceous varves. Plate4 shows thick minerogenic-detrital varves characterized by distinct differencesin grain size between summer and winter sublayers.

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using standard methods as described (12, 13), allowing directcomparison of element abundance data with mineralogicalinformation from petrographic microscopy. The analyticalsystem was an EAGLE III XL �-XRF spectrometer (Ront-genanalytik Messtechnik, Taunusstein, Germany) with a low-power Rh x-ray tube (Oxford Instruments, Scotts Valley, CA).The incident radiation from this source was focused onto thesample surface by a capillary lens system (XOS, Albany, NY).The f luorescent radiation emitted from the sample as a resultof the x-ray excitation was recorded by an energy dispersiveSi(Li) detector (EDAX International, Mahwah, NJ) with anactive area of 80 mm2 and a 10-�m Be window. The x-raydetector was connected to a multichannel analyzer (EDAXInternational) with a 10-eV spectral resolution. Finally, thef luorescence radiation was processed and translated into countrates (counts s�1). All measurements were performed with aspot size of 50 �m, a step size of 40 �m, and a counting timeof 60 s. X-ray tube voltage was adjusted to 40 kV, and currentwas modified to achieve a mean dead time of 30%. To avoid

loss of radiation intensity for light elements (Al, Si) as a resultof absorption by air, the sample chamber was evacuated duringthe measurements.

Standard methods applied in previous studies at the site anddescribed elsewhere were used for pollen analysis (43), tephro-chronology (15), general sediment lithological measurements(13), and varve measurement and counting (12, 13).

We thank two anonymous reviewers for constructive comments. The lateN. J. Shackleton (Department of Earth Sciences, University of Cam-bridge, Cambridge, U.K.) and M. F. Sanchez-Goni (Departement deGeologie et Oceanographie, Universite Bordeaux 1, Talence, France)provided data from MD95–2042. J. O. Grimalt [Consejo Superior deInvestigaciones Cientificas (CSIC), Barcelona, Spain] provided datafrom core ODP977A. Financial support was provided by GeoForschun-gsZentrum Potsdam (coring campaign; A.B., P.D., J.M., and S.W.) andNatural Environment Research Council Grant NER/A/S/2001/01122(pollen analysis; J.R.M.A.). This study is a contribution to the EuropeanLake Drilling Program and Past Global Changes Pole-Equator-PoleTransect III. B.H. holds a Royal Society–Wolfson Foundation ResearchMerit Award.

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