Abstracts of GRIP papers on isotopes and cosmogenics

This file contains abstracts of GRIP papers whose primary content concerns isotopes or cosmogenic species. Papers are listed alphabetically by first author. You can go straight to the abstract you want.


Baumgartner, S., Beer, J., Suter, M., DittrichHannen, B., Synal, H.A., Kubik, P.W., Hammer, C. & Johnsen, S. 1997. Chlorine 36 fallout in the Summit Greenland Ice Core Project ice core. Journal of Geophysical Research, 102, 26659-26662.

Corresponding author: Jurg Beer, Environmental Physics, Swiss Federal Institute for Environmental Science and Technology, CH-8600 Dubendorf, Switzerland.

The natural cosmogenic radioisotope Cl-36 has been measured in the Greenland Ice Core Project ice core from Summit, Greenland. Generally, a good correlation between Cl-36 and delta(18)O was found, even in glacial periods with strong delta(18)O oscillations. The Cl-36 flux is calculated assuming an exponential relationship between accumulation rate and delta(18)O. A prominent excursion is detected between 35 and 40 kyr B.P., which coincides with a similar Be-10 peak measured in the same samples. This sheds light on possible causes of this excursion. In the lowest part of the ice core the flux decreases smoothly. This can be interpreted as radioactive decay of Cl-36 (T-1/2 = 300 kyr).


Bond, G., Broecker, W., Johnsen, S., McManus, J., Labeyrie, L., Jouzel, J. & Bonani, G. 1993. Correlations between climate records from North Atlantic sediments and Greenland ice. Nature, 365, 143-147.

Corresponding author: Gerard Bond, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA.

Oxygen isotope measurements in Greenland ice demonstrate that a series of rapid wann-cold oscillations -called Dansgaard-Oeschger events-punctuated the last glaciation. Here we present records of sea surface temperature from North Atlantic sediments spanning the past 90 kyr which contain a series of rapid temperature oscillations closely matching those in the ice-core record, confirming predictions that the ocean must bear the imprint of the Dansgaard-Oeschger events. Moreover, we show that between 20 and 80 kyr ago, the shifts in ocean-atmosphere temperature are bundled into cooling cycles lasting on average 10 to I5 kyr, with asymmetrical saw-tooth shapes. Each cycle culminated in an enormous discharge of icebergs into the North Atlantic (a Heinrich event'), followed by an abrupt shift to a warmer climate. These cycles document a previously unrecognized link between ice sheet behaviour and ocean-atmosphere temperature changes. An important question that remains to be resolved is whether the cycles are driven by external factors, such as orbital forcing, or by internal ice-sheet dynamics.


Dahl-Jensen, D. 1993. Reconstruction of palaeo climate from temperature measurements in bore holes on the Greenland Ice Sheet. In Mosegaard, K., ed. Proceedings of the Interdisciplinary Inversion Workshop 2, Copenhagen. Copenhagen: University of Copenhagen, 11-14.

Corresponding author: Dorthe Dahl-Jensen, Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK2100 Copenhagen, Denmark.

Sorry, no abstract currently available for this paper.


Dahl-Jensen, D., Johnsen, S.J., Hammer, C.U., Clausen, H.B. & Jouzel, J. 1993. Past accumulation rates derived from observed annual layers in the GRIP ice core from Summit, central Greenland. In Peltier, W.R., ed. Ice in the Climate System. Berlin Heidelberg: Springer-Verlag, 517-532.

Corresponding author: Dorthe Dahl-Jensen, Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK2100 Copenhagen, Denmark.

Based on dated reference horizons down to 1623 m an ice flow model has been developed. The model is used to reconstruct past accumulation rates from the sequences of detected annual layers in the upper 2321 m of the 3029 m deep GRIP ice core. Comparison of these past time accumulation rates with the corresponding delta180 values show a strong correlation. This relationship can be used in a non steady state flow model, in which past accumulation rates, deduced from the continuous delta180 record, are used to model a time scale. The hereby determined time scale and the modelled annual layers compare well with the observed data.


Dansgaard, W., Johnsen, S.J., Clausen, H.B., Dahl-Jensen, D., Gundestrup, N.S., Hammer, C.U., Hvidberg, C.S., Steffensen, J.P., Sveinbjornsdottir, A.E., Jouzel, J. & Bond, G. 1993. Evidence for general instability of past climate from a 250-kyr ice-core record. Nature, 364, 218-220.

Corresponding author: Willy Dansgaard: Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK2100 Copenhagen O, Denmark

Recent results from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper) and during the previous Saale-Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record, in agreement with other land-based observations. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.


Ditlevsen, P.D., Svensmark, H & Johnsen, S.J., 1996. Contrasting atmospheric and climate dynamics of the last-glacial and Holocene periods. Nature, 379, 810-812.

Corresponding author: Peter Ditlevsen: Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK2100 Copenhagen O, Denmark

Our present climate is realtively stable compared to that of the Last Glacial Maximum about 20,000 years ago. Palaeoclimate records obtained from ice cores and deep-sea sediment cores for the last glacial period show abrupt temperature changes on timescales of a few hundred years, which have been attributed to cycles of ice build-up and release associated with large ice sheets (Dansgaard-Oeschger cycles and Heinrich events) and their coupling to ocean circulation. But little is known about the dynamics of the atmosphere during the last glaciation. Ice sheets influence atmospheric circulation, and studies using general circulation models have suggested stormier, more variable atmospheric dynamics during the Last Glacial Maximum than today. Here we report the results of an analysis of temporal trends over the past 91,000 years in the oxygen isotope signatures of a high-resolution ice-core record from Greenland. This analysis provides direct evidence that atmospheric circulation during the last glaciation was more turbulent than it is today.


Fronval, T., Jansen, E., Bloemendal, J. & Johnsen, S. 1995. Oceanic evidence for coherent fluctuations in Fennoscandian and Laurentide ice sheets on millenium timescales. Nature, 374, 443-446.

Corresponding author: Torben Fronval, Department of Geology, University of Bergen, Allegaten 41, 5007 Bergen, Norway.

Proxy temperature records from Greenland ice cores and North Atlantic sediment cores have provided evidence for a high degree of climate instability during the last glacial period. Much of this variability seems to be linked with the dynamics of the Laurentide ice sheet that covered North America at this time, which discharged iceberg flotillas into the North Atlantic that are now recorded in sediment cores as Heinrich events. How (if at all) this variability was manifested on the other side of the Atlantic in the Nordic seas and the ice sheets of northwest Europe and Scandinavia has been unclear. Here we present sediment, microfossil and oxygen isotope data from a sediment core in the Norwegian sea which reveal cooling events and iceberg discharges analogous to Heinrich events. We show that these climate fluctuations in the Norwegian Sea were in phase, or were phase-locked, with air temperatures over Greenland, suggesting that the rapid changes in heat fluxes in the North Atlantic recorded in previous records were felt in this high-latitude region. The iceberg discharges in our record seem to have come from the Fennoscandian ice sheet, implying that this and the Laurentide ice sheets fluctuated coherently on timescales shorter than those of Milankovitch orbital cycles.


Fuchs, A. & Leuenberger, M.C. 1996. Delta18O of atmospheric oxygen measured on the GRIP ice core document stratigraphic disturbances in the lowest 10% of the core. Geophysical Research Letters, 23, 1049-1052.

Corresponding author: Markus Leuenberger, Physics Institute, Sidlerstrasse 5, CH-3012 bern, Switzerland

Delta18O measured on oxygen in the bubble air from ice cores is a proxy for continental ice volume and is used to synchronise cores from Greenland and Antarctica. A record measured on ice samples from the Central Greenland deep ice core GRIP, spanning the Last Glacial Maximum and the Holocene, shows that delta18O of atmospheric oxygen lags delta18O of ice by about 4000 to 1000 years. The smooth isotope record of atmospheric oxygen shows a steady ice sheet decay beginning around 18000 years BP taking the time lag into account. However, measurements performed on ice from the GRIP core older than 100 kyrs do not correlate with the corresponding Vostok record and show transitions too fast to be typical for ice sheet build-up or decay. Furthermore, the expected time lag between delta18Oatm and delta18O of seawater or delta18O of ice is absent or has even turned into a lead. Climatic interpretation of the fast delta18Oice transitions is not consistent with our delta18Oatm results. The stratigraphy is possibly irregular and if so, this stops us from constructing a steady age-depth relation in the deepest part of the GRIP ice core.


GRIP Project Members 1993. Climate instability during the last interglacial period recorded in the GRIP ice core. Nature, 364, 203-207.

Corresponding author: David Peel, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK

Isotope and chemical analyses of the GRIP ice core from Summit, central Greenland, reveal that climate in Greenland during the last interglacial period was characterized by a series of severe cold periods, which began extremely rapidly and lasted from decades to centuries. As the last interglacial seems to have been slightly warmer than the present one, its unstable climate raises questions about the effects of future global warming.

Please be aware that these conclusions have been modified in the light of later findings. Please see later papers for more details.


Grootes, P.M., Stuiver, M., White, J.W.C., Johnsen, S. & Jouzel, J. 1993. Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores. Nature, 366, 552-554.

Corresponding author: Pieter Grootes, (now at) C-14 Laboratory of the Christian Albrechts Universitat Kiel, Leibnizstrasse 19, Kiel, Germany.

Recent results from the Greenland Ice-core Project (GRIP) Summit ice core suggest that the climate in Greenland has been remarkably stable during the Holocene, but was extremely unstable for the time period represented by the rest of the core, spanning the last two glaciations and the intervening Eemian interglacial. Here we present the complete oxygen isotope record for the Greenland Ice Sheet Project 2 (GISP2) core, drilled 28 km west of the GRIP core. We observe large, rapid climate fluctuations througout the last glacial period, which closely match those reported for the GRIP core. However, in the bottom 10% of the cores, spanning the Eemian interglacial and the previous glaciation, there are significant differences between the two records. It is possible that ice flow may have altered the chronological sequence of the stratigraphy for the bottom part of one or both of the cores. Considerable further work will be necessary to evaluate the likelihood of this, and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores.


Johnsen, S.J., Clausen, H.B., Dansgaard, W., Fuhrer, K., Gundestrup, N., Hammer, C.U., Iversen, P., Jouzel, J., Stauffer, B. & Steffensen, J.P. 1992. Irregular glacial interstadials recorded in a new Greenland ice core. Nature, 359, 311-313.

Corresponding author: Sigfus Johnsen, (address from 10 January 1996) Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark or Science Instute, University of Reykjavik, Dunhaga 3, Reykjavik 107, Iceland.

The Greenland ice sheet offers the most favourable conditions In the Northern Hemisphere for obtaining high-resolution continuous time series of climate-related parameters. Profiles of 18O/16O ratio along three previous deep Greenland ice cores seemed to reveal irregular but well-defined episodes of relatively mild climate conditions (interstadials) during the mid and late parts of the last glaciation, but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate, rather than artefacts due to disturbed stratification. Here we present results from a new deep ice core drilled at the summit of the Greenland ice sheet, where the depositional environment and the flow pattern of the ice are close to ideal for core recovery and analysis. The results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt. According to a preliminary timescale based on stratigraphic studies, the interstadials lasted from 500 to 2,000 years, and their irregular occurrence suggests complexity in the behaviour of the North Atlantic ocean circulation.


Johnsen, S.J., Clausen, H.B., Dansgaard, W., Gundestrup, N.S., Hammer, C.U. & Tauber, H. 1995. The Eem stable isotope record along the GRIP ice core and its interpretation. Quaternary Research, 43, 117-124.

Corresponding author: Sigfus Johnsen, Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark or Science Institute, University of Reykjavik, Dunhaga 3, Reykjavik 107, Iceland.

A 3029-m-long deep ice core extending nearly to bedrock has been drilled at the very top of the Greenland ice sheet (Summit) by the Greenland Ice-core Project (GRIP), an international European joint effort organized by the European Science Foundation. The ice core reaches back to 250,000 yr B. P. according to dating based partly on stratigraphic methods and partly on ice-flow modeling. A continuous and detailed stable isotope (delta18O) profile along the entire core depicts dramatic temperature changes in Greenland through the last two glacial cycles, including abrupt climatic shifts during the Eem/Sangamon Interglaciation, which is elsewhere recorded as a warm and stable period. The stratigraphic continuity of the Eemian layers has therefore been scrutinized. New ice core studies, comprising cloudy band observations, deconvolution, and frequency analyses, lead to the conclusion that the climate instability suggested during the Eem Intergiaciation in Greenland is likely to be real, though no conclusive evidence is available. Whereas latitudinal displacements of the North Atlantic Ocean current are considered the inunediate cause of the glacial climate instability, longitudinal displacements may be the immediate cause of the Eemian instability. If so, the Eemian climate changes will be much subdued outside the Arctic region and will probably only be recognizable in sedimentary sequences of high sensitivity and temporal resolution.


Johnsen, S.J., Dahl-Jensen,D., Dansgaard, W., Gundestrup, N.S. 1995. Greenland palaeotemperatures derived from GRIP borehole temperature and ice core isotope profiles. Tellus, 47B, 624-629.

Corresponding author: Sigfus Johnsen, Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark or Science Institute, University of Reykjavik, Dunhaga 3, Reykjavik 107, Iceland.

Modeling the temperature profile along the GRIP deep bore at the Summit of the Greenland ice sheet leads to conversion factors that allow interpretation of the dated stable isotope profile as a climatic temperature record spanning the last 113,000 years. When corrected for surface elevation changes, the late glacial to Boreal temperature shift appears to ahve been 22øC in central Greenland. The warming at the end of the last glaciation probably began earlier in Greenland, than in Antarctica.


Johnsen, S.J., Clausen, H.B., Dansgaard, W., Gundestrup, N.S., Hammer, C.U., Andersen, U., Andersen, K.K., Hvidberg, C.S., DahlJensen, D., Steffensen, J.P., Shoji, H., Sveinbjornsdottir, A.E., White, J., Jouzel, J. & Fisher, D. 1997. The delta O-18 record along the Greenland Ice Core Project deep ice core and the problem of possible Eemian climatic instability. Journal of Geophysical Research, 102, 26397-26410.

Corresponding author: Sigfus Johnsen, Geophysics Department, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark or Science Institute, University of Reykjavik, Dunhaga 3, Reykjavik 107, Iceland.

Over 70,000 samples from the 3029-m-long Greenland Ice Core Project (GRIP) ice core drilled on the top of the Greenland Ice Sheet (Summit) have been analyzed for delta(18)O. A highly detailed and continuous delta(18)O profile has thus been obtained and is discussed in terms of past temperatures in Greenland. We also discuss a three-core stacked annual delta(18)O profile for the past 917 years. The short-term (<50 years) variability of the annual delta(18)O signal is found to be 1 parts per thousand in the Holocene, and estimates for the coldest parts of the last glacial are 3 parts per thousand or higher. These data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the Eemian. Spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the delta(18)O signal, which for the Holocene ice is found to be considerably stronger than expected. We suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix. Deconvolution techniques were employed for restoring with great confidence the highly attenuated annual delta(18)O signal in the Holocene. We confirm earlier findings of dramatic temperature changes in Greenland during the last glacial cycle. Abrupt and strong climatic shifts are also found within the Eem/Sangamon Interglaciation, which is normally recorded as a period of warm and stable climate in lower latitudes. The stratigraphic continuity of the Eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile.


Jouzel, J., Alley, R.B., Cuffey, K.M., Dansgaard, W., Grootes, P., Hoffmann, G., Johnsen, S.J., Koster, R.D., Peel, D., Shuman, C.A., Stievenard, M., Stuiver, M. & White, J. 1997. Validity of the temperature reconstruction from water isotopes in ice cores. Journal of Geophysical Research, 102, 26471-26487.

Corresponding author: Jean Jouzel, LMCE, CE Saclay, 91191 Gif sur Yvette, France.

Well-documented present-day distributions of stable water isotopes (HDO and (H2O)-O-18) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (delta D and delta(18)O) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/ surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.


Keigwin, L.D., Curry, W.B., Lehman, S.J. & Johnsen, S. 1994. The role of the deep ocean in North Atlantic climate change between 70 and 130 kyr ago. Nature, 371, 323-326.

Corresponding author: Lloyd Keigwin, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA.

The suggestion that changes in North Atlantic Deep Water (NADW) production are linked through surface beat flux to the atmospheric temperature over Greenland is supported by earlier indications that NADW production decreased during glacial times, and by the subsequent finding that it declined during the Younger Dryas cool period at the end of the last glaciation. Changes in North Atlantic surface temperatures have been found to mirror high-frequency temperature changes recorded in Greenland ice cores over the past 80 kyr, but the connection to abyssal circulation has yet to be established, except for one or two isolated oscillations. Here we present carbon and oxygen isotope analyses of benthic foraminifera in a high-resolution North Atlantic deep-sea sediment core for the period 70-130 kyr ago. These data allow us to reconstruct the history of NADW production, which shows a close correlation with Greenland climate variability for much of this time interval, suggesting that the climate influence of NADW variability was widespread. We see no evidence, however, for changes in NADW production during substage 5e (the Eemian interglacial period), in contrast with recent ice-core data which suggest severe climate instability in Greenland during this time period. Our results may support suggestions, based on data from a second ice core, that this apparent instability is an artefact caused by ice flow. Alternatively, the Eemian climate instability may have had a different origin from the subsequent climate events.


Larsen, E., Sejrup, H.P., Johnsen, S.J. & Knudsen, K.L. 1995. Do Greenland ice cores reflect NW European interglacial climate variations? Quaternary Research, 43, 125-132

Corresponding author: Eiliv Larsen, Department of Geology, University of Tromso, N-9037 Tromso, Norway.

The climatic evolution during the Eemian and the Holocene in western Europe is compared with the sea-surface conditions in the Norwegian Sea and with the oxygen-isotope-derived paleotemperature signal in the GRIP and Renland ice cores from Greenland. The records show a warm phase (ca. 3000 yr long) early in the Eemian (substage 5e). This suggests that the Greenland ice sheet, in general, recorded the climate in the region during this time. Rapid fluctuations during late stage 6 and late substage 5e in the GRIP ice core apparently are not recorded in the climatic proxies from western Europe and the Norwegian Sea. This may be due to low resolution in the terrestrial and marine records and/or long response time of the biotic changes. The early Holocene climatic optimum recorded in the terrestrial and marine records in the Norwegian Sea-NW European region is not found in the Summit (GRIP and GISP2) ice cores. However, this warm phase is recorded in the Renland ice core. Due to the proximity of Renland to the Norwegian Sea, this area is probably more influenced by changes in polar front positions which may partly explain this discrepancy. A reduction in the elevation at Summit during the Holocene may, however, be just as important. The high amplitude shifts during substage 5e in the GRIP core could be due to Atlantic water oscillating closer to, and also reaching, the coast of East Greenland. During the Holocene, Atlantic water was generally located farther east in the Norwegian Sea than during the Eemian.


Leuenberger, M.C. 1997. Modeling the signal transfer of seawater delta O-18 to the delta O-18 of atmospheric oxygen using a diagnostic box model for the terrestrial and marine biosphere. Journal of Geophysical Research, 102, 26841-26850.

Corresponding author: Markus Leuenberger, Climate and Environmental Physics, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.

We make use of a simple diagnostic box model to determine the sensitivities of the influencing parameters for the isotopic signal transfer of seawater oxygen to atmospheric oxygen. We calculate the delta(18)O of atmospheric oxygen from prescribed oxygen fluxes of the living and dead biomes on land and in the ocean, respectively. The model is driven by an assumed (experiment 1) or measured (experiments 2 and 3) temporal seawater delta(18)O signal and a land biomass estimation. In experiment 1, we calculated the required changes of several model parameters in order to study fast variations of delta(18)O of atmospheric oxygen as seen in the Greenland Ice Core Project (GRIP) ice at depths assigned to the Eemian time period. Our calculations support evidence of stratigraphic problems at these depths in the GRIP ice core. In experiment 2, we adjusted the model output, which was driven by the benthic seawater delta(18)O record from V19-30, to the measured Greenland Ice Sheet Project 2 delta(18)O record of atmospheric oxygen for the last 110,000 years. by varying the model parameter. Single and multiparameter marchings were performed. The results for single-parameter runs exceed the uncertainty ranges for most of the parameters, while multiparameter variations are well within these ranges. The model calculations are most sensitive to the land respiration factor. Our results support the findings of Van de Water et al. [1994] that the fractionations associated with biomes activities were most probably lower during cold periods, which could point to a combination of fractionations with different temperature dependencies. The model results indicate periods of higher marine biological activity during the ice age than today. Temporal variations of the model parameters show a double peak around 10000 and 8000 years ago, which could be associated with meltwater pulses, as shown in experiment 3. However, they are hardly the well-known Fairbanks [Fairbanks er al., 1992] pulses since these occur 3000 to 4000 years earlier.


McManus, J.F., Bond, G.C., Broecker, W.S., Johnsen, S., Labeyrie, L. & Higgins, S. 1994. High-resolution climate records from the North Atlantic during the last interglacial. Nature, 371, 326-329.

Corresponding author: J McManus, Lamont-Doherty Earth Observatory of Coumbia University, Palisades, New York 10964, USA.

The two deep ice cores recovered by the GRIP and GISP2 projects at Summit, Greenland, agree in detail over the past 100,000 years and demonstrate dramatic climate variability in the North Atlantic region during the last glacial, before the current period of Holocene stability. This glacial climate instability has subsequently been docunented in the marine sedimentary record of surface-ocean conditions in the North Atlantic. Before 100 kyr ago the two ice core records are discrepant, however, casting doubt on whether the oxygen isotope fluctuations during the last interglacial (Eemian) seen in the GRIP core represent a true climate signal. Here we present high-resolution records of foraminiferal assemblages and ice-rafted detritus from two North Atlantic cores for the interval 65 kyr to 135 kyr ago, extending the surface-ocean record back to the Eemian. The correlation between our records and the Greenland ice-core records is good throughout the period in which the two ice cores agree, suggesting a regionally coherent climate response. During the Eemian, our marine records show a more stable climate than that implied by the GRIP ice core, suggesting that localized phenomena may be responsible for the variability in the latter record during the Eemian.


Thouveny, N., de Beaulieu, J.-L., Bonifay, E., Creer, K.M., Guiot, J., Icole, M., Johnsen, S., Jouzel, J., Reille, M., Williams, T. & Williamson, D. 1994. Climate variations in Europe over the past 140 kyr deduced from rock magnetism. Nature, 371, 503-506.

Corresponding author: Nicolas Thouveny, Laboratoire de Geology du Quaternaire, Luminy, Case 907, 13288 Marseille Cedex 09, France.

Rapid shifts in climate during the last glacial are now well documented, particularly from the oxygen isotope records of the two Greenland ice cores GRlP and GISP2. In the GRIP record these climate events are also seen during the preceding (Eemian) interglacial which may be an analogue for the future climate, warmed by the greenhouse effect. But these shifts are not found in the Eemian section of the GISP2 core, casting doubt on whether the rapid shifts in the GRIP oxygen isotope record really do represent a climate signal. Here we present magnetic susceptibility, pollen and organic carbon records from maar lake deposits in the Massif Central France. These data provide an independent record of past climate and we find that they correlate well with the ice-core records during the last glacial. During the Eemian, two rapid cooling events seen in our record also correlate with those seen in the GRIP ice core, supporting the idea that rapid climate change did occur in the Eemian interglacial and demonstrating that it extended to continental Europe.


White, J.W.C., Barlow, L.K., Fisher, D., Grootes, P., Jouzel, J., Johnsen, S.J., Stuiver, M. & Clausen, H. 1997. The climate signal in the stable isotopes of snow from Summit, Greenland: Results of comparisons with modern climate observations. Journal of Geophysical Research, 102, 26425-26439.

Corresponding author: Jim White, Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA.

Recent efforts to link the isotopic composition of snow in Greenland with meteorological and climatic parameters have indicated that relatively local information such as observed annual temperatures from coastal Greenland sites, as well as more synoptic scale features such as the North Atlantic Oscillation (NAG) and the temperature seesaw between Jakobshaven, Greenland, and Oslo, Norway, are significantly correlated with delta(18)O and delta D values from the past few hundred years measured in ice cores. In this study we review those efforts and then use a new record of isotope values from the Greenland Ice Sheet Project 2 and Greenland Ice Core Project sites at Summit, Greenland, to compare with meteorological and climatic parameters. This new record consists of six individual annually resolved isotopic records which have been average to produce a Summit stacked isotope record. The stacked record is significantly correlated with local Greenland temperatures over the past century (r = 0.471), as well as a number of other records including temperatures and pressures from specific locations as well as temperature and pressure patterns such as the temperature seesaw and the North Atlantic Oscillation. A multiple linear regression of the stacked isotope record with a number of meteorological and climatic parameters in the North Atlantic region reveals that five variables contribute significantly to the variance in the isotope record: winter NAG, solar irradiance (as recorded by sunspot numbers), average Greenland coastal temperature, sea surface temperature in the moisture source region for Summit (30 degrees-20 degrees N), and the annual temperature seesaw between Jakobshaven and Oslo. Combined, these variables yield a correlation coefficient of r = 0.71, explaining half of the variance in the stacked isotope record.


Yiou, P., Jouzel, J., Johnsen, S. & Rognvaldsson, O.E. 1995. Rapid oscillations in Vostok and GRIP ice cores. Geophysical Research Letters, 22, 2179-2182.

Corresponding author: Pascal Yiou, Laboratoire de Modelisation du Climat et de l'Environnement, DSM-CEA, l'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France.
E-mail: yiou@asterix.saclay.cea.fr

We investigate the spectral properties of climatic times series derived from two recent ice cores in Greenland and East Antarctica. We find that the signals behave in a similar way in the high frequency part of their spectra. The rapid oscillations found in the GRIP ice core were closely correlated to Heinrich Events. A comparable spectral feature is detected in the Vostok ice core. We discuss the possibilities of connections between the two hemispheres and proper ice sheet oscillations in the light of simple oscillating climate models.


Yiou, F., Raisbeck, G.M., Baumgartner, S., Beer, J., Hammer, C., Johnsen, S., Jouzel, J., Kubik, P.W., Lestringuez, J., Stievenard, M., Suter, M. & Yiou, P. 1997. Beryllium 10 in the Greenland Ice Core Project ice core at Summit, Greenland. Journal of Geophysical Research, 102, 26783-26794.

Corresponding author: Francoise Yiou, CSNSM, IN2P3-CNRS, Batiment 104-108, 91405 Orsay-Campus, France.

Concentrations of the cosmogenic isotope Be-10 have been measured in more than 1350 samples from the Greenland Ice Core Project (GRIP) ice core drilled at Summit, Greenland. Although a dust-associated component of Be-10 retained by 0.45 mu m filters in some of the samples complicates the interpretations, the results confirm that the first-order origin of Be-10 concentration variations is changes in precipitation rate associated with different climate regimes. This effect is seen not only between glacial and interglacial periods, but also during the shorter ''Dansgaard-Oeschger'' interstadials. By contrast, the Be-10 data do not support the interpretation of rapidly varying accumulation (i.e., climate) during the last interglacial. They can, however, be used to help place limits on the origin of the ice in these events. After taking into account variable snow accumulation effects, variations in the Be-10 flux are observed, probably caused by solar and geomagnetic modulation, but possibly also by primary cosmic ray variations. The most dramatic is a Be-10 peak similar to 40,000 years ago, similar to that found in the Vostok ice core, thus permitting a very precise correlation between climate records from Arctic and Antarctic ice cores. The Cl-36/Be-10 ratio (considering either ''total'' or only ice-associated Be-10) shows significant variability over the whole core depth, thus confirming the difficulty in using this parameter for ''dating'' ice cores.


Yiou, P., Fuhrer, K., Meeker, L.D., Jouzel, J., Johnsen, S. & Mayewski, P.A. 1997. Paleoclimatic variability inferred from the spectral analysis of Greenland and Antarctic ice-core data. Journal of Geophysical Research, 102, 26441-26454.

Corresponding author: Pascal Yiou, Laboratoire de Modelisation du Climat et de l'Environnement, DSM-CEA, l'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France.
E-mail: yiou@asterix.saclay.cea.fr

Paleoclimate variations occur at various time scales, between a few centuries for the Heinrich events and several hundreds of millenia for the glacial to interglacial variations. The recent ice cores from Greenland (Greenland Ice Core Project and Greenland Ice Sheet Project 2) and Antarctica (Vostok) span at least one glacial oscillation and provide many opportunities to investigate climate variations with a very fine resolution. The joint study of cores from both hemispheres allows us to distinguish between the sources of variability and helps to propose mechanisms of variations for the different time scales involved. The climate proxies we analyze are inferred from delta(18)O and delta D for temperature and chemical species (such as calcium) for the joint behavior of the major ions in the atmosphere, which yield an estimate of the polar circulation index. Those data provide time series of climatic variables from which we extract the information on the dynamics of the underlying system. We used several independent spectral analysis techniques, to reduce the possibility of spurious results. Those methods encompass the multitaper spectral analysis, singular-spectrum analysis, maximum entropy method, principal component analysis, minimum bias spectral estimates, and digital filter reconstructions. Our results show some differences between the two hemispheres in the slow variability associated with the astronomical forcing. Common features found in the three ice-core records occur on shorter periods, between 1 and 7 kyr. The Holocene also shows recurrent common patterns between Greenland and Antarctica. We-propose and discuss mechanisms to explain such behavior.