Isotope Climatic Record Over The Last 2.5 KA from Dome C, Antarctica, Ice cores

Benoist, Jean-Pierre; Jouzel, J.; Lorius, C.; Merlivat, L.; Pourchet, M.

doi:10.3189/s0260305500002457

Cited by 24 publications

(14 citation statements)

References 12 publications

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“…Local variations in the spatial pattern of snow accumulation lead to short-term differences in the time series of annually averaged parameters at adjacent drilling sites, the so-called "deposition noise" (the uncorrelated variance of two adjacent i!i time series), which has been estimated for several sites in Greenland [Robin, 1983;Fisher et al, 1985] and in Antarctica [Benoist et al, 1982;Peel, 1992], using data from duplicate cores. It is therefore possible to obtain a crude estimate of the length of averaging needed to reduce the deposition noise to a level needed to detect a given magnitude of "climatic" signal.…”

Section: Empirical Estimates Of the •/T• Relationshipsmentioning

confidence: 99%

Validity of the temperature reconstruction from water isotopes in ice cores

Jouzel¹,

Alley²,

Cuffey³

et al. 1997

J. Geophys. Res.

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587

445

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Abstract. Well-documented present-day distributions of stable water isotopes (HDO and H2180) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (/SD and/5•SO) 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. •

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Section: Empirical Estimates Of the •/T• Relationshipsmentioning

confidence: 99%

Validity of the temperature reconstruction from water isotopes in ice cores

Jouzel¹,

Alley²,

Cuffey³

et al. 1997

J. Geophys. Res.

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587

445

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“…On the contrary, less is known about the Southern Hemisphere and, in particular, about Antarctica. Previous stable isotope ice core records [i.e., Benoist et al , 1982; Mosley‐Thompson , 1992; Morgan and van Ommen , 1997; Stenni et al , 1999] suggested cooler conditions in East Antarctica during the time period encompassing the LIA, while δ 18 O records from West Antarctica suggested an opposite pattern [ Mosley‐Thompson et al , 1990]. Chemical ice core records at Siple Dome in West Antarctica [ Kreutz et al , 1997] suggested increased atmospheric circulation during the LIA starting from 1400 A.D. and probably still persisting today.…”

Section: Introductionmentioning

confidence: 99%

Eight centuries of volcanic signal and climate change at Talos Dome (East Antarctica)

et al. 2002

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[1] During the 1996 Programma Nazionale di Ricerche in Antartide-International Trans-Antarctic Scientific Expedition traverse, two firn cores were retrieved from the Talos Dome area (East Antarctica) at elevations of 2316 m (TD, 89 m long) and 2246 m (ST556, 19 m long). Cores were dated by using seasonal variations in non-sea-salt (nss) SO 4 2À concentrations coupled with the recognition of tritium marker level (1965 -1966) and nss SO 4 2À spikes due to the most important volcanic events in the past (Pinatubo 1991, Agung 1963, Krakatoa 1883, Tambora 1815, Kuwae 1452, Unknown 1259). The number of annual layers recognized in the TD and ST556 cores was 779 and 97, respectively. The dD record obtained from the TD core has been compared with other East Antarctic isotope ice core records (Dome C EPICA, South Pole, Taylor Dome). These records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries, which might be related to the Little Ice Age (LIA) cold period. Because of the high degree of geographical variability, the strongest LIA cooling was not temporally synchronous over East Antarctica, and the analyzed records do not provide a coherent picture for East Antarctica. The accumulation rate record presented for the TD core shows a decrease during part of the LIA followed by an increment of about 11% in accumulation during the 20th century. At the ST556 site, the accumulation rate observed during the 20th century was quite stable.INDEX TERMS: 3344

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“…Although ice-core datasets are known to be noisy to varying degrees (e.g. Benoist et al, 1982;White et al, 1997), a climate signal has been solidly established (e.g. Lorius, 1989;Delmas et al, 1992;Legrand and Mayewski, 1997;Shuman et al, 1998;Reusch et al, 1999); thus, we turn our attention to the data.…”

Section: General Issues and Limitationsmentioning

confidence: 99%

Towards ice-core-based synoptic reconstructions of west antarctic climate with artificial neural networks

Reusch

Alley

2005

Int. J. Climatol.

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Ice cores have, in recent decades, produced a wealth of palaeoclimatic insights over widely ranging temporal and spatial scales. Nonetheless, interpretation of ice-core-based climate proxies is still problematic due to a variety of issues unrelated to the quality of the ice-core data. Instead, many of these problems are related to our poor understanding of key transfer functions that link the atmosphere to the ice. This study uses two tools from the field of artificial neural networks (ANNs) to investigate the relationship between the atmosphere and surface records of climate in West Antarctica. The first, self-organizing maps (SOMs), provides an unsupervised classification of variables from the midtroposphere (700 hPa temperature, geopotential height and specific humidity) into groups of similar synoptic patterns. An SOM-based climatology at annual resolution (to match ice-core data) has been developed for the period 1979-93 based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 15-year reanalysis (ERA-15) dataset. This analysis produced a robust mapping of years to annual-average synoptic conditions as generalized atmospheric patterns or states. Feed-forward ANNs, our second ANN-based tool, were then used to upscale from surface data to the SOM-based classifications, thereby relating the surface sampling of the atmosphere to the large-scale circulation of the mid-troposphere. Two recorders of surface climate were used in this step: automatic weather stations (AWSs) and ice cores. Six AWS sites provided 15 years of near-surface temperature and pressure data. Four ice-core sites provided 40 years of annual accumulation and major ion chemistry. Although the ANN training methodology was properly designed and followed standard principles, limited training data and noise in the ice-core data reduced the effectiveness of the upscaling predictions. Despite these shortcomings, which might be expected to preclude successful analyses, we find that the combined techniques do allow ice-core reconstruction of annual-average synoptic conditions with some skill. We thus consider the ANN-based approach to upscaling to be a useful tool, but one that would benefit from additional training data.

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Isotope Climatic Record Over The Last 2.5 KA from Dome C, Antarctica, Ice cores

Cited by 24 publications

References 12 publications

Validity of the temperature reconstruction from water isotopes in ice cores

Validity of the temperature reconstruction from water isotopes in ice cores

Eight centuries of volcanic signal and climate change at Talos Dome (East Antarctica)

Towards ice-core-based synoptic reconstructions of west antarctic climate with artificial neural networks

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