Vostok (Antarctica) ice-core time-scale from datings of different origins Andrey N. Salamatin, Elena A. Tsyganova, Vladimir Y. Lipenkov, Jean-Robert Petit To cite this version: Andrey N. Salamatin, Elena A. Tsyganova, Vladimir Y. Lipenkov, Jean-Robert Petit. Vostok (Antarc- tica) ice-core time-scale from datings of different origins. Annals of Glaciology, International Glacio- logical Society, 2004, 39 (1), pp.283 à 292. 10.3189/172756404781814023. insu-00374921 HAL Id: insu-00374921 https://hal-insu.archives-ouvertes.fr/insu-00374921 Submitted on 7 May 2021 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. Distributed under a Creative Commons Attribution| 4.0 International License Annals of Glaciology 39 2004 283 Vostok (Antarctica) ice-core time-scale from datings of different origins Andrey N. SALAMATIN,1 Elena A. TSYGANOVA,1 Vladimir Ya. LIPENKOV,2 Jean Robert PETIT3 1Department of Applied Mathematics, Kazan State University, 420008 Kazan, Russia E-mail: [email protected] 2Arctic and Antarctic Research Institute, 199397 St Petersburg, Russia 3Laboratoire de Glaciologie et Ge´ophysique de l’Environnement du CNRS, 54 rue Molie`re, BP 96, 38402 Saint-Martin-d’He`res Cedex, France ABSTRACT. Three different approaches to ice-core age dating are employed to develop a depth–age relationship at Vostok, Antarctica: (1) correlating the ice-core isotope record to the geophysical metronome (Milankovich surface temperature cycles) inferred from the borehole temperature profile, (2) importing a known chronology from another (Devils Hole, Nevada, USA) paleoclimatic signal, and (3) direct ice-sheet flow modeling. Inverse Monte Carlo sampling is used to constrain the accumulation- rate reconstruction and ice-flow simulations in order to find the best-fit glaciological time-scale matched with the two other chronologies. The general uncertainty of the different age estimates varies from 2 to 6 kyr on average and reaches 6–15 kyr at maximum. Whatever the causes of this discrepancy might be, they are thought to be of different origins, and the age errors are assumed statistically independent. Thus, the average time-scale for the Vostok ice core down to 3350 m depth is deduced consistent with all three dating procedures within the standard deviation limits of ±3.6 kyr, and its accuracy is estimated as 2.2 kyr on average. The constrained ice-sheet flow model allows, at least theoretically, extrapolation of the ice age–depth curve further to the boundary with the accreted lake ice where (at 3530 m depth) the glacier-ice age may reach 2000 kyr. 1. INTRODUCTION others, 2002) may be appropriate for incorporating the principal laws of ice-sheet dynamics into the ice-core dating Ice age-dating is one of the principal steps in ice-core data procedure. interpretations and paleoclimatic reconstructions. There is Among different depth–age relationships developed for no universal and/or standard procedure to determine depth– Vostok, the geophysical metronome time-scale (GMTS), age relationships in polar ice sheets at deep-drilling sites. extended in Salamatin and others (1998a) and Salamatin The latter question is of primary importance for the record (2000) to the maximum depth 3350 m of the Vostok ice-core 3600 m deep ice core retrieved from the Antarctic ice sheet isotope record covering four interglaciations, represents the at Vostok station (Petit and others, 1999) above the vast so-called orbitally tuned chronologies. It is based on subglacial lake. correlation of the isotopic temperature signal with the Applicability of sophisticated two- and three-dimensional geophysical-metronome Milankovich components of past (2-D and 3-D) thermomechanical ice-flow models (Ritz, local surface temperature variations inferred from the 1992; Ritz and others, 2001) for solving this problem suffers borehole temperature profile. Possible errors and uncertain- significantly from uncertainties in initial and input data: ties in GMTS are discussed elsewhere (Salamatin and others, mainly in glacier bottom conditions and past accumulation 1998b; Salamatin, 2000), and its overall average accuracy rates. Nevertheless, the detailed analysis by Parrenin and was estimated as ±3.5–4.5 kyr. Orbital ice-age control points others (2001) shows that the modeling of ice-sheet dynamics used in Parrenin and others (2001) as model constraints becomes a useful tool for ice age prediction if a priori coincide (to within ±2 kyr) with the corresponding GMTS chronological information is used to fit the model par- ages. ameters. Although different sources of age markers and Another paleotemperature proxy signal spanning dated time series have their own specific errors, they may be >500 000 years is available from the calcite core (DH-11) considered reliable constraints if, in combination, they in Devils Hole, Nevada, U.S.A. (Winograd and others, 1992, deliver statistically valid and independent estimates of ice 1997). The principal advantage of this d18O record is that the age at various depth levels. The inverse Monte Carlo dense vein calcite provides material for direct uranium- sampling method (e.g. Mosegaard and Tarantola, 1995; series dating (Ludwig and others, 1992), with the standard Mosegaard, 1998) is especially helpful in this case (Parrenin errors increasing from 1 to 7 kyr with time up to 400 kyr BP.In and others, 2001) to fit the ice-sheet model on average, addition, the signal may be influenced by different hydro- uniformly vs depth, although without putting excess weight logical factors. In particular, a systematic underestimation of on local fluctuations of the simulated depth–age curve the ages determined, on the order of several thousands of caused by uncertainties in environmental conditions, years, may take place due to the groundwater travel time reconstructed ice accumulation and other paleoclimatic through the aquifer (Winograd and others, 1992; Landwehr characteristics. From this point of view, even simplified ice- and Winograd, 2001). Nevertheless, the correlation of the flow models (e.g. Salamatin and Ritz, 1996; Hondoh and Vostok ice-core deuterium–depth signal with the Devils Downloaded from https://www.cambridge.org/core. 07 May 2021 at 14:18:22, subject to the Cambridge Core terms of use. 284 Salamatin and others: Vostok ice-core time-scale Hole record (see US Geological Survey open-file report 97- (1977) and Ritz (1989, 1992). The accumulation-rate vari- 792 at http://pubs.water.usgs.gov/ofr97–792) can also be ations in central Antarctica are linked by means of the considered as an independent approach to dating the exponential factor b and the deuterium/inversion-tempera- longest paleoclimate archive from central Antarctica (Land- ture slope CT to the ice-core isotopic content ratios dD wehr and Winograd, 2001). corrected for past changes in the oxygen isotope com- d18 The possibility of using various gas studies of Vostok ice position of ocean water Osw (Sowers and others, 1993; d d18 cores for relative dating (correlation) with other Antarctic, Bassinot and others 1994). Deviations Dand Osw in Greenland or deep-sea core climatic records is not Equations (2) are referenced to their present-day values. For = considered here, because of the additional errors which relatively small ratio b CT the accumulation-rate variations arise from the uncertainty in the gas–ice age difference, become linearly dependent on isotopic temperatures. A preventing better constraints on the ice age. These questions more sophisticated relationship between the inversion are addressed by Salamatin and others (1998b) and with a temperature and the deuterium content in ice, directly deeper focus by Parrenin and others (2001). taking into account the water-vapor source temperature Thus, the principal goals of our study are (1) to combine variations, has recently been suggested by Cuffey and the above sources of chronological information in order to Vimeux (2001). Correspondingly, as emphasized and constrain ice-flow model parameters, reducing to a min- explained by Jouzel and others (2003), the correction of d d18 imum systematic errors in the glaciological time-scale based D to the sea-water isotopic content Osw enters the on simulations of the ice-sheet dynamics in the vicinity of transfer function with the factor of 4.8 rather than 8 (used Vostok station, (2) to deduce the average age–depth here for consistency with the earlier studies). As shown relationship consistent with different approaches to the below in section 4, this leads to slight overestimation of the ice-core dating within the upper 3350 m, and (3) to extend isotope/temperature gradient CT. the model predictions at Vostok to the deeper bottom part of Ice-sheet thickness fluctuations ÁðtÞ in the second of the glacier. Equations (2) are reconstructed after Salamatin and Ritz (1996). The latter model for Á was verified and its tuning parameters b and l were constrained on the basis of the 2- 2. MODEL DESCRIPTION AND D thermomechanically coupled model of Antarctic ice-sheet PARAMETERIZATION dynamics (Ritz, 1992). These results have also been recently Here we use a simplified 2-D approach to ice flowline supported by 3-D simulations (Ritz and others, 2001). As modeling developed for ice age predictions by Hondoh and follows from Salamatin and Ritz (1996), l is inversely others (2002). We introduce the longitudinal coordinate s as proportional to the modified Glen flow-law exponent , a distance from the ice divide along a reference flowline. which takes account of the vertical temperature gradient The flow tube configuration is described by its relative width (Lliboutry, 1979).