Abstract
AbstractThree 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 3350m 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 3530m depth) the glacier-ice age may reach ∼2000 kyr.
Highlights
Ice age-dating is one of the principal steps in ice-core data interpretations and paleoclimatic reconstructions
Among different depth–age relationships developed for Vostok, the geophysical metronome time-scale (GMTS), extended in Salamatin and others (1998a) and Salamatin (2000) to the maximum depth 3350 m of the Vostok ice-core isotope record covering four interglaciations, represents the so-called orbitally tuned chronologies
Orbital ice-age control points used in Parrenin and others (2001) as model constraints coincide with the corresponding GMTS ages. Another paleotemperature proxy signal spanning >500 000 years is available from the calcite core (DH-11) in Devils Hole, Nevada, U.S.A. (Winograd and others, 1992, 1997)
Summary
Ice age-dating is one of the principal steps in ice-core data interpretations and paleoclimatic reconstructions. Mosegaard and Tarantola, 1995; Mosegaard, 1998) is especially helpful in this case (Parrenin and others, 2001) to fit the ice-sheet model on average, uniformly vs depth, without putting excess weight on local fluctuations of the simulated depth–age curve caused by uncertainties in environmental conditions, reconstructed ice accumulation and other paleoclimatic characteristics. From this point of view, even simplified iceflow models From this point of view, even simplified iceflow models (e.g. Salamatin and Ritz, 1996; Hondoh and others, 2002) may be appropriate for incorporating the principal laws of ice-sheet dynamics into the ice-core dating procedure
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