Ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at Vostok Station (East Antarctica)

Abstract

Abstract. An interpretation of the deuterium profile measured along the Vostok (East Antarctica) ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis. An inverse problem is solved to infer a local "geophysical metronome," the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of Milankovich periods. By correlating the smoothed isotopic temperature record to the metronome, a chronostratigraphy of the Vostok ice core is derived with an accuracy of _+3.0-4.5 kyr. The developed timescale predicts an age of 241 kyr at a depth of 2760 m. The ratio 13D/13T i between deuterium content and cloud temperature fluctuations (at the top of the inversion layer) is examined by fitting simulated and measured borehole temperature profiles. The conventional estimate of the deuteriumtemperature slope corresponding to the present-day spatial ratio (9 per mil/øC) is confirmed in general. However, the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature, responsible for the thermal state of the ice sheet, to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record. With this assumption, we obtain the long-term temporal deuterium-temperature slope to be 5.8-6.5 per mil/øC which implies that the glacial-interglacial temperature increase over central Antarctica was about 15øC in the surface temperature and 10øC in the inversion temperature. Past variations of the accumulation rate and the corresponding changes in the ice-sheet surface elevation are simultaneously simulated.

What was the surface temperature in central Antarctica during the last glacial maximum?

“…The higher scenario (T WI ) is derived from today's spatial relation between temperature and N 18 O for Byrd [10]. For the lower temperature scenario (T BH ) we refer to the results from Salamatin et al [1] and increase the LG^Holocene temperature di¡erence to 15 ‡C. The accumulation rate was calculated following the approach from Jouzel et al [23] assuming a linear relation between accumulation rate and the derivative of the rate between water vapor partial pressure and temperature with respect to temperature.…”

“…Light black (blue) line: For this scenario (T BH 2) the T WI temperature record was stretched so that the increase from the last glacial to the Holocene becomes 15 ‡C. Grey (red) lines: Original temperature and accumulation rate from Salamatin et al [1] (¢g. 5, Scenario 1) used for our scenario T BH 1.…”

“…The water isotope based temperature reconstruction is questioned by a study based on bore hole temperature measurements at Vostok which roughly doubles the Vostok glacial^interglacial temperature di¡erence. Salamatin et al [1] established an independent time scale for the Vostok ice core. This time scale is based on the assumption that the orbital signal (harmonics of Milankovich periods) is imprinted in the surface temperature and therefore also in the bore hole temperature record.…”

Determination of the 2H/1H, 17O/16O, and 18O/16O isotope ratios in water by means of tunable diode laser spectroscopy at 1.39 μm

“…The 13 CO 2 / 12 CO 2 ratio is extremely useful to constrain the global atmospheric CO 2 budget [1][2][3][4][5], but also finds applications as a biomedical diagnostic tool, e.g. in the quantification of the amino acid metabolism by means of a 13 C-labeled leucine test [6 -8]. The 13 CH 4 / 12 CH 4 and 12 CH 3 D/ 12 CH 4 isotope ratios in atmospheric methane give information on source and sink processes, including its different production pathways [9][10][11].…”

“…The 13 CH 4 / 12 CH 4 and 12 CH 3 D/ 12 CH 4 isotope ratios in atmospheric methane give information on source and sink processes, including its different production pathways [9][10][11]. Isotope studies of water, arguably the molecule of highest environmental importance of all, find application in such diverse fields as hydrology, paleoclimatology [12][13][14], atmospheric chemistry, and biomedicine [15,16]. It is, therefore, discouraging that the traditional analytical tools available for measuring isotope ratios in water are far more cumbersome and inaccurate than for most other molecules.…”