Climate Histories from Ice Cores

Mountains, the climate history is preserved in long cores that penetrate the ice sheet along the central divide such as at Dome C and in the vicinity of the Russian research station known as Vostok. 

Reckling (R) moraines and at the ice fields adjacent to the Allan Hills (A). These measurements are used here to estimate the average annual temperatures of the source regions of the ice. The data point labeled S is the measured value of snow deposited in the Reckling Moraine in December of 1986, which therefore indicates that the average annual temperature at the Reckling Moraine at the present time is -32.1°C (Based on data by Lorius and Merlivat 1977) 

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Oeschger H., Beer J., Siegenthaler U., and Stauffer B. (1984) Late glacial climate history from ice cores. In Climate Processes and Climate Sensitivity Geophysical Monograph 29 (eds. J. E. Hansen and T. Takahashi). American Geophysical Union, Washington, DC, pp. 299-306. 

Blunier, T, E. Monnrn and J.-M. Bamola (2005) Atmospheric CO2 data from ice cores Four climatic cycles. In A history of atmospheric CO2 and its effects on plants, animals, and ecosystems (Eds. I R. Ehlermger, T. E. CerUng, and M. D. Dearing), Springer, New York, pp. 62-82... 

For an ice sheet of thickness H in equilibrium with a climate supplying accumulation at a rate a (thickness of ice per imit time), the vertical velocity near the ice-sheet surface is a and this velocity decreases to zero at the ice-sheet bed. A characteristic time constant for the ice core is H/a. The longest histories are therefore obtained from the thick and dry interiors of the ice sheets (particularly central East Antarctica, where H/a = 2 X 10 yrs). Unfortunately, records from low a sites are also low resolution, so to obtain a high-resolution record a high a site must be used and duration sacrificed (examples are the Antarctic Peninsula (H/a = 10 ) and southern Greenland H/a = 5 x 10 )). 

To infer accumulation rate history from an ice core, one needs to measure the thickness of annual layers (either directly if annual layers are resolvable, or by differentiating the depth-age scale determined by other means) and then correct for the thinning of these layers caused by the ice flow (the vertical strain Fig. 18-4). Estimates of vertical strain can be very uncertain for the deep part of an ice core. But vertical strain will not change rapidly with depth. Thus, if annual layers are resolvable one can learn relative accumulation rate changes across climate transitions with great confidence. 

Such a measurement can tell us about the chemical evolution of oxygen, such as whether the isotopes differentiated via a thermal cycle in which lighter leO fractionates from the heavier lsO, much as Vostok ice-core oxygen ratios reveal the Earth s prehistoric climate. From this fixed point of the Sun s oxygen ratios, we can then trace the history of water in other planetary bodies since their birth in the solar nebulae through the subsequent cometary bombardment [13]. In NASA s search for water on the Moon, important for the establishment of a future Moon base, such isotopic ratios will determine whether the water is a vast mother lode or just a recent cometary impact residue. 

Petit, J.R. Jouzel, J. et al. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 1999, 399, 429-436. 

Petit J. R., Jouzel J., Raynaud D., Barkov N. 1., Barnola J.-M., Basile L, Bender M., Chapellaz J., Davis M., Pelaygue G., Delmotte M., Kotylakov V. M., Legrand M., Lipankov V. Y., Lorius C., Pepin L., Ritz C., Saltzman E., and Stlevenard M. (1999) Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399, 429-436. 

The 8 0 values of ice collected 5-10 cm below the surface along surveyed lines at 100 m intervals also vary irregularly. Even samples collected at 10-m intervals at selected sites do not provide intelligible information about the climate history and structure of the ice sheet. These results therefore demonsfrate that the 8 0 values of ice collected systematically along the surface of the ice sheet do not constitute a horizontal core from which the structure of the ice sheet and a climate record can be determined. 

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