Beskrivelse

Discussion

This figure shows the climate record of Lisiecki and Raymo (2005) [1] constructed by combining measurements from 57 globally distributed deep sea sediment cores. The measured quantity is oxygen isotope fractionation (δ18O) in benthic foraminifera, which serves as a proxy for the total global mass of glacial ice sheets.

Lisiecki and Raymo constructed this record by first applying a computer aided process of adjusting individual "wiggles" in each sediment core to have the same alignment (i.e. wiggle matching). Then the resulting stacked record is orbitally tuned by adjusting the positions of peaks and valleys to fall at times consistent with an orbitally driven ice model (see: Milankovitch cycles). Both sets of these adjustments are constrained to be within known uncertainties on sedimentation rates and consistent with independently dated tie points (if any). Constructions of this kind are common, however they presume that ice sheets are orbitally driven, and hence data such as this can not be used in establishing the existence of such a relationship.

The observed isotope variations are very similar in shape to the temperature variations recorded at Vostok, Antarctica during the 420 kyr for which that record exists. Hence the right hand scale of the figure was established by fitting the reported temperature variations at Vostok (Petit et al. 1999) to the observed isotope variations. Hence, this temperature scale should be regarded as approximate and its magnitude is only representative of Vostok changes. In particular, temperature changes at polar sites, such as Vostok, frequently exceed the changes observed in the tropics or in the global average. A horizontal line at 0 °C indicates modern temperatures (circa 1950).

Labels are added to indicate regions where 100 kyr and 41 kyr cyclicity is observed. These periodicities match periodic changes in Earth's orbital eccentricity and obliquity respectively, and have been previously established by other studies (not relying on orbital tuning). For discussion of how such orbital changes might drive climate change, see Milankovitch cycles.

References

• Lisiecki, L. E., and M. E. Raymo (2005), A Pliocene-Pleistocene stack of 57 globally distributed benthic δ¹⁸O records, Paleoceanography, 20, PA1003, doi:10.1029/2004PA001071; data: doi:10.1594/PANGAEA.704257. — bundled as {{cite DOI|10.1029/2004PA001071}}
• Petit J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J., Delaygue G., Delmotte M., Kotlyakov V.M., Legrand M., Lipenkov V., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M. (1999) Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica, Nature, 399, pp.429-436, doi:10.1038/20859.

Lisensiering

Image from Global Warming Art

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