Five Million Years of Climate Change From Sediment Cores (Global Warming)

 

Five Million Years of Climate Change From Sediment Cores

This figure shows the climate record of Lisiecki and Raymo (2005) constructed by combining measurements from 57 globally distributed deep-sea sediment cores. The measured quantity is oxygen isotope fractionation 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. As a result, 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 degrees 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).

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