<p>δ<sup>18</sup>O ppm in deep sea sediment for aminifera carbonates over time from 0-600,000 years. Averaged over a large number of cores in order to isolate a global signal. Original caption: 
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<dl><dd>"The variations of 18O in carbonate averaged over a large number of different cores (in order to isolate a global signal) over the last 600,000 years. Most clear are the regular oscillations of the glacial ice volume which follows small changes to Earth's orbit around the Sun (Milankovitch forcing)."</dd></dl>
cited as reference: Schmidt, G.A. 1999. Forward modeling and interpretation of carbonate proxy data using oxygen isotope tracers in a global ocean model. Paleoceanography 14, 482-497.<a rel="nofollow" class="external autonumber" href="http://pubs.giss.nasa.gov/docs/1999/1999_Schmidt_2.pdf">[1]</a>; however, this image is not part of the cited publication. The source of the data shown in the graph is <b>unknown</b>.
Gavin Schmidt
1999-01
<p>"Science Briefs: Cold Climates, Warm Climates: How Can We Tell Past Temperatures?" (<a rel="nofollow" class="external text" href="http://www.giss.nasa.gov/research/briefs/schmidt_01/">giss.nava.gov</a>)
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direct link to image: <a rel="nofollow" class="external free" href="http://www.giss.nasa.gov/research/briefs/schmidt_01/specmap.GIF">http://www.giss.nasa.gov/research/briefs/schmidt_01/specmap.GIF</a>