Environment Counts | Devils Hole record 4,500 to 560,000 years ago does not support orbital forcing hypothesis
Author: Geoff Zeiss – Published At: 2012-04-08 10:24 – (1702 Reads)
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In this historically important paper, delta-oxygen-18 variations in a 36-centimeter-long core of vein calcite from Devils Hole, Nevada, provide a continuous 500,000-year paleotemperature record that exhibits all the major features in marine ice-volume and the Vostok (Antarctica) paleotemperature records. Comparing the timing of glacial terminations with calculated Northern Hemisphere insolation revealed that orbitally controlled (Milankovitch cycles) variations in solar insolation were not a major factor in triggering deglaciations. Continuous 500,000-Year Climate Record from Vein Calcite in Devils Hole, Nevada, Science, Vol. 258, 9 October 1992
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Introduction
Devils Hole is a cave in south-central Nevada. It is part of a cave system the walls of which are coated with dense vein calcite precipitated from the groundwater flowing through the cave system. The calcite, which can be up to 40 centimeters (cm) thick, contains a continuous record of the variation of the composition of stable oxygen isotopes in the ground water over time. Analysis of the delta-oxygen-18 (a paleotemperature proxy) variations in a 36-centimeter-long core of vein calcite provided an uninterrupted 500,000-year paleotemperature record that exhibits all the major features in marine ice-volume and Vostok (Antarctica) paleotemperature records.
Chronology of the the layers in the vein calcite can also be accurately established because the material has been found to be amenable to precise radioisotope decay dating utilizing the thorium 230-uranium 234-uranium 238 decay sequence.
Observations
The vein calcite samples have been dated using the uranium series decay sequence. The ages have been independently confirmed by non-USGS investigators using protactinium-231.
Recently two additional calcite specimens were obtained from a different cave in the system called Devils Hole Cave no. 2 (DHC2), which is approximately 200 meters north of Devils Hole. The calcite from this cave provides data that extends the analysis to up to 4,500 years before the present.
Comparison with other paleoclimate records
The Devils Hole delta-oxygen-18 record exhibits all the major features in marine ice-volume and the Vostok (Antarctica) paleotemperature records, although the timing of events does not appear to agree very closely.
In the figures the Devils Hole observations are compared with
- two marine cores TR163-19 retrieved in the east equatorial Pacific and ODP1020 retrieved off the Oregon-California border. The linear correlation coefficient r is shown for 4,500 to 360,000 years before present.
- Vostok Antarctica ice core record – Source: Donald Rapp, Ice Ages and Interglacials, 2009 Springer
Glacial-interglacial cycles compared to orbitally controllled insolation
Three important conclusion suggested that orbital forcing by itself was not able to explain the major glacial-interglacial cycles. First of all, the duration of the last four glacial cycles recorded in the calcite was not constant, but varied from 80,000 to 130,000 years. Secondly, cold and warm periods were asymmetric with interglacial climates lasting only about 20,000 years. Thirdly, comparison of the timing of glacial terminations with the calculated variation in Northern Hemisphere insolation revealed that the beginning of deglacial warming did not correspond to maxima in orbitally controlled insolation in the Northern Hemisphere. For example, for the second termination (TII), there was a 10,000 year discrepancy between the timing of TII revealed by the calcite record and the nearest insolation maximum. Based on these three findings it was concluded that the Devils Hole observations were inconsistent with the orbital forcing (Milankovitch) hypothesis for the origin of the major glacial cycles over the past 500,000 years.
