Predicting trends in atmospheric CO<sub>2</sub> across the Mid-Pleistocene Transition using existing climate archives
<p>During the Mid-Pleistocene Transition (MPT), ca. 1200–800 000 years ago (ka), the Earth's glacial cycles changed from 41 to 100 kyr periodicity. The emergence of this longer ice age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume i...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-11-01
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| Series: | Climate of the Past |
| Online Access: | https://cp.copernicus.org/articles/20/2487/2024/cp-20-2487-2024.pdf |
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| Summary: | <p>During the Mid-Pleistocene Transition (MPT), ca. 1200–800 000 years ago (ka), the Earth's glacial cycles changed from 41 to 100 kyr periodicity. The emergence of this longer ice age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume in interglacial periods. Since there is no known change in external orbital forcing across the MPT, it is generally agreed that the cause of this transition is internal to the Earth system. Resolving the climate, carbon cycle, and cryosphere processes responsible for the MPT remains a major challenge in Earth and palaeoclimate science. To address this challenge, the international ice core community has prioritised recovery of an ice core record spanning the MPT interval.</p>
<p>Here we present results from a simple generalised least-squares (GLS) model that predicts atmospheric <span class="inline-formula">CO<sub>2</sub></span> out to 1.8 Myr. Our prediction utilises existing records of atmospheric carbon dioxide (<span class="inline-formula">CO<sub>2</sub></span>) from Antarctic ice cores spanning the past 800 kyr along with the existing LR04 benthic <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi mathvariant="italic">δ</mi><msub><mrow class="chem"><msup><mi/><mn mathvariant="normal">18</mn></msup><mi mathvariant="normal">O</mi></mrow><mtext>calcite</mtext></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="e239a5aaf7eafa15f9a3873dd31d8c36"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-20-2487-2024-ie00001.svg" width="50pt" height="16pt" src="cp-20-2487-2024-ie00001.png"/></svg:svg></span></span> stack (Lisiecki and Raymo, 2005; hereafter “benthic <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> stack”) from marine sediment cores. Our predictions assume that the relationship between <span class="inline-formula">CO<sub>2</sub></span> and benthic <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> over the past 800 000 years can be extended over the last 1.5 million years. The implicit null hypothesis is that there has been no fundamental change in feedbacks between atmospheric <span class="inline-formula">CO<sub>2</sub></span> and the climate parameters represented by benthic <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>, global ice volume, and ocean temperature.</p>
<p>We test the GLS-model-predicted <span class="inline-formula">CO<sub>2</sub></span> concentrations against observed blue ice <span class="inline-formula">CO<sub>2</sub></span> concentrations, <span class="inline-formula"><i>δ</i><sup>11</sup>B</span>-based <span class="inline-formula">CO<sub>2</sub></span> reconstructions from marine sediment cores, and <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> of leaf-wax-based <span class="inline-formula">CO<sub>2</sub></span> reconstructions (Higgins et al., 2015; Yan et al., 2019; Yamamoto et al., 2022). We show that there is no clear evidence from the existing blue ice or proxy <span class="inline-formula">CO<sub>2</sub></span> data to reject our predictions or our associated null hypothesis. A definitive test and/or rejection of the null hypothesis may be provided following recovery and analysis of continuous oldest ice core records from Antarctica, which are still several years away. The record presented here should provide a useful comparison for the oldest ice core records and an opportunity for further constraints on the processes involved in the MPT.</p> |
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| ISSN: | 1814-9324 1814-9332 |