Evidence from giant-clam <i>δ</i><sup>18</sup>O of intense El Ninõ–Southern Oscillation-related variability but reduced frequency 3700 years ago
<p>Giant clams (<i>Tridacna</i>) are the largest marine bivalves, and their carbonate shells can be used for high-resolution paleoclimate reconstructions. In this contribution, <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>&...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-04-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/16/597/2020/cp-16-597-2020.pdf |
| Summary: | <p>Giant clams (<i>Tridacna</i>) are the largest marine bivalves, and their carbonate shells
can be used for high-resolution paleoclimate reconstructions. In this
contribution, <span class="inline-formula"><i>δ</i><sup>18</sup>O</span><span class="inline-formula"><sub>shell</sub></span> was used to estimate climatic
variation in the Xisha Islands of the South China Sea. We first evaluate sea
surface temperature (SST) and sea surface salinity (SSS) influence on the
modern resampled monthly (<span class="inline-formula"><i>r</i></span>-monthly) resolution of <i>Tridacna gigas</i> <span class="inline-formula"><i>δ</i><sup>18</sup>O</span><span class="inline-formula"><sub>shell</sub></span>. The results obtained reveal that <span class="inline-formula"><i>δ</i><sup>18</sup>O</span><span class="inline-formula"><sub>shell</sub></span> seasonal variation is mainly controlled by SST and
appears to be insensitive to local SSS change. Thus, the <span class="inline-formula"><i>δ</i><sup>18</sup>O</span>
of <i>Tridacna</i> shells can be roughly used as a proxy of local SST: a 1 ‰ <span class="inline-formula"><i>δ</i><sup>18</sup>O</span><span class="inline-formula"><sub>shell</sub></span> change is roughly equal to
4.41 <span class="inline-formula"><sup>∘</sup></span>C of SST. The <span class="inline-formula"><i>r</i></span>-monthly <span class="inline-formula"><i>δ</i><sup>18</sup>O</span> of a 40-year-old
<i>Tridacna</i> <i>squamosa</i> (<span class="inline-formula">3673±28</span> BP) from the North Reef of the Xisha Islands was analyzed
and compared with the modern specimen. The difference between the average
<span class="inline-formula"><i>δ</i><sup>18</sup>O</span> of the fossil <i>Tridacna</i> shell (<span class="inline-formula"><i>δ</i><sup>18</sup>O</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>=</mo><mo>-</mo><mn mathvariant="normal">1.34</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="41pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="2413dcffb35407d3792466e52a1cd2e8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-16-597-2020-ie00001.svg" width="41pt" height="10pt" src="cp-16-597-2020-ie00001.png"/></svg:svg></span></span> ‰) and the modern <i>Tridacna</i> specimen (<span class="inline-formula"><i>δ</i><sup>18</sup>O</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>=</mo><mo>-</mo><mn mathvariant="normal">1.15</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="41pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c2dddad30e09b42cac8a198c1a8d7426"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-16-597-2020-ie00002.svg" width="41pt" height="10pt" src="cp-16-597-2020-ie00002.png"/></svg:svg></span></span> ‰) probably implies a warm climate, roughly
0.84 <span class="inline-formula"><sup>∘</sup></span>C, 3700 years ago. The seasonal variation 3700 years ago
was slightly lower than that suggested by modern instrumental data, and the
transition between warm and cold seasons was rapid. Higher amplitudes of
reconstructed <span class="inline-formula"><i>r</i></span>-monthly and <span class="inline-formula"><i>r</i></span>-annual SST anomalies imply an enhanced climate
variability during this warm period. Investigation of the El
Ninõ–Southern Oscillation (ENSO) variation (based on the reconstructed
SST series) indicates reduced ENSO frequency but increased ENSO-related
variability and extreme El Ninõ winter events 3700 years ago.</p> |
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| ISSN: | 1814-9324 1814-9332 |