Magnesium (Mg∕Ca, <i>δ</i><sup>26</sup>Mg), boron (B∕Ca, <i>δ</i><sup>11</sup>B), and calcium (Ca<sup>2+</sup>) geochemistry of <i>Arctica islandica</i> and <i>Crassostrea virginica</i> extrapallial fluid and shell under ocean acidification
<p>The geochemistry of biogenic carbonates has long been used as proxies to record changing seawater parameters. However, the effect of ocean acidification (OA) on seawater chemistry and organism physiology could impact isotopic signatures and how elements are incorporated into the shell. In t...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/22/2831/2025/bg-22-2831-2025.pdf |
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| Summary: | <p>The geochemistry of biogenic carbonates has long been used as proxies to record changing seawater parameters. However, the effect of ocean acidification (OA) on seawater chemistry and organism physiology could impact isotopic signatures and how elements are incorporated into the shell. In this study, we investigated the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial fluid (EPF), and the shell – in two bivalve species: <i>Crassostrea virginica</i> and <i>Arctica islandica</i>. Additionally, we examined the effects of three ocean acidification conditions (ambient: 500 ppm <span class="inline-formula">CO<sub>2</sub></span>, moderate: 900 ppm <span class="inline-formula">CO<sub>2</sub></span>, and high: 2800 ppm <span class="inline-formula">CO<sub>2</sub></span>) on the geochemistry of the same three reservoirs for <i>C. virginica</i>. We present data on calcification rates, EPF pH, measured elemental ratios (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Mg</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="37pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d1f58fc3a76bb75dfaa8c6e5d7932caa"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00005.svg" width="37pt" height="14pt" src="bg-22-2831-2025-ie00005.png"/></svg:svg></span></span>, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">B</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="30pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="268c30f622405029dfe2603ae12c35f1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00006.svg" width="30pt" height="14pt" src="bg-22-2831-2025-ie00006.png"/></svg:svg></span></span>), and isotopic signatures (<span class="inline-formula"><i>δ</i><sup>26</sup>Mg</span>, <span class="inline-formula"><i>δ</i><sup>11</sup>B</span>). In both species, comparisons of seawater and EPF <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Mg</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="37pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="ba1c13ec1a2f7c9d61dc1e30484e1e0a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00007.svg" width="37pt" height="14pt" src="bg-22-2831-2025-ie00007.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">B</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="30pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="fa262b09298be535c8d15ab3220327b0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00008.svg" width="30pt" height="14pt" src="bg-22-2831-2025-ie00008.png"/></svg:svg></span></span>, <span class="inline-formula">Ca<sup>2+</sup></span>, and <span class="inline-formula"><i>δ</i><sup>26</sup>Mg</span> indicate that the EPF has a distinct composition that differs from seawater. Shell <span class="inline-formula"><i>δ</i><sup>11</sup>B</span> did not faithfully record seawater pH, and <span class="inline-formula"><i>δ</i><sup>11</sup>B</span>-calculated pH values were consistently higher than pH measurements of the EPF with microelectrodes, indicating that the shell <span class="inline-formula"><i>δ</i><sup>11</sup>B</span> may reflect a localized environment within the entire EPF reservoir. In <i>C. virginica</i>, EPF <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Mg</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="37pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="7ca9aaaf810bfdc376520af99d0fb49f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00009.svg" width="37pt" height="14pt" src="bg-22-2831-2025-ie00009.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">B</mi><mo>/</mo><mi mathvariant="normal">Ca</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="30pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3a69baccd1f850af4a07c62ad472aaae"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-22-2831-2025-ie00010.svg" width="30pt" height="14pt" src="bg-22-2831-2025-ie00010.png"/></svg:svg></span></span>, as well as absolute concentrations of <span class="inline-formula">Mg<sup>2+</sup></span>, B, and <span class="inline-formula">Ca<sup>2+</sup></span>, were all significantly affected by ocean acidification, indicating that OA affects the physiological pathways regulating or storing these ions, an observation that complicates their use as proxies. Reduction in EPF <span class="inline-formula">Ca<sup>2+</sup></span> may represent an additional mechanism underlying reduction in calcification in <i>C. virginica</i> in response to seawater acidification. The complexity of dynamics of EPF chemistry suggests boron proxies in these two mollusk species are not straightforwardly related to seawater pH, but ocean acidification does lead to both a decrease in microelectrode pH and boron-isotope-based pH, potentially showing applicability of boron isotopes in recording physiological changes. Collectively, our findings show that bivalves have high physiological control over the internal calcifying fluid, which presents a challenge in using boron isotopes for reconstructing seawater pH.</p> |
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| ISSN: | 1726-4170 1726-4189 |