Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model
<p>Iodine (I) abundance in marine carbonates (measured as an elemental ratio with calcium, I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml&...
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Copernicus Publications
2024-11-01
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| Series: | Biogeosciences |
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| author | K. Cheng A. Ridgwell D. S. Hardisty |
| author_facet | K. Cheng A. Ridgwell D. S. Hardisty |
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| description | <p>Iodine (I) abundance in marine carbonates (measured as an elemental ratio with calcium, I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="1b4178c77ca0d4bfee6c9ddd864f3a43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00001.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00001.png"/></svg:svg></span></span> Ca) is of broad interest as a proxy for local/regional ocean redox. This connection arises because the speciation of iodine in seawater, the balance between iodate (IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="53e1f98be2cdf70dbe180d95894fc6b5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00002.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00002.png"/></svg:svg></span></span>) and iodide (I<span class="inline-formula"><sup>−</sup></span>), is sensitive to the prevalence of oxic vs. anoxic conditions. However, although I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="57ee8123d9c9aefcf23d9c7f6463c158"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00003.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00003.png"/></svg:svg></span></span> Ca ratios are increasingly commonly being measured in ancient carbonate samples, a fully quantitative interpretation of this proxy requires the availability of a mechanistic interpretative framework for the marine iodine cycle that can account for the extent and intensity of ocean deoxygenation in the past. Here we present and evaluate a representation of marine iodine cycling embedded in an Earth system model (“cGENIE”) against both modern and paleo-observations. In this framework, we account for IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="8c72af1edd6d67ed562efcaf5163d22b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00004.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00004.png"/></svg:svg></span></span> uptake and release of I<span class="inline-formula"><sup>−</sup></span> through the biological pump, the reduction in ambient IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="76bbd0535ad9c3e987722e2e722d5d00"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00005.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00005.png"/></svg:svg></span></span> to I<span class="inline-formula"><sup>−</sup></span> in the water column, and the re-oxidation of I<span class="inline-formula"><sup>−</sup></span> to IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="78ed0f7e81615226176402cdd6a1afd5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00006.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00006.png"/></svg:svg></span></span>. We develop and test a variety of different plausible mechanisms for iodine reduction and oxidation transformation and contrast model projections against an updated compilation of observed dissolved IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="fa1148a5a7ab62133104fb46bf612014"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00007.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00007.png"/></svg:svg></span></span> and I<span class="inline-formula"><sup>−</sup></span> concentrations in the present-day ocean.</p>
<p>By optimizing the parameters controlling previously proposed mechanisms involved in marine iodine cycling, we find that we can obtain broad matches to observed iodine speciation gradients in zonal surface distribution, depth profiles, and oxygen-deficient zones (ODZs). However, we also identify alternative, equally well performing mechanisms which assume a more explicit mechanistic link between iodine transformation and environment – an ambiguity that highlights the need for more process-based studies on modern marine iodine cycling. Finally, to help distinguish between competing representations of the marine iodine cycle and because our ultimate motivation is to further our ability to reconstruct ocean oxygenation in the geological past, we conducted “plausibility tests” of different model schemes against available I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="8550e2e9970f84100ffbfa4da4f4f543"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00008.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00008.png"/></svg:svg></span></span> Ca measurements made on Cretaceous carbonates – a time of substantially depleted ocean oxygen availability compared to modern and hence a strong test of our model. Overall, the simultaneous broad match we can achieve between modeled iodine speciation and modern observations, and between forward proxy modeled I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="539a58614ea8688159b8effbc6d3da8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00009.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00009.png"/></svg:svg></span></span> Ca and geological elemental ratios, supports the application of our Earth system modeling in simulating the marine iodine cycle to help interpret and constrain the redox evolution of past oceans.</p> |
| format | Article |
| id | doaj-art-cab6a206fda34fe89cff4b0a87b695f0 |
| institution | Kabale University |
| issn | 1726-4170 1726-4189 |
| language | English |
| publishDate | 2024-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj-art-cab6a206fda34fe89cff4b0a87b695f02024-11-13T12:19:11ZengCopernicus PublicationsBiogeosciences1726-41701726-41892024-11-01214927494910.5194/bg-21-4927-2024Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system modelK. Cheng0A. Ridgwell1D. S. Hardisty2Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48823, USADepartment of Earth and Planetary Sciences, University of California Riverside, Riverside, CA 92521, USADepartment of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48823, USA<p>Iodine (I) abundance in marine carbonates (measured as an elemental ratio with calcium, I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="1b4178c77ca0d4bfee6c9ddd864f3a43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00001.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00001.png"/></svg:svg></span></span> Ca) is of broad interest as a proxy for local/regional ocean redox. This connection arises because the speciation of iodine in seawater, the balance between iodate (IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="53e1f98be2cdf70dbe180d95894fc6b5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00002.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00002.png"/></svg:svg></span></span>) and iodide (I<span class="inline-formula"><sup>−</sup></span>), is sensitive to the prevalence of oxic vs. anoxic conditions. However, although I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="57ee8123d9c9aefcf23d9c7f6463c158"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00003.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00003.png"/></svg:svg></span></span> Ca ratios are increasingly commonly being measured in ancient carbonate samples, a fully quantitative interpretation of this proxy requires the availability of a mechanistic interpretative framework for the marine iodine cycle that can account for the extent and intensity of ocean deoxygenation in the past. Here we present and evaluate a representation of marine iodine cycling embedded in an Earth system model (“cGENIE”) against both modern and paleo-observations. In this framework, we account for IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="8c72af1edd6d67ed562efcaf5163d22b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00004.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00004.png"/></svg:svg></span></span> uptake and release of I<span class="inline-formula"><sup>−</sup></span> through the biological pump, the reduction in ambient IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="76bbd0535ad9c3e987722e2e722d5d00"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00005.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00005.png"/></svg:svg></span></span> to I<span class="inline-formula"><sup>−</sup></span> in the water column, and the re-oxidation of I<span class="inline-formula"><sup>−</sup></span> to IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="78ed0f7e81615226176402cdd6a1afd5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00006.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00006.png"/></svg:svg></span></span>. We develop and test a variety of different plausible mechanisms for iodine reduction and oxidation transformation and contrast model projections against an updated compilation of observed dissolved IO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="fa1148a5a7ab62133104fb46bf612014"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00007.svg" width="9pt" height="16pt" src="bg-21-4927-2024-ie00007.png"/></svg:svg></span></span> and I<span class="inline-formula"><sup>−</sup></span> concentrations in the present-day ocean.</p> <p>By optimizing the parameters controlling previously proposed mechanisms involved in marine iodine cycling, we find that we can obtain broad matches to observed iodine speciation gradients in zonal surface distribution, depth profiles, and oxygen-deficient zones (ODZs). However, we also identify alternative, equally well performing mechanisms which assume a more explicit mechanistic link between iodine transformation and environment – an ambiguity that highlights the need for more process-based studies on modern marine iodine cycling. Finally, to help distinguish between competing representations of the marine iodine cycle and because our ultimate motivation is to further our ability to reconstruct ocean oxygenation in the geological past, we conducted “plausibility tests” of different model schemes against available I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="8550e2e9970f84100ffbfa4da4f4f543"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00008.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00008.png"/></svg:svg></span></span> Ca measurements made on Cretaceous carbonates – a time of substantially depleted ocean oxygen availability compared to modern and hence a strong test of our model. Overall, the simultaneous broad match we can achieve between modeled iodine speciation and modern observations, and between forward proxy modeled I <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="539a58614ea8688159b8effbc6d3da8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-21-4927-2024-ie00009.svg" width="8pt" height="14pt" src="bg-21-4927-2024-ie00009.png"/></svg:svg></span></span> Ca and geological elemental ratios, supports the application of our Earth system modeling in simulating the marine iodine cycle to help interpret and constrain the redox evolution of past oceans.</p>https://bg.copernicus.org/articles/21/4927/2024/bg-21-4927-2024.pdf |
| spellingShingle | K. Cheng A. Ridgwell D. S. Hardisty Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model Biogeosciences |
| title | Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model |
| title_full | Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model |
| title_fullStr | Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model |
| title_full_unstemmed | Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model |
| title_short | Characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an Earth system model |
| title_sort | characterizing the marine iodine cycle and its relationship to ocean deoxygenation in an earth system model |
| url | https://bg.copernicus.org/articles/21/4927/2024/bg-21-4927-2024.pdf |
| work_keys_str_mv | AT kcheng characterizingthemarineiodinecycleanditsrelationshiptooceandeoxygenationinanearthsystemmodel AT aridgwell characterizingthemarineiodinecycleanditsrelationshiptooceandeoxygenationinanearthsystemmodel AT dshardisty characterizingthemarineiodinecycleanditsrelationshiptooceandeoxygenationinanearthsystemmodel |