Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers
<p>The Arabian Sea (AS) was confirmed to be a net emitter of <span class="inline-formula">CO<sub>2</sub></span> to the atmosphere during the international Joint Global Ocean Flux Study program of the 1990s, but since then few in situ data have been collected,...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-02-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/19/907/2022/bg-19-907-2022.pdf |
| _version_ | 1819278565333532672 |
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| author | A. de Verneil A. de Verneil Z. Lachkar Z. Lachkar S. Smith S. Smith M. Lévy |
| author_facet | A. de Verneil A. de Verneil Z. Lachkar Z. Lachkar S. Smith S. Smith M. Lévy |
| author_sort | A. de Verneil |
| collection | DOAJ |
| description | <p>The Arabian Sea (AS) was confirmed to be a net emitter of <span class="inline-formula">CO<sub>2</sub></span> to the atmosphere during the international Joint Global Ocean Flux Study program
of the 1990s, but since then few in situ data have been collected, leaving data-based methods to calculate air–sea exchange with fewer and
potentially out-of-date data. Additionally, coarse-resolution models underestimate <span class="inline-formula">CO<sub>2</sub></span> flux compared to other approaches. To address these
shortcomings, we employ a high-resolution (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mn mathvariant="normal">24</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2572dcff9158dffcac416ba9a4f36d1b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-907-2022-ie00001.svg" width="27pt" height="14pt" src="bg-19-907-2022-ie00001.png"/></svg:svg></span></span><span class="inline-formula"><sup>∘</sup></span>) regional model to quantify the seasonal cycle of air–sea <span class="inline-formula">CO<sub>2</sub></span> exchange in the AS
by focusing on two main contributing factors, <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> and winds. We compare the model to available in situ <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> data
and find that uncertainties in dissolved inorganic carbon (DIC) and total alkalinity (TA) lead to the greatest discrepancies. Nevertheless, the model
is more successful than neural network approaches in replicating the large variability in summertime <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> because it captures the
AS's intense monsoon dynamics. In the seasonal <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> cycle, temperature plays the major role in determining surface
<span class="inline-formula"><i>p</i>CO<sub>2</sub></span> except where DIC delivery is important in summer upwelling areas. Since seasonal temperature forcing is relatively uniform,
<span class="inline-formula"><i>p</i>CO<sub>2</sub></span> differences between the AS's subregions are mostly caused by geographic DIC gradients. We find that primary productivity during
both summer and winter monsoon blooms, but also generally, is insufficient to offset the physical delivery of DIC to the surface, resulting in
limited biological control of <span class="inline-formula">CO<sub>2</sub></span> release. The most intense air–sea <span class="inline-formula">CO<sub>2</sub></span> exchange occurs during the summer monsoon when outgassing
rates reach <span class="inline-formula">∼</span> 6 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mol</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">C</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="71pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8c742b0a0f0d6972d9fd8c049585e8a8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-907-2022-ie00002.svg" width="71pt" height="15pt" src="bg-19-907-2022-ie00002.png"/></svg:svg></span></span> in the upwelling regions of Oman and Somalia, but the entire AS contributes <span class="inline-formula">CO<sub>2</sub></span> to the
atmosphere. Despite a regional spring maximum of <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> driven by surface heating, <span class="inline-formula">CO<sub>2</sub></span> exchange rates peak in summer due to
winds, which account for <span class="inline-formula">∼</span> 90 % of the summer <span class="inline-formula">CO<sub>2</sub></span> flux variability vs. 6 % for <span class="inline-formula"><i>p</i>CO<sub>2</sub></span>. In comparison with
other estimates, we find that the AS emits <span class="inline-formula">∼</span> 160 <span class="inline-formula">Tg C yr<sup>−1</sup></span>, slightly higher than previously reported. Altogether, there is
2<span class="inline-formula">×</span> variability in annual flux magnitude across methodologies considered. Future attempts to reduce the variability in estimates will likely
require more in situ carbon data. Since summer monsoon winds are critical in determining flux both directly and indirectly through temperature, DIC,
TA, mixing, and primary production effects on <span class="inline-formula"><i>p</i>CO<sub>2</sub></span>, studies looking to predict <span class="inline-formula">CO<sub>2</sub></span> emissions in the AS with ongoing climate
change will need to correctly resolve their timing, strength, and upwelling dynamics.</p> |
| first_indexed | 2024-12-24T00:14:02Z |
| format | Article |
| id | doaj.art-a93112083f2d4499b7399a107a49525e |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-24T00:14:02Z |
| publishDate | 2022-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-a93112083f2d4499b7399a107a49525e2022-12-21T17:24:49ZengCopernicus PublicationsBiogeosciences1726-41701726-41892022-02-011990792910.5194/bg-19-907-2022Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and driversA. de Verneil0A. de Verneil1Z. Lachkar2Z. Lachkar3S. Smith4S. Smith5M. Lévy6Center for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, UAEArabian Center for Climate and Environmental Sciences, New York University Abu Dhabi, Abu Dhabi, UAECenter for Prototype Climate Modeling, New York University Abu Dhabi, Abu Dhabi, UAEArabian Center for Climate and Environmental Sciences, New York University Abu Dhabi, Abu Dhabi, UAECourant Institute of Mathematical Sciences, New York University, New York, USAArabian Center for Climate and Environmental Sciences, New York University Abu Dhabi, Abu Dhabi, UAESorbonne Université (CNRS/IRD/MNHN), LOCEAN-IPSL, Paris, France<p>The Arabian Sea (AS) was confirmed to be a net emitter of <span class="inline-formula">CO<sub>2</sub></span> to the atmosphere during the international Joint Global Ocean Flux Study program of the 1990s, but since then few in situ data have been collected, leaving data-based methods to calculate air–sea exchange with fewer and potentially out-of-date data. Additionally, coarse-resolution models underestimate <span class="inline-formula">CO<sub>2</sub></span> flux compared to other approaches. To address these shortcomings, we employ a high-resolution (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mn mathvariant="normal">24</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2572dcff9158dffcac416ba9a4f36d1b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-907-2022-ie00001.svg" width="27pt" height="14pt" src="bg-19-907-2022-ie00001.png"/></svg:svg></span></span><span class="inline-formula"><sup>∘</sup></span>) regional model to quantify the seasonal cycle of air–sea <span class="inline-formula">CO<sub>2</sub></span> exchange in the AS by focusing on two main contributing factors, <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> and winds. We compare the model to available in situ <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> data and find that uncertainties in dissolved inorganic carbon (DIC) and total alkalinity (TA) lead to the greatest discrepancies. Nevertheless, the model is more successful than neural network approaches in replicating the large variability in summertime <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> because it captures the AS's intense monsoon dynamics. In the seasonal <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> cycle, temperature plays the major role in determining surface <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> except where DIC delivery is important in summer upwelling areas. Since seasonal temperature forcing is relatively uniform, <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> differences between the AS's subregions are mostly caused by geographic DIC gradients. We find that primary productivity during both summer and winter monsoon blooms, but also generally, is insufficient to offset the physical delivery of DIC to the surface, resulting in limited biological control of <span class="inline-formula">CO<sub>2</sub></span> release. The most intense air–sea <span class="inline-formula">CO<sub>2</sub></span> exchange occurs during the summer monsoon when outgassing rates reach <span class="inline-formula">∼</span> 6 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">mol</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">C</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="71pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8c742b0a0f0d6972d9fd8c049585e8a8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-907-2022-ie00002.svg" width="71pt" height="15pt" src="bg-19-907-2022-ie00002.png"/></svg:svg></span></span> in the upwelling regions of Oman and Somalia, but the entire AS contributes <span class="inline-formula">CO<sub>2</sub></span> to the atmosphere. Despite a regional spring maximum of <span class="inline-formula"><i>p</i>CO<sub>2</sub></span> driven by surface heating, <span class="inline-formula">CO<sub>2</sub></span> exchange rates peak in summer due to winds, which account for <span class="inline-formula">∼</span> 90 % of the summer <span class="inline-formula">CO<sub>2</sub></span> flux variability vs. 6 % for <span class="inline-formula"><i>p</i>CO<sub>2</sub></span>. In comparison with other estimates, we find that the AS emits <span class="inline-formula">∼</span> 160 <span class="inline-formula">Tg C yr<sup>−1</sup></span>, slightly higher than previously reported. Altogether, there is 2<span class="inline-formula">×</span> variability in annual flux magnitude across methodologies considered. Future attempts to reduce the variability in estimates will likely require more in situ carbon data. Since summer monsoon winds are critical in determining flux both directly and indirectly through temperature, DIC, TA, mixing, and primary production effects on <span class="inline-formula"><i>p</i>CO<sub>2</sub></span>, studies looking to predict <span class="inline-formula">CO<sub>2</sub></span> emissions in the AS with ongoing climate change will need to correctly resolve their timing, strength, and upwelling dynamics.</p>https://bg.copernicus.org/articles/19/907/2022/bg-19-907-2022.pdf |
| spellingShingle | A. de Verneil A. de Verneil Z. Lachkar Z. Lachkar S. Smith S. Smith M. Lévy Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers Biogeosciences |
| title | Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers |
| title_full | Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers |
| title_fullStr | Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers |
| title_full_unstemmed | Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers |
| title_short | Evaluating the Arabian Sea as a regional source of atmospheric CO<sub>2</sub>: seasonal variability and drivers |
| title_sort | evaluating the arabian sea as a regional source of atmospheric co sub 2 sub seasonal variability and drivers |
| url | https://bg.copernicus.org/articles/19/907/2022/bg-19-907-2022.pdf |
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