A modelling study of temporal and spatial pCO2 variability on the biologically active and temperature-dominated Scotian Shelf
Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air–sea carbon dioxide (CO 2 ) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO 2 , whereas mid- and high-latitude shelves act as net sinks...
| Published in: | Biogeosciences |
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| Main Authors: | , , , , |
| Format: | Text |
| Language: | English |
| Published: |
2021
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/bg-18-6271-2021 https://bg.copernicus.org/articles/18/6271/2021/ |
| Summary: | Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air–sea carbon dioxide (CO 2 ) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO 2 , whereas mid- and high-latitude shelves act as net sinks. Here, we combine a high-resolution regional model with surface water time series and repeat transect observations from the Scotian Shelf, a mid-latitude region in the northwest North Atlantic, to determine what processes are driving the temporal and spatial variability of partial pressure of CO 2 ( p CO 2 ) on a seasonal scale. In contrast to the global trend, the Scotian Shelf acts as a net source. Surface p CO 2 undergoes a strong seasonal cycle with an amplitude of ∼ 200–250 µ atm. These changes are associated with both a strong biological drawdown of dissolved inorganic carbon (DIC) in spring (corresponding to a decrease in p CO 2 of 100–200 µ atm) and pronounced effects of temperature, which ranges from 0 ∘ C in the winter to near 20 ∘ C in the summer, resulting in an increase in p CO 2 of ∼ 200–250 µ atm. Throughout the summer, events with low surface water p CO 2 occur associated with coastal upwelling. This effect of upwelling on p CO 2 is also in contrast to the general assumption that upwelling increases surface p CO 2 by delivering DIC-enriched water to the surface. Aside from these localized events, p CO 2 is relatively uniform across the shelf. Our model agrees with regional observations, reproduces seasonal patterns of p CO 2 , and simulates annual outgassing of CO 2 from the ocean of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M34" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>+</mo><mn mathvariant="normal">1.7</mn><mspace linebreak="nobreak" width="0.125em"/><mo>±</mo><mspace width="0.125em" linebreak="nobreak"/><mn mathvariant="normal">0.2</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="a9a51e3141dd10b574770b6e4d7cd2b8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-6271-2021-ie00001.svg" width="54pt" height="10pt" src="bg-18-6271-2021-ie00001.png"/></svg:svg> mol C m −2 yr −1 for the Scotian Shelf, net uptake of CO 2 by the ocean of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M38" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.5</mn><mspace linebreak="nobreak" width="0.125em"/><mo>±</mo><mspace width="0.125em" linebreak="nobreak"/><mn mathvariant="normal">0.2</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="5622c1f58b382f99f1223b44547710b1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-6271-2021-ie00002.svg" width="54pt" height="10pt" src="bg-18-6271-2021-ie00002.png"/></svg:svg> mol C m −2 yr −1 for the Gulf of Maine, and uptake by the ocean of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M41" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">1.3</mn><mspace linebreak="nobreak" width="0.125em"/><mo>±</mo><mspace linebreak="nobreak" width="0.125em"/><mn mathvariant="normal">0.3</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="ccbbf0cba159b71c4f5c0f34dd895ef0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-6271-2021-ie00003.svg" width="54pt" height="10pt" src="bg-18-6271-2021-ie00003.png"/></svg:svg> mol C m −2 yr −1 for the Grand Banks. |
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