Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system
Model studies suggested that human-induced increase in nutrient load may have stimulated primary production and thus enhanced the CO<sub>2</sub> uptake capacity in the coastal ocean. In this study, we investigated the seasonal variations of the surface water's partial pressure of CO...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2013-06-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/3889/2013/bg-10-3889-2013.pdf |
| _version_ | 1819142436036804608 |
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| author | W.-C. Chou G.-C. Gong W.-J. Cai C.-M. Tseng |
| author_facet | W.-C. Chou G.-C. Gong W.-J. Cai C.-M. Tseng |
| author_sort | W.-C. Chou |
| collection | DOAJ |
| description | Model studies suggested that human-induced increase in nutrient load may have stimulated primary production and thus enhanced the CO<sub>2</sub> uptake capacity in the coastal ocean. In this study, we investigated the seasonal variations of the surface water's partial pressure of CO<sub>2</sub> (<i>p</i>CO<sub>2</sub><sup>sw</sup>) in the highly human-impacted Changjiang–East China Sea system between 2008 and 2011. The seasonality of <i>p</i>CO<sub>2</sub><sup>sw</sup> has large spatial variations, with the largest extreme of 170 ± 75 μatm on the inner shelf near the Changjiang Estuary (from 271 ± 55 μatm in summer to 441 ± 51 μatm in autumn) and the weakest extreme of 53 ± 20 μatm on the outer shelf (from 328 ± 9 μatm in winter to 381 ± 18 μatm in summer). During the summer period, stronger stratification and biological production driven by the eutrophic Changjiang plume results in a very low dissolved inorganic carbon (DIC) in surface waters and a very high DIC in bottom waters of the inner shelf, with the latter returning high DIC to the surface water during the mixed period. Interestingly, a comparison with historical data shows that the average <i>p</i>CO<sub>2</sub><sup>sw</sup> on the inner shelf near the Changjiang Estuary has decreased notably during summer, but has increased during autumn and winter from the 1990s to the 2000s. We suggest that this decadal change is associated with recently increased eutrophication. This would increase both the photosynthetic removal of DIC in surface waters and the respiratory release of DIC in bottom waters during summertime, thereby returning more DIC to the surface during the subsequent mixing seasons and/or episodic extreme weather events (e.g., typhoons). Our finding demonstrates that increasing anthropogenic nutrient delivery from a large river may enhance the sequestration capacity of CO<sub>2</sub> in summer but may reduce it in autumn and winter. Consequently, the coastal ocean may not necessarily take up more atmospheric CO<sub>2</sub> in response to increasing eutrophication, and the net effect largely depends on the relative timescale of air–sea gas exchange and offshore transport of the shelf water. Finally, the case we report for the Changjiang system may have general ramifications for other eutrophic coastal oceans. |
| first_indexed | 2024-12-22T12:10:19Z |
| format | Article |
| id | doaj.art-c89c70844496459293f21e4ede3fdc01 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-22T12:10:19Z |
| publishDate | 2013-06-01 |
| publisher | Copernicus Publications |
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| series | Biogeosciences |
| spelling | doaj.art-c89c70844496459293f21e4ede3fdc012022-12-21T18:26:19ZengCopernicus PublicationsBiogeosciences1726-41701726-41892013-06-011063889389910.5194/bg-10-3889-2013Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea systemW.-C. ChouG.-C. GongW.-J. CaiC.-M. TsengModel studies suggested that human-induced increase in nutrient load may have stimulated primary production and thus enhanced the CO<sub>2</sub> uptake capacity in the coastal ocean. In this study, we investigated the seasonal variations of the surface water's partial pressure of CO<sub>2</sub> (<i>p</i>CO<sub>2</sub><sup>sw</sup>) in the highly human-impacted Changjiang–East China Sea system between 2008 and 2011. The seasonality of <i>p</i>CO<sub>2</sub><sup>sw</sup> has large spatial variations, with the largest extreme of 170 ± 75 μatm on the inner shelf near the Changjiang Estuary (from 271 ± 55 μatm in summer to 441 ± 51 μatm in autumn) and the weakest extreme of 53 ± 20 μatm on the outer shelf (from 328 ± 9 μatm in winter to 381 ± 18 μatm in summer). During the summer period, stronger stratification and biological production driven by the eutrophic Changjiang plume results in a very low dissolved inorganic carbon (DIC) in surface waters and a very high DIC in bottom waters of the inner shelf, with the latter returning high DIC to the surface water during the mixed period. Interestingly, a comparison with historical data shows that the average <i>p</i>CO<sub>2</sub><sup>sw</sup> on the inner shelf near the Changjiang Estuary has decreased notably during summer, but has increased during autumn and winter from the 1990s to the 2000s. We suggest that this decadal change is associated with recently increased eutrophication. This would increase both the photosynthetic removal of DIC in surface waters and the respiratory release of DIC in bottom waters during summertime, thereby returning more DIC to the surface during the subsequent mixing seasons and/or episodic extreme weather events (e.g., typhoons). Our finding demonstrates that increasing anthropogenic nutrient delivery from a large river may enhance the sequestration capacity of CO<sub>2</sub> in summer but may reduce it in autumn and winter. Consequently, the coastal ocean may not necessarily take up more atmospheric CO<sub>2</sub> in response to increasing eutrophication, and the net effect largely depends on the relative timescale of air–sea gas exchange and offshore transport of the shelf water. Finally, the case we report for the Changjiang system may have general ramifications for other eutrophic coastal oceans.http://www.biogeosciences.net/10/3889/2013/bg-10-3889-2013.pdf |
| spellingShingle | W.-C. Chou G.-C. Gong W.-J. Cai C.-M. Tseng Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system Biogeosciences |
| title | Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system |
| title_full | Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system |
| title_fullStr | Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system |
| title_full_unstemmed | Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system |
| title_short | Seasonality of CO<sub>2</sub> in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers: evidence from the Changjiang–East China Sea system |
| title_sort | seasonality of co sub 2 sub in coastal oceans altered by increasing anthropogenic nutrient delivery from large rivers evidence from the changjiang east china sea system |
| url | http://www.biogeosciences.net/10/3889/2013/bg-10-3889-2013.pdf |
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