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Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community

Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community
Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community
Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, the response of plankton communities to elevated CO2 has been studied primarily during nutrient-stimulated blooms. In this CO2 manipulation study, we used large-volume (~ 55 m3) pelagic in situ mesocosms to enclose a natural summer, post-spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. The carbonate system in the six mesocosms was manipulated to yield average fCO2 ranging between 365 and ~ 1230 ?atm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of 7 weeks. We observed higher sustained chlorophyll a and particulate matter concentrations (~ 25 % higher) and lower inorganic phosphate concentrations in the water column in the highest fCO2 treatment (1231 ?atm) during the final 2 weeks of the study period (Phase III), when there was low net change in particulate and dissolved matter pools. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 ?m) and were already established early in the experiment during an initial warm and more productive period with overall elevated chlorophyll a and particulate matter concentrations. However, the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III, when the contribution of the small size fraction (< 2 ?m) increased to up to 90 % of chlorophyll a. In this phase, a CO2-driven increase in water column particulate carbon did not lead to enhanced sinking material flux but was instead reflected in increased dissolved organic carbon concentrations. Hence ocean acidification may induce changes in organic matter partitioning in the upper water column during the low-nitrogen summer period in the Baltic Sea.
1726-4170
6181-6203
Paul, A.J.
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Bach, L.T.
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Schulz, K.-G.
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Boxhammer, T.
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Czerny, J.
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Achterberg, E.P.
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Hellemann, D.
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Trense, Y.
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Nausch, M.
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Sswat, M.
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Riebesell, U.
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Paul, A.J.
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Bach, L.T.
a0e7a67a-74c6-479c-9d9f-a1242c7fd2d5
Schulz, K.-G.
89e25f7c-0143-42c7-88c1-c9267a101ed5
Boxhammer, T.
dfacb1fd-b1c6-42e9-8270-74d2adf3f560
Czerny, J.
badf867d-4636-49fe-b7af-2bcabe24ae32
Achterberg, E.P.
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Hellemann, D.
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Trense, Y.
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Nausch, M.
46010a69-e91a-418c-afa8-266a09008006
Sswat, M.
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Riebesell, U.
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Paul, A.J., Bach, L.T., Schulz, K.-G., Boxhammer, T., Czerny, J., Achterberg, E.P., Hellemann, D., Trense, Y., Nausch, M., Sswat, M. and Riebesell, U. (2015) Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community. Biogeosciences, 12 (20), 6181-6203. (doi:10.5194/bg-12-6181-2015).

Record type: Article

Abstract

Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, the response of plankton communities to elevated CO2 has been studied primarily during nutrient-stimulated blooms. In this CO2 manipulation study, we used large-volume (~ 55 m3) pelagic in situ mesocosms to enclose a natural summer, post-spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. The carbonate system in the six mesocosms was manipulated to yield average fCO2 ranging between 365 and ~ 1230 ?atm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of 7 weeks. We observed higher sustained chlorophyll a and particulate matter concentrations (~ 25 % higher) and lower inorganic phosphate concentrations in the water column in the highest fCO2 treatment (1231 ?atm) during the final 2 weeks of the study period (Phase III), when there was low net change in particulate and dissolved matter pools. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 ?m) and were already established early in the experiment during an initial warm and more productive period with overall elevated chlorophyll a and particulate matter concentrations. However, the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III, when the contribution of the small size fraction (< 2 ?m) increased to up to 90 % of chlorophyll a. In this phase, a CO2-driven increase in water column particulate carbon did not lead to enhanced sinking material flux but was instead reflected in increased dissolved organic carbon concentrations. Hence ocean acidification may induce changes in organic matter partitioning in the upper water column during the low-nitrogen summer period in the Baltic Sea.

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Published date: 28 October 2015
Organisations: Ocean and Earth Science

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Local EPrints ID: 385316
URI: http://eprints.soton.ac.uk/id/eprint/385316
ISSN: 1726-4170
PURE UUID: 1fba33d7-a6f2-4592-9df2-36fcbc0e6bf9

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Date deposited: 22 Dec 2015 13:21
Last modified: 09 Jan 2022 02:21

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Contributors

Author: A.J. Paul
Author: L.T. Bach
Author: K.-G. Schulz
Author: T. Boxhammer
Author: J. Czerny
Author: E.P. Achterberg
Author: D. Hellemann
Author: Y. Trense
Author: M. Nausch
Author: M. Sswat
Author: U. Riebesell

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