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Effect of enhanced pCO2 levels on the production of dissolved organic carbon and transparent exopolymer particles in short-term bioassay experiments

Effect of enhanced pCO2 levels on the production of dissolved organic carbon and transparent exopolymer particles in short-term bioassay experiments
Effect of enhanced pCO2 levels on the production of dissolved organic carbon and transparent exopolymer particles in short-term bioassay experiments
It has been proposed that increasing levels of pCO2 in the surface ocean will lead to more partitioning of the organic carbon fixed by marine primary production into the dissolved rather than the particulate fraction. This process may result in enhanced accumulation of dissolved organic carbon (DOC) in the surface ocean and/or concurrent accumulation of transparent exopolymer particles (TEPs), with important implications for the functioning of the marine carbon cycle. We investigated this in shipboard bioassay experiments that considered the effect of four different pCO2 scenarios (ambient, 550, 750 and 1000 ?atm) on unamended natural phytoplankton communities from a range of locations in the northwest European shelf seas. The environmental settings, in terms of nutrient availability, phytoplankton community structure and growth conditions, varied considerably between locations. We did not observe any strong or consistent effect of pCO2 on DOC production. There was a significant but highly variable effect of pCO2 on the production of TEPs. In three of the five experiments, variation of TEP production between pCO2 treatments was caused by the effect of pCO2 on phytoplankton growth rather than a direct effect on TEP production. In one of the five experiments, there was evidence of enhanced TEP production at high pCO2 (twice as much production over the 96 h incubation period in the 750 ?atm treatment compared with the ambient treatment) independent of indirect effects, as hypothesised by previous studies. Our results suggest that the environmental setting of experiments (community structure, nutrient availability and occurrence of phytoplankton growth) is a key factor determining the TEP response to pCO2 perturbations.
1726-4170
3695-3706
MacGilchrist, G.A.
f1871abd-06a3-4412-acab-06d98fb98533
Shi, T.
266bd42e-7d15-4656-95c1-ef59522a93ef
Tyrrell, T.
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Richier, S.
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Moore, C.M.
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Dumousseaud, C.
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Achterberg, E.P.
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MacGilchrist, G.A.
f1871abd-06a3-4412-acab-06d98fb98533
Shi, T.
266bd42e-7d15-4656-95c1-ef59522a93ef
Tyrrell, T.
6808411d-c9cf-47a3-88b6-c7c294f2d114
Richier, S.
0fc0b375-6918-4c06-9d6f-229f6c4046ca
Moore, C.M.
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Dumousseaud, C.
31cc4879-0d45-4674-8eba-93105ee25c2e
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9

MacGilchrist, G.A., Shi, T., Tyrrell, T., Richier, S., Moore, C.M., Dumousseaud, C. and Achterberg, E.P. (2014) Effect of enhanced pCO2 levels on the production of dissolved organic carbon and transparent exopolymer particles in short-term bioassay experiments. Biogeosciences, 11 (13), 3695-3706. (doi:10.5194/bg-11-3695-2014).

Record type: Article

Abstract

It has been proposed that increasing levels of pCO2 in the surface ocean will lead to more partitioning of the organic carbon fixed by marine primary production into the dissolved rather than the particulate fraction. This process may result in enhanced accumulation of dissolved organic carbon (DOC) in the surface ocean and/or concurrent accumulation of transparent exopolymer particles (TEPs), with important implications for the functioning of the marine carbon cycle. We investigated this in shipboard bioassay experiments that considered the effect of four different pCO2 scenarios (ambient, 550, 750 and 1000 ?atm) on unamended natural phytoplankton communities from a range of locations in the northwest European shelf seas. The environmental settings, in terms of nutrient availability, phytoplankton community structure and growth conditions, varied considerably between locations. We did not observe any strong or consistent effect of pCO2 on DOC production. There was a significant but highly variable effect of pCO2 on the production of TEPs. In three of the five experiments, variation of TEP production between pCO2 treatments was caused by the effect of pCO2 on phytoplankton growth rather than a direct effect on TEP production. In one of the five experiments, there was evidence of enhanced TEP production at high pCO2 (twice as much production over the 96 h incubation period in the 750 ?atm treatment compared with the ambient treatment) independent of indirect effects, as hypothesised by previous studies. Our results suggest that the environmental setting of experiments (community structure, nutrient availability and occurrence of phytoplankton growth) is a key factor determining the TEP response to pCO2 perturbations.

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Published date: 10 July 2014
Organisations: Ocean and Earth Science

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Local EPrints ID: 366907
URI: http://eprints.soton.ac.uk/id/eprint/366907
ISSN: 1726-4170
PURE UUID: dec685ee-eabf-4f1a-8766-1239c939e8ba
ORCID for T. Tyrrell: ORCID iD orcid.org/0000-0002-1002-1716

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Date deposited: 14 Jul 2014 13:18
Last modified: 20 Jul 2019 01:17

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