Effect of enhanced <i>p</i>CO<sub>2</sub> 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 <i>p</i>CO<sub>2</sub> 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 accu...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-07-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/3695/2014/bg-11-3695-2014.pdf |
| Summary: | It has been proposed that increasing levels of <i>p</i>CO<sub>2</sub> 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 <i>p</i>CO<sub>2</sub> scenarios (ambient, 550,
750 and 1000 μatm) 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 <i>p</i>CO<sub>2</sub> on
DOC production. There was a significant but highly variable effect of <i>p</i>CO<sub>2</sub>
on the production of TEPs. In three of the five experiments, variation of
TEP production between <i>p</i>CO<sub>2</sub> treatments was caused by the effect of <i>p</i>CO<sub>2</sub> 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
<i>p</i>CO<sub>2</sub> (twice as much production over the 96 h incubation period in the 750 μatm
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 <i>p</i>CO<sub>2</sub> perturbations. |
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| ISSN: | 1726-4170 1726-4189 |