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Seasonal phosphorus and carbon dynamics in a temperate shelf sea (Celtic Sea)

Seasonal phosphorus and carbon dynamics in a temperate shelf sea (Celtic Sea)
Seasonal phosphorus and carbon dynamics in a temperate shelf sea (Celtic Sea)
The seasonal cycle of resource availability in shelf seas has a strong selective pressure on phytoplankton diversity and the biogeochemical cycling of key elements, such as carbon (C) and phosphorus (P). Shifts in carbon consumption relative to P availability, via changes in cellular stoichiometry for example, can lead to an apparent ‘excess’ of carbon production. We made measurements of inorganic P (Pi) uptake, in parallel to C-fixation, by plankton communities in the Celtic Sea (NW European Shelf) in spring (April 2015), summer (July 2015) and autumn (November 2014). Short-term (<8 h) Pi-uptake coupled with dissolved organic phosphorus (DOP) release, in parallel to net (24 h) primary production (NPP), were all measured across an irradiance gradient designed to typify vertically and seasonally varying light conditions. Rates of Pi-uptake were highest during spring and lowest in the low light conditions of autumn, although biomass-normalised Pi-uptake was highest in the summer. The release of DOP was highest in November and declined to low levels in July, indicative of efficient utilization and recycling of the low levels of Pi available. Examination of daily turnover times of the different particulate pools, including estimates of phytoplankton and bacterial carbon, indicated a differing seasonal influence of autotrophs and heterotrophs in P-dynamics, with summer conditions associated with a strong bacterial influence and the early spring period with fast growing phytoplankton. These seasonal changes in autotrophic and heterotrophic influence, coupled with changes in resource availability (Pi, light) resulted in seasonal changes in the stoichiometry of NPP to daily Pi-uptake (C:P ratio); from relatively C-rich uptake in November and late April, to P-rich uptake in early April and July. Overall, these results highlight the seasonally varying influence of both autotrophic and heterotrophic components of shelf sea ecosystems on the relative uptake of C and P.
0079-6611
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Davis, Clare E.
65fc2085-7fe4-4af4-b4de-32c06d98c8e7
Daniels, Chris J.
aec2572b-e302-4f8e-ab7a-86b8bdf1c155
Mayers, Kyle M.J.
9841ee5d-63fb-441e-a5e7-5b611468723d
Harris, Carolyn
e7ab7f86-a0e8-4940-942c-5a0aeb9d882c
Tarran, Glen A.
218a9233-a6ae-4d0c-a9ca-35ad0d5a35f7
Widdicombe, Claire E.
43b3ea18-b072-4f05-bda8-58a79aaf82ce
Woodward, E. Malcolm S.
3a11b7bf-b110-448a-b1ee-ae1ce7d0fef5
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Davis, Clare E.
65fc2085-7fe4-4af4-b4de-32c06d98c8e7
Daniels, Chris J.
aec2572b-e302-4f8e-ab7a-86b8bdf1c155
Mayers, Kyle M.J.
9841ee5d-63fb-441e-a5e7-5b611468723d
Harris, Carolyn
e7ab7f86-a0e8-4940-942c-5a0aeb9d882c
Tarran, Glen A.
218a9233-a6ae-4d0c-a9ca-35ad0d5a35f7
Widdicombe, Claire E.
43b3ea18-b072-4f05-bda8-58a79aaf82ce
Woodward, E. Malcolm S.
3a11b7bf-b110-448a-b1ee-ae1ce7d0fef5

Poulton, Alex J., Davis, Clare E., Daniels, Chris J., Mayers, Kyle M.J., Harris, Carolyn, Tarran, Glen A., Widdicombe, Claire E. and Woodward, E. Malcolm S. (2017) Seasonal phosphorus and carbon dynamics in a temperate shelf sea (Celtic Sea). Progress in Oceanography. (doi:10.1016/j.pocean.2017.11.001).

Record type: Article

Abstract

The seasonal cycle of resource availability in shelf seas has a strong selective pressure on phytoplankton diversity and the biogeochemical cycling of key elements, such as carbon (C) and phosphorus (P). Shifts in carbon consumption relative to P availability, via changes in cellular stoichiometry for example, can lead to an apparent ‘excess’ of carbon production. We made measurements of inorganic P (Pi) uptake, in parallel to C-fixation, by plankton communities in the Celtic Sea (NW European Shelf) in spring (April 2015), summer (July 2015) and autumn (November 2014). Short-term (<8 h) Pi-uptake coupled with dissolved organic phosphorus (DOP) release, in parallel to net (24 h) primary production (NPP), were all measured across an irradiance gradient designed to typify vertically and seasonally varying light conditions. Rates of Pi-uptake were highest during spring and lowest in the low light conditions of autumn, although biomass-normalised Pi-uptake was highest in the summer. The release of DOP was highest in November and declined to low levels in July, indicative of efficient utilization and recycling of the low levels of Pi available. Examination of daily turnover times of the different particulate pools, including estimates of phytoplankton and bacterial carbon, indicated a differing seasonal influence of autotrophs and heterotrophs in P-dynamics, with summer conditions associated with a strong bacterial influence and the early spring period with fast growing phytoplankton. These seasonal changes in autotrophic and heterotrophic influence, coupled with changes in resource availability (Pi, light) resulted in seasonal changes in the stoichiometry of NPP to daily Pi-uptake (C:P ratio); from relatively C-rich uptake in November and late April, to P-rich uptake in early April and July. Overall, these results highlight the seasonally varying influence of both autotrophic and heterotrophic components of shelf sea ecosystems on the relative uptake of C and P.

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More information

Accepted/In Press date: 1 November 2017
e-pub ahead of print date: 15 November 2017

Identifiers

Local EPrints ID: 417227
URI: http://eprints.soton.ac.uk/id/eprint/417227
ISSN: 0079-6611
PURE UUID: d7191414-e312-4bea-abee-b5117ac3ac7d

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Date deposited: 26 Jan 2018 17:30
Last modified: 27 Apr 2022 07:42

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Contributors

Author: Alex J. Poulton
Author: Clare E. Davis
Author: Chris J. Daniels
Author: Kyle M.J. Mayers
Author: Carolyn Harris
Author: Glen A. Tarran
Author: Claire E. Widdicombe
Author: E. Malcolm S. Woodward

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