The University of Southampton
University of Southampton Institutional Repository

Phytoplankton distribution and survival in the thermocline

Phytoplankton distribution and survival in the thermocline
Phytoplankton distribution and survival in the thermocline
Observations of the vertical structure of density, concentrations of chlorophyll a and nitrate, and turbulent dissipation rates were made over a period of 25 h in a well-stratified shelf region in the Western English Channel, between neap and spring tides. Maximum turbulent dissipation at the base of the thermocline occurred almost 5 h after maximum tidal currents. This turbulence aids phytoplankton growth by supplying bottom-layer nutrients into the subsurface chlorophyll maximum but reduces phytoplankton concentrations in the thermocline by mixing cells from the base of the subsurface maximum into the bottom mixed layer. The turbulent dissipation observations were used to estimate an average nitrate flux into the thermocline of 2.0 (0.8–3.2, 95% confidence interval) mmol m22d21, which is estimated to have been capable of supporting new phytoplankton growth at a rate of 160 (64–256)mg C m22 d21. Turbulent entrainment of carbon from the base of the subsurface biomass maximum into the bottom mixed layer was observed to be 290 (120–480) mg C m22 d21. This apparent excess export from the chlorophyll maximum is suggested to be a feature of the spring-neap cycle, with export dominating as the tidal turbulence increases toward spring tides and erodes the base of the thermocline. The observed rate of carbon export into the bottom mixed layer could account for as much as 25% of the gross annual primary production in stratifying shelf seas. Such turbulent losses, combined with grazing losses and low light levels, suggest that phytoplankton need to be highly adapted to environmental conditions within the thermocline in order to survive.
0024-3590
486-496
Sharples, Jonanthan
a44dd003-4b00-4e29-a88a-481e9edc1012
Moore, C. Mark
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Rippeth, Tom P.
249bf4a1-2416-4d49-b7a2-e1e2e1196219
Holligan, Patrick M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Hydes, David J.
ac7371d4-c2b9-4926-bb77-ce58480ecff7
Fisher, Neil R.
3ef4856c-4894-4da9-bef6-4160dd76e74d
Simpson, John H.
bcc55ee8-e770-46ad-b3cc-ff38fdc61c57
Sharples, Jonanthan
a44dd003-4b00-4e29-a88a-481e9edc1012
Moore, C. Mark
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Rippeth, Tom P.
249bf4a1-2416-4d49-b7a2-e1e2e1196219
Holligan, Patrick M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Hydes, David J.
ac7371d4-c2b9-4926-bb77-ce58480ecff7
Fisher, Neil R.
3ef4856c-4894-4da9-bef6-4160dd76e74d
Simpson, John H.
bcc55ee8-e770-46ad-b3cc-ff38fdc61c57

Sharples, Jonanthan, Moore, C. Mark, Rippeth, Tom P., Holligan, Patrick M., Hydes, David J., Fisher, Neil R. and Simpson, John H. (2001) Phytoplankton distribution and survival in the thermocline. Limnology and Oceanography, 46 (3), 486-496.

Record type: Article

Abstract

Observations of the vertical structure of density, concentrations of chlorophyll a and nitrate, and turbulent dissipation rates were made over a period of 25 h in a well-stratified shelf region in the Western English Channel, between neap and spring tides. Maximum turbulent dissipation at the base of the thermocline occurred almost 5 h after maximum tidal currents. This turbulence aids phytoplankton growth by supplying bottom-layer nutrients into the subsurface chlorophyll maximum but reduces phytoplankton concentrations in the thermocline by mixing cells from the base of the subsurface maximum into the bottom mixed layer. The turbulent dissipation observations were used to estimate an average nitrate flux into the thermocline of 2.0 (0.8–3.2, 95% confidence interval) mmol m22d21, which is estimated to have been capable of supporting new phytoplankton growth at a rate of 160 (64–256)mg C m22 d21. Turbulent entrainment of carbon from the base of the subsurface biomass maximum into the bottom mixed layer was observed to be 290 (120–480) mg C m22 d21. This apparent excess export from the chlorophyll maximum is suggested to be a feature of the spring-neap cycle, with export dominating as the tidal turbulence increases toward spring tides and erodes the base of the thermocline. The observed rate of carbon export into the bottom mixed layer could account for as much as 25% of the gross annual primary production in stratifying shelf seas. Such turbulent losses, combined with grazing losses and low light levels, suggest that phytoplankton need to be highly adapted to environmental conditions within the thermocline in order to survive.

Text
0486.pdf - Version of Record
Restricted to Repository staff only
Request a copy

More information

Published date: May 2001

Identifiers

Local EPrints ID: 7973
URI: http://eprints.soton.ac.uk/id/eprint/7973
ISSN: 0024-3590
PURE UUID: c4facf7e-62ce-4d4a-94d4-29bdae38087a
ORCID for C. Mark Moore: ORCID iD orcid.org/0000-0002-9541-6046

Catalogue record

Date deposited: 17 Aug 2004
Last modified: 16 Mar 2024 03:10

Export record

Contributors

Author: Jonanthan Sharples
Author: C. Mark Moore ORCID iD
Author: Tom P. Rippeth
Author: Patrick M. Holligan
Author: David J. Hydes
Author: Neil R. Fisher
Author: John H. Simpson

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×