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Basin-wide mechanisms for spring bloom initiation; how typical is the North Atlantic?

Basin-wide mechanisms for spring bloom initiation; how typical is the North Atlantic?
Basin-wide mechanisms for spring bloom initiation; how typical is the North Atlantic?
The annual phytoplankton bloom is a key event in pelagic ecosystems. Variability in the timing, or phenology, of these blooms affects ecosystem dynamics with implications for carbon export efficiency and food availability for higher trophic levels. Furthermore, interannual variability in phytoplankton bloom timing may be used to monitor changes in the pelagic ecosystem that are either naturally or anthropogenically forced. The onset of the spring bloom has traditionally been thought to be controlled by the restratification of the water column and shoaling of the mixed layer, as encapsulated in Sverdrup's critical depth hypothesis. However, this has been challenged by recent studies which have put forward different mechanisms. For example, the critical turbulence hypothesis attributes bloom initiation to a reduction in turbulent mixing associated with the onset of positive net heat fluxes (NHFs). To date, the majority of studies on bloom initiation mechanisms have concentrated on North Atlantic datasets leaving their validity in other subpolar regions unknown. Here, we use chlorophyll output from a model that assimilates satellite ocean colour data to calculate bloom initiation timing and examine the basin-wide drivers of spatial and interannual variability. We find that the date that the NHF turns positive is a stronger predictor for the date of bloom initiation, both spatially and interannually, across the North Atlantic than changes in the mixed layer depth. However, results obtained from the North Pacific and Southern Ocean show no such basin-wide coherency. The lack of consistency in the response of the subpolar basins indicates that other drivers are likely responsible for variability in bloom initiation. This disparity between basins suggests that the North Atlantic bloom initiation processes are unique and therefore that this region may not be a suitable model for a global, theoretical understanding of the mechanisms leading to the onset of the spring bloom.
bloom initiation, critical depth, critical turbulence, phytoplankton phenology
1054-3139
2029-2040
Cole, Harriet
7e6479d0-4450-483c-a723-20f5e99fa515
Henson, Stephanie
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Martin, Adrian
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Yool, Andrew
882aeb0d-dda0-405e-844c-65b68cce5017
Cole, Harriet
7e6479d0-4450-483c-a723-20f5e99fa515
Henson, Stephanie
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Martin, Adrian
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Yool, Andrew
882aeb0d-dda0-405e-844c-65b68cce5017

Cole, Harriet, Henson, Stephanie, Martin, Adrian and Yool, Andrew (2015) Basin-wide mechanisms for spring bloom initiation; how typical is the North Atlantic? ICES Journal of Marine Science, 72 (6), 2029-2040. (doi:10.1093/icesjms/fsu239).

Record type: Article

Abstract

The annual phytoplankton bloom is a key event in pelagic ecosystems. Variability in the timing, or phenology, of these blooms affects ecosystem dynamics with implications for carbon export efficiency and food availability for higher trophic levels. Furthermore, interannual variability in phytoplankton bloom timing may be used to monitor changes in the pelagic ecosystem that are either naturally or anthropogenically forced. The onset of the spring bloom has traditionally been thought to be controlled by the restratification of the water column and shoaling of the mixed layer, as encapsulated in Sverdrup's critical depth hypothesis. However, this has been challenged by recent studies which have put forward different mechanisms. For example, the critical turbulence hypothesis attributes bloom initiation to a reduction in turbulent mixing associated with the onset of positive net heat fluxes (NHFs). To date, the majority of studies on bloom initiation mechanisms have concentrated on North Atlantic datasets leaving their validity in other subpolar regions unknown. Here, we use chlorophyll output from a model that assimilates satellite ocean colour data to calculate bloom initiation timing and examine the basin-wide drivers of spatial and interannual variability. We find that the date that the NHF turns positive is a stronger predictor for the date of bloom initiation, both spatially and interannually, across the North Atlantic than changes in the mixed layer depth. However, results obtained from the North Pacific and Southern Ocean show no such basin-wide coherency. The lack of consistency in the response of the subpolar basins indicates that other drivers are likely responsible for variability in bloom initiation. This disparity between basins suggests that the North Atlantic bloom initiation processes are unique and therefore that this region may not be a suitable model for a global, theoretical understanding of the mechanisms leading to the onset of the spring bloom.

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More information

Accepted/In Press date: December 2014
Published date: July 2015
Keywords: bloom initiation, critical depth, critical turbulence, phytoplankton phenology
Organisations: Marine Systems Modelling, Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 372547
URI: http://eprints.soton.ac.uk/id/eprint/372547
ISSN: 1054-3139
PURE UUID: fa82c7af-cb9e-4aaf-8718-1afa0eb6e289

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Date deposited: 08 Dec 2014 16:20
Last modified: 08 Jan 2022 06:16

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Contributors

Author: Harriet Cole
Author: Adrian Martin
Author: Andrew Yool

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