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Phytoplankton spring bloom initiation: The impact of atmospheric forcing and light in the temperate North Atlantic Ocean

Phytoplankton spring bloom initiation: The impact of atmospheric forcing and light in the temperate North Atlantic Ocean
Phytoplankton spring bloom initiation: The impact of atmospheric forcing and light in the temperate North Atlantic Ocean
The spring bloom dominates the annual cycle of phytoplankton abundance in large regions of the world oceans. The mechanisms that trigger blooms have been studied for decades, but are still keenly debated, due in part to a lack of data on phytoplankton stocks in winter and early spring. Now however autonomous underwater gliders can provide high-resolution sampling of the upper ocean over inter-seasonal timescales and advance our understanding of spring blooms. In this study, we analyze bio-optical and physical observations collected by gliders at the Porcupine Abyssal Plain observatory site to investigate the impact of atmospheric forcing and light conditions on phytoplankton blooms in the temperate North Atlantic. We contrast three hypotheses for the mechanism of bloom initiation: the critical depth, critical turbulence, and dilution-recoupling hypotheses. Bloom initiation at our study site corresponded to an improvement in growth conditions for phytoplankton (increasing light, decreasing mixing layer depth) and was most consistent with the critical depth hypothesis, with the proviso that mixing depth (rather than mixed layer depth) was considered. After initiation, the observed bloom developed slowly: over several months both depth-integrated inventories and surface concentrations of chlorophyll a increased only by a factor of ~2 and ~3 respectively. We find that periods of convective mixing and high winds in winter and spring can substantially decrease (up to an order of magnitude) light-dependent mean specific growth rate for phytoplankton and prevent the development of rapid, high-magnitude blooms.
0079-6611
102202
Rumyantseva, Anna
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Henson, Stephanie
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Martin, Adrian
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Thompson, Andrew F.
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Damerell, Gillian M.
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Kaiser, Jan
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Heywood, Karen J.
83d91436-76bc-4d55-ae41-9af6a6fc8869
Rumyantseva, Anna
44ccfbcf-2dc4-48ea-86f3-85eb511acac6
Henson, Stephanie
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Martin, Adrian
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Thompson, Andrew F.
ed7c949e-64d9-43a3-833d-43380c8e104d
Damerell, Gillian M.
6ce386a9-11e7-4466-b7a2-2fc280332372
Kaiser, Jan
1f061b70-3cb8-421f-9db2-be14d5a075a2
Heywood, Karen J.
83d91436-76bc-4d55-ae41-9af6a6fc8869

Rumyantseva, Anna, Henson, Stephanie, Martin, Adrian, Thompson, Andrew F., Damerell, Gillian M., Kaiser, Jan and Heywood, Karen J. (2019) Phytoplankton spring bloom initiation: The impact of atmospheric forcing and light in the temperate North Atlantic Ocean. Progress in Oceanography, 178, 102202. (doi:10.1016/j.pocean.2019.102202).

Record type: Article

Abstract

The spring bloom dominates the annual cycle of phytoplankton abundance in large regions of the world oceans. The mechanisms that trigger blooms have been studied for decades, but are still keenly debated, due in part to a lack of data on phytoplankton stocks in winter and early spring. Now however autonomous underwater gliders can provide high-resolution sampling of the upper ocean over inter-seasonal timescales and advance our understanding of spring blooms. In this study, we analyze bio-optical and physical observations collected by gliders at the Porcupine Abyssal Plain observatory site to investigate the impact of atmospheric forcing and light conditions on phytoplankton blooms in the temperate North Atlantic. We contrast three hypotheses for the mechanism of bloom initiation: the critical depth, critical turbulence, and dilution-recoupling hypotheses. Bloom initiation at our study site corresponded to an improvement in growth conditions for phytoplankton (increasing light, decreasing mixing layer depth) and was most consistent with the critical depth hypothesis, with the proviso that mixing depth (rather than mixed layer depth) was considered. After initiation, the observed bloom developed slowly: over several months both depth-integrated inventories and surface concentrations of chlorophyll a increased only by a factor of ~2 and ~3 respectively. We find that periods of convective mixing and high winds in winter and spring can substantially decrease (up to an order of magnitude) light-dependent mean specific growth rate for phytoplankton and prevent the development of rapid, high-magnitude blooms.

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Accepted/In Press date: 2 October 2019
Published date: 10 October 2019

Identifiers

Local EPrints ID: 435603
URI: http://eprints.soton.ac.uk/id/eprint/435603
ISSN: 0079-6611
PURE UUID: 0d6cf4cd-bfd6-417f-9b3a-614593e196f0

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Date deposited: 14 Nov 2019 17:30
Last modified: 25 Nov 2021 23:52

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Contributors

Author: Anna Rumyantseva
Author: Adrian Martin
Author: Andrew F. Thompson
Author: Gillian M. Damerell
Author: Jan Kaiser
Author: Karen J. Heywood

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