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Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation

Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation
Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation
Photosynthetic CO2 uptake by oceanic phytoplankton and subsequent export of particulate organic carbon (POC) to the ocean interior comprises a globally significant biological carbon pump, controlled in part by the composition of the planktonic community. The strength and efficiency of this pump depends upon the balance of particle production in the euphotic zone and remineralization of those particles in the mesopelagic (defined here as depths between 150 and 300 m), but how these processes respond to climate-driven changes in the physical environment is not completely understood. In the Sargasso Sea, from ~1996–2007, we have observed a decade-long >50% increase in euphotic zone integrated autotrophic biomass (estimated from chlorophyll TChl-?), prokaryotic phytoplankton, primary production and shallow (150 m) POC export coinciding with a shift in the mean phase of the winter North Atlantic Oscillation (NAO) from consistently positive to neutral but variable. During this same period mesopelagic POC flux attenuation has doubled such that carbon sequestration below 300 m, the maximum winter/spring ventilation depth, has not changed. The increased mesopelagic POC attenuation appears mediated by changes in plankton community composition and metabolic activity in both the euphotic and mesopelagic zones. These changes are counter to extant hypotheses regarding inter-relationships between phytoplankton community composition, productivity and carbon export, and have significant impacts on how the Sargasso Sea ecosystem, at least, is modeled. Moreover, these time-series observations suggest that processes in the euphotic zone and mesopelagic are tightly coupled and should be considered together in future research.
1726-4170
57-70
Lomas, M.W.
84d523c2-4876-41d4-a160-f32c69b7c7c8
Steinberg, D.K.
a13f5f83-79e6-4982-ae05-49c8fd563595
Dickey, T.
95682138-1648-45a0-91e9-25392d63bdb1
Carlson, C.A.
d731df3d-5e0b-4a3b-a4b2-69befb08882c
Nelson, N.B.
f73fc726-e932-4e18-8e21-9cd2d24e479a
Condon, R.H.
74397bb5-f312-4f8e-aa4a-636c4df0ac1f
Bates, N.R.
954a83d6-8424-49e9-8acd-e606221c9c57
Lomas, M.W.
84d523c2-4876-41d4-a160-f32c69b7c7c8
Steinberg, D.K.
a13f5f83-79e6-4982-ae05-49c8fd563595
Dickey, T.
95682138-1648-45a0-91e9-25392d63bdb1
Carlson, C.A.
d731df3d-5e0b-4a3b-a4b2-69befb08882c
Nelson, N.B.
f73fc726-e932-4e18-8e21-9cd2d24e479a
Condon, R.H.
74397bb5-f312-4f8e-aa4a-636c4df0ac1f
Bates, N.R.
954a83d6-8424-49e9-8acd-e606221c9c57

Lomas, M.W., Steinberg, D.K., Dickey, T., Carlson, C.A., Nelson, N.B., Condon, R.H. and Bates, N.R. (2010) Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation. Biogeosciences, 7 (1), 57-70. (doi:10.5194/bg-7-57-2010).

Record type: Article

Abstract

Photosynthetic CO2 uptake by oceanic phytoplankton and subsequent export of particulate organic carbon (POC) to the ocean interior comprises a globally significant biological carbon pump, controlled in part by the composition of the planktonic community. The strength and efficiency of this pump depends upon the balance of particle production in the euphotic zone and remineralization of those particles in the mesopelagic (defined here as depths between 150 and 300 m), but how these processes respond to climate-driven changes in the physical environment is not completely understood. In the Sargasso Sea, from ~1996–2007, we have observed a decade-long >50% increase in euphotic zone integrated autotrophic biomass (estimated from chlorophyll TChl-?), prokaryotic phytoplankton, primary production and shallow (150 m) POC export coinciding with a shift in the mean phase of the winter North Atlantic Oscillation (NAO) from consistently positive to neutral but variable. During this same period mesopelagic POC flux attenuation has doubled such that carbon sequestration below 300 m, the maximum winter/spring ventilation depth, has not changed. The increased mesopelagic POC attenuation appears mediated by changes in plankton community composition and metabolic activity in both the euphotic and mesopelagic zones. These changes are counter to extant hypotheses regarding inter-relationships between phytoplankton community composition, productivity and carbon export, and have significant impacts on how the Sargasso Sea ecosystem, at least, is modeled. Moreover, these time-series observations suggest that processes in the euphotic zone and mesopelagic are tightly coupled and should be considered together in future research.

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Published date: 5 January 2010
Organisations: Ocean Biochemistry & Ecosystems

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Local EPrints ID: 357362
URI: http://eprints.soton.ac.uk/id/eprint/357362
ISSN: 1726-4170
PURE UUID: f79b1bda-8b17-4e86-9aa2-a8bb417b929c

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Date deposited: 24 Sep 2013 12:46
Last modified: 14 Mar 2024 14:58

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Contributors

Author: M.W. Lomas
Author: D.K. Steinberg
Author: T. Dickey
Author: C.A. Carlson
Author: N.B. Nelson
Author: R.H. Condon
Author: N.R. Bates

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