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Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean

Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean
Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean
The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50°N to 50°S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75–125 mg Chl m?2) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chl a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m?2. The estimated concentration of surface phytoplankton carbon (C) biomass was 5–15 mg C m?2 in the oligotrophic regions and increased over 40 mg C m?2 in richer areas. The deep chlorophyll maximum did not seem to constitute a biomass or productivity maximum, but resulted mainly from an increase in the Chl a to C ratio and represented a relatively small contribution to total integrated productivity. Primary production rates varied from 50 mg C m?2 d?1 at the central gyres to 500–1000 mg C m?2 d?1 in upwelling and higher latitude regions, where faster growth rates () of phytoplankton (>0.5 d?1) were also measured. In oligotrophic waters, microalgal growth was consistently slow [surface averaged 0.21±0.02 d?1 (mean±SE)], representing <20% of maximum expected growth. These results argue against the view that the subtropical gyres are characterized by high phytoplankton turnover rates. The latitudinal variations in were inversely correlated to the changes in the depth of the nitracline and positively correlated to those of the integrated nitrate concentration, supporting the case for the role of nutrients in controlling the large-scale distribution of phytoplankton growth rates. We observed a large degree of temporal variability in the phytoplankton dynamics in the oligotrophic regions: productivity and growth rates varied in excess of 8-fold, whereas microalgal biomass remained relatively constant. The observed spatial and temporal variability in the biomass specific rate of photosynthesis is at least three times larger than currently assumed in most satellite-based models of global productivity.
PHYTOPLANKTON, BIOMASS, BIOLOGICAL PRODUCTION, ATLANTIC OCEAN, GROWTH, CHLOROPHYLL, "JAMES CLARK ROSS", LATITUDINAL VARIATIONS
0967-0637
825-857
Maranon, E.
e0e574e3-c100-4772-a003-4213027c818d
Holligan, P.M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Varela, M.
e3f4b6fb-60b5-4212-a786-1f65120c3c9a
Mourino, B.
e03f18c9-9c81-4af0-a8f1-000c4d0e1f50
Bale, A.J.
e6734bc7-1c57-416e-9338-693d9231e8a8
Maranon, E.
e0e574e3-c100-4772-a003-4213027c818d
Holligan, P.M.
4c1d9d64-dfa7-49bf-9e15-37f891d59b7c
Varela, M.
e3f4b6fb-60b5-4212-a786-1f65120c3c9a
Mourino, B.
e03f18c9-9c81-4af0-a8f1-000c4d0e1f50
Bale, A.J.
e6734bc7-1c57-416e-9338-693d9231e8a8

Maranon, E., Holligan, P.M., Varela, M., Mourino, B. and Bale, A.J. (2000) Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean. Deep Sea Research Part I: Oceanographic Research Papers, 47 (5), 825-857. (doi:10.1016/S0967-0637(99)00087-4).

Record type: Article

Abstract

The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50°N to 50°S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75–125 mg Chl m?2) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chl a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m?2. The estimated concentration of surface phytoplankton carbon (C) biomass was 5–15 mg C m?2 in the oligotrophic regions and increased over 40 mg C m?2 in richer areas. The deep chlorophyll maximum did not seem to constitute a biomass or productivity maximum, but resulted mainly from an increase in the Chl a to C ratio and represented a relatively small contribution to total integrated productivity. Primary production rates varied from 50 mg C m?2 d?1 at the central gyres to 500–1000 mg C m?2 d?1 in upwelling and higher latitude regions, where faster growth rates () of phytoplankton (>0.5 d?1) were also measured. In oligotrophic waters, microalgal growth was consistently slow [surface averaged 0.21±0.02 d?1 (mean±SE)], representing <20% of maximum expected growth. These results argue against the view that the subtropical gyres are characterized by high phytoplankton turnover rates. The latitudinal variations in were inversely correlated to the changes in the depth of the nitracline and positively correlated to those of the integrated nitrate concentration, supporting the case for the role of nutrients in controlling the large-scale distribution of phytoplankton growth rates. We observed a large degree of temporal variability in the phytoplankton dynamics in the oligotrophic regions: productivity and growth rates varied in excess of 8-fold, whereas microalgal biomass remained relatively constant. The observed spatial and temporal variability in the biomass specific rate of photosynthesis is at least three times larger than currently assumed in most satellite-based models of global productivity.

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More information

Published date: 2000
Keywords: PHYTOPLANKTON, BIOMASS, BIOLOGICAL PRODUCTION, ATLANTIC OCEAN, GROWTH, CHLOROPHYLL, "JAMES CLARK ROSS", LATITUDINAL VARIATIONS

Identifiers

Local EPrints ID: 8707
URI: https://eprints.soton.ac.uk/id/eprint/8707
ISSN: 0967-0637
PURE UUID: 34bcf1b2-b143-4b4a-84aa-b5fefabd0b3f

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Date deposited: 25 Aug 2004
Last modified: 15 Jul 2019 19:38

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