Size-fractionated phytoplankton biomass and production in the tropical Atlantic

Enrique Moreno-Ostos,Xosé Anxelu G Morán,Emilio Marañón,Beatriz Mouriño-Carballido,María Huete-Ortega,Alejandra Calvo-Díaz,Ana Fernández

doi:10.3989/scimar.2011.75n2379

Enrique Moreno-Ostos, Xosé Anxelu G Morán + Show 5 more

Open Access

https://doi.org/10.3989/scimar.2011.75n2379

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Journal: Scientia Marina	Publication Date: Nov 8, 2010
Citations: 32	License type: cc-by

Affiliation: Universidade de Vigo

Abstract

SUMMARY: Two meridional transects were conducted in the tropical and subtropical Atlantic to describe (i) the spatial variability of total and size-fractionated (picophytoplankton and phytoplankton >2 mm) chlorophyll a (chl a) concentration and primary production, (ii) the relative contribution of each phytoplankton size fraction to total biomass and carbon fixation, and (iii) the spatial variability of size-fractionated phytoplankton growth rate (P/B) and assimilation number (P/chl a) in the ocean. The highest chl a for both size fractions was observed in the Western Tropical Atlantic province (WTRA), while the lowest chl a was found in the upper mixed layer (UML) of the South Atlantic Tropical gyre (SATL). A similar pattern was found for carbon fixation. Within the SATL, the highest picophytoplankton contribution to total production was recorded at the Deep Chlorophyll Maximum (DCM), while the contribution of phytoplankton >2 mm was higher in the UML. Additionally, the relative contribution of large phytoplankton to total integrated primary production was higher than its contribution to total biomass. Both size fractions depicted maximum P/B and P/chl a in WTRA surface waters. In the SATL province, phytoplankton >2 mm showed the highest P/B and P/chl a along the UML, while picophytoplankton P/B and P/chl a peaked around the DCM. We suggest that the differential impact of light on small and large phytoplankton may help to explain the contrasting dynamics of the two size classes.

Highlights

A full understanding of carbon cycling in the open ocean requires a detailed knowledge of the spatial and temporal variability of phytoplankton biomass and primary production
The highest chl a for both size fractions was observed in the Western Tropical Atlantic province (WTRA), while the lowest chl a was found in the upper mixed layer (UML) of the South Atlantic Tropical gyre (SATL)
Within the SATL, the highest picophytoplankton contribution to total production was recorded at the Deep Chlorophyll Maximum (DCM), while the contribution of phytoplankton >2 mm was higher in the UML

Summary

Introduction

A full understanding of carbon cycling in the open ocean requires a detailed knowledge of the spatial and temporal variability of phytoplankton biomass and primary production. Marañón et al (2001) described the main patterns of size-fractionated chl a and carbon fixation in the Atlantic Ocean and showed a marked discrepancy between the relative contribution of picophytoplankton to total chl a and primary production, in the oligotrophic gyres (see Teira et al, 2005). In these ecological domains, the relative contribution of picophytoplankton to total carbon incorporation was lower than its relative contribution to total chl a. It has been demonstrated that solar radiation induces considerable cell damage and mortality in the subtropical Atlantic (Llabrés and Agustí, 2006; Agustí and Llabrés, 2007), and Teira et al (2005) hypothesized that a considerable fraction of the picophytoplankton biomass should correspond to damaged and non-viable cells, resulting in discrepancies between their contribution to biomass and carbon fixation

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