Size-fractionated phytoplankton biomass and production in the tropical Atlantic

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.Keywords: phytoplankton, cell size, spatial variability, oligotrophic subtropical gyres, primary production, biomass.RESUMEN: Biomasa y producción en diferentes clases de tamaño de fitoplancton en el Atlántico tropical.-Se realizaron dos transectos latitudinales en el Atlántico tropical y subtropical para describir (i) la variabilidad espacial de la concentración de clorofila a (chl a) y de la producción primaria total y fraccionada en clases de tamaño de fitoplancton (picofitoplancton y fitoplancton >2 mm), (ii) la contribución relativa de cada clase de tamaño a la biomasa y fijación de carbono total, y (iii) la variabilidad espacial de la tasa de crecimiento (P/B) y del número de asimilación (P/chl a) para cada clase de tamaño en el océano. Las dos clases de tamaño consideradas presentaron la máxima chl a en el afloramiento ecuatorial y la mínima en la capa de mezcla del giro oligotrófico del Atlántico Sur. Se encontró un patrón similar en el caso de la fijación de carbono. En el giro oligotrófico del Atlántico Sur la mayor contribución del picofitoplancton a la producción total se registró en torno al máximo profundo de clorofila, mientras que la contribución de la fracción >2 mm fue mayor en la capa de mezcla. Además, la contribución relativa del fitoplancton >2 mm a la producción primaria total fue mayor que su contribución a la biomasa total. Ambas clases de tamaño presentaron máximos valores de P/B y P/chl a en las aguas superficiales del afloramiento ecuatorial. En el giro oligotrófico del Atlántico Sur la fracción de fitoplancto...

Phytoplankton Growth and Microzooplankton Grazing in the Subtropical Northeast Atlantic

“…[18], [43], [44]). Also, similar phytoplankton growth rates have been reported in the Subtropical Pacific using the 14 C method [45], [46], although the rates reported here were greater than most of the 14 C estimates reported in the NAST-E region [47], [48], [49]. Consequently, our pNPP estimates were also higher.…”

“…Slightly higher metabolic rates for the large phytoplankton were also reached in these latitudes by using the 14 C method [50], although similar [48], or even lower rates [49] were observed using the 14 C method too. McCarthy and Goldman [53] suggested the existence of microscale nutrient patches resulting from zooplankton excretion and degradation of particulate organic matter.…”

Temporal variability in total, micro- and nano-phytoplankton primary production at a coastal site in the Western English Channel

“…However, nano-and pico-phytoplankton appear to have relatively low biomass at station L4 (Tarran and Bruun, 2015), but significantly higher photosynthetic efficiency likely yielding higher photosynthetic rates (Barnes et al, 2014). Previous studies have reported pico-phytoplankton biomass and production to be consistently low and much less variable than larger size classes (Uitz et al, 2010), only contributing high proportions of productivity in oligotrophic gyres (Maranon et al, 2001;Moreno-Ostos et al, 2011). Nano-phytoplankton on the other hand often enhance production particularly in coastal upwelling regions (Hirata et al, 2009;Tilstone et al, 1999), due to a higher efficiency of light utilisation (Tilstone et al, 1999).…”

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…Plankton community structure is variable across space (tens of meters to ocean basins) and time (hours to decadal time scales), and may be a major factor determining the magnitudes of production rates and carbon export, and thus the efficiency of the biological carbon pump in sequestering carbon to the deep ocean [Karl et al 2001, 2012, Vaillancourt et al 2003, Richardson and Jackson 2007, Henson et al 2012. Investigators have described correlations of community structures with patterns of primary production and carbon export in a variety of nutrient regimes [Pollard et al 2009, Moreno-Ostos et al 2011, Cassar et al 2015. Transition regions at gyre edges between higher and lower nutrient regimes can be zones of high biomass and intensified production , Ostle et al 2015 with unique phytoplankton communities distinct from the regions to either side [Kavanaugh et al 2014a, Palevsky et al 2013, Ribalet et al 2010.…”