Spatial variability of phytoplankton pigment distributions in the Subtropical South Pacific Ocean: comparison between in situ and predicted data

Abstract

Abstract. In the frame of the BIOSOPE cruise in 2004, the spatial distribution and structure of phytoplankton pigments was investigated along a transect crossing the ultraoligotrophic South Pacific Subtropical Gyre (SPSG) between the Marquesas Archipelago (141 • W-8 • S) and the Chilean upwelling (73 • W-34 • S). A High Performance Liquid Chromatography (HPLC) method was improved in order to be able to accurately quantify pigments over such a large range of trophic levels, and especially from strongly oligotrophic conditions. Seven diagnostic pigments were associated to three phytoplankton size classes (pico-, nano and microphytoplankton). The total chlorophyll-a concentrations [TChla] in surface waters were the lowest measured in the centre of the gyre, reaching 0.017 mg m −3 . Pigment concentrations at the Deep Chlorophyll Maximum (DCM) were generally 10 fold the surface values. Results were compared to predictions from a global parameterisation based on remotely sensed surface [TChla]. The agreement between the in situ and predicted data for such contrasting phytoplankton assemblages was generally good: throughout the oligotrophic gyre system, picophytoplankton (prochlorophytes and cyanophytes) and nanophytoplankton were the dominant classes. Relative bacteriochlorophyll-a concentrations varied around 2%. The transition zone between the Marquesas and the SPSG was also well predicted by the model. However, some regional characteristics have been observed where measured and modelled data differ. Amongst these features is the extreme depth of the DCM (180 m) towards the centre of the gyre, the presence of a deep nanoflagellate population beneath the DCM or the presence of a prochlorophyte-enriched Correspondence to: J. Ras (josephine.ras@obs-vlfr.fr) population in the formation area of the high salinity South Pacific Tropical Water. A coastal site sampled in the eutrophic upwelling zone, characterised by recently upwelled water, was significantly and unusually enriched in picoeucaryotes, in contrast with an offshore upwelling site where a more typical senescent diatom population prevailed.

Variability in optical particle backscattering in contrasting bio‐optical oceanic regimes

“…Particles are collected onto 25-mm Whatman glassfiber filters GF/F (0.7-mm porosity) and then stored in liquid nitrogen, until algae pigment contents are measured in the laboratory using HPLC, following the method of Ras et al (2008). The total chlorophyll a concentration ( [Chl]) is computed as the sum of the concentrations of Chl a (including allomers and epimers), chlorophyllide a plus divinyl Chl a.…”

Shellfish Aquaculture from Space: Potential of Sentinel2 to Monitor Tide-Driven Changes in Turbidity, Chlorophyll Concentration and Oyster Physiological Response at the Scale of an Oyster Farm

“…The filters were frozen in liquid nitrogen and shipped for analysis at LOV, where HPLC analysis was performed according to Ras et al (2008). The total chlorophyll a (chl a) concentration was computed as the sum of the "true" chlorophyll a, divinylchlorophyll a, and chlorophyllide a.…”

Characterization of the bio-optical anomaly and diurnal variability of particulate matter, as seen from scattering and backscattering coefficients, in ultra-oligotrophic eddies of the Mediterranean Sea

“…Photosynthetic pigment (including total chlorophylla, TChl-a = chlorophyll-a + divinyl chlorophylla + chlorophyllide-a mg m −3 ) concentrations were measured at discrete depths collected from Niskin bottles (1 to 2.5 L) by High Performance Liquid Chromatography (HPLC) following the methodology described in Ras et al (2008). The relative proportion of pico-, nano-and microphytoplankton was computed using the chemotaxonomic pigment ratios described in Vidussi et al (2001) recently updated by Uitz et al (2006).…”