Distribution of calcifying and silicifying phytoplankton in relation to environmental and biogeochemical parameters during the late stages of the 2005 North East Atlantic Spring Bloom

Abstract

Abstract. The late stage of the North East Atlantic (NEA) spring bloom was investigated during June 2005 along a transect section from 45 to 66° N between 15 and 20° W in order to characterize the contribution of siliceous and calcareous phytoplankton groups and describe their distribution in relation to environmental factors. We measured several biogeochemical parameters such as nutrients, surface trace metals, algal pigments, biogenic silica (BSi), particulate inorganic carbon (PIC) or calcium carbonate, particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively), as well as transparent exopolymer particles (TEP). Results were compared with other studies undertaken in this area since the JGOFS NABE program. Characteristics of the spring bloom generally agreed well with the accepted scenario for the development of the autotrophic community. The NEA seasonal diatom bloom was in the late stages when we sampled the area and diatoms were constrained to the northern part of our transect, over the Icelandic Basin (IB) and Icelandic Shelf (IS). Coccolithophores dominated the phytoplankton community, with a large distribution over the Rockall-Hatton Plateau (RHP) and IB. The Porcupine Abyssal Plain (PAP) region at the southern end of our transect was the region with the lowest biomass, as demonstrated by very low chl-a concentrations and a community dominated by picophytoplankton. Early depletion of dissolved silicic acid (DSi) and increased stratification of the surface layer most likely triggered the end of the diatom bloom, leading to coccolithophore dominance. The chronic Si deficiency observed in the NEA could be linked to moderate Fe limitation, which increases the efficiency of the Si pump. TEP closely mirrored the distribution of both biogenic silica at depth and prymnesiophytes in the surface layer suggesting the sedimentation of the diatom bloom in the form of aggregates, but the relative contribution of diatoms and coccolithophores to carbon export in this area still needs to be resolved.

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

“…This is further corroborated by the presence of surface diatom-dominated blooms at stations where drawdown of alkalinity had occurred and PIC had accumulated below the pycnocline, reminiscent of prior coccolithophorid calcification (Table SP5) (Suykens et al, 2010). Furthermore, our findings confirm previous reports (Barlow et al, 1993(Barlow et al, , 2002Gibb et al, 2001;Joint et al, 2001;Lampert et al, 2002;Dandonneau et al, 2006;Leblanc et al, 2009) which show that the late spring blooms in the NE Atlantic are composed of mixed assemblages, dominated by diatoms and coccolithophores, but also with important contributions of prasinophytes and dinoflagellates.…”

“…for the La Chapelle area: SeaWiFS 8-day averaged chl a concentration [2006][2007][2008] between 15 April and 1 May: 1.80 ± 0.54 lg chl a l À1 compared to campaign periods: 0.89 ± 0.17 lg chl a l À1 ). The observed range in surface chl a (0.27-2.31 lg chl a l À1 at chl a maximum) is within the ranges reported by other studies of the NE Atlantic Leblanc et al, 2009;Painter et al, 2010a) or the Bay of Biscay and the Celtic Sea during a similar period as our campaigns (Joint et al, 1986(Joint et al, , 2001Rees et al, 1999;Lampert et al, 2002). There was considerable variation in phytoplankton areal biomass between campaigns (Figs.…”

“…The general scenario for phytoplankton bloom development and species succession in the NE Atlantic (Leblanc et al, 2009 and references therein): the replacement of early spring diatom blooms by coccolithophores, most probably occurs as a result of changing light conditions, mixed layer shoaling, and depletion of dSi levels (Boyd et al, 2010). Our data show that this generally accepted diatom-to-coccolithophore succession scenario is not universal, and that diatom and coccolithophore growth can (Fig.…”

“…Moreover, recent experiments comparing the effect of the incorporation of biogenic minerals from different sources into marine aggregates on their decomposition and sinking velocities have shown that ballasting by carbonate increased sinking velocities and reduced respiration rate compared to aggregates ballasted by opal (Iversen and Ploug, 2010). Leblanc et al (2009) suggested sedimentation of diatoms in the form of aggregates based on the correspondence between TEP and biogenic silica at depth, while they also observed TEP associated with prymnesiophytes in the surface layer. They concluded that the relative contribution of diatoms and coccolithophores to carbon export in the North East Atlantic was still unresolved.…”

“…Spring phytoplankton blooms are a prominent seasonal feature of the North East Atlantic Ocean (NE Atlantic) (Henson et al, 2006) and are characterised by an intense diatom bloom followed by nanoplankton (among others: prymnesiophytes, prasinophytes and cyanobacteria) when first dissolved silicate and then other nutrients become depleted, and increasing water column stratification hinders nutrient replenishment to the euphotic zone (Joint et al, 1986;Lochte et al, 1993;Rees et al, 1999;Raitsos et al, 2006;Leblanc et al, 2009). Especially, coccolithophores are a prominent feature of the late spring bloom, and this has been attributed to their tolerance for high irradiances, lower nutrient requirements and/or ability to utilise organic nitrogen or phosphorus sources (Palenik and Henson, 1997;Leblanc et al, 2009 and references therein).…”