Dissolved inorganic carbon dynamics and air‐sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay)

Abstract

[1] We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the coccolithophore Emiliania huxleyi occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity showed a nonconservative behavior as a function of salinity due to the cumulative effect of net community calcification (NCC) on seawater carbonate chemistry during bloom development. The cumulative effect of NCC and net community production (NCP) on DIC and the partial pressure of CO 2 (pCO 2 ) were evaluated. The decrease of DIC (and increase of pCO 2 ) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO 2 ) due to NCP (NCC:NCP ( 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO 2 (on average ∼−9.7 mmol C m −2 d −1 for the three cruises). The overall effect of NCC in decreasing the CO 2 sink during the cruises was low (on average ∼12% of total air-sea CO 2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the North Atlantic Ocean (where blooms of coccolithophores are the most intense and recurrent), and in the global ocean, then the potential feedback on increasing atmospheric CO 2 of the projected decrease of pelagic calcification due to thermodynamic CO 2 "production" from calcification is probably minor compared to potential feedbacks related to changes of NCP.

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

“…SP1 and SP2). 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.…”

“…Accumulation of these precursors and their subsequent aggregation are responsible for the formation of TEP (Zhou et al, 1998;Passow, 2002a) Even though we observed good congruence between high reflectance patches from remote sensing images and coccolithophore biomass (Fig. 3) Suykens et al, 2010), the lack of correlation between PIC and coccolithophore chl a biomass (Tables 6 and 7) emphasises the temporal and spatial (vertical) decoupling between the accumulation of biomass and the accumulation of coccoliths associated with cells or shed during the calcification phase of the bloom (Beaufort and Heussner, 1999). Interestingly, PIC had accumulated below the pycnocline at certain stations (6-4, 6-4b, 6-7, 6-8, 7-2b, 7-4, 7-5, 8-9, 8-10), which together with the draw-down of total alkalinity by calcification is indicative of prior pelagic calcification (Suykens et al, 2010).…”

“…Table 1). Dotted lines represent the main residual surface circulation (adapted from Suykens et al (2010)). …”

“…1 and Table 1). Near real-time MODIS Aqua remote sensing images were used to track phytoplankton community dynamics through phases of emergence and disintegration of coccolithophorid blooms during the campaigns (see also Suykens et al, 2010 for SeaWIFS images of ths study area). In order to put the campaign periods into context we generated time-series of [chl a], normalised water-leaving radiance at 555 nm (Lwn (555)), and photosynthetically active radiation (PAR) using data from NASA's Giovanni Ocean Color Radiometry 8-day Data Product Visualization portal (http://gdata1.sci.gsfc.nasa.gov/; accessed on January 6th 2011) (Fig.…”

“…We consider blooms of coccolithophores to be a sequence of events when their biomass constitutes a significant portion of the total phytoplankton community, enabling them to influence local biogeochemistry and trophodynamics (Smayda, 1997). These blooms further exhaust nutrients as the water column stratifies and the water mass is advected over the continental shelf, following the general residual circulation in the area (Pingree and Lecann, 1989;Huthnance et al, 2001;Suykens et al, 2010), while dinoflagellates, chrysophytes, prasinophytes and cryptophytes can become increasingly more important. This succession leads to the appearance of high reflectance (HR) patches which are associated with the dissipative stage of coccolithophorid blooms (of Emiliania huxleyi in particular), when coccoliths are shed into the water column, affecting the albedo of the surface water (Westbroek et al, 1993;Harlay et al, 2010).…”