Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006).

Harlay, J., Chou, L., De Bodt, C., Van Oostende, N., Piontek, Judith, Engel, Anja , Sabbe, K., Groom, S. and Borges, A. V. (2011) Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006). [Poster] In: EGU General Assembly 2011. , 03.-08.04.2011, Vienna, Austria .

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Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR)
were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the
shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based
on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed
sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the
continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles
of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental
shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom
development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that
triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi)
that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an
indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution
of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the
water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by
integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution
of PP, CAL and DCR to CO2 fluxes in the photic layer, and how they changed from one station to another along
the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net
autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular
production of carbon to sustain the bacterial demand in the photic and aphotic layers.

Document Type: Conference or Workshop Item (Poster)
Keywords: Marine Biology; coccolithophores; diatom bloom; Bay of Biscay;
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Date Deposited: 11 Oct 2011 11:44
Last Modified: 15 Mar 2012 12:31

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