Biogeochemistry of a late
Biogeochemistry of a late
coccolithophorid
coccolithophorid
bloom
bloom
at the continental margin of the Bay of Biscay
at the continental margin of the Bay of Biscay
J. Harlay
1, C. De Bodt
1, Q. d’Hoop
1, N. Roevros
1, A.V. Borges
2, B. Delille
2, K. Suykens
2, N. Van Oostende
3,
K. Sabbe
3, J. Piontek
4, N. Händel
4, S. Schmidt
5, S. Groom
6, A. Engel
4, and L. Chou
11Laboratoire d’Océanographie Chimique et Géochimie des Eaux (LOCGE), Université Libre de Bruxelles (ULB), B-1050 Brussels, Belgium
2Unité d’Océanographie Chimique, Université de Liège (ULg), B-4000, Liège, Belgium
3Protistologie & Aquatische Ecologie, Universiteit Gent (UG), B-9000, Gent, Belgium
4'Global change and the future marine carbon cycle', Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, Germany
5Environnements et Paléoenvironnements Océaniques (UMR 5805 EPOC – OASU), Université Bordeaux 1, F-33405 Talence, France
6Remote Sensing Group, Plymouth Marine Laboratory, Plymouth, United-Kingdom
jharlay@ulb.ac.be
Our results provide an original dataset on TEP within a natural population of the coccolithophore Emiliania huxleyi, during its exponential and calcifying growth phases.
Two methods were used to characterize the TEP in this study. TEPmicro refers to the
microscopic enumeration and size distribution of particles while TEPcolorcorresponds to
colorimetric measurements calibrated with gum Xanthan.
TEPcolorcould reach values exceeding 2000 µgXeq l-1 in surface at St 2 and St 1bis, corresponding to the higher range of concentrations observed during oceanic blooms.
The study of the size spectrum of TEPmicroindicated that the TEP (0.1-1 ppm volume
fraction) were small and equally distributed over the depths analyzed.
When converted into carbon units and compared to POC (Fig. 3) the two approaches give similar results and TEP-C could contribute to 1-5 % of the POC. Discrepancies may reflect either changes in chemical composition of TEP (polysaccharides, non-TEP inclusions), or changes in the intrinsic structure of TEP (aggregation). The potential for particle
aggregation can be observed at depth at St 7, where TEPmicro-C:POC increased
independently from TEPcolor-C. In contrast, the individual cells, coated with highly stainable
polysaccharides, probably contribute to the bulk TEPcolor-C in surface at St 2.
Background:
Coccolithophores, among which Emiliania huxleyi is a major species, are minute phytoplantonic organisms capable of producing large amounts of calcium carbonate as well as particulate organic carbon (POC). The presence of abundant suspended minute calcite plates in the water column results in a change in
seawater optical properties leading to a high reflectance (HR), which can be observed from space by remote sensing. Their contribution to carbon cycling in the ocean is not only linked to primary production and calcification. Coccolithophores also produce large amounts of transparent exopolymer particles (TEP) that may lead to the formation of marine snow by aggregation of suspended material in the water column. The formation of macro-aggregates, combined with the ballast effect of calcite, makes them good candidates for the export and sequestration of carbon in the ocean. Massive coccolithophorid blooms occur each year at the continental margin of the Bay of Biscay between April and July. Our study reports the relative importance of processes, such as primary production, calcification, respiration rates and air-sea CO2fluxes, measured during a campaign in early June 2006 . We compare the patterns of various parameters, including TEP and the bacterial community
structure at various sampling stations displaying different stages of the bloom.
Station 8 (TEP-C:POC) 0 20 40 60 80 100 120 140 160 010 20 30 40 50 de pt h ( m ) Station 7 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50 Station 1 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50 Station 2 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50 Station 4 0 20 40 60 80 100 120 140 160 010 20 30 40 50 Station 4bis 0 20 40 60 80 100 120 140 160 010 20 30 40 50 Station 1bis 0 20 40 60 80 100 120 140 160 0 10 20 30 40 50
Figure 3: Contributions to POC in % of TEPmicro-C (solid circles) and TEPcolor-C (open squares).
TEP-C was estimated based on two approaches:
∑
− × = − i D i i micro C nr TEP 0.25 106where D is the fractal dimension estimated from a semi-empirical relationship of the spectral slope of size distribution color color C TEP TEP − =0.0033× 2 . 26 / ) 64 ( −δ = D Figure 1: C uptake in organic (green) and inorganic (orange) matter (14C incorporation technique). Respiration rates (O
2consumption, yellow) converted into C units using a conversion factor C:O2= 1. Calculated air-sea CO2flux (based on measured air-sea CO2 gradient, purple); negative values correspond to a flux from air to sea. Isobaths 200 m and 500 m are indicated by black lines. Reflectance based on satellite image taken on 5 June 2006.
During an interdisciplinary biogeochemical study carried out in early June 2006 a huge coccolithophorid
bloom, characterized by HR patches located at the continental margin of the Bay of Biscay was sampled. Low
nutrient levels and a thermal stratification down to 40-60
m depth were observed. Sea surface temperatures ranged from 13°C to 15°C during the cruise.
Rates of primary production and calcification (Fig. 1) were lower within the HR patch than outside, which probably indicates a later stage of the bloom.
The intense calcification has also reduced the surface
seawater total alkalinity by up to 26 µmol kg-1 (see
Suykens et al. Poster session PS007). Pelagic
respira-tion rates were in the same range or exceeded those of
primary production, which increased at stations 1bis and 4bis revisited one week later. The investigated area was
however a net sink for atmospheric CO2, due to
phytoplankton activity, as shown by the negative air-sea
CO2flux in Fig. 1. Station 8 (C:N molar) 0 20 40 60 80 100 120 140 160 0 10 20 de pt h ( m ) Station 7 0 20 40 60 80 100 120 140 160 0 10 20 Station 1 (1bis) 0 20 40 60 80 100 120 140 160 0 10 20 Station 5 0 20 40 60 80 100 120 140 160 0 10 20 Station 2 0 20 40 60 80 100 120 140 160 0 10 20 Station (4bis) 0 20 40 60 80 100 120 140 160 0 10 20
Figure 2: C:N molar ratio in particulate organic matter. The dashed line indicates the Redfield C:N ratio.
The C:N ratio in particulate organic matter (Fig. 2) was significantly different from the Redfield ratio, suggesting a decoupling between dissolved nutrients dynamics and carbon cycling towards carbon excess production in surface.
Figure 4: Principal Components Analysis of the bacterial community structure (DGGE) with some plotted environmental variables (TEP, Hex-fuco, Fuco, Chl a). Stations are denoted by the first number in the sample code, P3 refers to the “particle-associated” or >3 µm bacterial size fraction, P2 to the “free-living” or <3 µm bacterial size fraction, the last numbers refer to the depth. The areas highlighted in green show the stations located outside the HR patch, while the yellow ones regroup the stations located within the HR patch.
Analysis of the pigment composition by HPLC indicated that St 1, St 2 and St 3 were dominated by coccolithophores (diagnostic pigment 19’-hexanoyloxyfucoxanthin, Hex-fuc). The stations within the HR patch were diatom-dominated (Rhizosolenia spp.).
The particle-associated and free-living bacterial fractions showed a clear distinction in their community structure (Fig. 4). Both the free-living and particle-associated bacterial communities displayed a different structure inside or outside the HR patch, but this distinction was more pronounced in the particle-associated fraction.
We hypothesize that the observed differences are mostly due to the chemical properties of the aggregates produced by coccolithophores and that the bacterial community plays an important role in the formation of marine snow and the export of C during a coccolithophorid bloom in the continental margin environment.
200 m 500 m 6d 9d St 8 -20 0 20 40 60 80 100 120 140 St 7 -20 0 20 40 60 80 100 120 140 St4 -20 0 20 40 60 80 100 120 140 St1 -20 0 20 40 60 80 100 120 140 St 5 -20 0 20 40 60 80 100 120 140 St 2 -20 0 20 40 60 80 100 120 140 Legend -20 0 20 40 60 80 100 120 140 PPCal R CO2 mm o lC .m -2.d -1 200 m 500 m 6d 9d St 8 -20 0 20 40 60 80 100 120 140 St 7 -20 0 20 40 60 80 100 120 140 St4 -20 0 20 40 60 80 100 120 140 St1 -20 0 20 40 60 80 100 120 140 St 5 -20 0 20 40 60 80 100 120 140 St 2 -20 0 20 40 60 80 100 120 140 Legend -20 0 20 40 60 80 100 120 140 PPCal R CO2 mm o lC .m -2.d -1 Stations 1-2-3 (1b) Stations 6-7-8 (4-4b) -1.0 1.5 -0 .8 0 .8 1-P3-3 1-P3-10 1-P3-40 1-P3-50 1-P3-80 1b-P3-3 1b-P3-10 1b-P3-20 1b-P3-40 1b-P3-50 1b-P3-80 2-P3-3 2-P3-10 2-P3-40 2-P3-50 2-P3-80 3-P3-3 3-P3-20 3-P3-40 4-P3-3 4-P3-10 4-P3-20 4-P3-40 4-P3-60 4-P3-80 4b-P3-34b-P3-10 4b-P3-20 4b-P3-40 4b-P3-50 4b-P3-80 6-P3-3 6-P3-10 6-P3-20 6-P3-40 6-P3-50 6-P3-80 7-P3-3 7-P3-10 7-P3-20 7-P3-40 7-P3-50 7-P3-80 8-P3-3 8-P3-10 8-P3-20 8-P3-408-P3-50 8-P3-80 1-P2-3 1-P2-10 1-P2-40 1-P2-50 1-P2-80 1b-P2-3 1b-P2-10 1b-P2-20 1b-P2-40 1b-P2-50 1b-P2-80 2-P2-3 2-P2-10 2-P2-20 2-P2-40 2-P2-50 2-P2-80 3-P2-3 3-P2-20 3-P2-40 3-P2-80 4-P2-3 4-P2-10 4-P2-20 4-P2-40 4-P2-60 4-P2-80 4b-P2-3 4b-P2-10 4b-P2-20 4b-P2-40 4b-P2-50 4b-P2-80 6-P2-3 6-P2-10 6-P2-20 6-P2-40 6-P2-50 6-P2-80 7-P2-3 7-P2-10 7-P2-20 7-P2-40 7-P2-50 7-P2-80 8-P2-3 8-P2-10 8-P2-20 8-P2-40 8-P2-50 8-P2-80 Hex-fuco TEP Chl a Fuco Free-living Particle-assoc.
The present study was carried out in the framework of the project PEACE, funded by the Belgian Federal Science Policy Office (contract no. SD/CS/03A). This is also a contribution to the EU FP6 IP CARBOOCEAN project (contract no. 511176) and the EU FP6 NoE EUR-OCEANS (contract no. 511106). We are very grateful to local organizing committee and IAPSO for a grant to JH to cover the conference expenses.
