Biogeochemistry of a late marginal coccolithophorid bloom in the Bay of Biscay

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Biogeochemistry of a late marginal

coccolithophorid bloom in the Bay of Biscay

J. Harlay

J. Harlay11_{, C. De Bodt}_{, C. De Bodt}11_{, Q. D}_{, Q. D}_’_’_Hoop_Hoop11_{, A.V. Borges}_{, A.V. Borges}22_{, K. Suykens}_{, K. Suykens}22_,_,

N. Van Oostende

N. Van Oostende33_{, K. Sabbe}_{, K. Sabbe}33_{, N. Roevros}_{, N. Roevros}11_{, S. Groom}_{, S. Groom}44 _{and L. Chou}_{and L. Chou}11

1 _{Laboratoire d’Océanographie Chimique et Géochimie des Eaux (LOCGE),}

Université Libre de Bruxelles, B-1050 Brussels, Belgium

2_{Unité d’Océanographie Chimique, Université de Liège, B-4000, Liège, Belgium} 3_{Protistologie & Aquatische Ecologie, Universiteit Gent, B-9000, Gent, Belgium} 4_{Remote Sensing Group, Plymouth Marine Laboratory, Plymouth, United Kingdom}

EGU General Assembly Vienna, Austria, 15-20 April 2007

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Introduction

http://www.co2.ulg.ac.be/peace/index.htm

role of primary production, calcification and export processes in coccolithophore blooms

the net ecosystem dynamics (primary production,

calcification

and pelagic respiration)

the link between

the bacterial community, TEP formation

and carbon export

Dynamics of coccolithophore blooms:

Contribution in climate regulation ?

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Coccolithophores:

From Rost & Riebesell, 2004

Introduction

Diatoms → Coccolithophores

Low requirements for inorganic phosphorus and micronutrients

« Organic phase » followed by the « calcifying phase » → release of coccoliths

With regard to the C-cycle:

Organic or biological pump

(photosynthesis)

Carbonate counter-pump (biocalcification)

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EGU General Assembly Vienna, Austria, 15-20 April 2007 (Nature, 441, 15 June 2006)

Introduction

stretched over 500 km

probably due to the common coccolithophore species Emiliania huxleyi June 2006

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31th _{May – 10}th _{June 2006}

Zone of

study

Celtic sea

Bay of Biscay

Reflectance (1/06/2006) SST° (11-13/06/2004)

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EGU General Assembly Vienna, Austria, 15-20 April 2007 Chl Chl--a a ((SeaWiFSSeaWiFS, 01/06/2006), 01/06/2006) [PO₄] ~ 0 µM [Si] < 2 µM [Chl-a] = 0.5 - 2 µg/l

Zone of

study

T°: 13-15 °C Sal: 35.5 – 35.7 Thermocline 40-50 m 8 7 5 4, 4bis 6 1, 1bis 2 3 Chl Chl-a-a ₈ 7 5 4, 4bis 6 1, 1bis 2 3 Reflectance Reflectance

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EGU General Assembly Vienna, Austria, 15-20 April 2007 1st _Leg ₂nd _Leg Station 4 0 20 40 60 80 100 120 140 160 0 1 2 Station 1 0 20 40 60 80 100 120 140 160 0 1 2 Moderate [Chl-a]

Deep Chl-a maximum ~ 20-40m

Chlorophyll

-

a

concentrations

µg/l µg/l

Depth

(m

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EGU General Assembly Vienna, Austria, 15-20 April 2007 2310 2320 2330 2340 2350 35.3 35.4 35.5 35.6 35.7 Salinity T A (µ m o l/k g -1 ) Con servativ e mixin g C alcif ica tio n TA = 64.9*S + 38.8 r2_{= 0.9714} Biogenic calcification: Ca2+ _{+ 2HCO} 3- → CaCO3 + H2O + CO2

Total alkalinity

Fingerprint of calcification inside the high reflectance patch

TA35.5 (µmol/kg-1) 0 25 50 75 100 125 150 2310 2330 2350 de p th ( m ) Station 4 Station 5 Station 6 Station 7 Station 8 TA35.5 (µmol/kg-1) 0 25 50 75 100 125 150 2310 2330 2350 de p th ( m ) Station 1 Station 2 Station 3

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Total alkalinity anomalies

Details in Suykens et al. (Poster BG0021 Today )

Dissolved inorganic carbon dynamics in the Gulf of Biscay (June 2006)

maximum range of 26 µmol kg-1

01/06/2006 TA_anomaly = TA_meas - TA_sal

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Sea

-

surface pCO

₂₂

sink for atmospheric CO₂ in early June 2006 ranged from 250 to 338 µatm

strong correlation: TA anomaly vs. pCO₂@13°

200 220 240 260 280 300 320 340 -25 -20 -15 -10 -5 0 5

TA anomalie top 50m [µmol/kg]

pC O 2 @ 1 3° C [µ atm ] r2_{= 0.84} Ca2+ _{+ 2HCO} 3- → CaCO3 + H2O + CO2

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Primary production and calcification

5th _{June 2006}

Primary production

< 1 gC m-2 _d-1 _{inside the patch}

> 1.5 gC m-2 _d-1 _{at station 2}

Calcification rates 0.2 - 0.5 gC m-2 _d-1

PIC:POC ~ 0.4

(molar uptake ratio)

St 8 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 St 7 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 St4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 St1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 St 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 St 5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Legend PP Cal gC .m -2 .d -1 6d 9d

Primary production decreased at stations 1 and 4

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Primary production and calcification

5th _{June 2006}

Zone dominated by the organic phase (1, 2)

Zone of transition (4, 5)

Zone dominated by the calcifying phase (7, 8) Organic Organic Phase Phase Calcifying Calcifying phase phase TRANSITION

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Pelagic respiration rates

5 4 1 2 8 ₇ 4bis 1bis LEG 1 LEG 2

Respiration rates exceed primary production rates, except at st 2

Ranging from 82 to 117 mmolC m-2 _d-1

Increase at revisited stations

Total respiration as a major source of CO₂ (76 → 90 %)

Station PP CAL RESP

(mmolC.m-2.d-1) 1 74.2 7.5 82.3 1bis 43.3 15.8 116.9 2 130.8 51.7 90.7 5 74.2 24.2 4 43.3 13.3 86.3 4bis 41.7 12.5 114.9 7 71.7 28.3 88.3 8 25.0 13.3 106.8

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Lysis

rate

Dissolved Esterase Activity method

(

Riegman et al., 2002

)

Station date Lysis (d-1)

2 1/06/2006 0.320 4 2/06/2006 0.253 8 6/06/2006 0.318 7 7/06/2006 0.178 1bis 9/06/2006 1.339 Cell Lysis Zooplankton grazing Viral activity Van Boeckel et al., 1992

Typical for a late-spring bloom situation 0.02-0.3 d-1 _{in Riegman & Winter (2003)}

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From Engel et al., (2004)

Transparent

Exopolymer

Particles

See also De Bodt et al. (Poster XY0734 Wednesday)

Calcification and transparent exopolymer particles (TEP) production in batch cultures of Emiliania huxleyi exposed to different pCO2

Adapted from Verdugo et al., (2004)

Solutes Colloids 1-10 kDa 1 nm 1 µm 1 mm Particles Polymers Gels TEP TEP DOM POM Aggregation Ehux

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Transparent

Exopolymer

Particles

Passow & Alldredge (1995):

920 µg Xeq/l (batch culture, Ehux)

Our study: 500-800 and up to 2000 µg Xeq/l Engel (2004): 28 to 120 µg Xeq/l NAO (June-July 1996) Passow et al. (2001):

500 µg Xeq/l (Santa Barbara Channel)

Station 8 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 7 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 4 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 1 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 5 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 2 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 6 0 20 40 60 80 100 120 140 160 0 1000 2000 Station 3 0 20 40 60 80 100 120 140 160 0 1000 2000

(TEP conc. in µg Xeq/l)

9 days

6 days

Size spectrum and specific polysaccharide

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Bacterial community structure

- α-proteobacteria (Roseobacter) - SAR86 lineage « particle-associated fraction » (> 3 µm) DMS-cleavage pathway Organic-S metabolism « free-living fraction » (0.2 – 3 µm) DGGE / PCR 16s rDNA Particle-associated fraction Free-living fraction

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CONCLUSIONS

The continental margin has hydrodynamic features that enhance biological activity and especially promote coccolithophore blooms.

This ecosystem was still a sink for atmospheric CO₂ due to the history of the bloom development.

But the intensity of the CO₂-producing processes is important and may switch the system from a sink to a source of CO₂.

The elevated concentrations of TEP, accompanied by high cell lysis rates, may lead to the production and subsequent export of macro-aggregates, which could be enhanced by the ballasting of calcite particles. “What is the role of bacteria in aggregates ? Dissolution of CaCO₃? DMS-cleavage pathway ?”

Contribution to C export and preservation via shelf-ocean exchanges Future of shelf carbonate sediments in a high-CO₂ world…

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Acknowledgements

Thank you for your attention

Officers and crew members of the RV Belgica for their logistic support during the cruise. J. Backers, J-P De Blauw and G. Deschepper for the acquisition of CTD data.

A. Engel for the constructive discussions on TEP dynamics. C. Brussaard for the protocol of DEA method and advices.

FNRS for travel grants to CDB & JH.

CDB funded by CARBOOCEAN, JH, KS and NVO by PEACE. This is also a contribution to Eur-Oceans.

R. Schlitzer for the Ocean Data View software (http://odv.awi.de)