Quantification of the Carbonate Pump: Case study of an Emiliania huxleyi bloom in the Bay of Biscay

QUANTIFICATION OF THE CARBONATE PUMP :

A Case Study of an

Emiliania huxleyi

bloom in the Bay of Biscay

Jérôme Harlay

1

, Lei Chou

1

, Nathalie Roevros

1

, Roland Wollast

1

, Bruno Delille

2

, Katrien Aerts

3

and Pascale-Emmanuelle Lapernat

4

1

Océanographie Chimique et Géochimie des Eaux, Université Libre de Bruxelles (Email: jerome.harlay@ulb.ac.be)

2

Unité d'Océanographie Chimique, Université de Liège

3

MiTAC, University of Antwerp

4

Laboratory of Ecology and Systematics, Vrij Universiteit Brussel

During the Belgica BG02/11 cruise (22 April - 11 May 2002) in the northern Bay of Biscay, a slope survey covering transects across the continental margin from the La Chapelle Bank to the Goban Spur area were conducted. The sampling campaign was assisted in addition by remote sensing data from SeaWiFS to locate the coccolithophore blooms, as characterised by white, highly reflective regions as shown by ocean colour imagery. Experiments of 14C incorporation were carried out along the shelf break to determine the production rate of both organic and inorganic particulate carbon.

INTRODUTION

AKNOWLEDGMENTS

This study is funded by the Belgian Federal Office for Scientific, Technical and Cultural Affairs (OSTC) under contract n° EV/11/5A. We would like to thank the captain, officers and crewmembers of the R/V Belgica for their logistic support. J. Backers and J.-P. De Blauwe from the Management Unit of the North Sea and Scheldt Estuary Mathematical Model (M.U.M.M.) in Ostend are greatly acknowledged for their assistance in the operation of the CTD rosette and in data acquisition. Data analysis and some representations are made by the ODV software, for which we are very grateful to Dr R. Schlitzer

(http://www.awi-bremerhaven.de/GEO/ODV/))

Project Internet Site: http://www.ulb.ac.be/sciences/dste/ocean/carbonate/frame.html

Coccolithophores, among which Emiliania

huxleyi is the most widespread species in the

world’s oceans, are the dominant calcifying phytoplankton in the area of investigation. Their importance in biogeochemical cycling is supported not only by their capacity for organic matter production via photosynthesis, the biological pump, but also by their ability to produce calcified coccoliths, the

carbonate pump, which represents a major contribution to

the particulate carbon flux to the deep ocean.

In the photic zone, the biological pump removes inorganic carbon from the surface ocean, while the carbonate pump, according to the equation Ca2+ + 2HCO3

-  CaCO

3 + H2O +

CO₂ releases CO₂ and consumes Total Alkalinity to produce biogenic calcium carbonate. It is generally accepted that the overall effect of photosynthesis and calcification constitutes a net sink of carbon from the atmosphere. There remains still large uncertainties in the production and fate of biogenic calcium carbonate in the oceanic carbon cycle.

SeaWiFS data received at the N E R C D u n d e e U n i v e r s i t y Receiving Station and processed by the Remote Sensing Group of the Plymouth Marine Laboratory.

The primary production observed during our field survey

was mainly associated with the coccolithophores. The total

transfer of dissolved inorganic carbon to the particulate

phase in the northern Bay of Biscay area is estimated to be

2.03 gC m

-2

d

-1

for the shelf break and 1.14 gC m

-2

d

-1

for

the slope region. Of this carbon, approximately 20 to 25%

is associated with the inorganic carbonate phase. The

organic carbon produced is rapidly remineralised in the

water column during settling, while the calcium carbonate

resists much better to dissolution. Consequently, the

carbon deposited and preserved in the sediments is mainly

present as calcium carbonate and inorganic carbon flux

becomes therefore significant at a global marine scale.

Recent investigations have shown that calcium carbonate

could dissolve even in shallow and intermediate waters

where this mineral phase is over-saturated. It is therefore

important to understand the mechanisms associated with

this process. This aspect constitutes the follow-up of the

present research.

Conclusions

Meriadzec Terrace

CARBON FLUXES IN THE PHOTIC ZONE

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 0 1 2 3 g C_{o rg .}g_{C h l-a}-1.h-1 g C_{in o r}.g_{C h l-a}-1.h-1 µ m o l p h o t o n s .m-2.s-1 gC. g Ch l-a -1 .h -1 14

C uptake vs. light intensity experiments have allowed the characterisation of the photosynthetic properties of the phytoplankton based on the classical Platt equation:

PB = PBmax [1-exp (- E / P B

max )] exp (- E / P B

max )

where PB is the photosythetic rate, PBmax the maximum photosynthesis rate,  the maximum light utilization coefficient,  the photoinhibition parameter and E the photosynthetically avalaible radiation (PAR). The light adaptation parameter Ek can also be defined by P

B

max/.

The results compared to the theoretical curves show that, in general, the plankton at depth exhibits a higher photosynthetic efficiency but is not affected by photoinhibition, which can be neglected in the present study. Interestingly enough, the rate of calcification follows a similar trend to the P vs. E curve and rate parameters of the Platt equation can be calculated accordingly.

The parallelism of the two curves indicates that photosynthesis and calcification are intimately coupled. Carbon fluxes in gC m-2 d-1 have been calculated by integrating the optimal primary production (wiith the simulated light intensity of a sunny day and its related photoperiod) and the associated calcification rate.

11 0 50 100 150 200 0 1 2 3 4 5 14 0 50 100 150 200 0 1 2 3 4 5 15 0 50 100 150 200 0 1 2 3 4 5 16 0 50 100 150 200 0 1 2 3 4 5 µg Ch l-a/L de p th ( m ) 12 0 50 100 150 200 0 1 2 3 4 5

HYDROGRAPHY

16 0 50 100 150 200 2.28 2.29 2.3 2.31 m e q/k g d e pt h ( m ) 14 0 50 100 150 200 2.28 2.29 2.3 2.31 15 0 50 100 150 200 2.28 2.29 2.3 2.31 11 0 50 100 150 200 2.28 2.29 2.3 2.31 12 0 50 100 150 200 2.28 2.29 2.3 2.31 8 0 50 100 150 200 2.28 2.29 2.3 2.31 5 0 50 100 150 200 2.28 2.29 2.3 2.31 2 0 50 100 150 200 2.28 2.29 2.3 2.31 4 0 50 100 150 200 2.28 2.29 2.3 2.31 7 0 50 100 150 200 2.28 2.29 2.3 2.31 2 0 50 100 150 200 0 1 2 3 4 5 4 0 50 100 150 200 0 1 2 3 4 5 5 0 50 100 150 200 0 1 2 3 4 5 7 0 50 100 150 200 0 1 2 3 4 5 8 0 50 100 150 200 0 1 2 3 4 5

Chlorophyll-a concentrations increase in surface waters

from less than 1 to more than 4 µg.l-1 as one moves from offshore (i.e. Station 7) towards the continental shelf (i.e. Station 5). Furthermore, there is a constant increase of Chl-a concentrChl-ation from north (StChl-ation 16) to south (StChl-ation 2). These concentrations are typical of those commonly observed during the spring phytoplankton bloom in this area.

The profiles of total alkalinity normalized to a salinity of 35 indicate a consumption by calcifying phytoplankton in surface waters. In the case of the offshore stations, the pattern of the the vertical distribution is almost linear, denoting a minor effect of primary production on this parameter.

The large decrease observed in surface waters of station 16 indicate a late stage of the bloom, when all the coccolithes a spread, giving milky waters), whereas southern stations are in an early stage.

This is rather a temporal effect of the sampling than a physiological delay due to low latitudes.

POSTER SESSION BG 14

P1854

Contribution EAE-03-A-09418

Poster presentation on Wednesday, 9 April 2003

Phytoplankton CH2O CaCO3 CO2 HCO3 -0.83 0.53 0.26 1.1 0.57 CH2O fluxes in gC.m-2.d-1 0.18 Phytoplankton CaCO3 0.45 CO2 HCO3 -0.36 0.09 0.27 mg Cinorg.m -2 .d-1 mg Corg.m -2 .d-1 Goban Spur 234 1222 131 547 152 626 55 177 477 1206 295 680 243 464 186 815 La Chapelle Bank