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84 - Primary Production 14C -

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PRIMARY PRODUCTION (¹⁴C METHOD)

Thierry MOUTIN

Centre d'Océanologie de Marseille, Laboratoire d'Océanographie et de Biogéochimie, Campus de Luminy, 13288 Marseille cédex 9

moutin@com.univ-mrs.fr

Carbon absorption has been quantified according to the experimental protocol recommended by France-JGOFS-P.F.O. (1991). Samples were obtained with 12-l Niskin bottles with silicone rubber closures and tubing that had been carefully checked to avoid introducing toxic metals during sampling. Up to 12 depths of sampling were chosen according to the " in vivo " fluorescence profiles. Each sample (320-ml polycarbonate bottle, 3 light and one dark sample per depth) was collected before sunrise, inoculated with 250 µl of the ¹⁴C working solution^a just before sunrise, and then incubated in situ (except 2 stations during POMME 1) where incubation was down in deck incubators equipped with Nickel screens. After 24h, the samples were filtered on 2µm polycarbonate filters deposited on GF/F filters to measure net absorption (A_N nmol l^-1). Filters were immediately covered with 500 µl of HCl 0.5 M and stored for counting at the laboratory. Each day, 3 samples were filtered immediately after inoculation for t_o determination, and 250 µl of sample was taken at random from 3 bottles and stored with 250 µl of ethanolamine to determine the quantity of added tracer (Q_i). At laboratory, samples were dried during 12 h at 60°C, 10 ml of ULTIMAGOLD-MV (Packard) were added to the filters and dpm was counted after 24h with a Packard Tri carb 2100 TR liquid scintillation analyser.

Net absorption A_N(Ti ;T) for dark and light bottles was calculated from :

A_N(Ti ;T) (nmol l^-1) = (dpm-dpm_(to))/(dpm_(Qi)*1280) * TCO2^b

where T_i corresponds to the starting time of the incubation since dawn and T to the incubation duration.

Primary production rates PP* (* = 24h from dawn-to-dawn) were obtained from :

PP* (nmol l^-1 d^-1) = A_Nlight* - A_Nblack* = A_{Nlight(Ti ;T)} / t _(Ti ;T)^c - (A_Nblack(T) /T)*24

Integrated primary production IPP* (nmol m^-2 d^-1) has been calculated with trapezium method assuming (1) that subsurface (about 5 m) rates are identical to surface rates (not measured) and (2) that rates are zero at 20 m below the deepest sampled depth.

^a Working solution : 12.5 ml of NaH¹⁴CO₃ (25 mCi, 50-60 mCi/mmole, Amersham CFA3) was added to a solution containing 0.09 g of Na₂CO₃ (Aldrich 20,442-0) per 300 ml of sterilized milliQ water. This solution was stored in sealed 15 ml glass flasks.

^b TCO2 = 2.08 mmol l^-1.

^c t _(Ti ;T) (conversion factor depending on the date and the latitudinal position) was determined according to Moutin et al. (1999). Applying this procedure allows to normalize primary production rates obtained from incubation duration £ 24h in a given region at a given date, to daily rates, thus allowing the comparison of data obtained from different experimental incubation durations.

Remark : for all the 24-h incubation duration, t _(Ti ;T) = 1.

Références :JGOFS, Core measurements protocols : report of the core measurement working group. JGOFS report n°6, Joint Global Ocean Flux Study, SCOR (1988) 1-40.

Moutin, T., P. Raimbault & J.C. Poggiale. 1999. Production primaire dans les eaux de surface de la Méditerranée occidentale : Calcul de la production journalière. . C. R. Acad. Sci. Paris, Sciences de la vie. 322 : 651-659.

 

Campagnes et legs:

POMME 1,2,3, LEGs 2


 

 

 

DESCRIPTIF des FICHIERS

column	identification
A	CTD number
B	Bottle number
C	Date
D	Depth of collection
E	Screen (%) or in situ incubation
F	Depth of incubation
G	Dark net carbon absorption
H	Mean of net carbon absorption in 3 light samples	filtered on 2 µm	polycarbonate filters
I	Standard deviation (H)
J	Mean of net carbon absorption in 3 light samples	filtered on GF/F	filters deposited under the 2 µm	polycarbonate filters
K	Standard deviation (J)
L	Sum of columns H and J
M	Sum of columns I and K
N	Primary production (PP)
O	Integrated primary production (IPP)

ATTENTION : Les unités sont indiquées dans les tableaux pour chaque colonne (ligne 4).