Primary production ( 14 C) and phosphate availability in the south Pacific ocean T. MOUTIN, P. RIMMELIN Laboratoire d Océanographie et de Biogéochimie Centre d Océanologie de Marseille

SurfaceOceanSurfaceOcean CO 2 DOC Export production Nutrients (N, P, Si, Fe) POC h Moutin, 2000 (Océanis) Biological pump : carbon transfert to the ocean interior by biological process CO 2 : mineral carbon including carbonates POC : Particulate Organic Carbon DOC : Dissolved Organic Carbon

Scientific objectives : To obtain reference measurements of primary production. To study phosphate availabilty, and its influence on planktonic community structure and on associated carbon fluxes. CO 2 P h POC

Primary production (JGOFS 14 C method, 24-h of incubation duration) « Against » biological diversity, a « simple » method to compare phytoplankton productivity in the ocean Phytoplankton Productivity : Bangor, March 18 th -22 nd 2002

Secondary objective concerning primary production : to validate the model established in the Mediterranean Sea for daily primary production rates (dawn-to-dawn) calculation. Phytoplankton Productivity : Bangor, March 18 th -22 nd 2002 POMME cruises in the Eastern North Atlantic Ocean

PO 4 Conceptual scheme showing competitive absorbtion of phosphate by bacteria and phytoplankton and possible implications on the carbon cycle in a simple trophic chain model (Moutin 2000 from Thingstad et al., 1997 and Thingstad 1998). Heterotrophic flagellates surfaceoceansurfaceocean Micro- zooplankton Heterotrophic bacteria Pico- phytoplankton New Production Regenerate production Phosphate flux DOC exportPOC export DOC Carbon flux Nano-micro phytoplankton Meso- zooplankton Si

PO 4 Heterotrophic Bacteria Pico- phytoplankton Nano-micro phytoplankton Carbon and phosphate uptakes 33 P and 14 C methods (Incubation duration << 24 h) Biomass (Particulate Phosphate, Chlorophylle a (who?), Bacterial Biomass ?) Phosphate availabilty -Characteritics of the phosphacline (Concentration vs depth measurements by the classic and/or the MAGIC method (if PO 4 <100 nM)) -Turnover times measurements (=>Indirectly estimated orthophosphate concentration) -Dissolved Organic Phosphate concentration (labile DOP at surface only) Size fractionation (0.2, 0.6, 2 µm) Planktonic production (C & P) To study phosphate availabilty, and its influence on planktonic community structure.

One profile each day number 2 for « three days » stations Needs : Radio-isotopes container CTD one hour before dawn 2.5 liters per depth (max 12 depth) in situ Primary production (JGOFS 14 C method 24-h) Planktonik production (C & P) One profile each « one day » station Needs : 3 meters of working lab outside of the RA container CTD two hours before solar noon 4.5 liters per depth (max 9 depths) Deck incubators

ALOHA SRP N-limitation Absence de Trichodesmium Présence de Trichodesmium D. Karl JGOFS Conference Ocean Biogeochemistry: A New Paradigm April Bergen D. Karl et al., Nature Time P-limitation ? BIOSOPE Image composite Seawifs Comparison between ALOHA and Chenal des Loyauté Station (DIAPALIS Cruises) Van Den Broeck et al., MEPS, in press. Lowest orthohosphate turnover time measured CHENAL ALOHA : 2 d CHENAL : 4 h

Collaborations : -Frede Thingstad : -to study the phosphate cycle in the upper photic zone of oligotrophic ocean. -France Van Wambeke : -to study bacterial production vs primary production and the role of heterotrophic bacteria in the DOP pool utilization. -Dave Karl : (in discussion) -to compare phosphate availabilities in the South and the North Pacific gyres (ALOHA station).

Gibraltar Ionnian Sea Moutin, Thingstad, Van Wambeke, Marie, Slawyk, Raimbault & Claustre, 2002 (Limnol. Oceanogr.) « Expected » results ! PROSOPE Cruise

2.5 h 1 day Turnover times 1 week 1 month

M IO Stations P i (nM) déduites de T Proposition d une méthode indirecte simple (Radio isotopique 33 P) pour évaluer indirectement la concentration en orthophosphate (L.D. < 0.02 nM) SRP (nM) [PO 4 ] ( nM ) ENAO Apr 2001 ENAO Sep :1 P i (nM) déduites de T SRP (nM) Mer Méditerranée { Océan Atllantique Nord Est Moutin, Thingstad, Van Wambeke, Marie, Slawyk, Raimbault & Claustre, 2002 (Limnol. Oceanogr.)

Nécessite l achat d une centrifugeuse grand volume 2 nM 0,8 nM 20 nM Limite de détection et sensibilité attendue

Container Radio-isotopes IFREMER

Chlorophylle a µg l -1 Absorption de phosphate nM h -1 Phosphate particulaire nM Station "UPWELLING" au large du MarocStation "M IO" en mer Ionienne Mission PROSOPE