Abstract: It is now well accepted that the increase ofatmospheric greenhouse effect gases, particularlycarbon dioxide, has an important impact on our climaticsystem, even if the true effect of the development ofhuman industrial activities is not totally assessed. Itis then necessary to have a good overall knowledge ofthe carbon dioxide cycle, and more particularly thefluxes exchanged the three CO$-2$/ tanks: atmosphere,ocean, and continental biosphere. Since the ocean isthe biggest carbon tank (60 times the atmosphere tank),it constitutes an important potenetial well for theatmospheric CO$-2$/. However, the data available showan uncertainty of ca. 30% on the estimated flux. It isthen important to assess the quantity of CO$-2$/ at thesurface of the ocean, and the correspondingatmosphere/ocean flux. The possible future atmosphericCO$-2$/ concentration corresponding to differentindustrial emission scenarii can then be assessed. Themethod measurement of the CO$-2$/ at the sea surfaceuse spectro- photometry of a sensitive dye, housed in atank which has walls immersed in the sea water. Thespectro-photometer especially designed, patented, andbuild-up by IFP has been developed with specialemphasis on high accuracy, rugged construction, ease ofoperation without maintenance, and calibration over aperiod of time of over one year. The leading idea wasto have as few internal moving parts as possible by theuse of fiber optics, and internal calibration by theuse of internal reference channels. Ancillary data arealso measured. Data is transmitted to the processingcenter via ARGOS. The equipment described is part ofthe EUREKA CARIOCA project (EU 819), supported by theFrench Ministere de l'Enseignement Superieur et de laRecherche (93 W 0011) and UK's DTI. The partners are:LODYC, LGE, INSU, SERPE-IESM (France), and ChelseaInstruments (UK). !4
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