Variability of sources and sinks of CO₂ in the western Indian and southern oceans during the year 1991

Abstract

we describe spatial and temporal variations of sea surface carbon dioxide fugacity (fCO2) in the Antarctic, Subantarctic, subtropical, and tropical regions of the Indian Ocean (including the Red Sea). The measurements were made continuously with an infrared technique during seven cruises. We study the temporal variations of fCO2 at daily, monthly and seasonal scales in selected areas. High-frequency variabilities of 20 gatm/d have been observed near polar frontal zone. Both spatial and temporal fCO2 variation• are large near the subtropical and Subantartic fronts. In the subtropical domain, fCO2 decreases regularly from austral summer to winter. In January this region is a small CO2 sink with values near equilibrium with the atmosphere. In July, low fCO 2 (300 gatm) leads to a CO2 flux of-4.5 mmol/m2/d into the ocean for the zonal band 23øS-35øS. A quantitative study of monthly and seasonal fCO2 budgets is presented for the subtropical area. Considering first the observations at seasonal scale, it is shown that changes in fCO2 can be explained by temperature variations and air-sea exchanges; the sum of biological and mixing processes, considered as the balance of the seasonal fCO2 budget, is close to zero. The monthly fCO2 budgets are then calculated. In that case, other processes must be taken into account to close the budget: the observations indicate that the effect of productivity exceeds the one of mixing in austral summer and the opposite in winter. We then describe the seasonal air-sea fCO2 differences (AfCO2) for the whole western Indian Ocean and corresponding Antarctic sector (18,000 observations). In the equatorial and tropical regions the ocean is a CO2 source as was previously observed in the 1960s. In the subtropical area the CO2 sink dominates but varies strongly on a monthly scale. In the circumpolar front zones there is a large potential CO2 sink in summer. In the Antarctic waters, fCO2 spatial variability is very high at mesoscale, especially in the area of the Kerguelen plateau. Finally, it is shown that in some oceanic areas, well-defined relations exist between fCO2 distribution and temperature and salinity. If we want to use them to constrain mappings of continuous fCO2 fields from sparse observations, such relations must be considered at regional and at least seasonal scales. Brewer, 1986; Andrid et al., 1986; Takahashi et a/.,1986; Goyet et al. , 1991; Metzl et al., 1991; Murphy et al., 1991 a; Inoue and Sugimura, 1992], some of which were used to draw a new world map of ApCO2 [Takahashi, 1989; Tans et al., 1990], fCO2 observations are still distributed sparsely in space and time. To improve the determination of regional or global air-sea CO2 flux (and the associated uncertainties), it is clear that more fCO2 observations are needed; there are big gaps, for instance, in the Pacific and Indian sectors of the southern ocean [Tans et al., 1990]. Furthermore, very few cruises have been made during the winter, especially in the southern ocean (south of 50øS) for which 22,759 22,760 POISSON ET A...

Variations of oceanic pCO2 and air‐sea CO2 flux in the eastern Indian sector of the Southern Ocean for the austral summer of 2001–2002

“…It is also seen that pCO 2 sea varies largely in the SSIZ, but causes are ascribed to physical and biological processes. These results suggest that it is possible to reconstruct pCO 2 sea for the area north of PFZ using the observed temperature dependence of pCO 2 sea , but more sophisticated methods are required for the SSIZ, as suggested by Poisson et al [1993] and demonstrated by Metzl et al [1995].…”

A new design of equilibrator to monitor carbon dioxide in highly dynamic and turbid environments

“…Until now, 3 designs of equilibrators, or combination of them, are commonly used: the ''bubble Weiss type'' equilibrator, the ''laminary flow type'' equilibrator and the ''shower type'' equilibrator (Takahashi, 1961;Keeling et al, 1965;Kelley, 1970;Weiss, 1981;Copin-Montegut, 1985;Goyet et al, 1991;Schneider et al, 1992;Poisson et al, 1993;Roberston et al, 1993;Wanninkhof and Thoning, 1993;Goyet and Peltzer, 1994). Ko¨rtzinger et al (1996) have recently proposed a review of these equilibrators and have compared results obtained at sea using two different designs of ''bubble type'' equilibrators.…”

Climatological variations of total alkalinity and total dissolved inorganic carbon in the Mediterranean Sea surface waters

“…The surface C T concentrations are influenced by lateral and vertical mixing, photosynthesis, oxidation of organic matter and changes in temperature and salinity (Poisson et al, 1993;Takahashi et al, 1993). All these processes are directly or indirectly correlated with sea surface temperature (Lee et al, 2000).…”