Roles of biological and physical processes in driving seasonal air-sea CO2 flux in the Southern Ocean: New insights from CARIOCA pCO2 (original) (raw)
Related papers
As one of the major oceanic sinks of anthropogenic CO2, the Southern Ocean plays a critical role in the climate system. However, due to the scarcity of observations, little is known about physical and biological processes that control air-sea CO2 fluxes and how these processes might respond to climate change. It is well established that primary production is one of the major drivers of air-sea CO2 fluxes, consuming surface Dissolved Inorganic Carbon (DIC) during Summer. Southern Ocean primary production is though constrained by several limiting factors such as iron and light availability, which are both sensitive to mixed layer depth. Mixed layer depth is known to be affected by current changes in wind stress or freshwater fluxes over the Southern Ocean. But we still don't know how primary production may respond to anomalous mixed layer depth neither how physical processes may balance this response to set the seasonal cycle of air-sea CO2 fluxes. In this study, we investigate th...
An empirical estimate of the Southern Ocean air-sea CO2 flux
Global Biogeochemical Cycles, 2007
1] Despite improvements in our understanding of the Southern Ocean air-sea flux of CO 2 , discrepancies still exist between a variety of differing ocean/atmosphere methodologies. Here we employ an independent method to estimate the Southern Ocean air-sea flux of CO 2 that exploits all available surface ocean measurements for dissolved inorganic carbon (DIC) and total alkalinity (ALK) beyond 1986. The DIC concentrations were normalized to the year 1995 using coinciding CFC measurements in order to account for the anthropogenic CO 2 signal. We show that independent of season, surface-normalized DIC and ALK can be empirically predicted to within $8 mmol/kg using standard hydrographic properties. The predictive equations were used in conjunction with World Ocean Atlas (2001) climatologies to give a first estimate of the annual cycle of DIC and ALK in the surface Southern Ocean. These seasonal distributions will be very useful in both validating biogeochemistry in general circulation models and for use in situ biological studies within the Southern Ocean. Using optimal CO 2 dissociation constants, we then estimate an annual cycle of pCO 2 and associated net air-sea CO 2 flux. Including the effects of sea ice, we estimate a Southern Ocean (>50°S) CO 2 sink of 0.4 ± 0.25 Pg C/yr. Our analysis also indicates a substantial CO 2 sink of 1.1 ± 0.6 Pg C/yr within the sub-Antarctic zone (40°S-50°S), associated with strong cooling and high winds. Our results imply the Southern Ocean CO 2 flux south of 50°S to be very similar to those found by , but on the higher end of a range of atmospheric/oceanic CO 2 inversion methodologies. This paper estimates for the first time basic seasonal carbon cycle parameters within the circumpolar Southern Ocean, which have up to now been extremely difficult to measure and sparse. The application of such an empirical technique using more widely available hydrographic parameters in the Southern Ocean provides an important independent estimate to not only CO 2 uptake, but also for other future biogeochemical studies. Refining and testing these empirical methods with new carbon measurements will be important to further reduce uncertainties and extend our understanding of Southern Ocean CO 2 dynamics.
Deep Sea Research Part II: Topical Studies in Oceanography, 2009
A climatological mean distribution for the surface water pCO 2 over the global oceans in non-El Niñ o conditions has been constructed with spatial resolution of 41 (latitude) Â 51 (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO 2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper . Global sea-air CO 2 flux based on climatological surface ocean pCO 2 , and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601II, 49, -1622. A time-trend analysis using deseasonalized surface water pCO 2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO 2 over these oceanic areas has increased on average at a mean rate of 1.5 matm y À1 with basinspecific rates varying between 1.270.5 and 2.170.4 matm y À1 . A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Niñ o periods in the equatorial Pacific and those made in coastal zones are excluded from the database.
Importance of water mass formation regions for the air-sea CO 2 flux estimate in the Southern Ocean
Global Biogeochemical Cycles, 2011
1] CARIOCA drifters and ship data from several cruises in the Subantarctic Zone (SAZ) of the Pacific Ocean, approximately 40°S-55°S, have been used in order to investigate surface CO 2 partial pressure (pCO 2 ) and dissolved inorganic carbon (DIC) patterns. The highest DIC values were determined in regions of deep water formation, characterized by deep mixed layer depths (MLD) as estimated from Argo float profiles. As a result, these areas act as sources of CO 2 to the atmosphere. Using an empirical linear relationship between DIC, sea surface temperature (SST), and MLD, we then combine DIC with A T based on salinity and compute pCO 2 . Finally, we derive monthly fields of air-sea CO 2 flux in the SAZ. Our fit predicts the existence of a realistic seasonal cycle, close to equilibrium with the atmosphere in winter and a sink when biological activity takes place. It also reproduces the impact that deep water formation regions close to the Subantarctic Front (SAF) and in the eastern part of the SAZ have on the uptake capacity of the area. These areas, undersampled in previous studies, have high pCO 2 , and as a result, our estimates (0.05 ± 0.03 PgC yr −1 ) indicate that the Pacific SAZ acts as a weaker sink of CO 2 than suggested by previous studies which neglect these source regions.
Journal of Geophysical Research, 2009
1] Four CARIOCA Lagrangian buoys were deployed in the northeast Atlantic Ocean as part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) dedicated to the study of the role of mesoscale eddies in biological production, the carbon budget, and the subduction of mode waters. An extensive set of hourly surface measurements of temperature, salinity, and carbon dioxide fugacity (fCO 2 ) was collected from February to August 2001. The high-frequency spatial and temporal variability observed in surface fCO 2 and in the derived dissolved inorganic carbon (DIC) concentrations suggests that abrupt changes of the carbon variables are being generated along frontal patterns and filaments by submesoscale and mesoscale eddy-eddy interactions, especially in winter. On the basis of a 1-D model of the diurnal mixed layer along the buoy trajectory, we show that under certain conditions the diel cycle of DIC is driven by the daily cycle of photosynthesis and metabolic CO 2 release at the ocean surface. This information is quantitatively used to derive in-situ primary production, carbon gross, and net community production. The analysis of 107 observed diel cycles of DIC shows that episodic biological production processes are triggered by the mesoscale activity of surface eddies. Over the sampled period, the POMME area is a sink for atmospheric CO 2 with an estimated flux of À4 mmol m À2 day À1 . The calculated amount of anthropogenic carbon transported into the ocean interior by subduction of subpolar mode water is equal to 2.8 10 13 gC yr À1 .
Coastal Southern Ocean: A strong anthropogenic CO 2 sink
Geophysical Research Letters, 2008
1] Large-scale estimates of the Southern Ocean CO 2 sink do not adequately resolve the fluxes associated with Antarctic continental shelves. Using a mechanistic threedimensional biogeochemical model of the Ross Sea, we show that Antarctic shelf waters are a strong sink for CO 2 due to high biological productivity, intense winds, high ventilation rates, and extensive winter sea ice cover. Net primary production (NPP) in these waters is $0.055 Pg C yr À1 . Some of this carbon sinks to depth, driving an influx of CO 2 of 20-50 g C m À2 yr À1 . Although currently unaccounted for, the total atmospheric CO 2 sink on the Ross Sea continental shelf of 0.013 Pg C yr À1 is equivalent to 27% of the most recent estimate of the CO 2 sink for the entire Southern Ocean. Given these results, these and other highly productive waters around the Antarctic continent need to be included in future budgets of anthropogenic CO 2 .
Quantifying the drivers of ocean-atmosphere CO2 fluxes
A mechanistic framework for quantitatively mapping the regional drivers of air-sea CO 2 fluxes at a global scale is developed. The framework evaluates the interplay between (1) surface heat and freshwater fluxes that influence the potential saturated carbon concentration, which depends on changes in sea surface temperature, salinity and alkalinity, (2) a residual, disequilibrium flux influenced by upwelling and entrainment of remineralized carbon-and nutrient-rich waters from the ocean interior, as well as rapid subduction of surface waters, (3) carbon uptake and export by biological activity as both soft tissue and carbonate, and (4) the effect on surface carbon concentrations due to freshwater precipitation or evaporation. In a steady state simulation of a coarse-resolution ocean circulation and biogeochemistry model, the sum of the individually determined components is close to the known total flux of the simulation. The leading order balance, identified in different dynamical regimes, is between the CO 2 fluxes driven by surface heat fluxes and a combination of biologically driven carbon uptake and disequilibrium-driven carbon outgassing. The framework is still able to reconstruct simulated fluxes when evaluated using monthly averaged data and takes a form that can be applied consistently in models of different complexity and observations of the ocean. In this way, the framework may reveal differences in the balance of drivers acting across an ensemble of climate model simulations or be applied to an analysis and interpretation of the observed, real-world air-sea flux of CO 2 .