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Biogeochemical floats can be used to improve measurements of sea-air CO2 exchanges, study shows

  • 16 March 2017
  • Number of views: 816
Biogeochemical floats can be used to improve measurements of sea-air CO2 exchanges, study shows

SOCATv4 pCO2sw data [Bakker et al., 2016] south of 30°S colored by month for years 1957−2015 for all months (a) and for only austral winter months (July−September; b). A map of trajectories of all SOCCOM floats from 26 March, 2014 to 4 January, 2017 with the floats used in this study colored in green (c). Courtesy Williams et al.

A study published as an early online release on Global Biogeochemical Cycles shows the value of calibrated biogeochemical floats for providing data measurements of surface ocean partial pressure of CO2 ( pCO2sw ), which is measured to determine air-sea CO2 exchanges. 

A certain degree of uncertainty exists in calculating pCO2sw from float pH, but researchers in this study show well-calibrated biogeochemical floats can be used to improve measurements of sea-air carbon exchanges. These measurements can improve climate models and future projections. 

Observations indicate that pCO2sw has increased globally with human caused CO2 emissions. However, researchers have limited understanding of how the ocean and the atmosphere exchange anthropogenic CO2 in many parts of the planet. 

This study was supported by the Ocean Observing and Monitoring Division

Read the paper


More than 74 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10-day intervals have been deployed throughout the Southern Ocean. Calculating the surface ocean partial pressure of carbon dioxide (pCO2sw) from float pH has uncertainty contributions from the pH sensor, the alkalinity estimate, and carbonate system equilibrium constants, resulting in a relative standard uncertainty in pCO2sw of 2.4% (or 10 µatm at pCO2sw of 400 µatm). The calculated pCO2sw from several floats spanning a range of oceanographic regimes are compared to existing climatologies. In some locations, such as the Subantarctic zone, the float data closely match the climatologies, but in the Polar Antarctic Zone significantly higher pCO2sw are calculated in the wintertime implying a greater air-sea CO2 efflux estimate. Our results based on four representative floats suggest that despite their uncertainty relative to direct measurements the float data can be used to improve estimates for air-sea carbon flux, as well as to increase knowledge of spatial, seasonal, and interannual variability in this flux.






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