Scaling and intermittent properties of oceanic and atmospheric pCO₂ time series and their difference

Abstract. In this study the multi-scale dynamics of 38 oceanic and atmospheric pCO₂ time series from fixed Eulerian buoys recorded with three-hour resolution are considered. The difference between these time series, the sea surface temperature and the sea surface salinity data were also studied. These series possess multi-scale turbulent-like fluctuations and display scaling properties from three hours to the annual scale. Scaling exponents are estimated through Fourier analysis and their average quantities considered globally for all parameters, as well as for different ecosystems (e.g. coastal shelf, coral reefs, open ocean). Sea surface temperature is the only parameter for which a spectral slope close to 5/3 is found, corresponding to a passive scalar in homogeneous and isotropic turbulence. The other parameters had smaller spectral slopes, from 1.18 to 1.35. By using empirical mode decomposition of the time series, together with generalized Hilbert spectral analysis, the intermittency of the time series was considered in the multifractal framework. Concave moment functions were estimated and Hurst index and intermittency parameters estimated in the framework of a lognormal multifractal fit. It is the first time that atmospheric and oceanic pCO₂ and their difference ∆pCO₂ are studied using such intermittent turbulence framework. The ∆pCO₂ time series was shown to possess power-law scaling with an exponent of β = 1.32 ± 0.2.