1506 / 2024-09-27 20:21:32
Statistical analysis of thermal and non-thermal components of oceanic pCO2 time series at fixed position
Turbulence,Carbon dioxide,High-frequency,Time series
Session 25 - IGAC-SOLAS: Chemistry and physics at surface ocean and lower atmosphere
Abstract Accepted
Kévin Robache / LOG; ULCO
François G. Schmitt / CNRS-LOG
The ocean plays a critical role in regulating Earth's climate by acting as a major sink for atmospheric CO2, absorbing approximately 25 % of anthropogenic CO2 emissions annually (Friedlingstein et al., 2023). However, at smaller spatial and temporal scales, the dynamics of ocean-atmosphere CO2 fluxes become more intricate. These fluxes are not always directed towards the ocean, as they depend on the partial pressure of CO2 (pCO2) difference, which is primarily influenced by fluctuations in oceanic pCO2 (Robache et al., 2024). This complexity is particularly evident in coastal regions, where spatio-temporal variability is high. In such regions, both thermal and non-thermal fluctuations of oceanic pCO2 play a significant role in driving these high-frequency dynamics. In this context, we used high-resolution data (30-minute intervals) from the ASTAN buoy, located in Brittany (France), which included measurements of sea surface temperature, salinity, fluorescence, oxygen saturation, and oceanic pCO2 (Gac et al., 2020). We further separated the thermal and non-thermal components of pCO2 using the methodology outlined by Takahashi et al. (1993, 2009). These datasets were analyzed using turbulence framework methods: Fourier spectral analysis to assess scaling properties, triple correlation function for reversibility analysis, and the Liang-Kleeman information flow index for causality analysis. Our results revealed that all data series exhibited scaling properties close to 5/3, as predicted by Kolmogorov-Obukhov in 1941 for homogeneous and isotropic turbulence. Notably, even the non-thermal component of pCO2 followed this pattern. Reversibility analysis suggested that biological processes appear to be reversible, whereas physical processes are not. Finally, we explored the causality between these time series, uncovering non-linear behavior, with varying values observed across different timescales.



References :

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Robache, K et al. (2024). Scaling and intermittent properties of oceanic and atmospheric pCO2 time series and their difference, Nonlin. Processes Geophys. Discuss. [preprint], https://doi.org/10.5194/npg-2024-7, in review.

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