Publication Date:
2024-05-02
Description:
Environmental parameters drive seasonal soil CO2 efflux toward the atmosphere. However, their influence is not fully understood in contexts of high CO2 fluxes where CO2 accumulates in the subsurface. A prime example are volcanoes subject to continuous CO2 diffuse degassing rising from deep magmatic reservoirs, through the subsurface and up to the atmosphere. For many of these volcanoes where soil CO2 is monitored, a seasonal influence of the atmosphere and water table is observed but not characterized. Here, we compare variations of air temperature, atmospheric pressure, rainfall and water table level with near-surface soil CO2 concentration by performing a time-lagged detrended cross-correlation analysis on years-long time series from the volcanoes of Piton de la Fournaise and Mayotte. At Piton de la Fournaise, soil CO2 variations correlate best with air temperature variations (0.81) and water table variations (0.74). In Mayotte, soil CO2 variations correlate best with atmospheric pressure variations (−0.95). We propose that at Piton de la Fournaise, the thick vadose zone and high permeability favor CO2 transfer by thermal convection. Additionally, energy transfer is decoupled from mass transfer. Slow heat transfer from the atmosphere down to the accumulated CO2 layers in the subsurface results in a delayed influence of air temperature and of the water table level on the thermal gradient between the subsurface and the atmosphere, and consequently on the efficiency of the CO2 transfer. In Mayotte, we propose that the thin vadose zone and the presence of a network of large fractures favor CO2 transfer by barometric pumping.
Description:
Hatari Project INTERREG V Indian Ocean N° Synergie RE0023208
Description:
Published
Description:
e2023JG007409
Description:
OSV3: Sviluppo di nuovi sistemi osservazionali e di analisi ad alta sensibilità
Description:
JCR Journal
Keywords:
Air temperature, atmospheric pressure, and water table level influence soil CO2 concentrations at a seasonal scale
;
The decoupling of heat and mass transfer in the subsurface induces a delayed response of soil CO2 concentrations to environmental forcing
;
Volcanic emission of CO2
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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