The effect of lunar declination on CO<sub>2 </sub>degassing from central Italian Apennines

Abstract

<p>The periodical degassing from CO<sub>2</sub> over-pressured reservoirs may have serious consequences for the environment making urgent understanding the processes and forecasting the frequency. Prediction though needs methods that depends from temporal and spatial properties of hydro-chemical and physical reservoir characteristics that unfortunately are often lacking. We have analyzed surface emissions of CO<sub>2</sub> attributed to over-pressured CO<sub>2</sub>-rich reservoirs in the Central Italian Apennines a zone characterized by significant periodical CO<sub>2</sub> degassing. Here aquifers are hosted in Mesozoic limestone with high pCO<sub>2</sub> groundwater and travertine deposits. We analyzed a 10-year temporal series and found that in the Apennines CO<sub>2</sub> flux and aquifer fluid composition are correlated with the lunar tides. In particular, our study reveals that low CO<sub>2</sub> flux corresponds with low lunar tidal potential values. We found a similar trend for dissolved calcium and water alkalinity, while pH values display a linear correlation with tidal cycles. The forces associated with tidal potentials are not capable of fracturing rock. However, they can, under certain conditions, drive the flow of fluids in over-pressured reservoirs, triggering sub-surface fluid movements that in turn modify the water�Crock reactivity. In the central Apennines, we show that these movements result in increased dolomite dissolution and an eventual return to calcite equilibrium. In this case, dolomite dissolution breaks the rock releasing calcium into ground water, which leads to calcite equilibrium and in turn to the formation of significant quantities of travertine and the concomitant release of CO<sub>2</sub> in the atmosphere.</p>