Magma-derived CO 2 emissions recorded in [formula omitted] and [formula omitted] content of plants growing in Furnas caldera, Azores

Abstract

The environmental impact of fumarolic and soil emanations of magma-derived carbon dioxide across Furnas caldera has been investigated by measuring the 14 C and 13 C content of 40 specimens of different C3 plants (leaves) growing within and outside the degassing areas. The results demonstrate a significant to large 14 C depletion in many of the plants due to assimilation of 14 C -free endogenous CO 2 during photosynthesis and leading to artificial radiocarbon ageing of up to 4400 years. The extent of 14 C ageing broadly correlates with the intensity of gas manifestations at the sampling sites, as inferred from field observations and measurements of excess CO 2 concentrations in the volcanic ground. It also provides a time-integrated measure of the amount of volcanic CO 2 locally admixed to the ambient air; at several sites this accounts for 15 to 40% of total CO 2 (420 to 600 ppm) in enriched air. In some of the plant species ( Azalea, Camellia and fern) 14 C depletion is correlated with an enrichment of 13 C due to assimilation of magma-derived CO 2 with a 4‰ higher δ 13 C than normal atmosphere. The rate of 13 C enrichment averages ca. 0.18‰ by percent of volcanic carbon fixed in the plant and includes enhanced 13 C discrimination during photosynthesis as a consequence of increased ambient pCO 2 (inferred at −0.0306‰ per added ppm of volcanic CO 2). Furnas is one of the few volcanoes where clear 13 C enrichment in plants due to endogenous degassing has been evidenced. Our results can be used to estimate the local intensity of volcanic soil gas fluxes in the emanating areas of Furnas caldera. They also have implications for radiocarbon dating of past eruptive events in the caldera, since plants artificially aged by previous degassing could be trapped in volcanic deposits.