Global carbon dioxide output of volcanic lakes in the Azores archipelago, Portugal

Abstract

The Azores archipelago (Portugal) contains 88 lakes, two located inside caves spread across six of the nine volcanic islands of the archipelago; the formation of the lakes is associated with various types of volcanic structures. Surveys were performed on 45 water bodies corresponding to a representative data set and omitting only small ephemeral ponds to extensively research CO2 emissions from the volcanic lakes.The modified accumulation chamber method was used to measure the CO2 flux at the surface of the lakes; 16,119 measurements were performed with flux values ranging from 0 to 20,960 g m−2 d−1. Graphical statistical approaches identified different geochemical populations from the CO2 flux data. Multiple populations associated with limnological and biogenic processes or volcanic/hydrothermal sources were identified in some cases. The influence of these sources was also confirmed by the determined δ13C content of the lakes.The lakes of the Azores emit approximately ~171 × 103 t yr−1 of CO2 into the atmosphere; much of this is released by the Furnas and Furna do Enxofre lakes, both showing mantle-derived CO2 origin. Deep-seated CO2 accounts for approximately 42% of the total degassing.