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

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 CO 2 emissions from the volcanic lakes. The modified accumulation chamber method was used to measure the CO 2 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 CO 2 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 CO 2 into the atmosphere; much of this is released by the Furnas and Furna do Enxofre lakes, both showing mantle-derived CO 2 origin. Deep-seated CO 2 accounts for approximately 42% of the total degassing. • Lake stratification influences the amount of CO 2 emitted to the atmosphere. • Higher CO 2 values are associated with lakes having CO 2 of volcanic origin. • Low CO 2 flux and δ13C content on lakes suggest biogenic CO 2 origin. • Total CO 2 degassing from Azores lakes to the atmosphere was estimated at ~171 × 103 t yr−1. • Total deep-seated CO 2 degassing was estimated at ~72 × 103 t yr−1. [ABSTRACT FROM AUTHOR]