Thermal stratification and carbon dioxide dynamics in tropical lakes: insights from a multi-year assessment

Tropical lakes play a significant role in the global carbon cycle, although their contributions remain poorly characterized. This study presents a comprehensive six-year monthly monitoring of two tropical lakes, Lake Nova (LN) and Lake Juparanã (LJ), in southeastern Brazil, aimed at understanding the influence of thermal stratification and wind on carbon dynamics, metabolism, and CO 2 fluxes at the air–water interface. Thermal profiles and metabolic indicators ( p O 2 , p CO 2 , respiration index (RI), dissolved organic carbon (DOC), and chlorophyll-α (Chl-α) were used to clarify when the lakes acted as CO 2 sources or as sinks. The results revealed a marked predominance of CO 2 fluxes in the atmosphere in both systems, with the highest emissions occurring during the mixing events. While LN exhibited stable stratification for most of the year, promoting CO 2 accumulation at depth and episodic releases during overturn, LJ underwent frequent mixing, resulting in more continuous but lower daily emissions than those of LN. The RI indicated that LN was net heterotrophic (RI < 1) during the stratified periods, whereas LJ remained autotrophic (RI > 1). The Generalized Linear Models analysis highlighted the role of thermal dynamics and wind forcing in modulating CO 2 variability within the water column. These findings underscore the need to incorporate lake-specific physical processes into global carbon models, particularly in tropical systems.