Large CO₂ disequilibria in tropical lakes

On the basis of a broad compilation of data onpCO₂ in surface waters, we show tropical lakes to be, on average, far more supersaturated and variable in CO₂ (geometric mean ± SE pCO₂ = 1804 ± 35 μatm) than temperate lakes (1070 ± 6 μatm). There was a significant negative relationship between pCO₂ and latitude, resulting in an average decrease of pCO₂ by 2.8 ± 0.5% per degree latitude. In addition, we found a general positive relationship between pCO₂ and water temperature across lakes involving an average increase (±SE) in 6.7 ± 0.8% per °C. A conservative annual efflux from global lakes to the atmosphere was reestimated to 0.44 Gt C. Our results show tropical lakes maintain large CO₂ disequilibria with the atmosphere, playing a disproportionate and variable role in the flux Of CO₂ between lakes and the atmosphere, thereby being a significant component of the global C cycle.