Large CO₂ disequilibria in tropical lakes

On the basis of a broad compilation of data on p CO 2 in surface waters, we show tropical lakes to be, on average, far more supersaturated and variable in CO 2 (geometric mean ± SE p CO 2 = 1804 ± 35 μ atm) than temperate lakes (1070 ± 6 μ atm). There was a significant negative relationship between p CO 2 and latitude, resulting in an average decrease of p CO 2 by 2.8 ± 0.5% per degree latitude. In addition, we found a general positive relationship between p CO 2 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 CO 2 disequilibria with the atmosphere, playing a disproportionate and variable role in the flux of CO 2 between lakes and the atmosphere, thereby being a significant component of the global C cycle.