Enhanced North American carbon uptake associated with El Nino Science Advances

Long-term atmospheric CO2 mole fraction and delta(CO2)-C-13 observations over North America document persistent responses to the El Nino-Southern Oscillation. We estimate these responses corresponded to 0.61 (0.45 to 0.79) PgC year(-1) more North American carbon uptake during El Nino than during La Nina between 2007 and 2015, partially offsetting increases of net tropical biosphere-to-atmosphere carbon flux around El Nino. Anomalies in derived North American net ecosystem exchange (NEE) display strong but opposite correlations with surface air temperature between seasons, while their correlation with water availability was more constant throughout the year, such that water availability is the dominant control on annual NEE variability over North America. These results suggest that increased water availability and favorable temperature conditions (warmer spring and cooler summer) caused enhanced carbon uptake over North America near and during El Nino.