abstract:The eastern equatorial Pacific is the predominant source area for atmospheric CO2, and the size of this source is significantly reduced during El Niño events. Here we apply a newly constructed 1999–2008 time series carbon chemistry trend to show a similar reduction can also be identified in the northern South China Sea. The net sea-to-air CO2 flux during the 2002–2003 El Niño event (1.57 ± 0.13~1.61 ± 0.28 g C m−2 a−1) at the SEATS time series site was significantly lower than that during the 2007–2008 La Niña event (10.35 ± 0.66~10.67 ± 0.93 g C m−2 a−1). The appreciable reduction (by ~85%) is a direct response to the diminished vertical mixing of CO2-rich subsurface waters from below and, possibly, an increase in the lateral flow transport from the western Pacific during the weakening winter monsoon in the El Niño years. Thus, the suppression of CO2 efflux during the El Niño events is a basin-wide phenomenon across from the eastern equatorial Pacific to the western subtropical Pacific including the northern South China Sea.