BIO-07\INT-08 DS4MES
Tropical Pacific Ocean Carbon Response to El NiƱos
Enhui Liao* , School of Oceanography, Shanghai Jiao Tong University, Shanghai, China
Laure Resplandy, Department of Geosciences, Princeton University, Princeton, NJ, USA
Junjie Liu, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Kevin Bowman, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Amplification of the ocean carbon sink during El Niño events partially offset terrestrial biosphere carbon losses to the atmosphere but uncertainties in the magnitude, timing, and spatial extent of the ocean response confound our understanding of the global carbon budget and its sensitivity to climate. Here, we examine the mechanisms controlling the anomalous tropical Pacific Ocean CO2 drawdown during El Niño events harnessing multidecadal ocean pCO2 observations in conjunction with a state-of-the-art ocean biogeochemical model. We show that poleward Ekman transport dramatically amplifies the near-equatorial pCO2 anomaly identified in prior work and that this amplification varies considerably between El Niño events. During central Pacific events, the CO2 flux anomaly can vary up to 4-fold between events (2002/03 vs. 2015/16), but it always recedes during the boreal winter-spring transition and the poleward transport of the anomaly mostly extends into the northern hemisphere. During eastern Pacific events characterized by an equatorially-centered intertropical convergence zone (e.g. 1997/98), the intense CO2 flux anomaly persists into boreal summer and can extend further into the southern hemisphere. The hemispheric asymmetry (northward vs southward extension) and the termination (boreal winter/spring for central Pacific events vs. boreal summer for eastern Pacific events) of the ocean CO2 response are tied to the El Niño dynamics in the near-equatorial region but also how it is amplified by poleward Ekman transport. Finally, we evaluate how differences in the ocean response influence atmospheric CO2 and discuss the potential of atmospheric CO2 satellite data to provide observational constraints.