Contrasting behaviors of the atmospheric CO 2 interannual variability during two types of El Niños

Abstract. El Nino has two different flavors: eastern Pacific (EP) and central Pacific (CP) El Ninos, with different global teleconnections. However, their different impacts on carbon cycle interannual variability remain unclear. We here compared the behaviors of the atmospheric CO 2 interannual variability and analyzed their terrestrial mechanisms during these two types of El Ninos, based on Mauna Loa (MLO) CO 2 growth rate (CGR) and Dynamic Global Vegetation Models (DGVMs) historical simulations. Composite analysis shows that evolutions of MLO CGR anomaly have three clear differences in terms of (1) negative and neutral precursors in boreal spring of El Nino developing years (denoted as “yr0”), (2) strong and weak amplitudes, and (3) durations of peak from December (yr0) to April of El Nino decaying year (denoted as “yr1”) and from October (yr0) to January (yr1) during EP and CP El Ninos, respectively. Models simulated global land–atmosphere carbon flux (F TA ) is able to capture the essentials of these characteristics. We further find that the gross primary productivity (GPP) over the tropics and extratropical southern hemisphere (Trop+SH) generally dominates the global F TA variations during both El Nino types. Regionally, significant anomalous carbon uptake caused by more precipitation and colder temperature, corresponding to the negative precursor, occurs between 30° S and 20° N from January (yr0) to June (yr0), while the strongest anomalous carbon releases, due largely to the reduced GPP induced by low precipitation and warm temperature, happen between equator and 20° N from February (yr1) to August (yr1) during EP El Nino events. In contrast, during CP El Nino events, clear carbon releases exist between 10° N and 20° S from September (yr0) to September (yr1), resulted from the widespread dry and warm climate conditions. Different spatial patterns of land temperature and precipitation in different seasons associated with EP and CP El Ninos account for the characteristics in evolutions of GPP, terrestrial ecosystem respiration (TER), and resultant F TA . Understanding these different behaviors of the atmospheric CO 2 interannual variability along with their terrestrial mechanisms during EP and CP El Ninos is important because CP El Nino occurrence rate might increase under global warming.