Contrasting interannual atmospheric CO2 variabilities and their terrestrial mechanisms for two types of El Ninos

摘要

El Nino has two different flavors, eastern Pacific (EP) and central Pacific (CP) El Ninos, with different global teleconnections. However, their different impacts on the interannual carbon cycle variability remain unclear. Here we compared the behaviors of interannual atmospheric CO2 variability and analyzed their terrestrial mechanisms during these two types of El Ninos, based on the Mauna Loa (MLO) CO2 growth rate (CGR) and the Dynamic Global Vegetation Model's (DGVM) historical simulations. The composite analysis showed that evolution of the MLO CGR anomaly during EP and CP El Ninos had three clear differences: (1) negative or neutral precursors in the boreal spring during an El Nino developing year (denoted as "yr0"), (2) strong or weak amplitudes, and (3) durations of the peak from December (yr0) to April during an El Nino decaying year (denoted as "yr1") compared to October (yr0) to January (yr1) for a CP El Nino, respectively. The global land-atmosphere carbon flux (F-TA) simulated by multi-models was able to capture the essentials of these characteristics. We further found that the gross primary productivity (GPP) over the tropics and the extratropical Southern Hemisphere (Trop + SH) generally dominated the global F-TA variations during both El Nino types. Regional analysis showed that during EP El Nino events significant anomalous carbon uptake caused by increased precipitation and colder temperatures, corresponding to the negative precursor, occurred between 30 degrees S and 20 degrees N from January (yr0) to June (yr0). The strongest anomalous carbon releases, largely due to the reduced GPP induced by low precipitation and warm temperatures, occurred between the equator and 20 degrees N from February (yr1) to August (yr1). In contrast, during CP El Nino events, clear carbon releases existed between 10 degrees N and 20 degrees S from September (yr0) to September (yr1), resulting from the widespread dry and warm climate conditions. Different spatial pattern