Impact of El Nino Southern Oscillation on CO₂ and Solar-Induced Fluorescence Over the Indo-Pacific Region

Over the tropical Indo-Pacific, we explore the variations of Solar-Induced Fluorescence (SIF), CO2, and precipitation during El Nino Southern Oscillation (ENSO) events verse other times. Based on various data sets, we analyze the time series of deseasonalized precipitation, vertical velocity, SIF, and CO2 across the Indo-Pacific region. Our analysis reveals that there is less precipitation, more sinking air, lower SIF, and higher carbon dioxide over the Indo-Pacific region during the El Nino events compared to other times. We also explore the spatial patterns of different variables to gain a deeper understanding of their relationships. The spatial analysis suggests that less precipitation resulting from predominant sinking air not only leads to lower SIF values by reducing photosynthetic activities but also triggers more biomass burning, which contribute to an increase in atmospheric CO2 levels across most areas of the Indo-Pacific region. The comparative study between observational analyses and numerical simulation by the NOAA CarbonTracker model indicates that the model can simulate the increase of atmospheric column CO2 during the El Nino event, although there are some difficulties in capturing the correct spatial pattern. The results of this study can significantly enhance our understanding of the spatial-temporal variabilities of atmospheric CO2 concentration and the observational characteristics can be used to enhance models. Furthermore, the complex interactions between ENSO and other variables revealed in this study improve our understanding of how ENSO influences the biosphere and carbon cycle.