Distinct Impacts of El Niño-Southern Oscillation and Indian Ocean Dipole on China’s Gross Primary Production

Abstract. Gross primary production (GPP) stands as a crucial component in the terrestrial carbon cycle, greatly affected by large-scale circulation adjustments. This study explores the influence of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on China’s GPP, utilizing long-term GPP data generated by the Boreal Ecosystem Productivity Simulator (BEPS). Partial correlation coefficients between GPP and ENSO reveal substantial negative associations in most parts of western and northern China during the September-October-November (SON) period of ENSO development. These correlations shift to strongly positive over southern China in December-January-February (DJF), then weaken in March-April-May (MAM) in the following year, eventually turning generally negative over southwestern and northeastern China in June-July-August (JJA). In contrast, the relationship between GPP and IOD basically exhibits opposite seasonal patterns. Composite analysis further confirms these seasonal GPP anomalous patterns. Mechanistically, we ascertain that, in general, these variations are predominantly controlled by soil moisture in SON and JJA, but temperature in DJF and MAM. Quantitatively, China's annual GPP demonstrates modest positive anomalies in La Niña and nIOD years, in contrast to minor negative anomalies in El Niño and pIOD years. This results from counterbalancing effects with significantly greater GPP anomalous magnitudes in DJF and JJA. Additionally, the relative changes in total GPP anomalies at the provincial scale display an east-west pattern in annual variation, while the influence of IOD events on GPP presents an opposing north-south pattern. We believe that this study can significantly contribute to our comprehension of how intricate atmospheric dynamics influence China’s GPP on an interannual scale.