The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The tropical Pacific exhibits not only interannual ENSO variability (2-7 years) but also decadal-to-multidecadal fluctuations on longer timescales. Of particular interest is the quasi-decadal sea surface temperature (SST) signal, with a period of approximately 12 years, which reaches its maximum in the Niño4 region. A heat budget analysis, based on ocean reanalysis data and hindcast simulations from a global ocean model, reveals that the development of quasi-decadal SST anomalies (SSTA) in the Niño4 region is primarily driven by zonal advective feedback ( ), upwelling feedback ( ), and thermocline feedback (' ). While the upwelling feedback is in-phase with the Niño4 SSTA, the thermocline and zonal advective feedbacks precede the Niño4 SSTA by about one year. Further analysis suggests that both the thermocline and zonal advective feedbacks are determined by subsurface (50-200m) temperature anomalies in the Niño4 region, which are also approximately one year ahead of SSTA, through anomalous vertical temperature gradients and zonal geostrophic currents. The Niño4 subsurface temperature anomalies are in-phase with the subsurface convergence between 5S and 5N to the east of Niño4 region (150W-110W). The enhanced convergence induces anomalous subsurface warming, weakened equatorial undercurrents, and thus anomalous westward heat transport into the Niño4 region. Our findings provide new insight into the tropical Pacific decadal variability and its potential predictability from the subsurface ocean.
 

tropical Pacific, decadal variability, ocean dynamics, subsurface ocean temperature