A significant decadal variability of the North Pacific Eastern Subtropical Mode Water (NPESTMW), related to the Pacific Decadal Oscillation, is identified from the gridded Argo and EN4 observational data sets. To investigate the decadal variability of the NPESTMW volume, the high‐resolution Estimating the Circulation and Climate of the Ocean, Phase II simulation is used to diagnose the volume budget of the NPESTMW density layer in the NPESTMW formation region (20°–36°N, 160°–120°W) between 1992 and 2016. Results show that NPESTMW is formed through subduction of low potential vorticity (PV) water. This low‐PV water subduction is mainly determined by mixed layer depth change and lateral induction, which account for approximately 58% and 32%, respectively. The decadal NPESTMW volume anomaly is originated from the Pacific Decadal Oscillation‐induced decadal anomaly of air‐sea buoyancy flux. This decadal buoyancy flux anomaly drives the decadal anomaly of mixed layer depth change, then causes anomalous subduction, and leads to anomalous low‐PV water subduction. The decadal NPESTMW volume anomaly is finally generated by this anomalous low‐PV water subduction.

Although intensive studies have documented the recent increase in the frequency of the Central Pacific (CP) El Niño events, the underlying mechanism remains unclear. This motivates us to investigate the change in the frequency of CP El Niño events. By analyzing the occurrence of the CP El Niño events between 1960 and 2022, we confirm a statistically significant increase in the frequency of CP El Niño events since 2000. Over the 40 years between 1960 and 1999, eight CP El Niño events appeared. In contrast, over the 23 years between 2000 and 2022, six CP El Niño events are seen. The significant period of the CP El Niño shortens from 4–5 years to 2–3 years. The increased frequency of CP El Niño events is closely related to more frequent warm sea surface temperature (SST) anomalies in the central equatorial Pacific (5° S–5° N, 170° W–122° W) during the CP El Niño developing phase (June to October). A heat budget analysis of the mixed layer reveals that the SST variability in the central equatorial Pacific during the developing phase is determined by zonal temperature advection. The frequent anomalous warm zonal advection drives more frequent warm SST anomalies, and finally, the increased frequency of CP El Niño events, as observed.

Ocean mesoscale eddies, characterized by substantial eddy kinetic energy (EKE), are ubiquitous throughout the global ocean and play an essential role in ocean circulation, climate, and biogeochemistry. In the North Pacific, high and variable EKE is primarily concentrated in the western Subtropical Gyre. In contrast, the EKE levels in the Subtropical Northeast Pacific are relatively lower. Nevertheless, the EKE in this region remains comparable to the local mean kinetic energy and exhibits significant variability across seasonal to interannual timescales. In this study, we investigated the decadal variability of EKE in the Subtropical Northeast Pacific using observational data from 1993 to 2024. Results reveal that the EKE in this region undergoes remarkable decadal variability with a significant period of 10–11 years. This variability is characterized by a monopole spatial pattern, with the largest amplitude centered northeast of the Hawaiian Archipelago, at approximately 154°W, 26°N. Additionally, the variability is also manifested by decadal changes in the amplitudes of both cyclonic and anticyclonic eddies. Mechanistically, the EKE decadal variability is primarily driven by decadal variations in baroclinic eddy available potential energy (EPE) to EKE conversion through vertical eddy density flux. These decadal variations in baroclinic instability are likely to originate from the Pacific Decadal Oscillation (PDO). The PDO is suggested first to modulate the eddy field of density, subsequently altering the baroclinic EPE to EKE conversion associated with baroclinic instability. Consequently, the EKE fluctuates correspondingly and exhibits significant decadal variability, with the PDO signal leading the observed EKE decadal variability by approximately 15 months. Given the vital role of eddies in the transport of heat and nutrients, the identified decadal variability of EKE is expected to cause significant decadal variations in the coastal ecosystem surrounding the Hawaiian Archipelago.