Using a suite of reanalysis products, model output, and observational data, the Southern Ocean (SO) is demonstrated to be undergoing a significant warming during recent decades, and this SO warming influences the subsurface heat redistribution in the South Indian Ocean (SIO) via two pathways. First, the increasing surface heat flux over the SO induces a poleward shift of the westerlies and the entire subtropical gyre. Consequently, waters on the equatorial side of the potential density troughs become cooler and those on the poleward side become warmer. The specific outcome is that the subsurface SIO is dominated by an extensive cooling, with a prominent deep‐reaching warming around 30°S‐20°S. Second, the SO warming signals are transmitted northward along isopycnal surfaces from around 40°S up to the tropical SIO through the meridional overturning circulation, modulating the decadal variability of the SIO. The present study highlights the role of the SO in regulating global ocean heat balance and facilitates a better understanding of the moderating effects of oceans on global climate.

The Kuroshio Intrusion (KI) into the South China Sea (SCS) is a key process that greatly modulates the variability of dominant phenomena in the northern SCS. Using the Regional Ocean Modeling System, the optimal precursor (OPR) triggering the KI is obtained by the Conditional Nonlinear Optimal Perturbation (CNOP) approach. The OPRs exhibit the anticyclonic eddies (AEs) spatial pattern in the southern region (19°N–20.3°N, 119°E–122°E) of the Luzon Strait. The evolution processes of the OPRs indicate that the northwestward movement and rapid growth of AEs force the Kuroshio to bend westward continuously, which leads to the transition of the Kuroshio path from leaping state to intruding state. Eddy‐energetic analyses suggested that the barotropic instabilities are responsible for the evolution of the OPRs and thus triggering the KI, while the local wind stress plays a minor role in the triggering process. Additional examinations based on satellite altimeter data and ocean reanalysis data further confirm that the AE‐like perturbation similar to the obtained OPR indeed plays a key role in the KI triggering process.

The three‐dimensional climatological spreading of South Pacific waters over the Maritime Continent is examined using eddy‐resolving simulations and a passive tracer method. Four pathways are summarized for the South Pacific Tropical Water and the Antarctic Intermediate Water through the Maritime Continent, including two direct pathways, namely, the Eastern Path and the Torres Strait Path, and two indirect pathways, namely, the Western Path and the South China Sea Path. Among them, according to tracer concentration distribution, the former two contribute most of the volume transport of the Indonesian Throughflow (ITF) originating from the South Pacific. The latter two experience two retroflections (i.e., the South Equatorial Current‐Equatorial Undercurrent and the North Equatorial Countercurrent‐North Equatorial Current) before entering the Indonesian Seas. The vertical distributions of the South Pacific waters along each path throughout the Indonesian Seas are also analyzed, revealing that the South Pacific salinity extrema greatly affect the intermediate and deep layers of the Indonesian Seas and ITF as well as the upper thermocline. Vertical fluxes, especially vertical advection, are vital to these Indo‐Pacific water exchange processes. Sensitivity tests are conducted for the vertical diffusion coefficient and initial conditions, the results of which are robust. According to current study, the South Pacific has substantial impacts on the water properties throughout the Maritime Continent and the mass‐energy exchanges between the Pacific and Indian Oceans.

The tropical Pacific currents from January 2004 to December 2018 are computed based on the gridded Argo temperatures and salinities using the P-vector method on an f plane and the geostrophic approximation on a β plane. Three branches of the South Equatorial Current (SEC) are identified, i.e., SEC(N) (2°S–5°N), SEC(M) (7°–3°S), and SEC(S) (20°–8°S), with the maximum zonal velocity of −55 cm s⁻¹ and total volume transport of −49.8 Sv (1 Sv ≡ 10⁶ m³ s⁻¹) occurring in the central-east Pacific. The seasonal variability of each branch shows a distinct and different westward propagation of zonal current anomalies, which are well mirrored by the SLA differences between 2°S and 5°N, between 3°S and 6°S, and between 8°S and 15°S, respectively. Most of the seasonal variations are successfully simulated by a simple analytical Rossby wave model, highlighting the significance of the first-mode baroclinic, linear Rossby waves, particularly those driven by the wind stress curl in the central-east Pacific. However, the linear theory fails to explain the SEC(M) variations in certain months in the central-east Pacific, where the first baroclinic mode contributes only around 50% of the explained variance to the equatorial surface currents. A nonlinear model involving higher baroclinic modes is suggested for a further diagnosis. Considering the crucial role played by the tropical Pacific in the natural climate variability via the El Niño–Southern Ocean dynamics and the ocean response to anthropogenic forcing via the ocean heat uptake in the eastern tropical Pacific, advancing the process understanding of the SEC from observations is critical.