The South Pacific is a vast and dynamic ocean basin that plays a critical role in regulating global climate. It is also a key gateway to Antarctica, where ocean warming can destabilize ice shelves, accelerate sea ice melt, and contribute to sea level rise.
In 2023, the global ocean experienced unprecedented marine heatwaves, with record-high sea surface temperatures (SSTs) observed across multiple regions, including the southwestern Pacific. The anomaly did not fade. Instead, it persisted and shifted eastward into the central South Pacific in 2024, where both SST and upper-2000-m ocean heat content (OHC) reached their highest levels since observations began—each exceeding three times the local standard deviation.
The persistent two-year warming event raised a fundamental scientific question: what processes continuously fueled the ocean warming over such an extended period? The answers could hold important lessons for predicting future climate extremes.
A research team from Xiamen University combined ocean observations, satellite measurements, and ocean–atmosphere reanalysis products to investigate the mechanisms responsible for the persistent South Pacific warming during 2023–2024. Their study, published in Advances in Atmospheric Sciences , reveals the key atmospheric and oceanic processes that sustained this extreme warming event.
More than 90% of the excess heat trapped by global warming has been absorbed by the ocean. The Southern Ocean, one of the largest heat reservoirs in the climate system, plays a crucial role in regulating global ocean heat uptake and storage. Previous studies have mainly focused on how much heat the Southern Ocean has absorbed over long-term period, but a key question remains unclear: why do certain regions of the Southern Ocean experience rapid and extreme warming?
The study shows that the anomalous warming that emerged in the southwestern Pacific in 2023 did not disappear after the marine heatwave weakened. Instead, it persisted and shifted eastward in 2024. The warming signal extended to depths of about 1000 m, ultimately leading to record-high SST and OHC in the central South Pacific.
The study reveals that the two-year, west-to-east evolving record-breaking warming event was primarily maintained by two consecutive anomalous anticyclones over the South Pacific. These anticyclonic circulation anomalies occurred successively over the western and central South Pacific in 2023 and 2024.
The associated changes in air–sea heat fluxes, particularly enhanced latent heat flux anomalies, dominated the surface warming. Meanwhile, anticyclone-induced downwelling continuously transported surface heat into the deeper ocean, allowing heat to accumulate below the surface rather than being rapidly released back to the atmosphere. As a result, both SST and ocean heat content continued to increase, eventually reaching unprecedented levels.
A key question is why these two anomalous anticyclones emerged successively in different regions of the South Pacific. The researchers found that their development was closely linked to the evolution of the Southern Hemisphere zonal wave-3 (ZW3) pattern. During 2023–2024, pronounced phase shifts of ZW3 caused the western and central South Pacific to remain under persistent anticyclonic circulation, creating favorable conditions for sustained surface warming and downward heat transport.
Interestingly, although 2023/24 was characterized by a strong El Niño event, its direct atmospheric teleconnection to the South Pacific was unexpectedly weak. Instead, enhanced deep convection over the tropical Indian Ocean generated a poleward and eastward propagating atmospheric wave train, which played an important role in adjusting the ZW3 phase and strengthening South Pacific anticyclonic anomalies.
Corresponding author Prof. Kewei Lyu explained the broader implications of the findings: "Our research reveals a potentially underestimated role of the tropical Indian Ocean in driving high-latitude climate variability and extreme ocean events. This provides a new perspective beyond traditional tropical Pacific teleconnection mechanisms and is essential for enhancing predictions of marine extremes and improving current climate prediction systems."
The persistent warming signal extending into the deep ocean may have further implications for Antarctic sea ice variability and ice-shelf stability. As climate change continues, similar extreme ocean warming events may become more frequent and intense. Understanding drivers and mechanisms of these events is essential for enhancing predictions of marine extremes and improving current climate prediction systems.
Advances in Atmospheric Sciences
Persistent Ocean Warming from 2023 to 2024 Set Another Record in the South Pacific
29-Jul-2026