This work stands apart: the nearest neighbors study ocean heat pumps, ocean conveyors, and the influence of rotation on the heat of icy moons, but none have examined a subsurface dipole in the South China Sea. It has already been shown that Enceladus's ocean acts as a heat pump and that the ocean conveyor is on the brink, yet the connection between subsurface temperature and the monsoon and El Niño in this region remained unexplored.
We used GLORYS reanalysis data at 1/12° resolution for 1993–2018. Subsurface temperature was averaged over the 50–150 m layer and decomposed using empirical orthogonal functions (EOF). For validation, we used Argo data in the north and ORAS5 reanalysis across the basin. The heat budget was calculated using an equation with advection and a residual term. Wind stress and pressure were taken from ERA5.
The leading mode (EOF1) explains about 33% of the variance and represents a meridional dipole with a boundary near 11°N. The mode's time series correlates with summer monsoon intensity (r = 0.69). During strong monsoon years (1994, 2002, 2018), the north is cold and the south is warm; during weak monsoon years (1995, 1998, 2010), the pattern reverses. Anomalies are most pronounced between 50 and 150 m, reaching depths of 300 m. The heat budget shows that vertical advection dominates: in the northern box in 2018 it contributes about −1.9×10¹³ W, and in the southern box +0.9×10¹³ W. Horizontal advection is secondary and sometimes compensates for vertical advection. The dipole is accompanied by a meridional circulation: during strong monsoon years, heat transport southward across 10.5°N is −9.75×10¹⁴ W, while during weak monsoon years, transport northward is +1.45×10¹⁵ W.
This work shows for the first time that subsurface temperature in the South China Sea is organized into a dipole driven by wind curl, not by surface heating. This distinguishes it from neighboring studies that focused on heat pumps or conveyors in other regions. The dipole links El Niño to upper-ocean heat content and may influence tropical cyclones and subsurface marine heatwaves.
This topic could develop toward forecasting subsurface marine heatwaves and their connection to tropical cyclones. Studying the dipole's influence on biogeochemistry and ecosystems is promising. It may also be extended to other marginal seas with monsoon climates.
It will affect forecasts of tropical cyclones, subsurface marine heatwaves, and the regional climate of Southeast Asia.
Verify the dipole in longer records and models, and study its connection to specific tropical cyclones.
An open question in oceanography is how subsurface heat anomalies interact with the atmosphere and influence extreme events. The dipole offers a new mechanism linking El Niño to the heat content of a marginal sea, which could aid in forecasting heatwaves and cyclones.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This study examines the summer subsurface temperature dipole in the South China Sea using GLORYS reanalysis data at 1/12° resolution from 1993 to 2018. EOF analysis identifies the leading mode, which explains about 33% of the variance, and its time series correlates with summer monsoon intensity (r = 0.69). The heat budget reveals the dominance of vertical advection linked to wind curl anomalies, along with an associated meridional circulation.
Where its strength is
This work is the first to show that subsurface temperature in the South China Sea is organized into a dipole driven by wind curl, not surface heating, and it links this dipole to the monsoon and El Niño. This provides a foundation for further study of the dipole's influence on tropical cyclones and subsurface marine heatwaves.
Where it could go next
Worth trying
Why this may matter
If the dipole proves to be stable and predictable, it could be used to refine seasonal forecasts of the thermal structure of the South China Sea, which is important for predicting tropical cyclones and marine heatwaves.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.52, against a usual 0.64. It looks like few have drilled nearby.
The subsurface dipole is invisible at the surface: during strong monsoon years, the entire basin cools at the surface due to evaporation and upwelling, while the dipole hides below 50 m.