El Niño and La Niña are often discussed as if their most important effect is simply making a place wetter or drier. New research from southeastern China suggests that this framing can miss a crucial part of the climate signal. In a region shaped by the East Asian monsoon, the timing of rainfall across the year may change more clearly than the annual total, and that seasonal rearrangement can leave a chemical fingerprint inside cave stalagmites.
A study published in the Journal of Geophysical Research: Atmospheres on 28 September 2026 combined instrumental observations, isotope-enabled climate modelling and a high-resolution stalagmite record from Yongquan Cave. The researchers found that El Niño generally shifted the balance away from East Asian Summer Monsoon rainfall and toward non-summer precipitation, while La Niña tended to produce the opposite pattern.
The result matters for more than understanding modern rainfall. Stalagmites can preserve oxygen-isotope variations for far longer than weather stations have existed. If scientists can identify what those isotope changes physically represent, cave deposits can become more reliable archives of past climate variability, including changes associated with the El Niño-Southern Oscillation, or ENSO.
A climate signal hidden in the seasons
Southeastern China sits within the core East Asian monsoon region, where rainfall is strongly seasonal. That makes annual precipitation totals only one part of the hydroclimatic picture. Two years can receive similar total rainfall while distributing that water very differently between summer and the rest of the year.
The researchers focused on the ratio between East Asian Summer Monsoon precipitation and Non-Summer Monsoon precipitation. This seasonal ratio provides a way to detect whether rainfall is becoming more concentrated in the summer monsoon or redistributed toward other parts of the year.
The study reports that ENSO affects southeastern China’s hydroclimate primarily through this seasonal balance rather than through a simple, uniform change in annual rainfall. During El Niño conditions, summer monsoon precipitation generally decreased while non-summer precipitation increased. This lowered the summer-to-non-summer precipitation ratio. La Niña conditions broadly reversed the pattern.
That distinction is important. A climate archive that responds to rainfall seasonality can contain a strong ENSO signal even when annual rainfall totals themselves do not show an equally straightforward relationship.
Combining weather observations, modelling and cave chemistry
The researchers did not rely on a single source of evidence. They brought together modern meteorological observations, large-scale circulation indicators, precipitation oxygen-isotope information and simulations from the Isotope-incorporated Global Spectral Model, known as IsoGSM.
They then compared these modern relationships with stalagmite YQ15-1 from Yongquan Cave in southeastern China. The high-resolution stalagmite record covers 1987 to 2015, providing 28 years in which the cave record could be assessed against the behaviour of the modern climate system.
The key measurement is oxygen isotope composition, expressed as δ18O. Oxygen occurs naturally in different isotopic forms, and the ratio preserved in precipitation can change with moisture source, transport, atmospheric circulation and the seasonal distribution of rainfall. Water reaching a cave can transfer part of this isotope signal into growing calcium carbonate layers in a stalagmite.
This means stalagmite δ18O is not simply a direct rain gauge frozen in stone. Interpreting it requires understanding the atmospheric processes that produced the isotope variation in the first place. The new study was designed around that problem.
El Niño and La Niña left opposite seasonal fingerprints
Across the modern analyses, El Niño events were generally associated with reduced East Asian Summer Monsoon precipitation and enhanced Non-Summer Monsoon precipitation in southeastern China. The resulting decline in the summer-to-non-summer precipitation ratio was accompanied by more enriched precipitation δ18O values.
La Niña tended to generate the inverse pattern: relatively more summer monsoon rainfall, a higher summer-to-non-summer precipitation ratio and more depleted isotope values.
The importance of this finding is conceptual as much as statistical. ENSO’s regional imprint is expressed through a redistribution of rainfall through the calendar. The isotope signal integrates that seasonal reorganisation, allowing it to appear in the chemical composition of precipitation and eventually in cave deposits.
The authors link these changes particularly to the Western Pacific Subtropical High, a major atmospheric circulation feature that influences moisture transport and convection over East Asia. ENSO-related shifts in this circulation system alter where moisture travels and when rainfall reaches southeastern China.
In other words, the chain begins far from the cave. Tropical Pacific ocean conditions influence atmospheric circulation. That circulation changes the seasonal balance and transport pathways of rainfall over southeastern China. Those changes affect precipitation isotopes, and the isotope variations can then be incorporated into stalagmite layers.
The stalagmite broadly followed the modern ENSO pattern
The strongest test of the proposed mechanism was whether the Yongquan Cave record behaved consistently with the relationships identified from observations and modelling.
It broadly did. The YQ15-1 stalagmite record showed positive δ18O anomalies during El Niño phases and negative anomalies during La Niña phases. These changes aligned with the instrumental ratio between summer monsoon and non-summer precipitation.
This agreement supports the interpretation that the stalagmite is recording an integrated seasonal response to ENSO rather than functioning as a simple measure of total annual rainfall.
That distinction can change how paleoclimate records are read. If a stalagmite isotope shift is interpreted only as “more rain” or “less rain,” researchers may overlook changes in rainfall timing, moisture source and atmospheric circulation that can generate the same chemical response.
Why 28 years of overlap can inform much older climate records
Instrumental climate records are exceptionally detailed but comparatively short. Stalagmites can extend environmental histories across centuries or millennia, sometimes with unusually fine chronological resolution. Their value, however, depends on establishing a defensible connection between the chemistry preserved in the cave and the climate process researchers want to reconstruct.
The 1987 to 2015 Yongquan Cave record gives researchers an opportunity to examine that connection during a period when instrumental climate data and modern modelling are also available. The study therefore acts as a calibration exercise as well as an investigation of ENSO.
By identifying precipitation seasonality and large-scale circulation as central links between ENSO and stalagmite δ18O, the research provides a process-based framework for interpreting older cave records from the region.
This does not mean every isotope fluctuation in every southeastern Chinese stalagmite can automatically be labelled an El Niño or La Niña event. Cave hydrology, local rainfall, moisture transport and other climate modes can also affect the signal. Rather, the study strengthens the physical basis for investigating ENSO-related variability in suitable high-resolution records.
Rainfall timing matters for climate risk too
The findings also have a modern relevance. Seasonal rainfall distribution affects water availability, agriculture, flood risk and drought exposure differently from annual rainfall totals alone. A shift that removes rainfall from one season and adds it to another can matter even when the yearly total changes relatively little.
Understanding how ENSO reorganises rainfall timing can therefore improve the interpretation of regional climate variability. The study points to the Western Pacific Subtropical High as an important atmospheric mechanism connecting tropical Pacific variability with southeastern China’s seasonal hydroclimate.
For paleoclimate science, the larger implication is that natural archives may preserve information about the structure of rainfall through the year, not merely its amount. That creates the possibility of reconstructing aspects of past ENSO behaviour beyond the instrumental era, provided that researchers continue testing the physical pathways linking ocean conditions, atmospheric circulation, precipitation isotopes and cave deposition.
Important limitations
The study’s conclusions should be interpreted within several boundaries. The directly evaluated stalagmite interval spans 1987 to 2015, which is long enough to include multiple ENSO events but short relative to the centuries or millennia over which paleoclimate reconstructions may ultimately be applied.
The work also combines observations with isotope-enabled model simulations. Models are valuable for isolating atmospheric processes and tracing moisture pathways, but their output depends on model structure, input data and representation of physical processes.
Stalagmite δ18O is influenced by several processes between ocean evaporation and carbonate deposition inside a cave. The study provides evidence for a seasonal ENSO pathway in this region, but the isotope record should not be treated as a perfectly specific or universal ENSO index.
Finally, the results concern southeastern China and a particular cave record. Replication across additional caves, longer modern calibration periods and other monsoon settings would help establish how consistently the proposed relationship holds across space and time.
A more precise way to read climate written in stone
The study adds an important layer to the interpretation of monsoon cave records. ENSO did not simply correspond to wetter or drier years in southeastern China. It altered the seasonal balance of precipitation, partly through changes in large-scale atmospheric circulation, and those shifts were reflected in oxygen isotopes.
The Yongquan Cave stalagmite broadly captured the same pattern. That makes its isotope chemistry potentially useful for looking beyond the short instrumental record, while also showing why paleoclimate interpretation requires more than translating one isotope value into one rainfall amount.
For researchers trying to reconstruct past ENSO variability, the message is that the calendar of rainfall can be as important as the total. In southeastern China, part of that calendar appears to have been written into stone.
Source Information
Original study: Li, Y., Zhang, H., Sinha, A., Li, H., Zhang, J., Song, Y., et al. (2026). Mechanisms of ENSO-modulated precipitation seasonality in Southeastern China and implications for stalagmite δ18O records. Journal of Geophysical Research: Atmospheres, 131, e2026JD047681.
DOI: 10.1029/2026JD047681
Publication date: 28 September 2026
Study type: Instrumental observations, isotope-enabled climate modelling and high-resolution stalagmite paleoclimate analysis.
