In the Gulf of Panama, the seasonal cooling of the sea plays a role in sustaining ecosystems. An episode in 2025, brought back into focus by Futura on 14 November, shows what can happen when this seasonal event becomes much less pronounced. It does, however, warrant careful reading: the study was published in September 2025 and does not describe an event that has just occurred.
What the wind brings to the sea
The phenomenon has an English name, “upwelling”, which can be translated as the rising of deep water. The NOAA, the US ocean and atmospheric observation agency, explains the principle: the wind moves surface waters; water from below rises to take their place.
This water is generally colder and rich in nutrients. Its arrival fuels biological production near the surface. This is one reason why areas where the phenomenon occurs regularly can provide good conditions for fishing. The mechanism occurs along coastlines as well as in the open sea. The reverse movement, when an accumulation of surface water eventually sinks, has another name: “downwelling”.
The wind therefore affects more than just the visible waves. It also helps move the resources on which marine life depends. To understand a change in the ocean, it is as necessary to look at its temperature and movements as it is to look at the animals that inhabit it.
Twelve cool days instead of sixty-six
The study published in PNAS combines satellite measurements, on-site observations and water-column profiles. In the coastal series studied, the temperature first fell below the 25 °C threshold on 4 March 2025, 42 days late. The researchers counted twelve days below this threshold, compared with the usual sixty-six, a decrease of 82%.
The lowest temperature measured in this series was 23.3 °C, compared with around 19 °C usually. These results describe a sharply reduced cooling. They do not mean that all vertical movements in the ocean ceased. Differences in methods or measurement locations can also produce a different minimum: indicators constructed in the same way need to be compared.
The authors link the episode to favourable winds that were less frequent and less persistent. When they did blow, they were not consistently weaker. The full atmospheric mechanism remains to be clarified; this one season is not enough to predict the next.
Concern for fisheries, not an established tally of losses
In its account of the research, the Smithsonian Tropical Research Institute highlights two benefits of these seasonal upwellings: they bring nutrients and cool reefs. Phytoplankton, a group of microscopic organisms that carry out photosynthesis, forms the basis of many food relationships. Corals, in turn, can benefit from the arrival of this cooler water when exposed to heat.
The Smithsonian nevertheless stresses that further research is needed to clarify the causes and consequences for fisheries. The risk to a resource and a loss that has actually been measured are not the same thing. A decline in fishing productivity cannot automatically be inferred from a single snapshot of the ocean: the species, catches and period concerned still need to be examined.
What to monitor next
One useful outcome of this work is also a question of monitoring. On what dates do the waters cool? For how long? Do the winds recover? Do biological indicators change in turn? Linking these observations would help distinguish an exceptional episode from a change that recurs.
For readers, the point of reference is simple: a study published in 2025 can still be informative in 2026, provided its date, geographical scope and limitations are kept in mind. Here, it documents the vulnerability of a seasonal mechanism. It is neither a global assessment of the oceans nor proof that all marine life in the Gulf has disappeared.
Archive photograph: the Gulf of Panama in July 2009. It does not show the 2025 measurements. Photo: ---=XEON=--- — Wikimedia Commons, CC BY 3.0.
