In early 2025, scientists working in the Gulf of Panama realised something was missing. The usual pulse of cold, nutrient-rich water that rises from the depths every dry season simply never appeared, disrupting marine life, local fisheries and raising new concerns about how fast the tropics are changing.
A coastal engine that suddenly stalled
Every year between December and April, strong trade winds blow across the Gulf of Panama. They push warm surface waters away from the coast and allow deeper, colder waters to well up to the surface — a process known as upwelling.
Those dark, cool patches on satellite images, rich in chlorophyll, are normally a sign that the system is working. They show microscopic algae thriving on nutrients brought from below, feeding plankton, fish, seabirds and marine mammals.
For at least four decades, this seasonal upwelling has been one of the most reliable features of Panama’s Pacific coast — until 2025.
A research team led by the Smithsonian Tropical Research Institute, working with Germany’s Max Planck Institute, was tracking the region as usual when the data began to look strange. Sea surface temperatures stayed high. Chlorophyll concentrations remained unusually low. Instruments showed a stark lack of nutrients in the upper ocean.
They checked the satellite record going back 40 years. Every year showed the same pattern of cooling and greening during the dry season. Every year, except 2025.
What upwelling really does for Panama
Upwelling might sound like a technical detail, but along this coast it underpins almost everything. Cold, nutrient-rich water is like fertiliser tipped into the sea. It transforms a relatively poor tropical environment into a powerhouse of productivity.
- Fisheries: It supports schools of sardines, mackerel and other small fish targeted by artisanal fleets.
- Coral reefs: It cools shallow reefs just enough to help them withstand extreme heat.
- Local climate: It moderates nearshore temperatures, making coastal waters more tolerable during heatwaves and peak tourist season.
For decades, the Gulf of Panama has depended on this natural ocean fertiliser. Fishers organise their work around it. Corals “expect” that seasonal cooling. Even coastal weather patterns are nudged by the temperature contrast between cooled gulf waters and the warmer Pacific beyond.
When that hidden engine stalls, the impact runs from microscopic plankton all the way to coastal economies.
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How weakened winds broke the cycle
The team’s measurements pointed quickly to a culprit: the winds themselves. The usually robust northerly trade winds were unusually weak and patchy at the start of 2025.
Without sustained wind, surface waters were not pushed away from the coast, and deeper waters stayed locked below. Data gathered from the research vessel S/Y Eugen Seibold, fitted with high‑precision ocean and weather sensors, showed a striking lack of vertical movement in the water column.
Climate scientists involved in the work highlighted two main suspects:
- natural multi‑year variability in Pacific climate, such as the Pacific Decadal Oscillation
- long‑term, human‑driven climate change reshaping wind patterns in the tropics
Atmospheric simulations showed a tight link between unusual pressure patterns over the eastern Pacific and the weaker trades. That suggests this was not just a random blip, but part of a broader shift in the region’s climate balance.
The Panama event hints that entire tropical coastlines could see their once‑dependable seasonal cycles become erratic.
From plankton to plate: the ecological chain reaction
Once the upwelling failed, a series of knock‑on effects spread through the gulf. The first sign was invisible to the naked eye: phytoplankton, the tiny plant‑like organisms that form the base of the marine food web, did not bloom as they usually do.
That meant less food for zooplankton, small fish and many larvae. Local fishers quickly noticed changes at sea. Catches of sardines, mackerel and some squid species fell, squeezing the income of small coastal communities already under pressure from warming waters and erratic weather.
The damage was not confined to the open water. Coral reefs along Panama’s Pacific shore normally get a seasonal reprieve from heat when upwelled waters wash over them. Without that cooling, reefs sat for weeks in unusually warm conditions, increasing episodes of coral bleaching as corals expelled the symbiotic algae they rely on for energy.
Without their usual cool-water safety net, corals along the Gulf of Panama faced prolonged thermal stress and higher disease risks.
Warmer, more stagnant surface waters are also less oxygenated. That can favour harmful microbes and stress bottom‑dwelling creatures such as sea cucumbers, crustaceans and some reef fish. Over time, repeated events of this kind could push certain species past their thresholds, leading to local collapses in populations and shifts in which species dominate.
Economic and social stakes for coastal communities
While the 2025 event was primarily an ecological shock, the human dimension is immediate. Many small‑scale fishers in Panama depend on the predictable seasonal surge in fish tied to upwelling. They rely on it for both income and food security.
| Sector | Short-term impact of lost upwelling |
|---|---|
| Artisanal fisheries | Lower catches, volatile income, potential debt for fuel and gear |
| Fish processing & markets | Less supply, higher prices, risk of job cuts |
| Tourism | Hotter coastal waters, stressed reefs, lower appeal for divers and snorkellers |
| Local food security | Reduced availability of affordable local fish, greater reliance on imports |
If events like this repeat, authorities may be forced to rethink how many boats can operate, which species can be targeted, and how quickly communities need financial support when the ocean fails to deliver.
A warning from an under‑monitored part of the planet
Despite the strategic role tropical seas play in climate regulation, global fisheries and biodiversity, they are comparatively under‑monitored. Large upwelling systems off California, Peru or northwest Africa have dense networks of instruments and decades of detailed data. Tropical coastal regions often rely on scattered measurements and satellite snapshots.
Scientists point out that if the 2025 Panama anomaly had not been caught by a dedicated research cruise, it might never have been recorded at all.
That matters because climate models need real‑world observations to detect emerging patterns and test how well they capture events like this. Without robust monitoring, policymakers are effectively flying blind when it comes to coastal adaptation, fisheries regulation and reef protection.
The team studying the Gulf of Panama combined satellite imagery, on‑board measurements, chemical analyses of water samples and sophisticated atmospheric modelling. They argue that this kind of multi‑layered approach should become routine in tropical basins, not an exception tied to a single cruise or grant.
Key concepts behind the crisis
What “upwelling” really means in plain language
For non‑specialists, upwelling can sound abstract, so picture a shaken bottle of salad dressing. Left still, the heavy particles sink and the clear oil sits on top. Now imagine a spoon lifting the richer, heavier layer from the bottom back to the top. Upwelling is that spoon, but on an ocean scale.
Winds and Earth’s rotation act together to pull surface waters aside, making room for deeper waters to rise. Those deep waters carry nutrients recycled from sinking organic matter. When they reach sunlight near the surface, microscopic plants suddenly have both light and fertiliser, and productivity surges.
How multiple stresses can pile up
The 2025 event did not happen in a vacuum. Coral reefs and fisheries in Panama, as in many tropical regions, are already dealing with warming, pollution and overfishing. Losing seasonal upwelling adds another layer of stress.
- Warmer water pushes corals close to their bleaching threshold.
- Less upwelling removes their main seasonal cooling pulse.
- At the same time, reduced nutrients mean less food for fish larvae and plankton.
On their own, any one of these pressures might be manageable. Together, they can tip ecosystems into new, less productive states. That cumulative effect is what alarms many researchers.
What could happen next
Scientists are already thinking in scenarios. One possibility is that 2025 remains an outlier, a rare combination of wind and pressure patterns that may not repeat soon. In that case, ecosystems could gradually recover, though some corals and fish populations may need years.
The more worrying scenario is that weakened or highly variable upwelling becomes more common as the climate warms. That would force a re‑evaluation of how many fish can be sustainably caught, where marine protected areas are placed, and how coastal livelihoods are supported during lean years.
The Gulf of Panama has offered a glimpse of how quickly a long‑standing “normal” in the tropics can unravel.
For now, the 2025 season stands as a stark data point: a year when the deep, cool waters that usually breathe life into Panama’s Pacific coast stayed down, and the surface world felt the absence.