The Deep Brief #33 | 21 March 2026
Your end-of-week ocean intelligence, built to inform, agitate, and equip you
Every year for at least four decades, the ocean off Panama’s Pacific coast inhaled. Cold, nutrient-rich water rose from the deep, feeding the food web and cooling coral reefs. In 2025, for the first time on record, the breath did not come. The water stayed warm. The nutrients never arrived. A rhythm that coastal communities had depended on for generations simply stopped.
That finding, documented in a study published last year in the Proceedings of the National Academy of Sciences and resurfacing this week as scientists track whether the 2026 season recovers, is one of four stories shaping this week’s Deep Brief.
Alongside it: a 3-million-year ocean temperature record extracted from Antarctic ice, a chemical pollution study revealing how thoroughly humans have altered the ocean’s chemistry, and the oldest whale song ever recorded, a humpback singing into an ocean that was ten times quieter than it is today.
Three deep dives. Three quick hits. One hard truth from the sea.
Deep Dives
The ocean off Panama stopped breathing
Every dry season, strong seasonal winds called trade winds sweep from the north across Central America and into the Gulf of Panama. Those winds push warm surface water aside, allowing cold, nutrient-loaded water from the deep to rise and take its place. Scientists call this process upwelling. It is the foundation of the region’s marine food web. The nutrients feed phytoplankton, the tiny drifting plants at the base of the food chain, and that productivity cascades upward through fish, seabirds, and the coastal communities that depend on them. The same cold water gives nearby coral reefs a seasonal break from heat stress.
In 2025, this did not happen.
A study published last year in the Proceedings of the National Academy of Sciences, led by Aaron O’Dea at the Smithsonian Tropical Research Institute, documented that for the first time in at least 40 years of records, the seasonal upwelling in the Gulf of Panama failed completely. The story resurfaced this week as scientists tracking the 2026 season report that upwelling has returned, raising the question of whether 2025 was a one-off shock or a warning of what comes next. The expected temperature drop, which had arrived by 20 January in every previous year, did not begin until 4 March. When it did arrive, it lasted 12 days instead of the usual two months, and the water never reached the colder temperatures recorded in previous years.
The cause was not a lack of cold water at depth. It was there, waiting. The problem was atmospheric: the trade winds that normally drive the upwelling formed far less frequently than usual. When they did blow, they were roughly as strong as in past years, but the calm periods between them lengthened, and the total wind over the season was not enough to start the process.
The biological consequences were immediate. Phytoplankton production declined sharply. Satellite observations confirmed extremely low chlorophyll concentrations, a direct measure of plant life in the water, across the Gulf during a period when biological productivity normally peaks. Fish species that depend on the seasonal nutrient surge, including sardines, mackerel, and squid, lost their food source. Coastal fishing communities lost their catch.
“The tropical Panamanian sea has lost its vital breath,” O’Dea said.
Researchers aboard the S/Y Eugen Seibold, a sailing research vessel operated jointly by the Smithsonian and the Max Planck Institute for Chemistry, confirmed from direct measurements that the water column remained layered with warm water on top, with none of the vertical mixing that defines upwelling. “If our oceanographic mission had not taken place, no one would have known the upwelling had stopped,” said researcher Hanno Slagter.
That observation matters beyond Panama. Tropical upwelling systems are poorly monitored compared to their counterparts off California and Peru, which have long-standing observation networks. Similar failures in other poorly instrumented tropical regions could go entirely undetected. The O’Dea Lab’s public monitoring page shows the 2026 season has so far returned to strong cooling, with trade winds arriving and surface temperatures dropping to 16°C in parts of the Gulf by early February. That return suggests 2025 may have been an anomaly rather than a permanent shift. Whether this was a one-off shock or the beginning of an intermittent pattern is the question scientists are now tracking week by week.
Three million years of ocean temperature, read from bubbles in Antarctic ice
A study published this week in Nature presents the first direct record of average ocean temperature spanning the past 3 million years, extracted from ancient ice recovered in the Allan Hills blue ice area of Antarctica.
Here is how they did it. When snow falls and compresses into ice, it traps tiny bubbles of air. Noble gases like xenon and krypton do not react chemically with anything, so they faithfully record the conditions when they were trapped. The ratio of these gases in the bubbles reflects the temperature of the ocean at the time, because the ocean and atmosphere exchange them at rates that depend on water temperature. By comparing the amounts of xenon and krypton in ice cores of known age, scientists can reconstruct what the ocean’s average temperature was millions of years ago.
The record shows two significant findings. First, the ocean cooled sharply around 2.7 million years ago, during a period when ice sheets first formed over the Northern Hemisphere. Second, and more puzzling, a companion study published alongside it in the same issue of Nature found that atmospheric carbon dioxide levels remained largely stable during this cooling, hovering below 300 parts per million for most of the past 3 million years. That means the long-term cooling of the planet was driven by something other than a straightforward decline in greenhouse gases, likely changes in how the ocean circulates and distributes heat between the surface and the deep.
Current atmospheric CO₂ exceeds 425 parts per million, a level not seen in at least 3 million years. The ocean’s temperature is now climbing, not falling. The ice core record shows what stable ocean conditions looked like across geological time. We have left those conditions behind, and the rate of change is hundreds to thousands of times faster than anything in the record.
The ocean’s chemistry has a human fingerprint everywhere scientists look
A study published this week in Nature Geoscience examined more than 2,300 seawater samples collected between 2017 and 2022, making it one of the most comprehensive chemical analyses of the marine environment to date. Led by researchers at the University of California, Riverside, with contributions from the Scripps Institution of Oceanography, the work catalogued industrial compounds that are rarely included in routine monitoring.
Plastic additives. Synthetic fragrances. Pharmaceuticals. Pesticides. The researchers found human-made chemicals across the ocean, from coastal waters to more than 20 kilometres offshore. In coastal zones, these compounds made up a substantial fraction of the dissolved organic matter, the mix of natural chemicals floating in seawater. Even far from shore, human-derived chemicals accounted for roughly 1 per cent of detected organic matter. At a global scale, that is a very large amount of material.
Some of the compounds sit at the boundary between traditional chemical molecules and nanoplastics, the smallest fragments of plastic pollution, blurring the line between chemical contamination and plastic contamination. The researchers suggest these chemicals may play an unrecognised role in the ocean’s carbon cycle and ecosystem functioning.
“The human footprint is in everything,” said Lihini Aluwihare, a chemical oceanographer at Scripps and co-author of the study. “What determines whether you find it is whether you look for it in your data.”
The implications are straightforward. The ocean’s chemistry is no longer purely natural. The question is no longer whether human-made chemicals are present in the marine environment. It is what they are doing there, how they interact with marine life, and whether the monitoring systems designed to protect ocean health are looking for the right things.
Quick Hits
The oldest whale song ever recorded. Researchers at the Woods Hole Oceanographic Institution discovered a recording of a humpback whale singing off the coast of Bermuda in March 1949, preserved on a plastic disc from a 1940s dictation machine called a Gray Audograph. It is the oldest known recording of whale song, predating the discovery of whale song as a scientific phenomenon by nearly 20 years. The recording is significant not only for what the whale is doing, but for what the ocean sounds like around it. The ocean of the late 1940s was far quieter than today’s. Some parts of the ocean are now ten times louder than they were in the 1960s, largely due to shipping. The recording provides a baseline for understanding how increasing noise may be changing the way whales communicate. “Scientists are going to listen to these recordings and make discoveries that I can’t even begin to imagine yet,” said Ashley Jester, who found the disc while digitising old recordings.
Second ScotWind lease cancelled. Ocean Winds, an offshore wind developer backed by two European energy companies, is terminating the lease option, the agreement that gave it the right to build on the site, for the 500-megawatt (MW) Arven South floating wind project off the Shetland Islands. The developer cited no viable grid connection, the high fees charged for connecting to the electricity grid in northern Scotland, and requests from local and national fishing industry representatives to consolidate away from the site. Ocean Winds is pressing ahead with the larger 1,800 MW Arven North complex nearby, planning to develop it incrementally as floating wind technology matures. Arven South is the second ScotWind lease to be handed back after Shell returned the 2 GW CampionWind site last year. Two of 20 ScotWind projects have now been cancelled. The pattern raises questions about whether the ScotWind round, once billed as a transformational moment for Scottish offshore wind, can deliver at the scale originally promised when projects that were supposed to build it are being handed back.
Ocean heat content set another record in 2025. Global upper ocean heat content increased again last year, continuing a trend that has accelerated since the mid-2000s. The ocean absorbed an additional 23 zettajoules of heat compared to 2024. For scale, the entire United States uses roughly one tenth of a zettajoule of energy in a year. The ocean absorbed more than 200 times that amount, according to analysis published in Advances in Atmospheric Sciences. About a third of the global ocean ranked among its three warmest years on record, with particularly intense warming in the tropical and South Atlantic, Mediterranean, North Indian, and Southern Oceans. The ocean stores more than 90 per cent of the excess heat from human-caused greenhouse gas emissions. This record sits alongside the 3-million-year ice core reconstruction covered above: CO₂ has not been this high in at least 3 million years, and the ocean is absorbing the consequences.
Hard Truth From The Sea
For 40 years, the ocean off Panama breathed on schedule. In 2025, it didn’t. For 3 million years, atmospheric CO₂ stayed below 300 parts per million. It is now above 425. For as long as we have measured the ocean’s chemistry, we assumed the organic matter dissolved in seawater was natural. It is not.
Each of these findings describes the same thing from a different angle: the ocean is no longer operating within the conditions it maintained before we changed them. The rhythms are breaking. The chemistry is altered. The heat is accumulating. The records, whether they span 40 years or 3 million, all point in the same direction.
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See you next week.
- Luke