Lanternfish fossils warn of looming ocean oxygen crisis

The ocean is slowly losing its breath, and fish that spend their days in the twilight depths are starting to pay the price.

A new study tracking 10,000 years of fossil ear bones shows that some of the most numerous vertebrates on Earth vanished whenever deep water oxygen fell below a critical threshold.

Lanternfish expert Sven Pallacks of the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (UAB) says the pattern is a clear warning for today’s warming seas.

The disappearance of a group with such enormous biomass would likely put many other marine species at risk as well.

Lanternfish need deep sea oxygen

Oxygen dissolves into seawater at the surface and is carried downward by currents and mixing. In parts of the mid water column, consumptive microbes form an oxygen minimum zone that can drop to just a few micromoles per liter.

Since the 1960s, the global ocean has already lost roughly two percent of its oxygen inventory, an amount equivalent to the volume needed to supply every person on the planet for a year. Less mixing and warmer water both make it harder for fresh oxygen to reach depth.

When that deficit climbs, the low oxygen layer expands upward, squeezing habitat for organisms caught between breathless water below and surface predators above. Fish that once sheltered hundreds of feet deep end up in plain sight, exposed and stressed.

Why lanternfish are important

The slim, glowing lanternfish make nightly ascents of up to 2,600 ft to feed, then retreat to 660 ft or deeper before sunrise. Their combined weight may reach six hundred million tons.

Because they commute between surface and depth, lanternfish shuttle carbon in their bodies into long term storage – a service called the biological pump.

A 2019 synthesis estimated that their nightly rise moves roughly four gigatons of carbon downward each year. That is more than the annual carbon emissions of the European Union, highlighting why the loss of lanternfish would weaken a key climate stabilizer.

Lanternfish also feed whales, tuna, and many squid, so their absence would ripple through commercial fisheries.

Fossils reveal what happened

Pallacks and colleagues recovered a sediment core from 1,835 feet down in the Aegean Sea. They sorted more than 3,200 fossil otoliths – the tiny calcified ear stones that record a fish’s identity like fingerprints.

Each layer of mud offered a snapshot of who was living above at the time it settled. Because the Aegean toggled between well oxygenated and suffocating states over the past ten millennia, it served as a natural experiment.

During the most severe low oxygen phase, called Sapropel S1, lanternfish counts plummeted to near zero. Anchovies and other surface dwellers filled some of the gap, but overall fish abundance stayed low until oxygen crept back.

Past loss warns the present

Archaeological evidence shows that early coastal cultures around the Mediterranean suffered reduced fish catches during the same sapropel interval, hinting at cascading effects on human food security.

Historical records suggest that once oxygen levels recovered, fish markets rebounded within a few generations.

The core indicates that oxygen rebounded about 6,000 years ago, and lanternfish stormed back, tripling total fish abundance within a few centuries. 

“Our findings corroborate expectations that future expansion of midwater deoxygenation could severely deplete mesopelagic fish communities,” noted the study authors.

When lanternfish vanish

Lanternfish sit at a crucial hinge in food webs. Many whales, seabirds, and predators such as swordfish depend on them for calories.

Lose the commuters, and both seafood supply and natural carbon sequestration take a hit. Models show that removing lanternfish from global ecology would cut twilight zone carbon export by at least twenty five percent.

Such a reduction would accelerate atmospheric warming, creating a feedback loop that drives oxygen even lower. The biological pump is not a luxury. It is planetary life support.

Climate models point to steeper declines

Earth system simulations that include projected emissions paths suggest oxygen minimum zones could grow by up to seven percent by 2100.

The upper boundary of low oxygen water could climb from roughly 1,300 feet today to less than 650 feet in some basins.

That shift would erase the safe daytime refuge for many mid-water species, forcing them closer to nets and predators. Warmer water also speeds fish metabolism, so they need more oxygen just as it becomes scarce.

What we can do now

Cutting greenhouse gas emissions remains the fastest lever for stabilizing ocean oxygen. Local steps, like reducing nutrient runoff that fuels coastal dead zones, protect regional fisheries while the planet decarbonizes.

Monitoring programs that deploy autonomous sensors into the mesopelagic zone now give managers early warning when oxygen starts to fall. Data from these floats already help reroute fishing effort away from emerging hypoxic patches

Scientists are also testing marine protected areas designed around depth bands rather than coastlines, preserving critical migration corridors. Protecting the pathways lanternfish use may buy time while global actions take hold.

What we don’t know about lanternfish

Lanternfish biomass estimates still span an order of magnitude, and only a handful of regions have been sampled with modern acoustics. Expanding surveys will refine how much organic carbon these fish ferry to depth.

Meanwhile, paleo records such as the Aegean core offer rare, long term baselines against which future change can be measured. More sediment cores from other basins will reveal whether regional oxygen thresholds line up globally.

What’s coming next

Technology that tracks individual fish with miniaturized tags is beginning to map their vertical routes in three dimensions. Combining that data with oxygen sensors will reveal tipping points beyond which migration breaks down.

Policy makers armed with such thresholds can set clearer targets for climate mitigation and fishery protection. The past cannot predict every detail, but it shows how sharply deep sea life responds when the ocean runs short of air.

The study is published in the journal Communications Earth & Environment.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–