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National Geographic
15 hours ago
- Science
- National Geographic
Jellyfish are finally giving up their secrets
Gelatinous zooplankton, colloquially known as jellies, are an evolutionary hodge-podge of squishy, translucent creatures composed mostly of water. While this group does include 'true jellyfish' with their iconic rounded bell and stinging tentacles, it is also host to a smattering of creatures such as worms, primitive chordates, and snails with wings. A California sheephead (Semicossyphus pulcher) takes a bite out of a twin-tailed salp (Thetys vagina.) Jellies are poorly suited to life near shore, so when they find themselves in a kelp forest, they can make easy prey. 'If being 95 percent water is what unites the group, that is where it ends,' says Grace Cawley, a PhD candidate at Scripps Institution of Oceanography. Some are passive grazers, others track down their prey. Some are the size of a thimble, others can grow longer than a blue whale. Some cruise along the air-sea interface, others live thousands of meters beneath the surface. Cawley joked that the common reaction with jellies was ''oh, it's gooey?' Throw it with the gelatinous zooplankton.' In failing to recognize their diversity, humankind has overlooked some of the most ancient creatures on our planet. But thanks to advances in technology, scientists are now racing to decipher how jellies will shape the future of Earth's oceans. The hard part about squishy bodies The study of gelatinous zooplankton began in the late 1800s by scooping specimens out of the water from docks and ships. 'A lot of [early inquiry] was really just, 'what is this thing'?' says Steven Haddock, a leader in zooplankton biology at Monterey Bay Aquarium Research Institute (MBARI). Typical methods for investigating evolutionary history simply didn't work. Jellies lack the bones and shells that make for good fossils—scientists struggled to keep them alive in the lab long enough to observe their life cycles—and attempts to preserve them resulted in jars of cloudy film that bore no resemblance to the original creature. The proliferation of larger, faster research vessels around the mid-1900s meant that it became possible to sample new and remote regions of the ocean. Scientists rushed to ask ''how many?' and 'how much?' before having answered 'who?' and 'how?'' wrote Haddock in an early paper . This 1 inch lemon jelly (Aegina citrea) may not seem intimidating, but it is a predator. Its prey are other gelatinous zooplankton like salps and ctenophores. Hula-skirt siphonophores (Physophora hydrostatica) normally live deeper than 700 meters, but strong currents will occasionally carry them to the surface. Many different groups have made the transition to life in the water column. This pelagic snail has evolved to be transparent, but it still retains its shell. These animals blur the line of what is considered a gelatinous zooplankton. In their case, it largely comes down to the context in which they are being studied. Many species of salp (colonial tunicates) have a complex life cycle that alternates between sexual and asexual reproduction. Once the individuals in the colony mature, they will break off to begin reproducing sexually. When Scripps Institution ecologist Elizabeth Hetherington began studying gelatinous zooplankton, she was shocked by how little was known about their lives. 'There were so many questions that seemed pretty simple, like basic questions about distribution and abundance … that I couldn't find answers to.' Since the early 2000s, advances in technology have revealed that they play a more vital role in the ocean's food web than scientists thought. One paper from 2022 suggested that pelagic tunicates—gelatinous sea creatures that float in the open ocean—could be responsible for transporting more than 10 percent of carbon that is eventually stored in the ocean floor. The discovery that this single group of jellies could play such an influential role in the carbon cycle surprised scientists. The significance of all the ocean's jellies combined is unclear; however, the role they play in helping store carbon is probably underestimated. New technology that allowed scientists to study tiny bits of DNA also yielded new insights into jellies themselves. One study published in 2023 found that ctenophores, the most fragile of the gelatinous zooplankton, may be the oldest animal species living on Earth. Not only did these new methods revolutionize the study of individual species, but they also transformed our understanding of the open ocean. Jellies were more prevalent than previously thought and enthusiastic participants in the food web , hunting and being hunted. Using DNA metabarcoding, a technique used to identify multiple species within a mixed sample, 'we [could] detect gelatinous zooplankton in the guts of predators' explains Hetherington. Though the remnants of jellies were rarely visible, their DNA has been found in stomach contents of a wide variety of birds, fish, and sea turtles, disproving the idea that they were just dead-ends in the food chain. As larvae, many fish species mimic the traits of gelatinous zooplankton to decrease their chances of being eaten. This larval cusk eel is nearly transparent which helps it hide in the open ocean. Scientists are still trying to answer major questions about how many species exist, in what numbers, and how those populations might be changing. 'In an oceanographic context, we're still a long way from having the big picture biogeochemistry stuff figured out' remarks Haddock. 'Questions like 'Are jellyfish increasing?', 'How much jellyfish biomass is there relative to fish biomass?', 'What is the true diversity of jellies?' … we're still struggling to answer those.' To answer these questions about jelly species, scientists must also learn more about how they fit in their ocean habitats. 'The ocean is not a stagnant place where nothing happens, the ocean is this dynamic, complicated system,' says Cawley. Jellies are no exception. Instead of maintaining a consistent, predictable population, many gelatinous zooplankton follow extreme boom and bust cycles that scientists are still trying to understand. One species of pelagic tunicate called a pyrosome can bloom with such intensity that it will make up 80 percent of the biomass in a given area. When blooms like this occur, they affect every aspect of an ecosystem from the food web to the chemistry of the water. With warming temperatures, overfishing, and pollution rapidly changing our oceans, answering these questions is becoming even more difficult. 'All of these ecosystems are impacted by warming and by pollution so it's important to get the baseline of where we are now,' but in a system as fluid as the ocean, a baseline is more complicated than a set of measurements, clarifies Hetherington. 'We should shift our thinking from baseline to baselines, that it's not this one thing, it's this dynamic range.' A baseline needs to capture the underlying patterns of our oceans. It's an intimidating challenge that begins with demystifying where these jellies are living and what they are doing. Still, in Haddock's eyes, it's an exciting time to study gelatinous zooplankton. 'There are new species within a stone's throw of New York City or Tokyo … if you just look in the right ways'
Yahoo
21-05-2025
- Science
- Yahoo
Deep sea mining threatens the unknown
When the submarine plunged to about 10,000 meters below sea level, somewhere off the coast of Hawaii, ecologist Jeff Drazen asked the pilots to cut the strobe lights that had been guiding them through the pitch-black waters. For a moment, they continued falling to the sea floor in complete darkness. Then, the creatures of the deep sea began dazzling the crew with a striking display of bioluminescent lights, emitting signals to one another as they encountered this new strange object in their habitat. 'It's like you are falling through the stars,' Drazen told Salon in a phone interview. 'There are twinkling lights everywhere.' Thousands of feet below sea level, the creatures that live in the deep sea survive without direct sunlight, plants or the warmth of the sun. Much of the deep ocean is vacant, with extremely cold, lightless regions making it difficult for life as we know it to survive. Yet spectacular animals reside there, including the vampire squid, which has the largest eyes proportional to its body of any animal (though this cephalopod is neither a vampire or a squid); a pearly white octopus nicknamed 'Casper'; and, of course, the toothy Angler fish that became an internet sensation when one rose to the surface earlier this year. Last month, President Donald Trump issued an executive order promoting deep sea mining, which is currently prohibited under international law. And on Tuesday, the Department of the Interior announced it is initiating the process to evaluate a potential mineral lease sale in the waters offshore American Samoa. As industry eyes nodules found on the ocean floor as a potential way to extract nickel, copper and cobalt for making things like electric car batteries, scientists warn that deep sea mining is likely to be detrimental to life that exists there. 'We don't know that much about the deep sea because we have explored so little,' said Jim Barry, a seafloor ecologist at the Monterey Bay Aquarium Research Institute, 'We should make sure we know what is there before we do much to destroy things.' The deep sea begins at about 200 meters below sea level, where light starts to diminish in a region called the twilight zone. The deepest part of the ocean lies in the Mariana Trench in the western Pacific Ocean, where the ocean floor lies almost 11,000 feet below sea level — a height that is taller than Mount Everest. The ocean covers 71% of the Earth's surface, so classifying the deep sea as a single habitat is like classifying all land as one habitat. Just as on land there are deserts, grasslands, rainforests and the arctic, so too in the deep sea there are numerous different ecosystems that differ by geography, temperature and the animals that live there. Earlier this month, scientists witnessed the first volcanic eruption underwater for the first time.'Even if you're just looking at forests in the U.S., you wouldn't think that the forest on the East Coast is going to look the same as the forest on the West Coast,' Drazen said. 'The same is true on the sea floor, and we actually have data that shows this: The communities that you find in the east on nodules are not the same as the communities you find in the west on nodules.' One study published in Science earlier this month found that with 44,000 deep-sea dives, just 0.001% of the deep seafloor has been visually observed — which is roughly the size of Yosemite National Park. The rest is a black box. The study authors also note 'Ninety-seven percent of all dives we compiled have been conducted by just five countries: the United States, Japan, New Zealand, France, and Germany. This small and biased sample is problematic when attempting to characterize, understand, and manage a global ocean.' Another 2023 study estimated that scientists had identified fewer than 1,000 of up to 8,000 species in one region of the deep sea called the Clarion–Clipperton zone, which stretches the width of the continental United States and is a potential target for deep sea mining. Scientists explore these regions in submarines like Drazen's, or they use remote-operated vehicles to collect samples and map the ocean floor. Depending on the depth of the seafloor being studied, it can take these vehicles hours to reach the bottom, Barry said. Each time scientists go on a deep sea expedition, they encounter previously unknown species. In 2018, a team at MBARI discovered an 'Octopus Garden' of as many as 20,000 octopuses nested on the seafloor off the coast of California in the largest gathering of octopuses on the planet. In total, four of these gardens have been discovered around the world thus far. In other expeditions, scientists have discovered creatures that evolved their enzymes to function better at high pressure, as the ocean pressure increases by about the same amount as it does on an airplane every 10 meters. Some invertebrates can live for thousands of years, and the oldest known sea sponges have been dated to be 18,000 years old, Levin said. Overall, there are more new species being discovered than there are taxonomists to properly catalog them. The deep sea has been called Earth's last frontier as the only largely untouched place on the planet. For scientists on these trips, exploring the deep sea seems almost like they are exploring the moon or a distant planet. 'We're the first people that have ever seen some of the sites that we dive at,' Barry told Salon in a phone interview. 'In fact, almost any site you go to offshore, unless you've been there before, none of it's been viewed.' Many species in the deep sea have developed adaptations like bioluminescence or large eyes that help them navigate the dark waters. Others living in regions called oxygen-minimum zones — also known as 'dead zones' or 'shadow zones' — have developed elaborate breathing structures that look like lungs outside of their bodies in order to maximize the surface area they use to absorb oxygen, said Lisa Levin, an oceanographer at the Scripps Institution of Oceanography. On the seafloor, you can find canyons, volcanoes and vast abyssal planes. In some regions called chemosynthetic ecosystems, creatures produce food using the energy from chemical reactions rather than sunlight. 'Deep water isn't uniform, it's kind of layered, and there are different water masses,' Levin told Salon in a video call. 'It's really a whole mosaic of ecosystems and habitats.' As remote as it may seem, the deep sea is just one degree of separation from anyone who eats seafood, Drazen said. The deep sea provides food to many species in shallower waters, like the swordfish, which dives up to 1,200 meters to feed. The ocean also produces half of the oxygen we breathe on land and is the largest carbon sink on Earth, absorbing about 30% of all carbon dioxide emissions from humans. With the deep sea covering so much of the ocean's volume, it plays a major role in reducing the effects of global heating. Unfortunately, as CO2 emissions increase, it acidifies the ocean, which can make it less hospitable for life. Some crustaceans, for example, have a hard time developing hard outer shells made of calcium carbonate if the water is too acidic. Not only that, but the creatures of the deep sea could provide scientists with molecules or compounds that help them develop better medicines or lead to other breakthrough discoveries. In the early 1980s, for example, scientists synthesized ziconotide, a natural pain-killer 1,000 times stronger than morphine without the addictive side effects. The molecule came from the Conus magus, a sea snail found in the deep sea. Overall, more than 60% of our drugs come from analogs in nature. 'If you think about pharmaceuticals, there's a repository of genetic material down there with all these weird animals,' Barry said. 'People want to collect deep sea animals to see if they have important, novel chemicals that could have some use for us, whether it might be antibiotics or cancer treatments or something else.' Scientists are also still uncovering exactly how sensitive the deep sea is to environmental changes and human impacts. However, compared to shallower waters, which are more easily subjected to changes in things like temperature, acidity or oxygen levels, these environmental changes take longer to reach the deep sea. As a result, creatures of the deep sea are likely to be more sensitive and vulnerable to changes that do occur in their environment. 'Animals that inhabit shallow waters have evolved to cope with variability in environmental conditions, but in the deep sea, there's very little change in oxygen or temperature or pH across the year,' Barry said. 'A similar change in pH or oxygen [that occurs at shallower levels], might be far less tolerable for animals in the deep sea.' Additionally, deep sea creatures are impacted by changes that occur in regions closer to the surface because many rely on food that falls from those heights. About 90% of food sources are lost every 1,000 meters deeper you go in the ocean, so any disruptions to the food supply could be detrimental to sealife at these depths, Barry said. 'When the productivity of the surface water changes, that affects the amount of detritus, or dead material, that sinks to the deep sea floor that is the food supply for those organisms,' Drazen said. 'That is reducing the food supply to the deep sea.' Many of the minerals involved in proposed deep sea mining operations are located on black, potato-shaped nodules that lie on the seafloor. Yet a community of animals lives on the nodules themselves, and they would be eradicated if they are mined, said Lauren Mullineaux, a senior scientist at the Woods Hole Oceanographic Institution. Additionally, mining operations scrape up the seafloor, producing sediment plumes that can disrupt an area up to hundreds of kilometers away from the operating site, Mullineaux said. Even a fine dusting of this sediment might change the habitat enough to kill some of those species, she explained. 'It can take many decades for the habitat to look like it did before it was mined,' Mullineaux told Salon in a phone interview. The ocean is a globally shared resource, and stewarding the deep sea may be society's last chance to protect the remaining virgin Earth. The majority of creatures living in the abysmal sea remain unknown to us, but in order to protect them, we must first know they exist. After all, these creatures surely have a lot to teach us about how to survive and evolve in an increasingly harsh environment. 'If we want to be sustainable stewards of the resources that we depend on, it would be nice to know what is there first,' Barry said.
Observer
12-05-2025
- Science
- Observer
It Took a Century to Find This Colossal Squid
In March, Kat Bolstad returned from an Antarctic expedition where she had used a new camera system specially built to search for the elusive colossal squid. No one had captured footage of one of these animals swimming in the deep sea. She didn't spot one on this voyage either. On the day she left the ship, though, Bolstad, a deep sea cephalopod biologist, learned about a recent video taken March 9 from the South Sandwich Islands. A team searching for new marine life and remotely using a Schmidt Ocean Institute submersible, had happened upon a young cephalopod, and people wanted Bolstad's help identifying it. The juvenile was about 30 centimeters long (a little less than a foot), with a transparent body, delicate arms and brown spots. It was a colossal squid. 'Pretty much as soon as I saw the footage, I knew there was a good chance,' said Bolstad, a cephalopod biologist at the Auckland University of Technology in New Zealand. She consults remotely for Schmidt's Antarctic work. It's been 100 years since the colossal squid was formally described in a scientific paper. In its adult form, the animal is larger than the giant squid, or any other invertebrate on Earth, and can grow to 6 or 7 meters long, or up to 23 feet. Scientists' first good look at the species in 1925 was incomplete — just arm fragments from two squid in the belly of a sperm whale. Adults are thought to spend most of their time in the deep ocean. A full-grown colossal squid occasionally appears at the ocean's surface, drawn up to a fishing boat while it's 'chewing on' a hooked fish, Bolstad said. Younger specimens have turned up in trawl nets. Yet until now, humans had not witnessed a colossal squid at home, swimming in the deep Antarctic sea. One reason they're so elusive is the sheer size of that home. Additionally, the squid are probably avoiding us, Bolstad said. 'They're very aware of their surroundings, because any disturbance in the water column around them might mean a predator.' Sperm whales, the squid's main predator, can dive up to 2 kilometers (1.25 miles). Perhaps to help them avoid the whales, colossal squid have evolved the world's largest eyes — bigger than a basketball. They also have 'a unique combination of suckers and hooks on the arms and the tentacles,' Bolstad said, which is how she was able to confirm that the young sea creature in the new footage was a colossal squid. The footage was taken by a remotely operated submersible called SuBastian, which the Schmidt Ocean Institute uses to explore the deep sea. This particular dive was a partnership with Ocean Census, an initiative to discover unknown species. The submersible stopped for a few minutes on descent to film the small, transparent cephalopod. 'I think it's very exciting,' said Christine Huffard, a biologist at the Monterey Bay Aquarium Research Institute in California who wasn't involved in the expedition. Huffard has used other remotely operated submersibles in her research. She said these exploratory missions have 'tremendous value.' For example, her observations of octopuses walking bipedally on the ocean floor — using two arms to stroll, and the other six to possibly camouflage themselves as a clump of algae or a coconut — happened by chance. The findings have been useful to researchers in soft robotics, she said. Capturing footage of rarely seen marine animals like the colossal squid, Huffard said, can also inform decisions about human activities like deep-sea mining. She said it would help to know where these animals spend their time, where they travel to mate or spawn, or how long they live. The young colossal squid in the video was swimming around 600 meters down, Bolstad said, not in the deeper waters where adults likely dwell. Other deep-sea squids spend their early lives in shallower waters, she said. Having a transparent body may help the baby swim undetected by predators before it descends as an opaque, reddish adult to the darker ocean. A submersible's camera can detect the squid — and transmit images instantaneously. Unlike the scientists of a century ago, who had to dig through partly digested carnage in a whale's belly, anyone could watch the Schmidt 'dive-stream' from home to be part of the moment of finding the colossal squid, Bolstad said. 'To be able to participate in these explorations and discoveries, essentially in real time, from anywhere on the planet — that's an amazing thing that humans can do.' She'll continue looking for a full-grown animal. 'I can't wait to see what a live adult colossal squid looks like, at home in the deep sea where it belongs,' she said. But she said she was also glad that the first sighting of the species in the wild was not of the adult version — an enormous, hook-wielding leviathan, but 'this beautiful early life stage that looks like a little glass sculpture.' 'I actually love that this is our first glimpse of what will become a true giant,' Bolstad said. —NYT
Yahoo
29-04-2025
- Science
- Yahoo
How the biggest flood in the history of the Earth created the Mediterranean
Six million years ago, the Mediterranean Sea wasn't nearly as picturesque as it is today. It was barely even a sea; tectonic activity had raised a mountain range in the Strait of Gibraltar, cutting off the Mediterranean from the Atlantic. Without a constant inflow of water the sea evaporated under the baking sun, and all that remained were a few scattered, briny lakes surrounded by mile after mile of salt and gypsum. Today, scientists call this the Messinian Salinity Crisis: in the dying days of the Miocene epoch, most of the Mediterranean died. But if, on a certain day about 5.3 million years ago, you happened to go for a stroll along that mountain range, you might have discovered something odd: a trickle of water, making its way down one of the mountains from the Atlantic ocean beyond it. The mountains had been slowly sinking until their summits were level with the ocean's surface; one day, the mountains sank just enough for some of the water to spill over their edges. Once they did, the water carved an unstoppable path downhill. The trickle turned into a stream, which widened into a river, and soon the ocean was pouring into the desiccated Mediterranean basin with the force of a thousand Amazon Rivers, suddenly ending the 600,000-year-long dry spell. The water moved so quickly — 32 meters per second, or about 72 miles per hour, by the time it hit the coast of modern-day Sicily — that it dragged the air behind it, creating tropical storm-force winds as it moved. If you managed to somehow see through all the muddy sediment stirred up by the flood waters, you might have found a few surprised fish in the depths, stunned or struck dead outright by the force of the rapids that carried them in from the Atlantic. As the water refilled the Mediterranean, it ushered in a new geological era: the Zanclean. 'I don't think any human has ever seen anything like this,' says Aaron Micallef, a National Geographic Explorer and marine geoscientist at the Monterey Bay Aquarium Research Institute who studies this event, called the Zanclean megaflood. Micallef and his colleagues have spent years putting together the puzzle pieces of what the flood looked like, and this story is largely built on their research, which melds geologic evidence with computer modeling. While evidence for the flood is still accumulating, this is the scientist's best picture yet of what's likely the largest flood in the history of the Earth. Micallef and his colleagues found that the Mediterranean, which had been obliterated once when the sea dried up, was transformed completely again by the megaflood. The fossil record is difficult to read in much detail, but scientists think that before the sea dried up it was filled with all kinds of creatures, from ancient sharks and pinnipeds to fish and a rainbow of coral. Only eighty-six of the 780 or so species from the sea that existed before the salinity crisis have survived into the modern-day Mediterranean, and the fact that they lived through the flood is a minor miracle. Those creatures, a collection of mollusks, plankton, and one standout sea slug, most likely survived by finding refuge in the few patches of water that remained after the sea dried up. (Rome is teeming with mysterious crypts filled with popes—and secrets) As the water poured in, the western Mediterranean began refilling at a tremendous rate; Micallef estimates the water flowed at a rate of somewhere between 68 and 100 million cubic meters per second, filling the sea by as much as ten meters, or nearly 33 feet, each day. The weight of the rising waters pressed down on the Earth's crust, making it slide across the molten mantle underneath. This, says Daniel Garcia-Castellanos, a Geophysicist at CSIC Barcelona and a pioneer on research into the Zanclean megaflood, would have triggered earthquakes that rippled through the region. For the goat-antelope creature Myotragus, which had walked across the dry sea to make its home on modern-day Mallorca and Menorca, the earthquakes, water, and wind combined must have sounded like the roar of a monstrous predator — surely, this was the end of the world as they knew it. Eventually, the rising waters streamed over the lip of Sicily, and as the current moved east it ate away at the land, leaving behind hundreds of long ridges as if a giant hand had clawed through the dirt. A little bit further east, the water hit another wall that we now call the Malta Escarpment. This barrier divided the Mediterranean into west and east, turning the western mediterranean into a giant bowl: for the water to make its way east, it first had to fill the western half of the sea. Once the western half of the sea filled up enough for the water to make its way over the top of the wall, it tipped over into the east and down a cliff about 1.5 kilometers deep, creating the largest waterfall in the history of our planet; imagine the Niagara Falls, but 30 times taller. The crash of the water triggered more earthquakes, and the flood dumped mounds of sediment at the bottom of the sea as it rushed into the east. As the water rose in the east to meet the waters of the western Mediterranean, the earth stopped shaking. The wind died down. The water started clearing as it settled, sediment falling to the sea floor. Somewhere between two and sixteen years after the first waters broke through the Strait of Gibraltar — not even the blink of an eye in geological time — the Mediterranean leveled off with the Atlantic. From the surface, all signs of upheaval disappeared. The Atlantic flowed lazily into the newly reformed Mediterranean, which was now free of walls or waterfalls. This sea, with its comparatively mild waters, looked much as it would millions of years later, when ancient Greece and Rome established themselves on its edges, When the Greek poet Homer wrote of the sea monsters Scylla and Charybdis living off the coast of Sicily, he had no way of knowing that Charybdis, who often takes the form of a whirlpool pulling unfortunate sailors to their death in the depths, had already been upstaged by the sea's own history. It would take surprisingly long for any new sea creatures, monstrous or otherwise, to make a home in the Mediterranean. 'In geological terms, we should have been seeing marine fauna immediately, but that's not what is happening,' Konstantina Agiadi, a geologist at the University of Vienna who co-authored a paper on the impact of the salinity crisis and flood on marine biodiversity. The water in the immediate aftermath of the flooding would have made a poor home, devoid of nutrients and far too salty for most creatures to live in; the ones that existed in the sea before the flood struggled by for a few millennia before the water became hospitable enough for any potential newcomers, and even today the Mediterranean is considerably saltier than the Atlantic. 'It took a lot of time for the situation to settle enough for organisms that were coming from the Atlantic to actually establish healthy populations and grow,' Agiadi the sea is a biodiversity hotspot, filled with all varieties of sea creatures. (How archaeologists found one of the oldest cities on Earth) Even though the flood happened millions of years ago, Micallef says, it holds important clues about the future of our planet. Climate change is making flooding from melting glaciers more common, and understanding the dynamics of the Zanclean megaflood — even though it was much larger than anything we have seen from glaciers so far — can help us model what future flooding will look like, mapping both the flow of water and its effect on the landscape around it. And, says Agiadi, there's another important lesson too: The world transformed when the Messinian Salinity Crisis and Zanclean megaflood happened, and there was no going back. The creatures that live in the Mediterranean now, wonderful as they may be, are nothing like what lived there before it dried up. That's true of climate change too. 'The flood is kind of like a natural experiment,' Agiadi says. 'The Mediterranean, after the flooding, eventually became a marine basin that is a biodiversity hotspot today. But it never became, even after millions of years, what it was before. So it's kind of a natural test of if we can fix things. If you try to bring back a species without fixing the underlying problems, it will never be okay. But it might be something different.' The nonprofit National Geographic Society, committed to illuminating and protecting the wonder of our world, funded Explorer Aaron Micallef's work. Learn more about the Society's support of Explorers.
National Geographic
28-04-2025
- Science
- National Geographic
How the biggest flood in the history of the Earth created the Mediterranean
The mediterranean was once a dried-up expanse of salt and gypsum. Then the floodwaters came rushing in. Photograph by NASA/Six million years ago, the Mediterranean Sea wasn't nearly as picturesque as it is today. It was barely even a sea; tectonic activity had raised a mountain range in the Strait of Gibraltar, cutting off the Mediterranean from the Atlantic. Without a constant inflow of water the sea evaporated under the baking sun, and all that remained were a few scattered, briny lakes surrounded by mile after mile of salt and gypsum. Today, scientists call this the Messinian Salinity Crisis: in the dying days of the Miocene epoch, most of the Mediterranean died. But if, on a certain day about 5.3 million years ago, you happened to go for a stroll along that mountain range, you might have discovered something odd: a trickle of water, making its way down one of the mountains from the Atlantic ocean beyond it. The mountains had been slowly sinking until their summits were level with the ocean's surface; one day, the mountains sank just enough for some of the water to spill over their edges. Once they did, the water carved an unstoppable path downhill. The trickle turned into a stream, which widened into a river, and soon the ocean was pouring into the desiccated Mediterranean basin with the force of a thousand Amazon Rivers, suddenly ending the 600,000-year-long dry spell. The water moved so quickly — 32 meters per second, or about 72 miles per hour, by the time it hit the coast of modern-day Sicily — that it dragged the air behind it, creating tropical storm-force winds as it moved. If you managed to somehow see through all the muddy sediment stirred up by the flood waters, you might have found a few surprised fish in the depths, stunned or struck dead outright by the force of the rapids that carried them in from the Atlantic. As the water refilled the Mediterranean, it ushered in a new geological era: the Zanclean . 'I don't think any human has ever seen anything like this,' says Aaron Micallef, a National Geographic Explorer and marine geoscientist at the Monterey Bay Aquarium Research Institute who studies this event, called the Zanclean megaflood. Micallef and his colleagues have spent years putting together the puzzle pieces of what the flood looked like, and this story is largely built on their research, which melds geologic evidence with computer modeling . While evidence for the flood is still accumulating, this is the scientist's best picture yet of what's likely the largest flood in the history of the Earth. A 3D rendering depicts how the Zanclean flood may have progressed. InTheBox/Daniel García-Castellanos How the modern Mediterranean was formed Micallef and his colleagues found that the Mediterranean, which had been obliterated once when the sea dried up, was transformed completely again by the megaflood. Get a bonus issue with all magazines EXPLORE SUBSCRIPTION OPTIONS The fossil record is difficult to read in much detail, but scientists think that before the sea dried up it was filled with all kinds of creatures, from ancient sharks and pinnipeds to fish and a rainbow of coral. Only eighty-six of the 780 or so species from the sea that existed before the salinity crisis have survived into the modern-day Mediterranean, and the fact that they lived through the flood is a minor miracle. Those creatures, a collection of mollusks, plankton, and one standout sea slug, most likely survived by finding refuge in the few patches of water that remained after the sea dried up. (Rome is teeming with mysterious crypts filled with popes—and secrets) As the water poured in, the western Mediterranean began refilling at a tremendous rate; Micallef estimates the water flowed at a rate of somewhere between 68 and 100 million cubic meters per second, filling the sea by as much as ten meters, or nearly 33 feet, each day. The weight of the rising waters pressed down on the Earth's crust, making it slide across the molten mantle underneath. This, says Daniel Garcia-Castellanos , a Geophysicist at CSIC Barcelona and a pioneer on research into the Zanclean megaflood, would have triggered earthquakes that rippled through the region. For the goat-antelope creature Myotragus, which had walked across the dry sea to make its home on modern-day Mallorca and Menorca, the earthquakes, water, and wind combined must have sounded like the roar of a monstrous predator — surely, this was the end of the world as they knew it. This video animates the evolution, and end, of the Messinian salinity crisis. University of Malta/Aaron Micallef, D. Garcia-Castellanos, and A. Camerlenghi. Eventually, the rising waters streamed over the lip of Sicily, and as the current moved east it ate away at the land, leaving behind hundreds of long ridges as if a giant hand had clawed through the dirt. A little bit further east, the water hit another wall that we now call the Malta Escarpment. This barrier divided the Mediterranean into west and east, turning the western mediterranean into a giant bowl: for the water to make its way east, it first had to fill the western half of the sea. Once the western half of the sea filled up enough for the water to make its way over the top of the wall, it tipped over into the east and down a cliff about 1.5 kilometers deep, creating the largest waterfall in the history of our planet; imagine the Niagara Falls, but 30 times taller. The crash of the water triggered more earthquakes, and the flood dumped mounds of sediment at the bottom of the sea as it rushed into the east. As the water rose in the east to meet the waters of the western Mediterranean, the earth stopped shaking. The wind died down. The water started clearing as it settled, sediment falling to the sea floor. Somewhere between two and sixteen years after the first waters broke through the Strait of Gibraltar — not even the blink of an eye in geological time — the Mediterranean leveled off with the Atlantic. Life returned… eventually From the surface, all signs of upheaval disappeared. The Atlantic flowed lazily into the newly reformed Mediterranean, which was now free of walls or waterfalls. This sea, with its comparatively mild waters, looked much as it would millions of years later, when ancient Greece and Rome established themselves on its edges, When the Greek poet Homer wrote of the sea monsters Scylla and Charybdis living off the coast of Sicily, he had no way of knowing that Charybdis, who often takes the form of a whirlpool pulling unfortunate sailors to their death in the depths, had already been upstaged by the sea's own history. It would take surprisingly long for any new sea creatures, monstrous or otherwise, to make a home in the Mediterranean. 'In geological terms, we should have been seeing marine fauna immediately, but that's not what is happening,' Konstantina Agiadi , a geologist at the University of Vienna who co-authored a paper on the impact of the salinity crisis and flood on marine biodiversity. The water in the immediate aftermath of the flooding would have made a poor home, devoid of nutrients and far too salty for most creatures to live in; the ones that existed in the sea before the flood struggled by for a few millennia before the water became hospitable enough for any potential newcomers, and even today the Mediterranean is considerably saltier than the Atlantic. 'It took a lot of time for the situation to settle enough for organisms that were coming from the Atlantic to actually establish healthy populations and grow,' Agiadi the sea is a biodiversity hotspot, filled with all varieties of sea creatures. (How archaeologists found one of the oldest cities on Earth) Even though the flood happened millions of years ago, Micallef says, it holds important clues about the future of our planet. Climate change is making flooding from melting glaciers more common, and understanding the dynamics of the Zanclean megaflood — even though it was much larger than anything we have seen from glaciers so far — can help us model what future flooding will look like, mapping both the flow of water and its effect on the landscape around it. And, says Agiadi, there's another important lesson too: The world transformed when the Messinian Salinity Crisis and Zanclean megaflood happened, and there was no going back. The creatures that live in the Mediterranean now, wonderful as they may be, are nothing like what lived there before it dried up. That's true of climate change too. 'The flood is kind of like a natural experiment,' Agiadi says. 'The Mediterranean, after the flooding, eventually became a marine basin that is a biodiversity hotspot today. But it never became, even after millions of years, what it was before. So it's kind of a natural test of if we can fix things. If you try to bring back a species without fixing the underlying problems, it will never be okay. But it might be something different.' The nonprofit National Geographic Society, committed to illuminating and protecting the wonder of our world, funded Explorer Aaron Micallef's work. Learn more about the Society's support of Explorers.
