Oceans

It’s one of the most massive migrations on Earth: a huge biomass of tiny plankton that travel from deep in the sea toward the surface. Yet not all of those organisms have limbs to propel themselves upward. So how some of them manage to undergo such a long journey has been a mystery.

Now, a team of researchers has shown that one species of phytoplankton has an ingenious solution: swelling to six times its original size. The process reduces its density and allows it to float upward like a helium balloon, bioengineer Manu Prakash and his colleagues at Stanford University report October 17 in Current Biology. More

As dust from the Sahara blows thousands of kilometers across the Atlantic Ocean, it becomes progressively more nutritious for marine microbes, a new study suggests.

Chemical reactions in the atmosphere chew on iron minerals in the dust, making them more water soluble and creating a crucial nutrient source for the iron-starved seas, researchers report September 20 in Frontiers in Marine Science.

Dust clouds settling on the Atlantic can spawn phytoplankton blooms that support marine ecosystems, says Timothy Lyons, a biogeochemist at the University of California, Riverside. “Iron is incredibly important for life,” he says. Phytoplankton require it to convert carbon dioxide into sugars during photosynthesis. More

The ocean’s circulatory system may not be doing as poorly as previously thought.

A vital ocean artery known as the Florida Current, a bellwether for the ocean’s ability to regulate Earth’s climate, has seemingly been weakening for decades. But that recent decline might not be quite as severe as suspected. The current has actually remained stable over recent decades, researchers report September 5 in Nature Communications.

A previously reported decline in the flow had prompted speculations that a major system of ocean currents — known for regulating Earth’s climate — may have weakened recently due to human-caused climate change. Some researchers have suggested that the larger system, known as the Atlantic Meridional Overturning Circulation, or AMOC, could collapse sometime this century, dramatically cooling the northern hemisphere and raising the sea level along some Atlantic coastlines by up to 70 centimeters. More

Abby Wallace is the digital engagement producer at Science News. She has an undergraduate degree in biology from George Washington University in Washington, D.C., and a master’s degree in journalism from the University of Maryland — College Park. More

In an unexpected twist, metal-rich nodules found on the seafloor are generating oxygen, new research suggests. This meager but steady supply of the vital gas may help support seafloor ecosystems in areas currently targeted for deep-sea mining, scientists say.

Scientists have long presumed that much of the dissolved oxygen in the deep sea was transported there from surface waters. It can be generated at the surface by plant life via photosynthesis or diffuse from the atmosphere as a result of wave action, says Andrew Sweetman, a deep-sea ecologist at the Scottish Association for Marine Science in Oban. More

BURLINGTON, Vt. — For the first time, a researcher has found a “milky sea” without relying on happenstance.

For centuries, sailors have been amazed and mystified by a rare phenomenon: the water around their ship glowing as far as the eye can see. Scientists have struggled to study such milky seas because they had no way of knowing when and where one would occur.

But now, using weather and ocean temperature data, atmospheric scientist Justin Hudson of Colorado State University in Fort Collins has successfully predicted — or rather, postdicted — an occurrence of the phenomenon. More

Heat waves don’t just strike on land — they can also occur in the ocean. And roughly a third of marine heat waves aren’t detectable at the ocean’s surface, a new study reports. The findings, published in the December Nature Geoscience, suggest that far more of these potentially harmful events might be occurring than previously believed.

Ocean heat waves can have a slew of adverse effects on marine ecosystems because many forms of life cannot rapidly adapt to changes in temperature. For instance, cod populations were devastated from 2013 to 2015 when a marine heat wave lingered off the West Coast of North America. Given the interconnectedness of marine food webs, seabirds suffered, too (SN: 1/15/20).

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Marine heat waves are often identified with satellite observations that measure the temperature of the ocean surface. But these data leave the ocean depths unmonitored.   

To literally take a deeper look, statistician Furong Li and colleagues turned to computer simulations of the ocean’s temperature, salinity and currents, among other parameters, created from both satellite and subsurface data stretching back to the early 1990s. Such simulations are a powerful way of studying the ocean on a global scale, says Li, of the Ocean University of China in Qingdao.

The researchers pinpointed ocean heat waves in the simulations by looking for layers of water that remained unusually warm — up to a few degrees Celsius above surrounding levels — for at least five days. Such events can be caused by changes in atmospheric circulation, for instance, or shifts in ocean currents.

Li and her collaborators spotted several hundred marine heat waves per year. But the real surprise was finding that about 1 in 3 of those events consistently lurked out of view and were never visible in the uppermost 10 meters of the water. “We discovered a great number of marine heat waves hidden below the sea surface,” Li says.

Researchers might accordingly be missing a lot of these events, says Mike Jacox, an oceanographer at the National Oceanic and Atmospheric Administration in Monterey, Calif., not involved in the research. “Just looking at the surface temperature might not be enough.”

Marine life might therefore be contending with significantly more ocean heat waves than previously thought. And that means additional stress on marine ecosystems. In 2020, Jacox and his colleagues showed that animals seeking to escape marine heat waves would have to swim hundreds of kilometers on average (SN: 8/10/20). And when creatures are unable to move, marine heat waves often prove deadly. Warming in the Great Barrier Reef, for example, has been linked to coral bleaching (SN: 4/7/20). More

The Deepest MapLaura TretheweyHarper Wave, $32

In 2019, the multimillionaire and explorer Victor Vescovo made headlines when he became the first person to visit the deepest parts of all five of Earth’s oceans. But arguably the real star of the expedition was marine geologist Cassie Bongiovanni, the lead ocean mapper who ensured Vescovo piloted his submersible to the actual deepest depths.

Today, only 25 percent of the seafloor is well mapped. When Vescovo set out to score his record, the exact deepest location in each ocean was unknown. Bongiovanni, Vescovo and their crew had to chart these regions in detail before each dive.

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“Traditionally, captains never cared about the seafloor as long as it stayed far enough away from the hulls of their ships,” journalist Laura Trethewey writes in The Deepest Map. The book explores humankind’s quest to map the seafloor, framed around Bongiovanni’s adventures.

Seafloor topography has been a big concern for militaries patrolling Neptunian frontiers with nuclear submarines and companies facilitating intercontinental communication via subsea cables (SN: 4/10/21, p. 28). In recent decades, seafloor data have become crucial to the deep-sea mining industries searching for metals needed to produce green technology.

Satellites have revealed many of the knobs and crevices visible in the deep blue of Google Maps. But with that relatively coarse information, entire mountains can be missed. To see the seafloor in high resolution requires a sophisticated sonar system aboard a big ship that sends sound signals from the sea surface into the abyss.

Mappers like Bongiovanni calculate depth from the time it takes for the signal to travel down and bounce back to the surface. These state-of-the-art sonar systems transform “the satellite-predicted blur into a sharp three-dimensional terrain of ripples, cracks and tears in the seafloor,” Trethewey writes. “The seafloor is ‘heard,’ rather than seen.”

Through Trethewey’s tale, she twines stories of tagging along with scientists and ocean mappers. That includes her inaugural adventure at sea, which a crew member noted was “pretty rough for a first-timer,” as he and Trethewey clung to a doorframe in near gale force winds. On this cruise aboard research vessel E/V Nautilus, which was surveying a poorly mapped stretch of California’s coast, Trethewey (and readers) are introduced to the art and science of seafloor mapping. On this day, Trethewey learned that mapping is especially difficult — and sometimes impossible — when the ocean is angry.

Trethewey’s insightful writing helps readers understand just why mapping the ocean — even in shallow coastal waters — is crucial to so many endeavors. She visits a remote Inuit village on the western bank of Canada’s Hudson Bay, where she joins hunters who map ever-changing coastlines for their own safety. Later, she scuba dives with archaeologists in Florida who use underwater maps to explore remnants of early human history that have been submerged for thousands of years.

A distant, possibly unreachable goal envisions creating a complete map of the entire seafloor by the end of this decade, an effort known as Seabed 2030. Because the oceans are vast and replete with remote and dangerous places that people simply can’t or shouldn’t go, this effort will almost certainly require autonomous surface vehicles armed with sonar. Such devices are already probing the depths and sending back data.

Staring at computer screens in a sun-filled conference room, Trethewey watches as a drone outfitted with cameras, environmental sensors and a sonar system maps a bit of seafloor off California as she sips her coffee. “The future of ocean mapping weirdly felt a lot like checking social media or doing anything else on your phone these days,” she wryly observes.

Trethewey’s book is about more than just mapping the oceans. It’s also about what can go wrong when explorers explore. It’s hard to read The Deepest Map without being reminded of the recent implosion of the Titan submersible in the North Atlantic that killed everyone on board in June. Indeed, Trethewey describes how, during Vescovo’s first solo dive, his colleagues endured 25 minutes of apprehension-turned-alarm when they didn’t hear from him.

She also reminds us how easily exploration can turn into exploitation. In the not-so-distant past, Europeans “discovered” the so-called New World and mapped it, Trethewey writes. Exploitation followed. Scientists and environmentalists alike are now concerned that a full, detailed map of the ocean floor might lead to the destruction of delicate, mostly unknown habitats if deep-sea miners are allowed to extract metals.

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Trethewey envisions a different outcome. Seabed 2030’s mapping effort may help people see that “the weird, wonderful deep-sea world is not a blank space, another frontier to use up and throw away,” and should be safeguarded for scientists “to uncover our past and protect our future.”

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