The world’s strongest ocean current, the Antarctic Circumpolar Current, is speeding up, according to new research, mostly because of rising ocean temperatures.
The ACC carries water around the globe, pushing more water than any other ocean current.
It’s not entirely clear what accelerating currents mean for the ocean, but additional research has suggested it will likely alter waters’ heat distribution and impact the way in which nutrients are carried in oceans across the globe.
Earth’s strongest ocean current is getting faster, new research has found, and it’s largely because of humans.
The study, published late last month in the journal Nature Climate Change, concluded that “robust acceleration” in the Antarctic Circumpolar Current was driven mostly by human activity, which has caused ocean temperatures to climb. When the gap in temperatures between hot and cold water widens, the currents that border them pick up speed.
“Anthropogenic ocean warming is the dominant driver,” researchers at the University of California San Diego and the University of California Riverside wrote. The current is also heavily influenced by wind.
The ACC separates the Southern Ocean from the Atlantic, Pacific and Indian Oceans and carries water clockwise around the globe. It pushes more water than any other current and is the only ocean current that is not blocked by land masses, though Antarctica is surrounded by it.
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Researchers in the study used satellite data on the height of the sea surface and data collected by Argo floats, data-gathering robotic instruments in oceans all over the world used to track the temperature and salinity of ocean water.
Limitations of prior research have masked the ocean’s “dynamic” response to warming before now, researchers wrote, and, because the region absorbs much of the atmospheric heat generated by humans, the current should continue to quicken as the planet warms.
Scientists are still working to understand the knock-on effects of accelerating currents, but it’s believed they will alter oceans’ heat distribution, affecting marine life receiving mostly warmer waters. Faster circulation will also change how nutrients are carried in oceans around the world.
Researchers earlier this year discovered the ACC once sped up between 115,000 and 130,000 years ago during the last interglacial period, which likely caused massive weather disruptions and lowered the ocean’s ability to absorb carbon dioxide.
“The birds are emaciated – they are little more than skin and bone with many half their usual weight which is catastrophically low,” he added.
“They have been seen feeding very close to beaches in amongst swimmers, when normally they steer clear of people, and have been observed up to 20 miles up rivers, which is unheard of for this marine bird.
“These are signs that the birds are getting desperate in their search for food.”
Dr Daunt said the fact that the birds appeared to be starving “might suggest a lack of good quality fish in the sea” but the presence of many feeding flocks along the coasts suggested it was “caused by something else”.
Other birdwatchers have seen birds washed up in clusters with live birds “just bobbing about beyond the surf”, apparently not feeding.
Large colonies of guillemots nest annually on islands off the coasts of Scotland and Northumberland.
They spend most of their time at sea and come back to land to breed.
Senior curator in charge of birds at the Natural History Museum, Dr Alex Bond, said mass deaths, known as wrecks, were not unusual but usually occurred in winter and during bad weather.
“Guillemots spend most of their time on water, not on land, so a big storm can beat them up a bit,” he said.
“The fact we’re seeing lots of them in unusual places suggests this wreck is something quite different.”
The CEH is recording the number and location of dead birds and will carry out post-mortem examinations on their bodies.
It will then monitor breeding colonies next spring to see if numbers are reduced.
By Dan Fastenberg, Reuters | Posted – July 17, 2021 at 2:36 p.m.
Waves at high tide make their way over rocks and onto the road in Oceanside, California, Nov. 27, 2019. New research finds a regular lunar cycle will magnify rising sea levels caused by climate change. (Mike Blake, Reuters)
WASHINGTON — U.S. coastlines will face increasing flooding in the mid-2030s thanks to a regular lunar cycle that will magnify rising sea levels caused by climate change, according to research led by NASA scientists.
A key factor identified by the scientists is a regular “wobble” in the moon’s orbit — first identified in the 18th century — that takes 18.6 years to complete. The moon’s gravitational pull helps drive Earth’s tides.
In half of this lunar cycle, Earth’s regular daily tides are diminished, with high tides lower than usual and low tides higher than usual. In the cycle’s other half, the situation is reversed, with high tides higher and low tides lower.
The expected flooding will result from the combination of the continuing sea level rise associated with climate change and the arrival of an amplification part of the lunar cycle in the mid-2030s, the researchers said.
“This effect from the moon causes the tides to vary, so what we found is that this effect lines up with the underlying sea level rise, and that will cause flooding specifically in that time period from 2030 to 2040,” Hamlington said.
The researchers studied 89 tide gauge locations in every coastal U.S. state and territory aside from Alaska. The effect of the dynamic applies to the entire planet except for far northern coastlines like in Alaska.
The prediction pushes previous estimates for serious coastal flooding forward by about 70 years.
The study, published this month in the journal Nature Climate Change, was led by members of a NASA science team that tracks sea level change. The study focused on U.S. coasts but the findings are applicable to coasts worldwide, NASA said.
“This is eye-opening for a lot of people,” Hamlington said. “It’s really critical information for planners. And I think there’s a great amount of interest in trying to get this information from science and scientists into the hands of planners.”
Hamlington said city planners should plan accordingly.
“A building or particular piece of infrastructure, you may want to be there for a very long amount of time, whereas something else you may just want to protect or have access to for a few years.”
(Reporting by Dan Fastenberg; Editing by Diane Craft and Will Dunham)
By GABE CHERRY, UNIVERSITY OF MICHIGAN JUNE 27, 2021
Satellites reveal ocean microplastic fluctuation in the Great Pacific Garbage Patch and releases from the Yangtze River in China.
An estimated eight million tons of plastic trash enters the ocean each year, and most of it is battered by sun and waves into microplastics—tiny flecks that can ride currents hundreds or thousands of miles from their point of entry. The bits can harm sea life and marine ecosystems, and they’re extremely difficult to track and clean up.
Now, University of Michigan researchers have developed a new way to spot ocean microplastics across the globe and track them over time, providing a day-by-day timeline of where they enter the water, how they move, and where they tend to collect. The approach relies on the Cyclone Global Navigation Satellite System (CYGNSS) and can give a global view or zoom in on small areas for a high-resolution picture of microplastic releases from a single location.
The technique is a major improvement over current tracking methods, which rely mainly on spotty reports from plankton trawlers that net microplastics along with their catch.
“We’re still early in the research process, but I hope this can be part of a fundamental change in how we track and manage microplastic pollution,” said Chris Ruf, the Frederick Bartman Collegiate Professor of Climate and Space Science at U-M, principal investigator of CYGNSS and senior author on a newly published paper on the work.
Season changes in the Great Pacific Garbage Patch
The team found that global microplastic concentrations tend to vary by season, peaking in the North Atlantic and Pacific during the Northern Hemisphere’s summer months. June and July, for example, are the peak months for the Great Pacific Garbage Patch, a convergence zone in the North Pacific Ocean where microplastic collect in massive quantities. Concentrations in the Southern Hemisphere reach their peak during its summer months of January and February. Concentrations tend to be lower during the winter months, likely due to a combination of stronger currents that break up microplastic plumes and increased vertical mixing that drives them further beneath the water’s surface.
The data also showed several brief spikes in microplastic concentration at the mouth of the Yangtze River—long suspected to be a chief source.
“It’s one thing to suspect a source of microplastic pollution, but quite another to see it happening,” Ruf said. “The microplastics data that has been available in the past has been so sparse, just brief snapshots that aren’t repeatable.”
The researchers produced visualizations that show microplastic concentrations around the globe. Often, the areas of accumulation are due to prevailing local water currents and convergence zones, with the Great Pacific Garbage Patch being the most extreme example.
“What makes the plumes from major river mouths noteworthy is that they are a source into the ocean, as opposed to places where the microplastics tend to accumulate,” Ruf said.
Ruf says the information could help organizations that clean up microplastics deploy ships and other resources more efficiently. The researchers are already in talks with Dutch cleanup organization The Ocean Cleanup on working together to validate the team’s initial findings. Single-point release data may also be useful to United Nations agency UNESCO, which has sponsored a task force to find new ways to track the release of microplastics into the world’s waters.
Hurricane-tracking satellites set their sights on plastic pollution
Developed by Ruf and U-M undergraduate Madeline C. Evans, the tracking method uses existing data from CYGNSS, a system of eight micro-satellites launched in 2016 to monitor weather near the heart of large storm systems and bolster predictions on their severity. Ruf leads the CYGNSS mission.
The key to the process is ocean surface roughness, which CYGNSS already measures using radar. The measurements have mainly been used to calculate wind speed near the eyes of hurricanes, but Ruf wondered whether they might have other uses as well.
“We’d been taking these radar measurements of surface roughness and using them to measure wind speed, and we knew that the presence of stuff in the water alters its responsiveness to the environment,” Ruf said. “So I got the idea of doing the whole thing backward, using changes in responsiveness to predict the presence of stuff in the water.”
Using independent wind speed measurements from NOAA, the team looked for places where the ocean seemed less rough than it should be given the wind speed. They then matched those areas up with actual observations from plankton trawlers and ocean current models that predict the migration of microplastic. They found a high correlation between the smoother areas and those with more microplastic.
Converging ocean currents
Ruf’s team believes the changes in ocean roughness may not be caused directly by the microplastics themselves, but instead by surfactants—a family of oily or soapy compounds that lower the surface tension on a liquid’s surface. Surfactants tend to accompany microplastics in the ocean, both because they’re often released along with microplastics and because they travel and collect in similar ways once they’re in the water.
“Areas of high microplastic concentration, like the Great Pacific Garbage Patch, exist because they’re located in convergence zones of ocean currents and eddies. The microplastics get transported by the motion of the water and end up collecting in one place,” Ruf said. “Surfactants behave in a similar way, and it’s very likely that they’re acting as sort of a tracer for the microplastics.”
The research team is currently testing this hypothesis, working with naval architecture and marine engineering assistant professor Yulin Pan to conduct experiments in a wave-generating tank in the Aaron Friedman Marine Hydrodynamics Lab.
“We can see the relationship between surface roughness and the presence of microplastics and surfactants, so the goal now is to understand the precise relationship between the three variables, as well as the reasons behind them,” Pan said. “The wave tank and its ultrasonic sensors enable us to focus on those relationships by taking measurements under very precisely monitored wave, surfactant and microplastic conditions.”
Reference: “Toward the Detection and Imaging of Ocean Microplastics With a Spaceborne Radar” by Madeline C. Evans and Christopher S. Ruf, 9 June 2021, IEEE Transactions of Geoscience and Remote Sensing. DOI: 10.1109/TGRS.2021.3081691
1 of 2This image provided by Marc Herbin shows the development stages of the coelacanth fish. The “living fossil,” still around from the time of the dinosaurs, can live for 100 years, according to a study released in the Thursday, June 17, 2021 edition of Current Biology. And for females it may seem longer because scientists calculate that the live-birth bearing fish stays pregnant for five years. (Marc Herbin/MNHN via AP)
The coelacanth — a giant weird fish still around from dinosaur times — can live for 100 years, a new study found.
These slow-moving, people-sized fish of the deep, nicknamed a “living fossil,” are the opposite of the live fast, die young mantra. These nocturnal fish grow at an achingly slow pace.
Females don’t hit sexual maturity until their late 50s, the study said, while male coelacanths are sexually mature at 40 to 69 years. And maybe strangest of all, researchers figure pregnancy in the fish lasts about five years.
Coelacanths, which have been around for 400 million years, were thought extinct until they were found alive in 1938 off South Africa. Scientists long believed coelacanths live about 20 years. But by applying a standard technique for dating commercial fish, French scientists calculated they actually live close to a century, according to a study in Thursday’s Current Biology.ADVERTISEMENThttps://33bc879a5f65206c333e77d682acae5a.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html
Coelacanths are so endangered that scientists can only study specimens already caught and dead.
In the past, scientists calculated fish ages by counting big lines on a specific coelacanth scale. But the French scientists found they were missing smaller lines that could only be seen using polarized light — the technique used to figure out the age of commercial fish.
Study co-author Bruno Ernande, a marine evolutionary ecologist at France’s marine research institute, said polarized light revealed five smaller lines for every big one. The researchers concluded the smaller lines better correlated to a year of coelacanth age — and that indicated their oldest specimen was 84 years old.
Using the technique, the scientists studied two embryos and calculated the largest was five years old and the youngest was nine years old. So, Ernande said, they figured pregnancy lasts at least five years in coelacanths, which have live births.
That five-year gestation is “very strange” for fish or any animal, said Scripps Institution of Oceanography’s Harold Walker, who wasn’t part of the research.
Even though coelacanths are unrelated genetically and show wide evolutionary differences, they age slowly like other dwellers of the deep, sharks and rays, Ernande said. “They might have evolved similar life histories because they are sharing similar type habitats,” he said.
Last week, scientists conducting research on Western Australia’s Ashmore Reef became the first humans to lay eyes on a short-nosed sea snake at the site in more than two decades. Olive-colored and critically endangered, the snakes have been thought locally extinct for 23 years.
Like cobras, taipans, and death adders, the short-nosed sea snake is a member of the Elapidae family, meaning that it possesses short, hollow fixed fangs capable of injecting predominantly neurotoxic venom.
In short, it’s not an animal you want to encounter in the course of a swim. Luckily for them, the scientists were safe inside a research vessel “equipped with advanced robotic technologies” at the time of rediscovery, according to ABC Science.
“The robot was looking at a dead shell and [the researchers] were trying to pick it up and it had a sea snake sitting next to it,” Blanche D’Anastasi, a sea snake expert at the Australian Institute of Marine Science, said. “They asked to zoom in on it and they [both] realized straight away it was a short-nosed sea snake. They contacted me soon after and were like, ‘Is this what we think it is?'”NEWSWEEK NEWSLETTER SIGN-UP >
It was, much to her surprise. Short-nosed sea snakes were once abundant on Ashmore Reef, according to D’Anastasi, but their numbers began to decline in the 1970s and bottomed out in the early 2010s. The downward trend is of significant concern to marine biologists.
“You used to find about 50 snakes per day if you were walking the reef site,” D’Anastasi said. “By 2002 it was down to 20 snakes per day, by 2010 it was down to 10, and then in 2012 there were no snakes left in the shallows.”
The species was presumed extinct in 1998 when it disappeared from Ashmore, but Kate Sanders, a reptile ecologist at the University of Adelaide, and her team managed to locate a few small, isolated populations along the coast in 2016.NEWSWEEK SUBSCRIPTION OFFERS >
“Cable Beach in Broome, we’ve had a single specimen from there, and scattered distributions from the Exmouth Gulf,” she said.
However, their members differed from the animals that had been previously observed on the reef in several significant ways, raising the possibility that they represented a distinct species of sea snake entirely. For example, they had smaller heads.
From photos, it’s impossible to definitively identify the new specimen as either a reef snake or a coastal snake. It was found curled up on the seabed about 220 feet below the surface in the ocean’s twilight zone. Not to be confused with the 1960s sci-fi show of the same name, the twilight zone refers to the region of the ocean that receives only a minimal amount of sunlight.
That location, Sanders said, suggests one of two scenarios. In the first, the original short-nosed sea snakes have been inhabiting the reef all along at depths that put them out of the natural reach of humans. In the second, the coastal snakes have simply expanded their territory.
“Could they have recolonized from the coast? That’s a really important question,” Sanders said. “If it’s the coastal population that’s recolonized, that would suggest we’ve lost that historical diversity that used to be present on Ashmore.”
Lifeguards found the 25-foot emaciated gray whale at Dockweiler Beach, south of Marina del Rey, around 4 p.m. local time, the Los Angeles County Fire Department, Lifeguard Division said Thursday on its Facebook page.
They and personnel from Marine Animal Rescue were advised to not help the animal, who they didn’t want to risk injuring critically, according to tweet from the fire department lifeguards’ official account.
Originally, the Lifeguards, animal rescue and NOAA Fisheries — who directed them to leave the whale be — hoped the creature would manage to get back to the water during high tide, according to the Facebook post.
The whale though was declared dead around 8 p.m.
“With great sadness the stranded whale has been determined to be deceased,” the fire department lifeguards tweeted.
The whale’s removal, it said, would be coordinated by the Los Angeles County Department of Beaches and Harbors, with a necropsy planned for Thursday.
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We think of mass extinctions as brief moments of havoc — profoundly devastating but over within a geologic instant. The Devonian, the second of the so-called “Big Five,” defies this notion. If the other great die-offs are short stories of death and destruction, this one is an epic akin to War and Peace. Even that paradoxical title seems fitting: The Devonian extinction ravaged Earth on and off for 25 million years, and although it ultimately killed three-quarters of all species, it also cleared the way for a new balance of animal life that endures to this day.
The extinction began roughly 380 million years ago, midway through the segment of geologic time known as the Devonian period, or the age of fish. (Vertebrates hadn’t yet made the leap onto land.) The prehistoric waters teemed not with the likes of tuna, sardines and salmon, but with their bizarre, long-dead predecessors. At the top of the food chain sat the placoderms, a race of heavily-armored and sometimes massive fish. The most famous of these mean-mugging beasts, Dunkleosteus, may have grown as long as 30 feet, probably winning it the distinction of largest animal — until the dinosaurs.
An illustration of the enormous extinct prehistoric fish Dunkleosteus swimming in search of food within a Devonian Sea. (Credit: AuntSpray/Shutterstock)about:blankabout:blank
But for all their might, Dunkleosteus and its kin wouldn’t survive the age that bears their name. “A series of crises piled up to affect life on Earth,” says Michael Coates, a biologist at the University of Chicago. Annihilation crept in, and slowly swept away the dominant Devonian species. This opened ecological niches to a new cast of organisms — no less than, in Coates’ words, “the signature of modern vertebrate life on the planet.”
Gasping for Air
In terms of its time scale, “the Devonian extinction is quite different from the others,” says University of Cincinnati geologist Thomas Algeo. Over the course of millions of years, as many as 10 distinct events raised the loss of biodiversity above the normal background rate, or baseline. Two, however, stand out: the Kellwasser and Hangenberg events, which occurred in the middle of and at the end of the Devonian period, respectively.
Clear-cut answers are rare in the realm of extinction, but researchers broadly agree that both events were accompanied by widespread ocean anoxia, or low oxygen levels. Some of the best evidence is found in the layers of black shale — which form under anoxic conditions — that date to the time. It’s likely, then, that one of the major kill mechanisms throughout the Devonian period was asphyxiation. Along with the armored fish, reef-builders like corals and sponges died en masse, as did trilobites, nautilus-like goniatites and many more creatures.
It’s more difficult to say why the oceans suddenly became unbreathable for them. Volcanic activity is a perennial suspect in extinction investigations, and scientists have duly scoured the rock record for traces of it in the Devonian extinction. “There’s been a lot of searching for a plausible candidate,” Algeo says. Nothing has been found yet to compare with the monstrous eruptions of the later Permian extinction, but some evidence does suggest that volcanism in a large igneous province called the Viluy Traps may have played a role, including, perhaps, via mercury poisoning. An asteroid also struck Earth during this period, leaving behind the 40-mile-wide Siljan crater.
One recent study concluded that the trigger for the Hangenberg event was ultraviolet radiation, penetrating the atmosphere through a break in the ozone layer. The researchers collected Devonian rock samples from mountains in Greenland and the Andes, and, after dissolving them, found malformed plant spores consistent with DNA damage from UV exposure.about:blankabout:blank
Life Turns on Itself
Algeo has his own, astounding theory: Death came not from geologic or climatic processes, but as a “natural consequence of the evolution of the whole biosphere.” In other words, the enemy of Devonian life was life itself. He believes that as vascular plants — basically everything except moss and lichen — first colonized dry ground, their deep roots broke up Earth’s surface rocks, releasing nutrients and minerals that fueled algal blooms. This left the oceans riddled with dead zones devoid of oxygen. While the plants thrived, the rest died.
Plants also absorb carbon dioxide, or CO2, the atmosphere-warming greenhouse gas. As they spread, they could have chilled the planet, bringing on an ice age that would have made life even less sustainable. (Indeed, some research suggests global cooling was involved in the Devonian extinction, disproportionately affecting tropical species.) Over the long term, though, the greatest legacy of this newfangled vegetation may lie in the extinction’s rebound.
Whether or not the vascular plants were to blame for the extinction, they were undoubtedly pervasive by the end of it, with trees and ferns forming the first modern forests. The above-water world had finally grown complex enough to support a menagerie of animal life, and sea-faring species took notice. “Everyone’s looking at that, and there’s stuff to exploit,” Coates says. “They’ve suddenly got this golden opportunity.”
New World Order
The tetrapods, our oldest terrestrial ancestors, abandoned the ocean for this new environment. Every single vertebrate that has walked the Earth since is a descendent of these primitive, four-legged landlubbers: “grotesque amphibians slumping around in swamps,” Coates calls them, half-jokingly.
A drawing of Elginerpeton pancheni, an early tetrapod from the Late Devonian period. (Credit: Nobu Tamura/CC by 3.0/Wikimedia Commons)
After the Devonian extinction ended, around 360 million years ago, Romer’s gap began. This void in the fossil record, named for Harvard professor Alfred Sherwood Romer, puzzled scientists for decades. Most significantly, it thwarted attempts to piece together the improbable history of the first land animals whose lineage eventually leads to us. For the most part, tetrapods were bit players before the extinction: a few weird, lungfish hybrids like acanthostega, sprouting half-hearted limbs where they should have had fins. They certainly didn’t look like they were only an evolutionary hop, skip and jump from world domination. about:blankabout:blank
But after Romer’s gap, “when you pick them up again,” Coates says, “they’re diverse and doing all sorts of exciting things.” Lumbering amphibians are suddenly walking on land, and steadily improving at it. One of the most famous specimens is ichthyostega, a meter-long creature that’s a bit reminiscent of the Chinese giant salamander. In another few million years, the amphibians diverge from the shelled-egg-laying reptiles, which themselves later give rise to the dinosaurs and mammals.
The Devonian extinction ushered in not only the land-bound tetrapods, but also the animals that command the marine vertebrate world to this day: ray-finned (or bony) fish, and cartilaginous fish, like sharks, rays and chimeras. Though we see ourselves in the tetrapods, the progeny of post-Devonian fish is, in its own way, even more impressive — today’s marine vertebrates (including the bristlemouth, likely the most abundant vertebrate on Earth) far outweigh their dry-ground cousins. If a Martian biologist were to select one vertebrate at random from our planet, Coates says, “chances are it would be something like a herring.”
It’s not clear to what extent the Devonian extinction actually altered the flow of evolution. Maybe the tetrapods, sharks and bony fish would have outcompeted their rivals anyway. According to Algeo, the extinction “probably served mostly to finish off these groups that were already not doing well.” Still, it was the extinction that finished them off, yielding the ecological floor decisively to the forms of life we see today. As Coates put it, “the modern vertebrate biota is the product of this big editing event.” In no small sense, we may have the Devonian extinction to thank for our existence.
Thu 19 Nov 2020 03.00 ESTLast modified on Thu 19 Nov 2020 03.02 EST
Endangered marine mammals and sea turtles are routinely being entangled in or are swallowing pieces of plastic that now riddle the oceans off US coastlines, a new report has found.
The plastic-induced toll stretches from Florida, where a manatee was found dead with a stomach filled with plastic bags and straws, to Virginia where a sei whale died after swallowing a DVD case causing stomach lacerations, to California, where a juvenile elephant seal was discovered with a packing strap wrapped around its neck. In South Carolina, a loggerhead sea turtle defecated out almost 60 pieces of plastic while being rehabilitated.
In total there is evidence of more than 1,800 marine animals from 40 species suffering from contact with plastics over the past decade, according to the first formal tally drawn from government and NGO data. Some examples of this phenomenon become well known – such as the whale that washed up with 40kg of plastic in its stomach last year – but the true toll is certainly far higher, with most entanglements unseen by humans.
“We may never know the true number but the details we do have are heartbreaking,” said Kimberly Warner, a senior scientist at Oceana, the conservation organization that collated the report. “The plastic is everywhere, even within deep-diving animals that you rarely see, and it is getting worse.”Advertisementhttps://01bca2c3102d9380c567e9ca95a2c385.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html
Animals can inadvertently swallow floating pieces of plastic while feeding or may even mistake the pieces for food. The Oceana report found that plastic bags, balloons, recreational fishing line, plastic sheeting and food wrappers were the most commonly ingested items, causing internal injuries or hampering the ability of the animals to feed.
Other pieces of plastic can become wrapped around necks, fins or flippers, causing deep injuries or hampering movement. In Hawaii, a monk seal was found with a plastic water bottle stuck on its snout while in California a food wrapper was discovered lodged in the esophagus of a dolphin. This blight could prove a material threat to the viability of some species, with the Oceana report finding that 88% of creatures recorded with plastic on or in them are from species listed as threatened or endangered by the US.
Around 11m tonnes of plastic flow into the oceans a year, with this amount set to nearly triple to 29m tonnes a year by 2040 – the equivalent of 50kg for each meter of coastline in the world – if current trends continue. The plastic often breaks down into tiny pieces and is now ubiquitous in our oceans, found from the deepest reaches of the marine world to even sea ice in the Arctic.
Some jurisdictions within the US have moved to phase out plastic straws or bags – New York is now finally enforcing a ban on plastic bags after a pandemic-related delay – but advocates are hoping to push Joe Biden’s incoming administration to more aggressive national action.
“We need to quit blaming other countries and pass laws limiting the use of single-use plastics,” said Warner. “I know Biden is very concerned about climate change and plastic is a huge supplier of greenhouse gases. I’m hoping the US will finally come to the party and do something about this.”
The severe droughts in the USA and Australia are the first sign that the tropics, and their warm temperatures, are apparently expanding in the wake of climate change. But until now, scientists have been unable to conclusively explain the reasons for this, because they were mostly focusing on atmospheric processes. Now, experts at the AWI have solved the puzzle: the alarming expansion of the tropics is not caused by processes in the atmosphere, but quite simply by warming subtropical ocean.
Forest fires in Australia and California, droughts and water shortages in the Mediterranean—in the last few years, events such as these have become more frequent. Researchers attribute this to the fact that the tropics, the warm region surrounding the Equator, appear to be expanding. And that leads to the affected areas becoming hotter and drier. According to the official definition, the tropics extend across the Equator between the latitudes of 23 degrees North and 23 degrees South. The central area is humid, with a great deal of precipitation, while the marginal regions in the north and south are hot and dry. As a result of climate change, however, for some time now the dry regions have been expanding northwards in the Northern Hemisphere—as far as Southern California—and southwards in the Southern Hemisphere.
But up to now, climate researchers have had a problem. They couldn’t conclusively explain this obvious expansion of the tropics using their climate models. The models simply didn’t show the magnitude and the regional characteristic of the observed expansion. A team working with the physicists Hu Yang and Gerrit Lohmann at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Bremerhaven (AWI) has now discovered the likely cause. As the AWI experts report in the Journal of Geophysical Research Atmospheres, the reason for the expansion appears to be an altered warming of the ocean. To date, experts assumed that processes in the atmosphere played a major role—for instance a change in the ozone concentration or the aerosols. It was also thought possible that the natural climate fluctuations that occur every few decades were responsible for the expansion of the tropics. For many years researchers had been looking in the wrong place, so to speak.
“Our simulations show that an enhanced warming over the subtropical ocean in both the Northern and Southern Hemispheres are the main drivers,” says Hu Yang, the study’s lead author. These subtropical warming patterns are generated by the dynamic of subtropical ocean gyres, measuring several hundreds of kilometers in diameter, which rotate slowly. These currents are especially well-known in the Pacific, because the majority of floating marine litter is concentrated in them. “Because the currents in the region bring together the surface warming water masses particularly intensely, it’s easier for the subtropical ocean surface to accumulate warmth than in other regions—and the same applies to plastic,” says Lohmann. As a result of this warming of the subtropical ocean, the tropical warm ocean regions are expanding. According to his calculations, this phenomenon is the catalyst for the tropics expanding to the north and south. “Previous researchers had been taking an overly complicated approach to the problem, and assumed it was due to complex changes in the atmosphere. In reality, it’s due to a relatively simple mechanism involving ocean currents.”
What led the experts to explore this avenue: data on ocean gyres that they happened to come across five years ago—data on ocean temperatures and satellite-based data, freely available on databases. Both sources indicated that the gyres were becoming warmer and more powerful. “That’s what led us to believe that they might be a decisive factor in the expansion of the tropics,” explains Hu Yang.
The AWI experts were right: their findings perfectly correspond to actual observations and the latest field data on tropical expansion. Just like in reality, their climate model shows that the tropics are now stretching farther to the north and south alike. In the Southern Hemisphere, the effect is even more pronounced, because the ocean takes up more of the overall area there than in the Northern Hemisphere.
Yet when it comes to the question of whether the droughts in Australia, California and the Mediterranean are due to the expansion of the tropics, Gerrit Lohmann can’t give a definitive answer. “When talking about climate change, it’s always difficult to quantify the respective parameters with absolute certainty,” he says. “However, we can safely assume that the ocean currents and expansion of the tropics make droughts and hurricanes more likely to occur.”