November 21, 2013
Over the course of 1700 miles, they sampled the water for small pieces of plastic more than 100 times. Every single time, they found a high concentration of tiny plastic particles. “It doesn’t look like a garbage dump. It looks like beautiful ocean,” Miriam Goldstein, the chief scientist of the vessel sent by Scripps Institution of Oceanography, said afterward. “But then when you put the nets in the water, you see all the little pieces.”
In the years since, a lot of public attention has been justifiably paid to the physical effects of this debris on animals’ bodies. Nearly all of the dead albatrosses sampled on Midway island, for instance, were found to have stomachs filled with plastic objects that likely killed them.
But surprisingly little attention has been paid to the more insidious chemical consequences of this plastic on food webs—including our own. “We’d look over the bow of the boat and try to count how many visible pieces of plastic were there, but eventually, we got to the point that there were so many pieces that we simply couldn’t count them,” says Chelsea Rochman, who was aboard the expedition’s Scripps vessel and is now a PhD student at San Diego State University. “And one time, I was standing there and thinking about how they’re small enough that many organisms can eat them, and the toxins in them, and at that point I suddenly got goosebumps and had to sit down.”
“This problem is completely different from how it’s portrayed,” she remembers thinking. “And, from my perspective, potentially much worse.”
In the years since, Rochman has shown how plastics can absorb dangerous water-borne toxins, such as industrial byproducts like PCB (a coolant) and PBDE (a flame retardant). Consequently, even plastics that contain no toxic substances themselves, such as polyethylene—the most widely used plastic, found in packaging and tons of other products—can serve as a medium for poisons to coalesce from the marine environment.
But what happens to these toxin-saturated plastics when they’re eaten by small fish? In a study published today in Scientific Reports, Rochman and colleagues fill in the picture, showing that the toxins readily transfer to small fish through plastics they ingest and cause liver stress.This is an unsettling development, given that we already know such pollutants concentrate further the more you move up the food chain, from these fish to the larger predatory fish that we eat on a regular basis.
In the study, researchers soaked small pellets of polyethylene in the waters of San Diego Bay for three months, then tested them and discovered that they’d absorbed toxins leached into the water from nearby industrial and military activities. Next, they put the pollution-soaked pellets in tanks (at concentrations lower than those found in the Great Pacific garbage patch) with a small, roughly one-inch-long species called Japanese rice fish. As a control, they also exposed some of the fish to virgin plastic pellets that hadn’t marinated in the Bay, and a third group of fish got no plastic in their tanks at all.
Researchers still aren’t sure why, but many small fish species will eat these sort of small plastic particles—perhaps because, when covered in bacteria, they resemble food, or perhaps because the fish simply aren’t very selective about what they put in their mouths. In either case, over the course of two months, the fish in the experiment consumed many plastic particles, and their health suffered as a result.
“We saw significantly greater concentrations of many toxic chemicals in the fish that were fed the plastic that had been in the ocean, compared to the fish that got either clean plastic or no plastic at all,” Rochman says. “So, is plastic a vector for these chemicals to transfer to fish or to our food chain? We’re now fairly confident that the answer is yes.”
These chemicals, of course, directly affected the fishes’ health. When the researchers examined the tiny creatures’ livers (which filter out toxins in the blood) they found that the animals exposed to the San Diego Bay-soaked plastic had significantly more indications of physiological stress: 74 percent showed severe depletion of glycogen, an energy store (compared to 46 percent of fish who’d eaten virgin plastic and zero percent of those not exposed to plastic), and 11 percent exhibited widespread death of individual liver cells. By contrast, the fish in the other treatments showed no widespread death of liver cells. One particular plastic-fed fish had even developed a liver tumor during the experimental period.
All this is bad news for the entire food webs that rest upon these small fish, which include us. “If these small fish are eating the plastic directly and getting exposed to these chemicals, and then a bigger fish comes up and eat five of them, they’re getting five times the dose, and then the next fish—say, a tuna—eats five of those and they have twenty-five times the dose,” Rochman explains. “This is called biomagnification, and it’s very well-known and well-understood.”
This is the same reason why the EPA advises people to limit their consumption of large predatory fish like tuna. Plastic pollution, whether found in high concentrations in the Great Pacific garbage patch or in the waters surrounding any coastal city, appears to be central to the problem, serving as a vehicle that carries toxins into the food chain in the first place.
November 19, 2013
The North Pole is losing about 30,000 square miles of sea ice per year. Over the past century, average global temperatures have climbed by 1.5 degrees Fahrenheit. And yet, over the past few years, the sea ice that surround the South Pole has steadily been growing.
This past September, at the end of the Southern Hemisphere’s winter, the extent of Antarctica’s sea ice reached 19.51 million square kilometers, breaking a 35-year record that dated back to the start of data being collected in 1978. (In comparison, from 1981 to 2010, the average extent on the same date was just 18.5 million square miles.)
Why are the Arctic and Antarctic such polar opposites? Climate change deniers have pounced upon the unexpected divergence to argue that the planet’s temperature isn’t actually rising. But new research suggests that a different mechanism—unrelated to climate change—is responsible for the ice growth. The real answer, says University of Washington oceanographer Jinlun Zhang, can be found blowing in the wind.
Specifically, according to a study he and colleagues published in the Journal of Climate, the vortex of winds that swirl around the South Pole has both strengthened and converged, a trend that can explain about 80 percent of the growth in ice extent that has been detected in recent years.
Atmospheric scientists had previously observed that these swirling winds had gradually strengthened since the 1970s. Using a computer model, Zhang’s team found that this mechanism drives ice growth—even in the face of rising temperatures—by pushing floating layers of sea ice together, compressing them into thick ridges that are slower to melt.
“Ice ridging increases the amount of open water and areas with thin ice, which are then exposed to cold air in winter, leading to enhanced ice growth,” Zhang says. “Meanwhile, the ridges, driven together by the wind, shrink less during the summer, because thicker ice tends to survive longer.” Based on this mechanism, the model accurately predicted ice growth in the same areas—the Weddell, Bellingshausen, Amundsen and Ross seas—that it’s been most distinctly observed.
Of course, the explanation brings to mind another question: Why is this vortex of swirling winds growing more powerful in the first place? Scientists are still unsure, but a few hypotheses have been put forth.
One possible culprit is the hole in the ozone layer, caused by lingering CFCs that were emitted before their use was phased out by the Montreal Protocol. Because ozone absorbs ultraviolet light from the Sun, missing ozone affects the local balance and transfer of energy, potentially leading to stronger winds. Another possibility is that the strengthened winds can simply be chalked up to natural variability.
Whatever the cause, the observed effect—a growth in Antarctic ice—has been relatively small, especially in comparison to the rapidly melting ice in the Arctic. For now, the winds are causing ice growth, but going forward, that trend is likely to be overwhelmed by a far more potent one: the continued rise in greenhouse gas emissions and the climate change they’re rapidly driving. “If the warming continues, at some point the trend will reverse,” Zhang says.
September 25, 2013
Sure, it’s not much to look at. But stare long enough, and you’ll see a jaw (jutting out towards the right), a pair of nostrils (small perforations directly above the mouth cavity) and even a tiny eye socket (just above the mouth, to the left of the nostrils, staring out sideways).
This admittedly homely fish fossil, the 419-million-year old Entelognathus primordialis, was recently discovered in China and described for the first time in an article published today in Nature. What makes it remarkable is everything that’s come after it: It’s the oldest known creature with a face, and may have given rise to virtually all the faces that have followed in the hundreds of millions of years since, including our own.
The uncommonly well-preserved, three-dimensional fossil, analyzed by a group of researchers from the Chinese Academy of Sciences, was excavated near Xiaoxiang Reservoir in Southeast China, in a layer of sediment that dates to the Silurian period, which ranged from roughly 419 to 443 million years ago. All other fish specimens from this era are jawless fish (a group of more primitive creatures that still live on today as lampreys and hagfish), so this is the first one that has what we might call a face: a mouth, nose and two eyes.
It’s difficult to conclude very much about the behavior or lifestyle of the ancient creature, but we do know that it swam in water (land animals didn’t begin to evolve until the Devonian period, which spanned 359 to 419 million years ago) and was likely a top-level predator of the early ocean ecosystem.
What has scientists so excited, though, is that the particular anatomical features of this fossil could upend our understanding of how vertebrates evolved over time. “When I first saw this, I was completely blown away,” says Matt Friedman a paleobiologist at the University of Oxford that reviewed the paper and wrote an accompanying article in Nature. “It’s the kind of fossil you might see once or twice in your lifetime, as a research scientist.”
Friedman and others find the fossil so remarkable because it combines a series of characteristics from two different groups: placoderms, an ancient class of armored fish that went extinct millions of years ago, and bony fish, a lineage that gave rise to all modern fish with jaws and bone skeletons. Previously, it was assumed that placoderms died out completely (and that the other, more recent types of fish with similar armor plating had independently re-evolved it much later), while a different, shark-like group of fish called acanthodians led to the bony fishes.
“What a fossil like this shows is that maybe that’s not the case,” Friedman says. “Because if you look at just the top of the skull and the body, it looks like a placoderm. But when you look at the side, and the front, you see it has jaws that, bone for bone, closely resemble the jaws of bony fish.”
This is significant because of what happened next: bony fish gave rise to all modern vertebrate fish, along with all amphibians, reptiles, birds and mammals, including ourselves. In other words, this fossil might mean that the placoderms didn’t go extinct, but rather evolved into the tremendous diversity of animals that live on both land and sea—and that this ancient, strange-looking face belongs to one of your oldest ancestors.
Scientists won’t immediately jump to reorganize their evolutionary family trees overnight, but the new finding will prompt a period of renewed scrutiny of the previous model. “It’s going to take a while for people to digest it and figure out what it all means,” Friedman says. “From a fossil like this, you’ve got a cascade of implications, and this is just the first paper to deal with them.”
Eventually, though, this finding could help transform our understanding of just how evolution occurred in our planet’s ancient oceans—and how the primitive creatures that swam in them eventually gave rise to the faces we see everyday.
August 28, 2013
Over the past 15 years, a strange thing has happened. On one hand, carbon dioxide concentrations have kept on shooting up thanks to humans burning fossil fuels—in May, we passed 400 parts per million for the first time in human history.
On the other hand, despite certain regions experiencing drastically warmer weather, global average temperatures have stopped increasing. Climate change deniers have seized upon this fact to argue that, contrary to the conclusions reached by major science academies (PDF) around the world, greenhouse gas emissions do not cause global warming.
As it turns out, the truth is much grimmer. A pair of scientists from Scripps Institution of Oceanography have determined that the underlying process of global warming has merely been masked by natural decade-scale variations in the temperature of Pacific Ocean surface waters, related to the El Niño/La Niña cycle. Once that’s finished, our planet’s warming will march onward as usual.
Climate scientists have speculated about the possibility that ENSO (the El Niño-Southern Oscillation, the proper term for the cycle) was behind the apparent hiatus in warming for some time, but the scientists behind the new study—Yu Kosaka and Shang-Ping Xie—are the first to take a quantitative look at the role of Pacific surface temperatures in pausing global warming as a whole. Their paper, published today in Nature, uses climate models to show that the abnormally cool surface waters observed over the Pacific since 1998 can account for the lack of recent warming entirely.
Why has the Pacific been abnormally cool for the past 15 years? Naturally, as part of ENSO, a large swath of the ocean off the western coast of South America becomes notably warmer some years (called El Niño events) and cooler in others (La Niña events). Scientists still don’t fully understand why this occurs, but they do know that the warmer years are related to the formation of high air pressures over the Indian Ocean and Australia, and lower pressures over the eastern part of the Pacific.
Because winds move from areas of high pressure to low pressure, this causes the region’s normal trade winds to reverse in direction and move from west to east. As they move, they bring warm water with them, causing the El Niño events; roughly the reverse of this process happens in other years, bringing about La Niña. As it happens, colder surface temperatures in the Pacific—either official La Niña events or abnormally cool years that don’t quite qualify for that designation—have outweighed warm years since 1998.
That, say Kosaka and Xie, is the reason for the surprising lack of increase in global average temperatures. To come to this conclusion, they developed a climate model that, along with factors like the concentration of greenhouse gases over time and natural variations in the solar cycle, specifically takes the ENSO-related cycle of Pacific surface temperatures into account.
Typically, climate models mainly use radiative forcing—the difference between the amount of energy absorbed by the planet and the amount sent back out to space, which is affected by greenhouse gas emissions—as a data input, but they found that when their model did so, it predicted that global average temperatures would increase much more over the past 15 years than they actually have. However, when the abnormally-cool waters present in the eastern Pacific were taken into account, the temperatures predicted by the model matched up with observed temperatures nicely.
In models, the presence of these cooler waters over a huge area (a region within the Pacific that makes up about 8.2% of the Earth’s surface) serves to absorb heat from the atmosphere and thus slow down the underlying warming process. If the phenomenon is representative of reality, the team’s calculations show that it has caused the planet’s overall average temperature to dip by about 0.27°F over the past decade, combating the effects of rising carbon dioxide emissions and causing the apparent pause in warming.
This isn’t the first localized climate-related event to have effects on the progression of climate change as a whole. Last week, other researchers determined that in 2010 and 2011, massive floods in Australia slowed down the global rise in sea level that would have been been expected from observed rates of glacier melting and the thermal expansion of sea water. In many cases, it seems, the subtle and complex dynamics of the planet’s climate systems can camouflage the background trend of warming, caused by human activity.
But that trend is continuing regardless, and so the most obvious impact of this new finding is a disconcerting one: the Pacific will eventually return to normal temperatures, and as a result, global warming will continue. The scientists don’t know exactly when this will happen, but records indicate that the Pacific goes through this longer-term cycle every decade or so, meaning that the era of an abnormally-cool Pacific will probably soon be over.
Perhaps most distressing, the study implies that the extreme warming experienced in recent years in some areas—including much of the U.S.—is actually less warming than would be expected given the amount of carbon dioxide we’ve released. Other regions that haven’t seen much warming yet, meanwhile, are likely in line for some higher temperatures soon.
August 20, 2013
The menu says red snapper, but it’s actually tilapia. The white tuna, meanwhile, is really escolar, while the seabass is Antarctic toothfish.
Welcome to the wild world of modern seafood, where not everything is as it seems. New research is revealing that merchants and fish dealers often mislabel their product as an entirely different species to fetch a better price at market. A study realeased last week by UK researchers found that a number of species in the skate family are sold as “sting ray wings,” while a separate study produced in February by the group Oceana found that, of 1215 seafood samples from 674 restaurants and grocery stores in 21 U.S. states, a full third were mislabeled. In Chicago, New York, and Washington, DC, every single sushi bar that was tested was found to sell at least one mislabeled fish species.
How did the researchers figure all this out? Through the innovative use of DNA barcoding, in which a specific segment of genetic material (analogous to a product’s barcode) in a piece of fish is used to determine exactly which species it truly belongs to. For years, we had no real way of determining the true species of a piece of seafood—a filet of fish, after all, often looks like any other filet—but this new application of an existing scientific technique is rapidly becoming a crucial tool in combating seafood fraud.
Testing a piece of fish to determine its species is fairly straightforward—scientists perfected DNA barcoding years ago, albeit typically as part of other sorts of projects, like cataloging the complete assortment of species in a given ecosystem. Analyzing the DNA in a piece of fish is a relatively similar process.
To start, researchers acquire a piece of fish and freeze it, as fresher and better-preserved tissue samples generally yield more accurate results. Then, in the lab, they slice off a tiny piece of the sample for testing.
To extract and isolate the DNA from the tissue, scientists break open the cells—either physically, by grinding them or shaking them in a test tube filled with tiny beads, or chemically, by exposing them to enzymes that chew through the cell membrane. Next, they remove other components of the cell with various chemicals: proteases digest proteins, while RNAase digests RNA, an alternate form of genetic material that could cause errors in DNA testing if left in place.
Once these and other substances are removed, the remaining sample is put in a centrifuge, which spins it at high speed so that the densest component—in this case, DNA—is isolated at the bottom of the tube in a pellet. A variety of different approaches are currently used to sequence the DNA, but all of them achieve the same end—determining the sequence of base pairs (the building blocks of DNA that are unique to each organism), at one specific location in the fish’s genome. All fish of the same species share the same sequence at that location.
As part of broader DNA barcoding projects, other scientists have analyzed the sequence of base pairs at that same genetic location in thousands of pieces of fish tissue that can definitively linked to species. Thus, by comparing the genetic sequence in the mystery fish tissue to databases of other species’ known genetic sequences, such as FISH-BOL (which stands for Fish-Barcode Of Life and contains the barcodes of 9769 fish species so far), scientists can tell you if, say, the grouper you thought you were buying was actually Asian catfish.
Figuring out which species a piece of fish truly belongs to has significance that goes far beyond gastronomy. For one, cheaper fish species are most often substituted for more expensive ones: tilapia, which goes for around $2.09 per pound, is billed as red snapper, which can commonly fetch $4.49 per pound. (The fact that inexpensive fish is so commonly passed off as a pricier variety, while the reverse occurs much more rarely, indicates that intentional mislabeling by sellers is at play, rather than innocent misidentification.)
Additionally, species that are dangerously overfished and are on the verge of ecological collapse—such as orange roughy—are sometimes substituted for more environmentally-benign varieties. Customers that make the effort to choose sustainable types of seafood, in these cases, are thwarted by mislabeling.
Eating different species can also have vastly different effects on your own health. For one, different fish species can have different fat and calorie contents, so mislabeling can lead the nutrition-conscious astray. Moreover, certain species, like tilefish, are on the FDA’s “do not eat” list for sensitive groups of people (such as pregnant women) because of their high mercury content. The Oceana study, though, found several instances of tilefish being sold as red snapper. Perhaps even worse, 94 percent of the white tuna tested in the study was actually a fish called escolar, which has been found to contain a toxin that when ingested, even in small quantities, can cause severe diarrhea.
So, what to do? Testing the fish’s DNA at home is probably beyond most people’s capabilities. So to avoid being duped, Oceana recommends asking sellers lots of questions about a fish’s origin, scrutinizing the price—if a fish is being sold far below market value, it’s probably mislabeled as a different species—and buying whole fish at markets when possible.