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Atlantic currents seem to have started fading last century

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Enlarge / The Gulf Stream, as imaged from space.

The major currents in the Atlantic Ocean help control the climate by moving warm surface waters north and south from the equator, with colder deep water pushing back toward the equator from the poles. The presence of that warm surface water plays a key role in moderating the climate in the North Atlantic, giving places like the UK a far more moderate climate than its location—the equivalent of northern Ontario—would otherwise dictate.

But the temperature differences that drive that flow are expected to fade as our climate continues to warm. A bit over a decade ago, measurements of the currents seemed to be indicating that temperatures were dropping, suggesting that we might be seeing these predictions come to pass. But a few years later, it became clear that there was just too much year-to-year variation for us to tell.

Over time, however, researchers have figured out ways of getting indirect measures of the currents, using material that is influenced by the strengths of the water’s flow. These measures have now let us look back on the current’s behavior over the past several centuries. And the results confirm that the strength of the currents has dropped dramatically over the last century.

On the conveyor

The most famous of the currents at issue is probably the Gulf Stream, which runs up the east coast of the US and Canada, taking warm water from the tropics toward Europe. But the Gulf Stream is just one part of a far larger ocean conveyor system, which redistributes heat in all the major ocean basins outside of the Arctic. And while its reach is global, a lot of the force that drives the system develops in the polar regions. That’s where surface waters cool off, increase in density, sink to the ocean floor, and begin to flow south. It’s that process that helps draw warmer water north to replace what has sunk.

It’s the density of the cold, salty water that is key to the whole process—and that’s where climate change can intervene to slow down or halt the water’s turnover. The Arctic is warming faster than any other area on Earth, which means that the surface waters are starting to take longer to cool off. The Arctic warming is also melting off a lot of the ice, both on land and in the floating ice sheets that have typically covered the Arctic Ocean. This process can form a layer of fresher water over the surface of the ocean nearby that, even after it cools, won’t be as dense as the salt water beneath it.

If this process has kicked in, we should be able to detect it by measuring the strength of the currents flowing north. But that has turned out to be less informative than we might want. While we have detected significant drops in some years, they were often countered by large rises in others. This internal variability in the system is so large that it would take decades for any trend to reach the point of statistical significance.

The alternative would be to extend our records back in time. But since we can’t retroactively place buoys in the North Atlantic early last century, researchers have to identify other ways of figuring out how strong the flow of water was before we had accurate measurements.

Current by proxy

The research community as a whole has identified a number of ways to figure out what was going on in the oceans in the past. Some are pretty direct. For example, stronger ocean currents can keep larger particles of sediment flowing in the water for longer. So examining the average particle size deposited in sediments on the ocean floor can tell us something about the currents that flowed past that site. Other measures are a bit less direct, like nitrogen isotope ratios in corals, which tell us something about the productivity of the ocean in that area.

Overall, there are about a half-dozen different ways of understanding past ocean conditions used in the new study. Each has different levels of uncertainty, and many don’t provide an exact measure of conditions in a single year, instead giving a sense of what the average conditions were over a period of several decades.

Complicating matters further, the measures don’t all come from the same locations. Samples taken from deeper waters will capture the equator-directed cold water flow, while shallow sites will yield data on the warm waters flowing north. The Gulf Stream also breaks up into multiple individual currents in the North Atlantic so that some sites only capture a small part of the total picture.

Given all this, it’s not possible to build a complete picture of the Atlantic currents in the past. But with enough sites covered, it’s possible to get a sense of whether there have been any general changes at any point over the last 1,600 years based on the overlaps of the different records.

To identify any major transitions, a research team did change-point analysis, essentially searching for points in the history where the mean behavior before and after are significantly different. They found two change points that show up consistently in the data from multiple proxies. One occurred in the late 1800s, and the second happened around 1960, when the current period of warming really started to take off.

Of the 11 different records examined in the researchers’ work, 10 show that the current’s lowest strength has been within the past century. And that identification is statistically significant in nine of them. “Together, these data consistently show that the modern [current] slowdown is unprecedented in over a thousand years,” the paper’s authors conclude.

Obviously, we’d like to build up better records that more fully capture the dynamics of what has been going on and, if possible, give us more direct measures of the currents’ actual strengths. It’s also important to emphasize that this doesn’t necessarily portend a sudden, radical shift to a completely new climate. Europe might see a little less warming from ocean currents, but it’s also going to be seeing a lot more warming due to rising atmospheric temperatures. However, the drop in this current will have wide-reaching effects, both on the land surrounding the North Atlantic and the ecosystems within it. So getting more data should be a high priority.

Nature Geoscience, 2021. DOI: 10.1038/s41561-021-00699-z  (About DOIs).

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More J&J troubles: Vaccine manufacturing halted and more possible clot cases

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Enlarge / The Emergent BioSolutions plant, a manufacturing partner for Johnson & Johnson’s Covid-19 vaccine, in Baltimore, Maryland, on April 9, 2021.

The US Food and Drug Administration last week asked Emergent BioSolutions to stop making Johnson & Johnson’s COVID-19 vaccine at its troubled facility in Baltimore, according to a regulatory filing Emergent released Monday.

The FDA had begun an inspection of the contract manufacturer’s facility on April 12 but requested on April 16 that production be halted “pending completion of the inspection and remediation of any resulting findings,” the filing reads. Any vaccine materials already made at the plant will be held in quarantine.

The production halt follows news last month that a mishap at the plant led to the ruin of 15 million doses of Johnson & Johnson’s one-shot COVID-19 vaccine. The ruined doses had reportedly been contaminated with ingredients from AstraZeneca’s COVID-19 vaccine, which was also being manufactured at the plant at the time.

The accident was a major stumbling block for Johnson & Johnson’s vaccine production—but not a consumer safety issue. All of the doses of Johnson & Johnson’s vaccine that has been used in the US so far have been produced in the Netherlands. The Emergent facility in Baltimore had not yet been authorized by the FDA for vaccine production when the doses were ruined, and none of the spoiled doses completed the production process.

Early this month, the Biden administration put Johnson & Johnson in charge of the facility and ordered AstraZeneca’s vaccine production out to prevent further cross-contamination problems. At the time, the company said that, despite the setback, it still expected to meet its commitment to deliver nearly 100 million doses of its vaccine to the US government by the end of May. But the current production pause again raises questions of whether the company will still be able to meet that goal.

“At this time, it is premature to speculate on any potential impact this could have on the timing of our vaccine deliveries” the company told Reuters.

In a statement to Politico, Emergent said:

While we await the FDA’s full feedback, we are working with J&J and the FDA on strengthening the supply chain for this vitally important vaccine… We acknowledge that there are improvements we must make to meet the high standards we have set for ourselves and to restore confidence in our quality systems and manufacturing processes.

Pause beyond pause

For now, Biden officials say they have enough vaccine supply from Moderna and Pfizer-BioNTech to continue the current pace of vaccinations, which has exceeded 3 million doses a day recently.

Regardless of the production pause, use of Johnson & Johnson’s vaccine was already on pause as federal health experts and advisors review data linking the vaccine to an extremely rare but dangerous blood-clotting condition.

Last week, the FDA and the Centers for Disease Control and Prevention said that, out of more than 6.8 million vaccine doses administered, they had identified six cases of the unusual condition, which leads to dangerous life-threatening blood clots in combination with low levels of platelets. One person died of the condition, and another was said to be in critical condition.

A vaccine advisory committee for the CDC, called ACIP, held an emergency meeting last week but punted on making any recommendations for use of Johnson & Johnson’s vaccine going forward. Instead, the committee scheduled another public meeting for this Friday, April 23 from 11 am to 5 pm EDT where it will review further data and analyses.

In a White House press briefing Monday, CDC director Rochelle Walensky said that the agency had received additional reports of blood-clotting cases possibly linked to the vaccine.

There have been “a handful of cases, not an overwhelming number of cases,” Walensky said in the briefing. “We are working through and adjudicating them and verifying whether they do in fact reflect a true case.” The CDC and the FDA will then present their findings to ACIP on Friday, she said.

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Missing Arctic ice fueled the “Beast of the East” winter storm

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Enlarge / Picking up moisture from the ice-free sea, a storm builds and heads towards Europe.

Extreme weather has become the new normal—whether it’s precipitation, drought, wind, heat, or cold. The question of how the ever-shrinking layer of Arctic sea ice has contributed to any of these changes has prompted some lively discussion over the past few years. Researchers have proposed that a weakened jet stream driven by vanishing Arctic sea ice might play a large role in extreme winter events like the descending polar vortex that struck North America earlier this year. But the idea hasn’t held up well in light of more recent evidence.

But now, researchers have identified a direct link between extreme winter weather and sea ice loss. The 2018 “Beast of the East” winter storm hit Europe with record-breaking snowfall and low temperatures. And potentially as much as 88 percent of that snowfall originated from increased evaporation of the Barents Sea.

The working hypothesis is that Arctic sea ice acts as a cap for Arctic waters, limiting evaporation. Less sea ice and warmer Arctic temperatures mean more evaporation, potentially explaining the increased severity of winter storms like the Beast of the East. Until now, it’s been tough to measure direct evidence linking sea ice loss to extreme European winters, but recent advances in technology are making this a little less challenging.

Secrets of the north

With sub-freezing temperatures, 24-hour darkness in winter, and, well, not very much land, the Arctic is among the world’s most hostile research environments. To date, much of the direct data from the region has been collected by hands-on research boats, but these expeditions are expensive and limited in where and when they can be used.

Instead, this latest research used a recent technology—an isotope and gas-concentration analyzer—that automatically collects real-time data at the impressive frequency of nearly one measurement per second. Although the researchers haven’t installed the instrument in the furthest reaches of the Arctic, they have added one at a weather station in Pallas-Yllästunturi National Park, northern Finland, just a few hundred kilometers from the Norwegian Sea.

They installed the instrument in late 2017, and it’s been allowing them to detect the naturally occurring stable isotopes in water vapor—i.e., hydrogen and oxygen—since then. Two of these isotopes, 18O and 2H, have been widely used for tracking hydrological processes over the last 70 years. Because these isotopes are a little heavier, they are less likely to evaporate, creating unique isotope “fingerprints” for phase transitions such as evaporation, cloud formation, rain, and snow. This has made it possible to trace the origins of storm systems—and the research team put this instrument in place just in time for a whopper of a storm.

The Beast

Within months of installing the instrument, the team noticed a huge isotope spike in March of 2018, just as the Beast of the East arrived in Europe. The researchers could trace this spike in vapor back to unusually high amounts of evaporation from the Barents Sea, which was warmer and more ice-free than historical norms.

“The data from our study represent the first ‘real measurements’ that prove that sea ice loss through enhanced evaporation is contributing to extreme mid-latitude snowfall events,” says first author Hannah Bailey. “Up until now scientists have explored the link between Arctic sea ice loss and extreme snowfalls using climate models and, without this technology we’re using, it simply wouldn’t be possible to capture these types of natural events and processes in real-time.”

The team also combined satellite data and modeling to calculate that up to 88 percent of the snow from the Beast storm—140 billion tons—may have come from the Barents Sea.

Less ice, more snowfall

The team focused on the Barents Sea because it is a literal “hotspot” of decreasing sea ice in the Arctic. Maximum March sea ice levels there have dropped 54 percent since 1979. Using historical satellite observations and atmospheric models, the team confirmed that smaller amounts of Barents Sea ice have regularly correlated with higher evaporation and heavier March snowfall across northern Europe over the last 30 years.

This evidence also suggests that this trend may intensify with further sea ice loss in the Barents Sea, which some researchers have predicted may be ice-free by 2061-2088. The team hopes to establish a network of these isotope monitoring instruments throughout the Arctic—both on ships and on land—in order to better measure these changes moving forward.

“There is scientific consensus that the decline of Arctic sea ice impacts mid-latitude weather, but there is a lack of consensus among the models used to investigate these processes,” says Bailey. “There’s huge potential for atmospheric vapor isotope data to improve weather forecasting, as well as aid in the prediction of extreme weather events that impact society.”

Nature Geoscience, 2021. DOI: 10.1038/s41561-021-00719-y  (About DOIs).

K.E.D. Coan is a freelance journalist covering climate and environment stories at Ars Technica. She has a Ph.D. in Chemistry and Chemical Biology.

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Denisovans may have met us in the Pacific

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Enlarge / The highlands of Papua New Guinea.

David Kirkland | Getty Images

The inhabitants of the Pacific came in waves. Aboriginal Australians were the first to cross the area, and they were followed by separate populations that inhabited New Guinea and nearby island chains. Later still, the Polynesians, descendants of early East Asians, spread through the distant islands of the Pacific.

While modern genetics has made these rough outlines clear, it has also made it clear that these different populations sometimes interacted, sharing DNA along with technology and trade goods. Paleontology finds have made it clear that at least three distinct hominin species had occupied some of these islands before modern humans arrived, including the enigmatic Hobbits of Indonesia and a similarly diminutive species in the Philippines.

A recent study of the genomes of Pacific island populations provides a map of some of the major interactions that took place in the Pacific. And it suggests at least one of these involved the introduction of additional Denisovan DNA.

New genomes

The work started with the sequencing of over 300 genomes volunteered by individuals from 20 different populations throughout the Pacific. The research team grouped these populations according to whether they came from Near Oceania (Indonesia, New Guinea, and the Philippines) or more distant islands of the Pacific (collectively Far Oceania). The latter is largely populated by the Polynesians, who arrived relatively late and had a distinct genetic history. But there were clearly interactions between the two groups, and the border between the areas each occupies is fuzzy in locations.

By comparing the genome sequences with each other and ancestral populations, it’s possible to make estimates of which groups are related to which others, as well as the time at which the different populations branched off. In addition, it’s possible to detect interbreeding among the populations, based on the appearance of stretches of DNA that are found in one population but are more similar to those from another.

The people who live in the highlands of Papua New Guinea have the earliest split, separating from the populations of other islands about 40,000 years ago. The branches of that lineage who inhabit the Bismarck and Solomon Islands separated from each other about 20,000 years ago.

But things get much less neat in Vanuatu, a group of islands out past the eastern end of the Solomons. About a third of their genome comes from Bismarck islanders, and that was a recent arrival, the result of interactions that took place only about 3,000 years ago. The rest comes from a group that started out in Papua but interbred with the Solomon Islands population en route. All of that means that Vanuatu is like a melting pot of near oceanic populations.

Then there are the Polynesians. They seem to have interbred with both the Bismarck and Solomon islanders. The best fit to the data involves one interaction right as the Polynesians arrived in the area about 3,500 years ago and a second interaction that occurred a thousand years later.

Premodern humans

All of the populations sampled seem to have roughly similar amounts of Neanderthal DNA, present in similar locations in the genome, suggesting there was nothing unusual about their genetic history compared to other groups in the region. But that was not the case with the Denisovans. The amount of Denisovan DNA varied considerably among the populations, with the highest percentage found in those from the New Guinea highlanders.

Analysis of the Denisovan DNA segments was used to determine two things. The length of the DNA provided a measure of how long ago the interbreeding took place, as the Denisovan DNA segments would get shorter over time thanks to recombination. The sequence itself could be compared to the genome of a Denisovan bone in Siberia, which tells us a bit about how diverse the Denisovan population was.

East Asian populations and the Polynesians appear to have had two different periods of interbreeding with Denisovans, both of which were reasonably closely related to the Siberian population.

The people of Papua New Guinea also showed signs of two periods of interbreeding. But, rather critically, they weren’t the same ones seen in East Asians. The first involved interbreeding around 45,000 years ago with a population that had separated from the Siberian Denisovans by roughly 200,000 years—a genetic contribution shared with the East Asians and Polynesians. But the second interbreeding event took place about 25,000 years ago—after the point where the population was out in the Pacific.

And that’s a bit strange. In terms of fossil evidence, we know that Homo erectus was in the area before modern humans arrived, but its DNA would be substantially different from that of Denisovans. There are two other species—the Hobbits of Flores and an equally odd hominin from the island of Luzon. While these look very different from modern humans (having some traits shared with the earlier Australopiths), we can’t rule out that they are closely related to the Denisovans, which would explain the origin of this DNA.

The researchers checked, and the only signs of distantly related DNA can be accounted for by Neanderthals and Denisovans. So if these island species aren’t Denisovans, then it appears we didn’t interbreed with them in a way that left its mark on modern genomes.

What this tells us

Modern humans reached places that required travel across the open ocean very early during their expansion out of Africa. That would seem to suggest that ocean-going voyages were well within our abilities. But these data indicate that most populations remained relatively isolated from each other once they were established. That suggests that, even though the technology was available to manage this travel, it wasn’t widely used—certainly, there’s no indication of longstanding trade until the Polynesians arrive.

Once the Polynesians did arrive, however, there are indications that they interacted at least twice with the inhabitants of the islands near New Guinea. And Vanuatu, at the border between Near Oceania and Polynesia, seems to have an exceedingly complicated history.

To an extent, it seems that, outside of Vanuatu, these people groups interacted with each other about as often as their ancestors interacted with the Denisovans. The genomic data provides evidence of several distinct periods of interbreeding, including one that for now appears specific to a group that is native to the Philippines. This indicates that some of the interbreeding likely went on after modern humans had migrated out into the Pacific islands.

Since we don’t know of any Denisovan remains in the region, it suggests two possibilities. One is that the Denisovans were in the area undetected—not a huge surprise, given how long their presence in Asia went undetected. But the more intriguing prospect is that one of the species we’re aware of from skeletal remains—Homo luzonensis or Homo floresiensis—represents a branch of the Denisovan lineage. So far, all attempts to extract DNA from these skeletons have failed, so it’s not clear if or how we’d be able to figure this out.

Nature, 2021. DOI: 10.1038/s41586-021-03236-5  (About DOIs).

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