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By Marlene Cimons
Much of the deep sea has never been explored close-up by humans. Some submarines have plumbed its depths, but reaching the ocean bottom is a complicated and expensive journey, challenging because the seabed lies under more than three miles of water, which exerts huge amounts of pressure. "We know more about space than about the bottom of the oceans in our own planet, even though more than two-thirds of the surface of the Earth is covered by marine sediments," said Olivier Sulpis, a researcher and doctoral student at McGill University's department of earth and planetary sciences.
Thus, "we hear less about the effects of human activity at the seafloor than on corals, for instance, simply because coral bleaching sounds more appealing than mud dissolving at the bottom of the sea," he added. "When you think that before Google maps arrived, it took humans several centuries to map the continents, it's easy to understand why exploring the deep sea is so hard."
Nevertheless, he and his colleagues found a way to study it without actually going there. They recreated its environment in the lab, building little boxes filled with sediments overlain by sea water, keeping them in the dark. They duplicated sea water temperature and chemistry, as well as the composition of the sediment. By mimicking seabed conditions, "we don't need to go to the bottom of the sea to do measurements, and we save some time and energy." Sulpis said.
Sulpis and his team studied ocean floor sediment from the middle of the North Atlantic. Olivier Sulpis
What they found was worrisome. It has already been established that climate change—specifically atmospheric carbon dioxide emitted by fossil fuel burning—has been acidifying the oceans, damaging fragile coral reefs and disturbing vulnerable marine ecosystems. But the McGill scientists discovered that carbon dioxide also has begun to drift to the ocean bottom, dissolving the very materials that help put the brakes on acidification.
"Humans have become a geological force, and there is not a single part of the surface of our planet where we cannot find a trace of human activity," Sulpis said. "Paleoclimate scientists and Earth sciences students have heard and described many times past abrupt climate change and ocean acidification episodes, millions of years ago, that caused mass extinctions all around the world. These events were caused by meteoritic impacts, global wildfires, volcanic eruptions, etc. Today, it seems that we are at the dawn of one of these catastrophic events, and we don't need to look far to find the cause of it. Each one of us is the cause of it."
A diver surveys coral bleaching.The Ocean Agency
Normally, the seafloor is chalky white, largely made up of calcite formed from the skeletons and shells of planktonic organisms and corals. Calcite neutralizes carbon dioxide acidity, keeping seawater from becoming too acidic. But these days, at least in certain hotspots such as the North Atlantic and the southern oceans, the ocean's chalky bed is turning murky brown, the result of human activities that are causing carbon dioxide levels in the water to become too high and the water too acidic, according to new research published in Proceedings of the National Academy of Sciences. Eventually, the researchers predicted, the calcite won't be able to keep pace with acidification, dissolving before it can do its job.
"The calcite at the bottom of the ocean is like a big anti-acid pill," Sulpis said. "It dissolves when there is too much CO2 and this neutralizes excess CO2 in the process. If the seafloor runs out of calcite, the ocean loses its anti-acid pill, and we could go towards a scary state of runaway ocean acidification."
The researchers measured how fast sediments dissolved when placed in boxes covered by seawater. "We did this for a few years, and eventually we realized that we understand this dissolution reaction well enough to describe it using simple mathematical equations," Sulpis explained. "If we know the chemical conditions and the sediment properties down there, we can compute the dissolution rate of calcite in these sediments. "
They used state-of-the-art ocean models, computing calcite dissolution rates across the seafloor. The experiments produced insights as to what controls calcite dissolution in marine sediments. By comparing pre-industrial and modern seafloor dissolution rates, they could determine how much of the total dissolution was caused by humans.
Scientists know that calcite has historically helped de-acidify the ocean. "What is surprising and concerning, however, is that it is already happening now," Sulpis said. "Scientists thought it would take much longer before we start seeing some calcite dissolution at the seafloor that is caused by our CO2. We know how our climate works. We know how our oceans works, but what we are incapable of predicting is our society and how we will adapt our behavior to this changing world."
The findings have far-reaching implications. "Just as climate change isn't just about polar bears, ocean acidification isn't just about coral reefs," said David Trossman, now a research associate at the University of Texas-Austin and co-author of the study. "Our study shows that the effects of human activities have become evident all the way down to the seafloor in many regions, and the resulting increased acidification in these regions may impact our ability to understand Earth's climate history."
In future work, the researchers plan to study how dissolution likely will progress in the coming centuries. Since much of the carbon dioxide from burning fossil fuels still remains on the ocean surface, it could take decades, possibly even centuries, for CO2 to drop down to the bottom of the ocean, the scientists said. So all isn't lost—at least not yet, he said.
"Luckily for us, there is a lot of calcite out there, and only so much fossil fuel we can burn," Sulpis said. "That doesn't mean we have the green light to pollute more—it simply means that the oceans will be there to clean our mess, should it take thousands of years…" Hopefully, he added, "by then we will likely have stopped burning some fossil fuel, either because we ran out or—a smarter option—because we would have developed alternative, renewable energies."
Reposted with permission from our media associate Nexus Media.
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A central player in the fight against the novel coronavirus is our immune system. It protects us against the invader and can even be helpful for its therapy. But sometimes it can turn against us.
How does our immune system react to the coronavirus?<p>The coronavirus is — like any other virus — not much more than a shell around genetic material and a few proteins. To replicate, it needs a host in the form of a living cell. Once infected, this cell does what the virus commands it to do: copy information, assemble it, release it.</p><p>But this does not go unnoticed. Within a few minutes, the body's immune defense system intervenes with its innate response: Granulocytes, scavenger cells and killer cells from the blood and lymphatic system stream in to fight the virus. They are supported by numerous plasma proteins that either act as messengers or help to destroy the virus.</p><p>For many viruses and bacteria, this initial activity of the immune system is already sufficient to fight an intruder. It often happens very quickly and efficiently. We often notice only small signs that the system is working: We have a cold, a fever. </p>
Is there an immunity? How long does it last?<p>The good news is that it is very likely there is an immunity. This is suggested by the proximity to other viruses, epidemiological data and animal experiments. Researchers <a href="https://www.biorxiv.org/content/10.1101/2020.03.13.990226v1" target="_blank">infected four rhesus monkeys,</a> a species close to humans, with SARS-CoV-2. The monkeys showed symptoms of COVID-19, the disease caused by the coronavirus, developed neutralizing antibodies and recovered after a few days. When the recovered animals were reinfected with the virus, they no longer developed any symptoms: They were immune. </p><p>The bad news: It is not (yet) known how long the immunity will last. It depends on whether a patient has successfully developed neutralizing antibodies. Achim Hörauf estimates that the immunity should last at least one year. Within this year, every new contact with the virus acts as a kind of booster vaccination, which in turn might prolong the immunity.</p><p>"The virus is so new that nobody has a reasonable immune response," says the immunologist. He believes that lifelong immunity is unlikely. This "privilege" is reserved for viruses that remain in the body for a long time and give our immune system a virtually permanent opportunity to get to know it. Since the coronavirus is an RNA (and not a DNA) virus, it cannot permanently settle in the body, says Hörauf.</p><p>The Heidelberg immunologist <a href="https://www.klinikum.uni-heidelberg.de/immunologie/immunologie" target="_blank">Stefan Meuer</a> predicts that the novel coronavirus will also mutate like all viruses. He assumes that this could be the case in 10 to 15 years: "At some point, the acquired immunity will no longer be of any use to us because then another coronavirus will return, against which the protection that has now been formed will not help us because the virus has changed in such a way that the antibodies are no longer responsible. And then no vaccination will help either."</p>
How can we take advantage of the antibody response of the immune system?<p>Researchers are already collecting plasma from people who have successfully survived an infection with SARS-CoV-2 and are using it to treat a limited number of patients suffering from COVID-19. The underlying principle: <a href="https://www.dw.com/en/coronavirus-drugs-can-antibodies-from-survivors-help/a-52806428" target="_blank">passive immunization.</a> The studies carried out to date have shown positive results, but they have usually been carried out on only a few people.</p><p>At best, passive immunization is used only when the patient's own immune system has already started to work against the virus, says Achim Hörauf: "The longer you can leave the patients alone with the infection before you protect them with passive immunization, the better." Only through active immunization can one be protected in the long term. At the same time, it is difficult to recognize the right point in time.</p><p>PCR (polymerase chain reaction) tests are currently used to find out whether a person is infected with the coronavirus. With the help of PCR, it is not possible to tell whether or not there is reproducible viral RNA; it is just a proof of whether the virus is still present, dead or alive. A PCR test cannot tell us whether our immune system has already intervened, i.e. whether we have had contact with the virus in the past, have formed antibodies and are now protected. Researchers are therefore working on tests that check our blood for the presence of antibodies. They are already in use in Singapore, for example, and are nearing completion in the USA. With the help of these tests, it would finally be possible to gain an overview <a href="https://www.dw.com/en/corona-confusion-how-to-make-sense-of-the-numbers-and-terminology/a-52825433" target="_blank">of the unclear case numbers.</a> In addition, people who have developed antibodies against the virus could be used at the forefront of health care, for example. An "immunity passport" is even under discussion.</p>
Is it possible to become infected and/or ill several times with the coronavirus?<p>"According to all we know, it is not possible with the same pathogen," says Achim Hörauf. It is possible to become infected with other coronaviruses or viruses from the SARS or MERS group if their spike proteins look different. "As far as the current epidemic is concerned, it can be assumed that people who have been through COVID-19 will not become ill from it for the time being and will not transmit the virus any further," he says.</p>
How long before you're no longer contagious?<p>A study <a href="https://www.nature.com/articles/s41586-020-2196-x" target="_blank">carried out on the first coronavirus patients in Germany</a> showed that no viruses that are capable of replication can be found from day eight after the onset of symptoms, even though PCR can still detect up to 100,000 gene copies per sample. This could change the current quarantine recommendations in the future.</p><p>According to the Robert Koch Institute, patients can currently be discharged from hospital if they show two negative PCR samples from the throat within 24 hours. If they have had a severe case of the disease, they should remain in domestic isolation for another two weeks. For each discharge, whether from hospital or home isolation, they should have been symptom-free for at least 48 hours.</p>
Why do people react differently to the virus?<p>While some people get off with a mild cold, others are put on ventilators or even die of SARS-Cov-2. Especially people with <a href="https://www.dw.com/en/coronavirus-who-is-particularly-at-risk-and-why/a-52710881" target="_blank">pre-existing conditions</a> and older people seem to be worst-affected by the virus. Why? This is the hottest question at the moment.</p><p>It will still take a very, very long time to understand the mechanistic, biological basis for why some people are so much more severely affected than others, virologist Angela Rasmussen told <em>The Scientist</em>. "The virus is important, but the host response is at least as important, if not more important," her colleague Stanley Perlman told the magazine.</p><p>Stefan Meuer sees a fundamental survival principle of nature in the different equipment and activity of our immune systems: "If we were all the same, one and the same virus could wipe out the entire human species at once. Due to the genetic range, it is quite normal that some people die from a viral disease while others do not even notice it. "</p><p>Achim Hörauf also suspects immunological variants that could be genetically determined. Since interstitial pneumonia is observed with the coronavirus, the focus is probably on an overreaction of the immune system. However, it is also possible that each person affected may have been loaded with a different dose of the virus, which in turn leads to different outcomes. And finally, it makes a difference how robust the body and lungs are: Competitive athletes simply have more lung volume than long-time smokers. </p>
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