Oxygen Levels in Oceans Plummet as Planet Warms
By Tim Radford
U.S. scientists who have been warning that warmer oceans are more likely to be poorer in dissolved oxygen have now sounded the alarm: ocean oxygen levels are indeed falling, and seemingly falling faster than the corresponding rise in water temperature.
That colder water can hold more dissolved gas than warmer water is a commonplace of physics: it is one reason why polar seas are teeming with marine life and tropical oceans are blue, clear and often relatively impoverished.
In 2013, an international consortium of marine scientists warned that oxygen levels in the oceans could fall by between one percent and seven percent by the century's end. And this could, other scientists predicted, lead to what they politely called "respiratory stress" for some marine life.
Ocean ecologists in the U.S. and Germany warned last year that parts of the deep oceans were already showing signs of oxygen deprivation with corresponding dead zones.
Earlier this year, another research group looked at the computer simulations for the years 1920 to 2100 and predicted that the hazards were likely to increase with warming.
Now the team has returned to the issue. They report in Geophysical Research Letters that they looked at data for the last 50 years and found the oxygen levels started dropping in the 1980s, as ocean temperatures began to climb—and falling unexpectedly rapidly.
"The trend of oxygen falling is about two to three times faster than what we predicted from the decrease of solubility associated with ocean warming," said Takamitsu Ito, of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, who led the study.
"This is most likely due to the changes in ocean circulation and mixing associated with the heating of the near-surface waters and the melting of polar ice."
The sea's oxygen content comes from air absorbed at the surface or released by phytoplankton photosynthesis, and carried deeper by ocean currents. But as water warms it becomes more buoyant, which means mixing with cooler subsurface waters becomes less likely. And melting ice delivers more fresh water to the ocean surface, which also interferes with the pattern of circulation.
"After the mid-2000s, this trend became apparent, consistent and statistically significant—beyond the envelope of year-to-year fluctuations," Dr. Ito said. "The trends are particularly strong in the tropics, eastern margins of each basin and the sub-polar North Pacific."
That the oceans are at risk of oxygen loss is harder to establish: the oceans cover seven-tenths of the planet, and systematic study of the oceans began only relatively recently. And, of course, such research is bedevilled by natural patterns of local variation: it becomes harder to make any link with manmade global warming.
But, the researchers concluded, "The evidence is consistent with anthropogenic warming acting as the primary driver of long-term trends in ocean 02. The trends we document are suggestive of the effects of warming beginning to supersede natural variability and emerge as a recognizable signal."
And, they added: "If it is a warming signal, we should expect to see continued widespread declines in oceanic O2. The impact of ocean deoxygenation may be profound."
Reposted with permission from Climate News Network.
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The Washington Redskins will retire their controversial name and logo, the National Football League (NFL) team announced Monday.
By Alyssa Murdoch, Chrystal Mantyka-Pringle and Sapna Sharma
Summer has finally arrived in the northern reaches of Canada and Alaska, liberating hundreds of thousands of northern stream fish from their wintering habitats.
A Good News Story?<p>On the surface, the <a href="https://doi.org/10.1111/fwb.13569" target="_blank">results from our study</a> appear to provide a "good news" story. Warming temperatures were linked to higher numbers of fish, more species overall and, therefore, potentially more fishing opportunities for northerners.</p><p>Initially, we were surprised to learn that warming was increasing the distribution of cold-adapted fish. We reasoned that modest amounts of warming could lead to benefits such as increased food and winter habitat availability without reaching stressful levels for many species.</p>
Photo of Arctic grayling (left) and Dolly Varden trout (right). Alyssa Murdoch / Lilian Tran / Nunavik Research Centre and Tracey Loewen / Fisheries and Oceans Canada<p>Yet, not all fish species fared equally well. Ecologically unique northern species — those that have evolved in colder, more nutrient-poor environments, such as Arctic grayling and Dolly Varden trout — were showing declines with warming.</p>
Fish Strandings and Buried Eggs<p>Recent news headlines run the gamut for Pacific salmon — from their increased escapades <a href="https://nunatsiaq.com/stories/article/more-pacific-salmon-showing-up-in-western-arctic-waters/" target="_blank">into the Arctic</a> to <a href="https://www.juneauempire.com/news/warm-waters-across-alaska-cause-salmon-die-offs/" target="_blank">massive pre-spawning die-offs</a> in central Alaska. Similarly, results from our study revealed different outcomes for fish depending on local climatic conditions, including Pacific salmon.</p><p>We found that warmer spring and fall temperatures may be helping juvenile salmon by providing a longer and more plentiful growing season, and by supporting early egg development in northern regions that were previously too cold for survival.</p><p>In contrast, salmon declined in regions that were experiencing wetter fall conditions, pointing to an increased risk of flooding and sedimentation that could bury or dislodge incubating eggs.</p>
Headwaters of the Wind River within the largely intact Peel River watershed in northern Canada. Don Reid / Wildlife Conservation Society Canada / Author provided<p>Interestingly, we found that certain climatic combinations, such as warmer summer water temperatures with decreased summer rainfall, were important in determining where Pacific salmon could survive. Summer warming in drier watersheds led to declines, suggesting that lowered streamflows may have increased the risk of fish becoming stranded in subpar habitats that were too warm and crowded.</p>
The Fate of Northern Fisheries<p>The promise of a warmer and more accessible Arctic has attracted mounting interest in new economic opportunities, <a href="https://doi.org/10.1016/j.marpol.2019.103637" target="_blank">including fisheries</a>. As warming rates at higher latitudes are already <a href="https://www.ipcc.ch/sr15/" target="_blank">two to three times global levels</a>, it seems probable that northern biodiversity will experience dramatic shifts in the coming decades.</p><p>Despite the many unknowns surrounding the future of Pacific salmon, many fisheries are currently <a href="https://doi.org/10.1080/03632415.2017.1374251" target="_blank">thriving following warmer and more productive northern oceans</a>, and some <a href="https://doi.org/10.14430/arctic68876" target="_blank">Arctic Indigenous communities are developing new salmon fisheries</a>.</p><p>As warming continues, the commercial salmon fishing industry is poised to expand northwards, but its success will largely depend on extenuating factors such as <a href="https://www.eenews.net/stories/1060023067" target="_blank">changes to marine habitat and food sources</a> and <a href="https://www.yukon-news.com/news/promising-chinook-salmon-run-failed-to-materialize-in-the-yukon-river-panel-hears/" target="_blank">how many fish are caught during the freshwater stages of their journey</a>.</p><p>Even with the potential for increased northern biodiversity, it is important to recognize that some northern communities may be unable to adapt or may <a href="https://thenarwhal.ca/searching-for-the-yukon-rivers-missing-chinook/" target="_blank">lose individual species that are associated with important cultural values</a>.</p>
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“You’ve Been Exposed”<p>After the case interview, contact tracers will get to work calling the folks who may have been exposed to the coronavirus by the person who tested positive.</p><p>"We give them recommendations about quarantining or isolating, getting tested, and what to do if they become sick. If they're not already sick, we still want them to self-quarantine so that they don't spread the disease to anyone else if they were to become sick," said Labus.</p><p>Generally, the contact tracer won't ask for additional contacts unless they happen to call someone who is sick or has a confirmed case of the virus. They will help ensure the contact has the resources they need to isolate themselves, if necessary. The contact tracer may continue to stay in touch with that person over the next 14 days.</p><p>"We follow the percentage of people that were contacts, then converted into being actual cases of the virus. It's an important marker to help us understand what kind of transmission happens in our community and how to control the virus," said Gullett.</p>
Why You Should Participate (and What Happens If You Don’t)<p>A <a href="https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30457-6/fulltext" target="_blank">Lancet study</a> from June 16, which looked at data from more than 40,000 people, found that COVID-19 transmission could be reduced by 64 percent through isolating those who have the coronavirus, quarantining their household, and contacting the people they may have exposed.</p><p>The combination strategy was significantly more effective than mass random testing or just isolating the sick person and members of their household.</p><p>However, contact tracing is only as effective as people's willingness to participate, and a small number of people who've contracted the coronavirus or were potentially exposed are reluctant to talk.</p><p>"Contact tracers have all been hung up on, cussed at, yelled at," said Gullet.</p><p>The hesitation to talk to contact tracers often stems from concerns over privacy — a serious issue in healthcare.</p>
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