Seals Reveal How Antarctic Sea Ice Melt Affects Ocean Currents
By Tim Radford
Scientists have recruited the elephant seal—the bruiser of the pinniped world—to explore and report back on the dynamics of ocean currents in the Antarctic winter.
Elephant seal carrying satellite-linked sensor in Prydz Bay, Antarctica.University of Tasmania
And the mammals have delivered a potentially ominous message: because fresh water is melting from the sea ice, the density of southern ocean surface waters is significantly reduced.
If there is too dramatic a reduction, the all-important dense waters that descend to the depths and power the ocean conveyor system that drives circulation—and climate—could falter.
The southern elephant seal, Mirounga leonine, has been pressed into service as an all-weather submersible to investigate and record data from the polynya system—polynyas are patches of ocean, surrounded by shelf ice, that fail to freeze—of the southern ocean sea ice.
And the researchers report in Nature Communications journal that their study "highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of the ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate."
The choice of elephant seals rather than humans is a simple one: shipboard research is all but impossible in the Antarctic winter.
Biologists had already enrolled the elephant seals—by sedating them, and gluing to their bulging necks a data monitor and radio transmitter that falls off with the next moulting season—to settle their own marine biological questions
So physicists and oceanographers have now taken advantage of the temperature and salinity data radioed back to them from each animal's 60 dives a day.
"We became very interested in the seal data once we saw they were foraging in the polynya regions, in particular the fact they were there through the winter, a critical period of time for dense shelf water formation, and a time that we really struggle to observe in any other way," said Guy Williams, a physical oceanographer at the University of Tasmania's Institute for Marine and Antarctic Studies.
Sea ice freezes as fresh water and rejects the salt into the water beneath it. This creates an insulating layer that cuts off the ocean from the freezing atmosphere, so sea ice never gets deeper than two meters.
But Dr Williams told Climate News Network:
"In polynyas, the surface of the ocean remains open, while the freezing continues, as newly-formed ice is swept away by persistent offshore winds. And certain topographic effects—coast, glacier tongues, icebergs—also help to keep the area open.
"Like a constantly emptied and refilled ice tray in the fridge, polynyas can generate up to 20 meters of sea ice growth in a winter, and, correspondingly, a much greater amount of salt rejection.
"It leads to this very important water mass called dense shelf water—dense enough once it escapes the continental shelf to mix all the way to the bottom of the ocean basins in the production of Antarctic bottom water."
This is the agency that drives the global ocean overturning system, a planetary-scale phenomenon, carrying heat around the globe and nutrients and dissolved atmospheric oxygen and carbon dioxide to deep layers of the ocean.
"Any reduction to Antarctic bottom water will slow the conveyor belt, and equally thin the conveyor belt, as the density, and depth to which it ultimately goes, decreases," Dr Williams said.
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It's going to be back-to-school time soon, but will children go into the classrooms?
Keeping Schools Safe<p>What will safer schools look like?</p><p>In a <a href="https://jamanetwork.com/journals/jama/fullarticle/2766822" target="_blank">JAMA article</a> published last month, <a href="https://www.jhsph.edu/faculty/directory/profile/1781/joshua-m-sharfstein" target="_blank">Dr. Joshua Sharfstein</a>, a pediatrician and professor at the Johns Hopkins Bloomberg School of Public Health, outlined suggestions — many of which are similar to AAP's.</p><p>Remote learning protocols must stay in place, especially as some schools stagger home and in-building learning. If another shutdown needs to occur, children will rely on distance learning completely, so it must be easy to switch to, he said.</p><p>He suggested giving parents a daily checklist to document their child's health. Kids should be screened quickly on arrival and be given hygiene supplies. Maintenance staff should use appropriate PPE and have regular cleaning schedules. A notification system should be in place if a case is identified, Sharfstein recommended.</p><p><a href="https://www.albany.edu/rockefeller/faculty/erika-martin" target="_blank">Erika Martin</a>, PhD, an associate professor of public administration and policy at University at Albany, said nutrition assistance and health services should be included. She called for tutoring programs with virtual options as well as technology access.</p>
Supporting Staff<p>Teachers and staff will be affected by safeguarding measures, noted <a href="https://directory.sph.umn.edu/bio/sph-a-z/rachel-widome" target="_blank">Rachel Widome</a>, PhD, an associate professor of epidemiology and community health at University of Minnesota.</p><p>"In order for all of the in-school precautions to work well, we'll be asking a lot of teachers and staff," Widome told Healthline. In addition to their usual workload, they'll now be asked to monitor mask-wearing, ensure children are keeping distance, and be aware of any symptoms.</p><p>Along with Sharfstein, Widome called for an increase in financial support. More employees will likely be required so teachers and staff members can keep up with the added demands.</p>
Should Kids Go Back?<p>While these guidelines may help get some schools to reopen, many people don't think children should go back to school over fears they could contract the disease and spread it to other vulnerable family members like grandparents, infant siblings, or their parents.</p><p>In a <a href="https://pediatrics.aappublications.org/content/early/2020/07/08/peds.2020-004879" target="_blank">Pediatrics</a> commentary, <a href="https://www.md.com/doctor/william-raszka-md" target="_blank">Dr. William V. Raszka, Jr.</a>, an infectious disease specialist at The University of Vermont Medical Center, argued that schools should open because school-aged children are far less important drivers of COVID-19 than adults.</p><p>But he says the risk and benefit is not equal among all students ages 5 to 18.</p><p>"Elementary schools are arguably higher priority for face-to-face schooling, since younger children are at lower risk for infection and transmission, and since parental supervision of younger children's distance learning may be particularly challenging," added Sorensen, who penned a <a href="https://jamanetwork.com/channels/health-forum/fullarticle/2767411" target="_blank">June article in JAMA</a> with reopening tips. "That means middle and high schools are more likely to emphasize distance learning."</p><p>Specific student populations, such as special education students and students with disabilities, would also benefit greatly from more time spent in face-to-face environments, Sorensen said.</p>
What Parents Can Do<p>Parents should ask for and receive frequent updates from schools about plans for the fall. They should also be informed about plans if and when COVID infections are identified, Sharfstein said.</p><p>"I'd like to see parents investing now, during the summer, in doing things that can slow and stop the spread of the virus in their communities," Widome said.</p><p>"Now is a good time for kids to practice wearing masks and get used to them as they may be wearing them for longer stretches if school starts up in person," Widome suggested.</p><p>She recommends parents try different mask designs and materials to see what children are more comfortable wearing.</p><p>"If you are using cloth face coverings, it's good to have extras on hand," Widome added.</p><p>Parents should model healthy behavior at home and while out in public — another thing that could affect how well children adapt to reopening practices, Sorensen said.</p><p>"Children may want to know more about face coverings," added <a href="https://www.linkedin.com/in/leescott/" target="_blank">Lee Scott</a>, chairwoman of the Educational Advisory Board at <a href="https://www.goddardschool.com/" target="_blank">The Goddard School</a>. "Dramatic play, such as creating or wearing a face covering, may help some children adjust to this concept." Schools can also show children photos of what faculty members look like in their masks so the students are familiar with that appearance.</p><p>Johns Hopkins University recently released its eSchool+ Initiative, a slew of resources surrounding education during the pandemic. These include a <a href="https://equityschoolplus.jhu.edu/reopening-checklist/" target="_blank">checklist for administrators</a>, report on <a href="https://equityschoolplus.jhu.edu/ethics-of-reopening/" target="_blank">ethical considerations</a>, and a tracker of <a href="https://equityschoolplus.jhu.edu/reopening-policy-tracker/" target="_blank">state and local reopening plans</a>.</p>
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