How Underwater Microphones Are Helping Scientists Measure Climate Change
By Kristen Pope
Melting and crumbling glaciers are largely responsible for rising sea levels, so learning more about how glaciers shrink is vital to those who hope to save coastal cities and preserve wildlife.
But it is hard to get good pictures and measurements because glaciers typically are in remote, difficult-to-reach, and even dangerous locations. Satellites are often used to measure glacial retreat, but these images are far from complete, especially when it's cloudy, foggy, raining, or snowing.
So researchers have turned to hydrophones, instruments that use underwater microphones to gather data beyond the reach of any camera or satellite. Hydrophones can record underwater in all conditions. Originally used by the military to detect submarines, hydrophones are now one more tool scientists have to learn about climate change. The devices collect data continuously and they are relatively inexpensive and easy to deploy and maintain in many different areas of the world to monitor sea ice, underwater earthquakes, ship noise, and even wildlife patterns.
Groans, Creaks, Icebergs’ Calving Splashes
Oskar Glowacki already knew that melting glacial ice sounds like frying bacon. As ice bubbles burst, anyone nearby can hear crackling and popping, said Glowacki, a postdoctoral scholar at the Scripps Institution of Oceanography. Using hydrophones, he and other scientists now can make more nuanced measurements of how a changing climate sounds underwater, from the groans, creaks and splashes of a calving iceberg to the changes in whale songs as the ocean warms.
Glowacki recently used a pair of hydrophones to study the underwater world of glaciers, publishing his findings in The Cryosphere. He and co-author Grant B. Deane measured glacier retreat by recording the sounds of ice – from small chunks to enormous slabs – falling off the glacier and splashing into the water.
During the summer of 2016, Glowacki's team placed two hydrophones near Hansbreen Glacier in Hornsund Fjord, Svalbard. For a month and a half, they recorded sounds, also using three time-lapse cameras to collect images – including the "drop height" (how far the ice fell into the water) – so they could compare photos to the recordings. The team created a formula to represent the relationship between the size of a piece of ice falling from a glacier and the sound it makes underwater, also accounting for the pieces of ice falling from varying heights. (Hear an example of the sound an iceberg makes while calving here.)
"Iceberg calving, defined as mechanical loss of ice from the edges of glaciers and ice shelves, is thought to be one of the most important components of the total ice loss," they note in their paper. They mention also that 32-40% of the Greenland ice sheet's mass loss is from solid ice discharge. However, Glowacki says it isn't just one process leading to glaciers losing mass: Surface melt, calving, and under-sea melting are all contributing factors.
Satellites are often used to measure glacial retreat, but the images they provide don't present a complete picture, and Glowacki and other scientists say they hope hydrophones can help provide more answers. Given that glaciers are typically remote and difficult to reach, collecting data remotely is key. Hydrophones, on the other hand, can record underwater in all these conditions.
Hydrophones also collect acoustic data and smaller events hard to find from a satellite image. "In a single day, [you] can have 100 or 200 icebergs breaking off from a single glacier," Glowacki says.
Glowacki says he and his team plan to further study iceberg calving, including studying additional glaciers, and collecting data for longer periods of time.
Unlocking Information About Antarctic Ice Shelf
Other researchers also are using hydrophones to learn more about crumbling glaciers. Bob Dziak, research oceanographer with the NOAA/Pacific Marine Environmental Laboratory acoustics research group, captured a massive calving event of the Nansen Ice Shelf in Antarctica with a hydrophone. He published the results with colleagues in Frontiers in Earth Science
On April 7, 2016, satellite images showed a massive calving event had occurred on the ice shelf. The paper described it as the "first large scale calving event in >30 years."
However, once Dziak and colleagues delved into the data from three hydrophones deployed 60 kilometers east of the ice shelf, they uncovered a series of "icequakes" from January to early March 2016. He and other researchers believe that much of the ice actually broke free in mid-January to February, but it remained in the same location until an April storm – which their paper described as the "largest low-pressure storm recorded in the previous seven months" – broke the ice free.
"We suspected that the icebergs broke apart but remained in place – kind of pinned in place – until a major storm with high winds passed through the area and, finally, it was that last push that pushed the icebergs out to sea," Dziak says.
He and his co-authors wrote that "fortuitous timing and proximity of the hydrophone deployment presented a rare opportunity to study cryogenic signals and ocean ambient sounds of a large-scale ice shelf calving and iceberg formation event."
Listening to Songs of Humpback Whales
Monterey Bay Aquarium Research Institute studies the ocean, including its acoustics. One of the institute's projects involves examining the soundscape of California's Monterey Bay, including sounds from animals, humans, weather, and geologic processes like earthquakes. The researchers once even recorded an under-sea landslide. They also focus on recording and analyzing the songs of humpback whales. Male humpback whales' songs can be over 15 minutes in length, and they can be repeated for long periods of time – even hours. Listening to these songs and analyzing them can provide unique insights into the lives of these complex animals.
"Any time we want to study marine mammals, sound gives us a window into their lives because they use sound for all of their essential life activities, really," says institute biological oceanographer John Ryan. "Communication, foraging, reproduction, navigation – depending on the species, of course."
Previously, scientists had thought singing occurred only during courtship and mating, but now they think whales may also use song while migrating and hunting. They know song has a crucial role in the whales' lives.
"There's a whole other dimension to humpback whale song," Ryan says. "It is a mode of cultural transmission in this species. They learn songs from each other. They share songs as a population, and when populations mix and mingle, they learn new ideas, they explore with their song, improvise, and it's a real essential part of their culture."
In 2015, institute researchers placed a hydrophone 3,000 feet deep, recording and analyzing humpback whale songs. Between 2015 and 2018, they collected over 26,000 hours of audio, which they used computer software to analyze. The researchers determined "peak singing season" in November through January, and they found most singing occurred at night. During peak season, songs were heard around 70% of the night.
However, from September 2015 to May 2016, they detected whales singing only about 11% of the time. Those months correlated with a period when the water temperature was especially high, depleting stocks of vital food sources like anchovies and krill, and correlating also with a toxic algal bloom. Scientists think the whales may have had to devote more time and energy to finding food, leaving less for singing. As researchers continue to study the worlds' oceans, they will undoubtedly learn more about underwater mysteries.
Listen to MBARI's live stream from beneath the bay here.
Reposted with permission from Yale Climate Connections.
By Dana M Bergstrom, Euan Ritchie, Lesley Hughes and Michael Depledge
In 1992, 1,700 scientists warned that human beings and the natural world were "on a collision course." Seventeen years later, scientists described planetary boundaries within which humans and other life could have a "safe space to operate." These are environmental thresholds, such as the amount of carbon dioxide in the atmosphere and changes in land use.
The Good and Bad News<p><span>Ecosystems consist of living and non-living components, and their interactions. They work like a super-complex engine: when some components are removed or stop working, knock-on consequences can lead to system failure.</span></p><p>Our study is based on measured data and observations, not modeling or predictions for the future. Encouragingly, not all ecosystems we examined have collapsed across their entire range. We still have, for instance, some intact reefs on the Great Barrier Reef, especially in deeper waters. And northern Australia has some of the most intact and least-modified stretches of savanna woodlands on Earth.</p><p><span>Still, collapses are happening, including in regions critical for growing food. This includes the </span><a href="https://www.mdba.gov.au/importance-murray-darling-basin/where-basin" target="_blank" rel="noopener noreferrer">Murray-Darling Basin</a><span>, which covers around 14% of Australia's landmass. Its rivers and other freshwater systems support more than </span><a href="https://www.abs.gov.au/ausstats/[email protected]/latestproducts/94F2007584736094CA2574A50014B1B6?opendocument" target="_blank" rel="noopener noreferrer">30% of Australia's food</a><span> production.</span></p><p><span></span><span>The effects of floods, fires, heatwaves and storms do not stop at farm gates; they're felt equally in agricultural areas and natural ecosystems. We shouldn't forget how towns ran out of </span><a href="https://www.mdba.gov.au/issues-murray-darling-basin/drought#effects" target="_blank" rel="noopener noreferrer">drinking water</a><span> during the recent drought.</span></p><p><span></span><span>Drinking water is also at risk when ecosystems collapse in our water catchments. In Victoria, for example, the degradation of giant </span><a href="https://theconversation.com/logging-must-stop-in-melbournes-biggest-water-supply-catchment-106922" target="_blank" rel="noopener noreferrer">Mountain Ash forests</a><span> greatly reduces the amount of water flowing through the Thompson catchment, threatening nearly five million people's drinking water in Melbourne.</span></p><p>This is a dire <em data-redactor-tag="em">wake-up</em> call — not just a <em data-redactor-tag="em">warning</em>. Put bluntly, current changes across the continent, and their potential outcomes, pose an existential threat to our survival, and other life we share environments with.</p><p><span>In investigating patterns of collapse, we found most ecosystems experience multiple, concurrent pressures from both global climate change and regional human impacts (such as land clearing). Pressures are often </span><a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2664.13427" target="_blank" rel="noopener noreferrer">additive and extreme</a><span>.</span></p><p>Take the last 11 years in Western Australia as an example.</p><p>In the summer of 2010 and 2011, a <a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637" target="_blank" rel="noopener noreferrer">heatwave</a> spanning more than 300,000 square kilometers ravaged both marine and land ecosystems. The extreme heat devastated forests and woodlands, kelp forests, seagrass meadows and coral reefs. This catastrophe was followed by two cyclones.</p><p>A record-breaking, marine heatwave in late 2019 dealt a further blow. And another marine heatwave is predicted for <a href="https://www.theguardian.com/environment/2020/dec/24/wa-coastline-facing-marine-heatwave-in-early-2021-csiro-predicts" target="_blank" rel="noopener noreferrer">this April</a>.</p>
What to Do About It?<p><span>Our brains trust comprises 38 experts from 21 universities, CSIRO and the federal Department of Agriculture Water and Environment. Beyond quantifying and reporting more doom and gloom, we asked the question: what can be done?</span></p><p>We devised a simple but tractable scheme called the 3As:</p><ul><li>Awareness of what is important</li><li>Anticipation of what is coming down the line</li><li>Action to stop the pressures or deal with impacts.</li></ul><p>In our paper, we identify positive actions to help protect or restore ecosystems. Many are already happening. In some cases, ecosystems might be better left to recover by themselves, such as coral after a cyclone.</p><p>In other cases, active human intervention will be required – for example, placing artificial nesting boxes for Carnaby's black cockatoos in areas where old trees have been <a href="https://www.environment.gov.au/biodiversity/threatened/publications/factsheet-carnabys-black-cockatoo-calyptorhynchus-latirostris" target="_blank" rel="noopener noreferrer">removed</a>.</p><p><span>"Future-ready" actions are also vital. This includes reinstating </span><a href="https://www.abc.net.au/gardening/factsheets/a-burning-question-fire/12395700" target="_blank" rel="noopener noreferrer">cultural burning practices</a><span>, which have </span><a href="https://theconversation.com/australia-you-have-unfinished-business-its-time-to-let-our-fire-people-care-for-this-land-135196" target="_blank" rel="noopener noreferrer">multiple values and benefits for Aboriginal communities</a><span> and can help minimize the risk and strength of bushfires.</span></p><p>It might also include replanting banks along the Murray River with species better suited to <a href="https://www.abc.net.au/gardening/factsheets/my-garden-path---matt-hansen/12322978" target="_blank" rel="noopener noreferrer">warmer conditions</a>.</p><p>Some actions may be small and localized, but have substantial positive benefits.</p><p>For example, billions of migrating Bogong moths, the main summer food for critically endangered mountain pygmy possums, have not arrived in their typical numbers in Australian alpine regions in recent years. This was further exacerbated by the <a href="https://theconversation.com/six-million-hectares-of-threatened-species-habitat-up-in-smoke-129438" target="_blank" rel="noopener noreferrer">2019-20</a> fires. Brilliantly, <a href="https://www.zoo.org.au/" target="_blank" rel="noopener noreferrer">Zoos Victoria</a> anticipated this pressure and developed supplementary food — <a href="https://theconversation.com/looks-like-an-anzac-biscuit-tastes-like-a-protein-bar-bogong-bikkies-help-mountain-pygmy-possums-after-fire-131045" target="_blank" rel="noopener noreferrer">Bogong bikkies</a>.</p><p><span>Other more challenging, global or large-scale actions must address the </span><a href="https://www.youtube.com/watch?v=iICpI9H0GkU&t=34s" target="_blank" rel="noopener noreferrer">root cause of environmental threats</a><span>, such as </span><a href="https://www.nature.com/articles/s41559-018-0504-8" target="_blank" rel="noopener noreferrer">human population growth and per-capita consumption</a><span> of environmental resources.</span><br></p><p>We must rapidly reduce greenhouse gas emissions to net-zero, remove or suppress invasive species such as <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12080" target="_blank" rel="noopener noreferrer">feral cats</a> and <a href="https://theconversation.com/the-buffel-kerfuffle-how-one-species-quietly-destroys-native-wildlife-and-cultural-sites-in-arid-australia-149456" target="_blank" rel="noopener noreferrer">buffel grass</a>, and stop widespread <a href="https://theconversation.com/to-reduce-fire-risk-and-meet-climate-targets-over-300-scientists-call-for-stronger-land-clearing-laws-113172" target="_blank" rel="noopener noreferrer">land clearing</a> and other forms of habitat destruction.</p>
Our Lives Depend On It<p>The multiple ecosystem collapses we have documented in Australia are a harbinger for <a href="https://www.iucn.org/news/protected-areas/202102/natures-future-our-future-world-speaks" target="_blank">environments globally</a>.</p><p>The simplicity of the 3As is to show people <em>can</em> do something positive, either at the local level of a landcare group, or at the level of government departments and conservation agencies.</p><p>Our lives and those of our <a href="https://theconversation.com/children-are-our-future-and-the-planets-heres-how-you-can-teach-them-to-take-care-of-it-113759" target="_blank">children</a>, as well as our <a href="https://theconversation.com/taking-care-of-business-the-private-sector-is-waking-up-to-natures-value-153786" target="_blank" rel="noopener noreferrer">economies</a>, societies and <a href="https://theconversation.com/to-address-the-ecological-crisis-aboriginal-peoples-must-be-restored-as-custodians-of-country-108594" target="_blank" rel="noopener noreferrer">cultures</a>, depend on it.</p><p>We simply cannot afford any further delay.</p><p><em><a rel="noopener noreferrer" href="https://theconversation.com/profiles/dana-m-bergstrom-1008495" target="_blank" style="">Dana M Bergstrom</a> is a principal research scientist at the University of Wollongong. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/euan-ritchie-735" target="_blank" style="">Euan Ritchie</a> is a professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences at Deakin University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/lesley-hughes-5823" target="_blank">Lesley Hughes</a> is a professor at the Department of Biological Sciences at Macquarie University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/michael-depledge-114659" target="_blank">Michael Depledge</a> is a professor and chair, Environment and Human Health, at the University of Exeter. </em></p><p><em>Disclosure statements: Dana Bergstrom works for the Australian Antarctic Division and is a Visiting Fellow at the University of Wollongong. Her research including fieldwork on Macquarie Island and in Antarctica was supported by the Australian Antarctic Division.</em></p><p><em>Euan Ritchie receives funding from the Australian Research Council, The Australia and Pacific Science Foundation, Australian Geographic, Parks Victoria, Department of Environment, Land, Water and Planning, and the Bushfire and Natural Hazards CRC. Euan Ritchie is a Director (Media Working Group) of the Ecological Society of Australia, and a member of the Australian Mammal Society.</em></p><p><em>Lesley Hughes receives funding from the Australian Research Council. She is a Councillor with the Climate Council of Australia, a member of the Wentworth Group of Concerned Scientists and a Director of WWF-Australia.</em></p><p><em>Michael Depledge does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</em></p><p><em>Reposted with permission from <a href="https://theconversation.com/existential-threat-to-our-survival-see-the-19-australian-ecosystems-already-collapsing-154077" target="_blank" style="">The Conversation</a>. </em></p>
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