An ancient migration across the ocean was no accident
A new study shows that at least one long-ago journey would have required deliberate navigation.
08 December, 2020
Credit: Yosuke Kaifu/University of Tokyo
- Historians have wondered whether ancient mariners drifted from Taiwan to Japan or navigated there on purpose.
- The passage between Taiwan and the Ryukyu islands contains one of the world's strongest currents.
- Thousands of buoys suggests that the journey was anything but an accident.
<p>It's something experts are still piecing together, but there's a growing body of evidence that as humans left Africa and scattered across the globe, they often did so by traversing land bridges that are now underwater, and, in other cases, by crossing oceans.</p><p>There was really no other way they might have gotten to <a href="https://australian.museum/learn/science/human-evolution/the-spread-of-people-to-australia/" target="_blank">Australia</a>, for example, even linked as it was for a time with New Guinea as the Sahul landmass. There was always ocean between the continent and Asia, from which its early inhabitants apparently came. It may well have been a less daunting passage at times of lower sea levels, however.</p><p>What, if anything, guided ancient mariners to the places they reached remains an intriguing riddle. Did they just drift on currents hoping to bump into somewhere to land, or was their navigation more intentional?</p><p>A new study from researchers at the University of Tokyo suggests the latter, at least in the case of the ancient migration from Taiwan to the Ryukyu Islands in southwestern Japan—Okinawa is one of the those islands—some 30,000 to 35,000 years ago.</p><p>The study is published in the journal <a href="https://www.nature.com/articles/s41598-020-76831-7" target="_blank" rel="noopener noreferrer">Scientific Reports</a>.</p>
Not an easy trip
<p><span style="background-color: initial;"><a href="https://www.u-tokyo.ac.jp/focus/en/people/k0001_03383.html" target="_blank">Yosuke Kaifu</a></span> of the University Museum at the University of Tokyo and his colleagues sought to answer the longstanding riddle. "There have been many studies on Paleolithic migrations to Australia and its neighboring landmasses," said Kaifu in a <a href="https://www.u-tokyo.ac.jp/focus/en/press/z0508_00149.html" target="_blank">press release</a>, "often discussing whether these journeys were accidental or intentional."</p><p>"Our study looks specifically at the migration to the Ryukyu Islands because it is not just historically significant, but is also very difficult to get there." </p><p>The ancient sailors would have known of the islands because they were visible from the top of a mountain on the coast of Taiwan, although not down along the coast itself.</p><p>The waters between Taiwan and the Ryukyu Islands represented an opportunity for the researchers since they are dominated by the Kuirishio current, one of the strongest currents in the world. The researchers' hypothesis was that sailors were unlikely to have crossed it accidentally. Says Kaifu, "If they crossed this sea deliberately, it must have been a bold act of exploration."</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDkzMTczNi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyMDE5MzY3Mn0.bwWV2NA1Dh_b0cfYKtJ6wmsBMiEvWOPMQHgHQdtCOS0/img.jpg?width=980" id="03baf" class="rm-shortcode" data-rm-shortcode-id="e298d9ae8b5e41ce6b1f1fd2f39a7716" data-rm-shortcode-name="rebelmouse-image" data-width="1440" data-height="810" />Okinawa shoreline
Credit: w.aoki/Adobe Stock
Buoys will be buoys
<p>Kaifu had long been interested in devising some kind of experiment to better understand those who made the journey but, "had no idea how to demonstrate the intentionality of the sea crossings." Upon meeting the study's Taiwanese co-authors, experts in the Kuirishio, the outlines of a plan because clear.</p><p>To test the possibility of an accidental arrival at the Ryukyu Islands, Kaifu and his team set 138 satellite-tracked buoys adrift and tracked how many of them managed to float over to the islands.</p><p>"Only four of the buoys came within 20 kilometers of any of the Ryukyu Islands, and all of these were due to adverse weather conditions," explains Kaifu. This was an unlikely factor in the human travelers' voyage because, "If you were an ancient mariner, it's very unlikely you would have set out on any kind of journey with such a storm on the horizon."</p><p>The results reveal that the current was more likely to take ancient sailors anywhere <em>but</em> the islands. "What this tells us is that the Kuroshio directs drifters away from, rather than towards, the Ryukyu Islands; in other words, that region must have been actively navigated."</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDkzMTc2NC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNDA3MzIyMH0.S3kwkamV4-AkzOeC_J5RDPFKptV1G9lYPVmJU-nnBV8/img.jpg?width=980" id="8a663" class="rm-shortcode" data-rm-shortcode-id="4a38c1086300eb13308ef3a17204d44e" data-rm-shortcode-name="rebelmouse-image" data-width="2331" data-height="2532" />Where the buoys traveled
Credit: Tien-Hsia Kuo/University of Tokyo
An old current
<p>Supporting the researchers findings are geologic records from the area that suggests the Kuirishio hasn't changed since the mariners' journey so long ago — it's been present in its current form for about 100,000 years.</p><p>The research appears to answer the riddle of at least this one ancient migration, says Kaifu: "Now, our results suggest the drift hypothesis for Paleolithic migration in this region is almost impossible. I believe we succeeded in making a strong argument that the ancient populations in question were not passengers of chance, but explorers."</p>
Keep reading
Show less
Stanford engineers develop new light and sound tech to finally map the ocean floor
A clever new design introduces a way to image the vast ocean floor.
02 December, 2020
Credit: ValentinValkov/Adobe Stock
- Neither light- nor sound-based imaging devices can penetrate the deep ocean from above.
- Stanford scientists have invented a new system that incorporates both light and sound to overcome the challenge of mapping the ocean floor.
- Deployed from a drone or helicopter, it may finally reveal what lies beneath our planet's seas.
<p>A great many areas of the ocean floor covering about 70 percent of the Earth remain unmapped. With current technology, it's an extremely arduous and time-consuming task, accomplished only by trawling unmapped areas with sonar equipment dangling from boats. Advanced imaging technologies that work so well on land are stymied by the relative impenetrability of water.</p><p>That may be about to change. Scientists at Stanford University have announced an innovative system that combines the strengths of light-based devices and those of sound-based devices to finally make mapping the entire sea floor possible from the sky.</p><p>The new system is detailed in a study published in <a href="https://ieeexplore.ieee.org/document/9228880" target="_blank">IEEE Explore.</a></p>
The challenge
<p>"Airborne and spaceborne radar and laser-based, or LIDAR, systems have been able to map Earth's landscapes for decades. Radar signals are even able to penetrate cloud coverage and canopy coverage. However, seawater is much too absorptive for imaging into the water," says lead study author and electrical engineer <a href="https://web.stanford.edu/~arbabian/Home/Welcome.html" target="_blank">Amin Arbabian</a> of Stanford's School of Engineering in <a href="https://news.stanford.edu/2020/11/30/combining-light-sound-see-underwater/" target="_blank">Stanford News</a>.</p><p>One of the most reliable ways to map a terrain is by using sonar, which deduces the features of a surface by analyzing sound waves that bounce off it. However, If one were to project sound waves from above into the sea, more than 99.9 percent of those sound waves would be lost as they passed into water. If they managed to reach the seabed and bounce upward out of the water, another 99.9 percent would be lost.</p><p>Electromagnetic devices—using light, microwaves, or radar signals—are also fairly useless for ocean-floor mapping from above. Says first author <a href="https://profiles.stanford.edu/aidan-fitzpatrick" target="_blank">Aidan Fitzpatrick</a>, "Light also loses some energy from reflection, but the bulk of the energy loss is due to absorption by the water." (Ever try to get phone service underwater? Not gonna happen.)</p>PASS
<p>The solution presented in the study is the Photoacoustic Airborne Sonar System (PASS). Its core idea is the combining of sound and light to get the job done. "If we can use light in the air, where light travels well, and sound in the water, where sound travels well, we can get the best of both worlds," says Fitzpatrick.</p><p>An imaging session begins with a laser fired down to the water from a craft above the area to be mapped. When it hits the ocean surface, it's absorbed and converted into fresh sound waves that travel down to the target. When these bounce back up to the surface and out into the air and back to PASS technicians, they do still suffer a loss. However, using light on the way in and sound only on the way out cuts that loss in half.</p><p>This means that the PASS transducers that ultimately retrieve the sound waves have plenty to work with. "We have developed a system," says Arbabian, "that is sensitive enough to compensate for a loss of this magnitude and still allow for signal detection and imaging." Form there, software assembles a 3D image of the submerged target from the acoustic signals.</p><p>PASS was initially designed to help scientists image underground plant roots.</p>Next steps
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="e35b46b6902d17d10ce48241adc0565a"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/2YyAnxQkeuk?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>Although its developers are confident that PASS will be able to see down thousands of meters into the ocean, so far it's only been tested in an "ocean" about the size of a fish tank—tiny and obviously free of real-world ocean turbulence. </p><p>Fitzpatrick says that, "current experiments use static water but we are currently working toward dealing with water waves. This is a challenging, but we think feasible, problem."</p><p>Scaling up, Fitzpatrick adds, "Our vision for this technology is on-board a helicopter or drone. We expect the system to be able to fly at tens of meters above the water." </p>
Keep reading
Show less
For starlet sea anemones, more food means more arms
A new study finds that starlet sea anemones have the unique ability to grow more tentacles when they've got more to eat.
16 September, 2020
Credit: Smithsonian Environmental Research Center/Wikimedia
- These anemones belong to the Cnidaria phylum that continues developing through its lifespan.
- The starlet sea anemone may grow as many as 24 tentacles, providing there's enough food.
- When deprived of the chance to reproduce, they also grow more tentacles.
<p>By now, you've probably worked out your personal go-to strategy for those times when you discover — a little bit too late — that you've eaten too much. Maybe you're the proactive type, arriving at the table in sweatpants. Otherwise, maybe a quick postprandial nap or a loosened belt is your thing. A new paper published in the journal <a href="https://www.nature.com/articles/s41467-020-18133-0" target="_blank">Nature Communications</a> describes the unique way that starlet sea anemones deal with extra food: They simply grow a pair of new tentacles, as if to make room.</p>
Starlet sea anemone basics
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5Mzk3MS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0Njc2MDk0OX0.q_e2-_VyGcBaOoGM53Uu1XZPaaVxsPhsn7shaxVGu1c/img.jpg?width=980" id="ac056" class="rm-shortcode" data-rm-shortcode-id="200a59225bbce7ddda78d80a20fc267d" data-rm-shortcode-name="rebelmouse-image" alt="sea anemone" data-width="1440" data-height="1422" />Credit: Smithsonian Environmental Research Center/Flickr
<p>The <a href="https://en.wikipedia.org/wiki/Starlet_sea_anemone" target="_blank">starlet sea anemone</a>, or <em>Nematostella vectensis</em>, lives burrowed into the mud and silt of coastal salt marshes. Research suggests it's originally native to the east coast of North America, although it can also be found along the continent's west coast, around Nova Scotia, and in U.K. coastal marshes.</p><p>Being stationary creatures, starlet sea anemones have to reach out and grab nutrition floating by. Their natural diet is mainly copepods and midge larvae, though they're also perfectly happy eating brine shrimp in a laboratory setting. The anemones grab food with their tentacles whose cilia then wiggle the meal down to their mouths.</p><p>In the larval stage, the anemones have a quartet of tentacles, though they may develop up to 24 of them. A more typical amount is 16.</p><p>While the starlet sea anemone may grow larger in a lab setting, in the wild its clear, worm-like body typically extends from 10 to 19 millimeters (about three quarters of an inch) in length. Tentacles may add another 8 mm.</p><p>Members of the phylum to which the starlet sea anemone belongs, the <a href="https://en.wikipedia.org/wiki/Cnidaria" target="_blank"><em>Cnidaria</em></a> phylum, have the unique ability to grow new body parts throughout their lives in response to environmental influences. Among these influences are fluctuations in the amount of available food. Nonetheless, no other animal has yet been seen growing new appendages when they get extra sustenance.</p>The study
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5NDAwOS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyOTMzMTcyMX0.aSMrGNPw3Hz_dAmy-PGe7sWHp-ePGZFhi4AT2M5zEfE/img.jpg?width=980" id="7f3ff" class="rm-shortcode" data-rm-shortcode-id="fb709c543b60912c99dc5ee9c2871d49" data-rm-shortcode-name="rebelmouse-image" data-width="1440" data-height="595" />Tentacles budding, or not, under different feeding conditions
Credit: Ikmi, et al./Nature Briefing
<p>Observations of starlet sea anemones in his lab prompted lead author of the paper, <a href="https://www.embl.de/research/units/dev_biology/ikmi/members/index.php?s_personId=CP-60026325" target="_blank">Aissam Ikmi</a> of the European Molecular Biology Lab Heidelberg, to undertake the new research. He'd noticed what seemed to be an association between the amount of brine shrimp being consumed and the sprouting of new tentacles.</p><p>Ikmi and his team raised over 1,100 starlet sea anemone polyps to which they fed brine shrimp. Some of them began with 4 tentacles while the rest already had 16.</p><p>For over six months, the researchers varied the animals' food supply at cyclical intervals, feeding the anemones for a few days and then stopping for a few days.</p><p>The scientists tracked tentacle growth throughout the experiment, creating a spatio-temporal map that identified periods of tentacle growth in relation to feeding cycles.</p><p>They found that the anemones grew new tentacle pairs during feeding periods, and new tentacle production did indeed stop when their food supply was temporarily cut off. Tentacle-pair budding occurred at the same time as an anemone also doubled its body size.</p><p style="margin-left: 20px;">"When food was available, however, primary polyps grew and sequentially initiated new tentacles in a nutrient-dependent manner, arresting at specific tentacle stages in response to food depletion." — Ikmi, et al.</p>Two ways to bud
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5NDA1NS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY2OTkwNjMzMX0.VN5Q8MFO7QnQRiBTVY4xg_hqMN-VvqBqDBLlNCb1mL0/img.jpg?width=980" id="5aff3" class="rm-shortcode" data-rm-shortcode-id="3ac439c1ad951d3a2aa2afa4b3a8a14b" data-rm-shortcode-name="rebelmouse-image" data-width="1440" data-height="470" />In this illustration from the paper, development from 4 to 12 tentacles is characterized by trans budding. Cis budding is present beginning with 16 tentacles.
Credit: Ikmi, et al./Nature Briefing
<p>The team identified two budding modalities, they named "cis" and "trans." In both modes, pairs of tentacles were produced, budding either simultaneously or consecutively. In:</p><ul><li><em>Trans budding</em> — the two new tentacles budded on opposite sides of the anemone.</li><li><em>Cis budding</em> — the two new tentacles budded from within the same segment.</li></ul><div>The experiments also suggest that the starlet sea anemone appears to have ability to make good use of available energy dependent on its situation. Being prevented from spawning, for example, prompted the anemones to grow more tentacles, as if they were rechanneling the energy they'd have otherwise directed to reproduction.</div>
Keep reading
Show less
Some shark species have evolved to walk
The relatively quick evolution of nine unusual shark species has scientists intrigued.
24 January, 2020
Image source: Mark Erdmann
- Living off Australia and New Guinea are at least nine species of walking sharks.
- Using fins as legs, they prowl coral reefs at low tide.
- The sharks are small, don't be frightened.
<p>Natural selection takes time. According to the fossil record, sharks, for example, have been essentially the same for hundreds of millions of years. But something's up lately, and by "lately" we mean the last nine million years. Sharks off of Australia have learned to walk. Not Great Whites, fortunately. Small sharks that feed on coral reefs. Cute sharks, actually.</p><p>Scientists have known for some time that five such shark species exist, but new research nearly doubles that number to nine. The new information comes from a 12-year study from an an international team of scientists from <a href="https://www.uq.edu.au/news/article/2020/01/walking-sharks-discovered-tropics" target="_blank">University of Queensland</a> (UQ), <a href="https://www.conservation.org/" target="_blank">Conservation International</a>, <a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwj1nde31ZznAhXaUs0KHduNCLYQFjAAegQIFhAC&url=https%3A%2F%2Fwww.csiro.au%2F&usg=AOvVaw15ny3Vy66_Z5og_7ffRdcO" target="_blank">CSIRO</a>, the Florida Museum of Natural History, and the Indonesian Institute of Sciences and Indonesian Ministry of Marine Affairs and Fisheries published in <em> </em><a href="https://www.publish.csiro.au/MF/MF19163" target="_blank"><em>Marine and Freshwater Research</em></a>.</p>
Don't mess with success
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjYwMzkxNS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1MDMyOTcyOH0.8IxVi0ssd9VhYYbf7ytjeis1794LxD7QXE_h8h1JWlE/img.jpg?width=980" id="1539e" class="rm-shortcode" data-rm-shortcode-id="4762300cf2aedafae299ef7d032e8810" data-rm-shortcode-name="rebelmouse-image" /><p>Over the last 400 million years, only about 1,200 shark species have emerged. "We see animals from 180 million years ago with exactly the same teeth," <a href="https://www.floridamuseum.ufl.edu/sharks/people/" target="_blank">Gavin Naylor</a> of the Florida Program for Shark Research at the University of Florida tells <a href="https://www.nationalgeographic.com/animals/2020/01/walking-sharks-new-species-evolving-fast/" target="_blank"><em>National Geographic</em></a>. While it's true they're not the most prolific reproducers, and have a long life span, that's still plenty of time for useful mutations to arise. On the other hand, if it ain't broke, don't fix it — Earth and the oceans may change, but as predators, sharks do just fine as they are. Even if, as Naylor says of sixgill sharks, they "seem stuck back in time."</p>Walking to dinner
<div style="padding:56.25% 0 0 0;position:relative;"><iframe src="https://player.vimeo.com/video/385921449" style="position:absolute;top:0;left:0;width:100%;height:100%;" frameborder="0" allow="autoplay; fullscreen" allowfullscreen></iframe></div><script src="https://player.vimeo.com/api/player.js"></script><p>The walking sharks, or "epaulette sharks," live in coastal waters off northern Australia and the island of New Guinea. They prowl coral reefs when the tide goes out, walking through shallow water on their pectoral fins in the front and pelvic fins in the back, on the hunt for crabs, shrimp, small fish. They're adept at wriggling their way into tight nooks to find food, too. "At less than a meter long on average," says <a href="https://researchers.uq.edu.au/researcher/1251" target="_blank">Christine Dudgeon</a> of UQ, "walking sharks present no threat to people, but their ability to withstand low oxygen environments and walk on their fins gives them a remarkable edge over their prey of small crustaceans and mollusks." Says Dudgeon, "During low tides, they became the top predator on the reef."</p><p>The abilities of the small sharks — they're less than three feet in length — definitely put them in a class of their own, says Dudgeon: "These unique features are not shared with their closest relatives the bamboo sharks or more distant relatives in the carpet shark order including wobbegongs and whale sharks."</p><p>Though the five epaulette species don't look much alike, varying in markings and color, their DNA identified them as family. Says Dudgeon, "We estimated the connection between the species based on comparisons between their mitochondrial DNA which is passed down through the maternal lineage. This DNA codes for the mitochondria which are the parts of cells that transform oxygen and nutrients from food into energy for cells."</p>What's the hurry?
<div id="e313b" class="rm-shortcode" data-rm-shortcode-id="PRFA261579893663"><blockquote class="instagram-media" data-instgrm-captioned data-instgrm-version="4" style=" background:#FFF; border:0; border-radius:3px; box-shadow:0 0 1px 0 rgba(0,0,0,0.5),0 1px 10px 0 rgba(0,0,0,0.15); margin: 1px; max-width:658px; padding:0; width:99.375%; width:-webkit-calc(100% - 2px); width:calc(100% - 2px);"> <div style="padding:8px;"> <div style=" background:#F8F8F8; line-height:0; margin-top:40px; padding:50% 0; text-align:center; width:100%;"> <div style=" background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACwAAAAsCAMAAAApWqozAAAAGFBMVEUiIiI9PT0eHh4gIB4hIBkcHBwcHBwcHBydr+JQAAAACHRSTlMABA4YHyQsM5jtaMwAAADfSURBVDjL7ZVBEgMhCAQBAf//42xcNbpAqakcM0ftUmFAAIBE81IqBJdS3lS6zs3bIpB9WED3YYXFPmHRfT8sgyrCP1x8uEUxLMzNWElFOYCV6mHWWwMzdPEKHlhLw7NWJqkHc4uIZphavDzA2JPzUDsBZziNae2S6owH8xPmX8G7zzgKEOPUoYHvGz1TBCxMkd3kwNVbU0gKHkx+iZILf77IofhrY1nYFnB/lQPb79drWOyJVa/DAvg9B/rLB4cC+Nqgdz/TvBbBnr6GBReqn/nRmDgaQEej7WhonozjF+Y2I/fZou/qAAAAAElFTkSuQmCC); display:block; height:44px; margin:0 auto -44px; position:relative; top:-22px; width:44px;"> </div></div><p style=" margin:8px 0 0 0; padding:0 4px;"> <a href="https://www.instagram.com/p/B7q3XyIl4ra/" style=" color:#000; font-family:Arial,sans-serif; font-size:14px; font-style:normal; font-weight:normal; line-height:17px; text-decoration:none; word-wrap:break-word;" target="_top">Conservation International on Instagram: “A new paper from @ConservationOrg, @uniofqld, @lipiindonesia, @csirogram and @uflorida, confirms walking sharks are the most recently…”</a></p> </div></blockquote></div><p>The researchers theorize that a few factors may have accelerated the epaulets' evolution. First off, they keep to themselves in their own separate region, with extensive inbreeding perhaps speeding up the rate of mutation. "Data suggests the new species evolved after the sharks moved away from their original population, became genetically isolated in new areas and developed into new species," explains Dudgeon. "They may have moved by swimming or walking on their fins, but it's also possible they 'hitched' a ride on reefs moving westward across the top of New Guinea, about two million years ago."</p><p>Another possible factor are the ever-changing reefs themselves. They're continually in flux as oceans change and as corals live and die, with rising and falling sea levels, as well as changing currents and temperatures. The epaulettes' success depends on adapting quickly to a very dynamic environment, about which Naylor says, "It's the shark equivalent of the Galápagos, where you can see shark evolution in action."</p><p>Beachgoers needn't fear for their tootsies just yet, but just wait another few million years, and who knows?</p>
Keep reading
Show less
Study: Much of the surface ocean will shift in color by end of 21st century
Climate-driven changes in phytoplankton communities will intensify the blue and green regions of the world’s oceans.
04 February, 2019
Jennifer Chu | MIT News Office
February 4, 2019
Climate change is causing significant changes to phytoplankton in the world's oceans, and a new MIT study finds that over the coming decades these changes will affect the ocean's color, intensifying its blue regions and its green ones. Satellites should detect these changes in hue, providing early warning of wide-scale changes to marine ecosystems.
<p>Writing in <em>Nature Communications</em>, researchers report that they have developed a global model that simulates the growth and interaction of different species of phytoplankton, or algae, and how the mix of species in various locations will change as temperatures rise around the world. The researchers also simulated the way phytoplankton absorb and reflect light, and how the ocean's color changes as global warming affects the makeup of phytoplankton communities.</p><p>The researchers ran the model through the end of the 21st century and found that, by the year 2100, more than 50 percent of the world's oceans will shift in color, due to climate change.</p><p>The study suggests that blue regions, such as the subtropics, will become even more blue, reflecting even less phytoplankton — and life in general — in those waters, compared with today. Some regions that are greener today, such as near the poles, may turn even deeper green, as warmer temperatures brew up larger blooms of more diverse phytoplankton.</p><p>“The model suggests the changes won't appear huge to the naked eye, and the ocean will still look like it has blue regions in the subtropics and greener regions near the equator and poles," says lead author Stephanie Dutkiewicz, a principal research scientist at MIT's Department of Earth, Atmospheric, and Planetary Sciences and the Joint Program on the Science and Policy of Global Change. “That basic pattern will still be there. But it'll be enough different that it will affect the rest of the food web that phytoplankton supports."</p><p>Dutkiewicz's co-authors include Oliver Jahn of MIT, Anna Hickman of the University of Southhampton, Stephanie Henson of the National Oceanography Centre Southampton, Claudie Beaulieu of the University of California at Santa Cruz, and Erwan Monier, former principal research scientist at the MIT Center for Global Change Science, and currently assistant professor at the University of California at Davis, in the Department of Land, Air and Water Resources.</p><p><strong>Chlorophyll count</strong></p><p>The ocean's color depends on how sunlight interacts with whatever is in the water. Water molecules alone absorb almost all sunlight except for the blue part of the spectrum, which is reflected back out. Hence, relatively barren open-ocean regions appear as deep blue from space. If there are any organisms in the ocean, they can absorb and reflect different wavelengths of light, depending on their individual properties.</p><p>Phytoplankton, for instance, contain chlorophyll, a pigment which absorbs mostly in the blue portions of sunlight to produce carbon for photosynthesis, and less in the green portions. As a result, more green light is reflected back out of the ocean, giving algae-rich regions a greenish hue.</p><p>Since the late 1990s, satellites have taken continuous measurements of the ocean's color. Scientists have used these measurements to derive the amount of chlorophyll, and by extension, phytoplankton, in a given ocean region. But Dutkiewicz says chlorophyll doesn't necessarily have reflect the sensitive signal of climate change. Any significant swings in chlorophyll could very well be due to global warming, but they could also be due to “natural variability" — normal, periodic upticks in chlorophyll due to natural, weather-related phenomena.</p><p>“An El Niño or La Niña event will throw up a very large change in chlorophyll because it's changing the amount of nutrients that are coming into the system," Dutkiewicz says. “Because of these big, natural changes that happen every few years, it's hard to see if things are changing due to climate change, if you're just looking at chlorophyll."</p><p><strong>Modeling ocean light</strong></p><p>Instead of looking to derived estimates of chlorophyll, the team wondered whether they could see a clear signal of climate change's effect on phytoplankton by looking at satellite measurements of reflected light alone.</p><p>The group tweaked a computer model that it has used in the past to predict phytoplankton changes with rising temperatures and ocean acidification. This model takes information about phytoplankton, such as what they consume and how they grow, and incorporates this information into a physical model that simulates the ocean's currents and mixing. </p><p>This time around, the researchers added a new element to the model, that has not been included in other ocean modeling techniques: the ability to estimate the specific wavelengths of light that are absorbed and reflected by the ocean, depending on the amount and type of organisms in a given region.</p><p>“Sunlight will come into the ocean, and anything that's in the ocean will absorb it, like chlorophyll," Dutkiewicz says. “Other things will absorb or scatter it, like something with a hard shell. So it's a complicated process, how light is reflected back out of the ocean to give it its color."</p><p>When the group compared results of their model to actual measurements of reflected light that satellites had taken in the past, they found the two agreed well enough that the model could be used to predict the ocean's color as environmental conditions change in the future.</p><p>“The nice thing about this model is, we can use it as a laboratory, a place where we can experiment, to see how our planet is going to change," Dutkiewicz says.</p><p><strong>A signal in blues and greens</strong></p><p>As the researchers cranked up global temperatures in the model, by up to 3 degrees Celsius by 2100 — what most scientists predict will occur under a business-as-usual scenario of relatively no action to reduce greenhouse gases — they found that wavelengths of light in the blue/green waveband responded the fastest.</p><p>What's more, Dutkiewicz observed that this blue/green waveband showed a very clear signal, or shift, due specifically to climate change, taking place much earlier than what scientists have previously found when they looked to chlorophyll, which they projected would exhibit a climate-driven change by 2055.</p><p>“Chlorophyll is changing, but you can't really see it because of its incredible natural variability," Dutkiewicz says. “But you can see a significant, climate-related shift in some of these wavebands, in the signal being sent out to the satellites. So that's where we should be looking in satellite measurements, for a real signal of change."</p><p>According to their model, climate change is already changing the makeup of phytoplankton, and by extension, the color of the oceans. By the end of the century, our blue planet may look visibly altered.</p><p>“There will be a noticeable difference in the color of 50 percent of the ocean by the end of the 21st century," Dutkiewicz says. “It could be potentially quite serious. Different types of phytoplankton absorb light differently, and if climate change shifts one community of phytoplankton to another, that will also change the types of food webs they can support. “</p><p>This research was supported, in part, by NASA and the Department of Energy.</p><p>--</p><p>Reprinted with permission of <a href="http://news.mit.edu/" target="_blank">MIT News</a></p></div>
Keep reading
Show less
Popular
