From the United States Geological Survey (USGS) via phys.org: “Where is the greatest risk to our mineral resource supplies?”

From the United States Geological Survey (USGS)

via

phys.org

February 21, 2020
Alex Demas, United States Geological Survey

Bastnaesite (the reddish parts) in Carbonatite. Bastnaesite is an important ore for rare earth elements, one of the mineral commodities identified as most at-risk of supply disruption by the USGS in a new methodology. Credit: Scott Horvath, USGS

Policymakers and the U.S. manufacturing sector now have a powerful tool to help them identify which mineral commodities they rely on that are most at risk to supply disruptions, thanks to a new methodology by the U.S. Geological Survey and its partners.

“This methodology is an important part of how we’re meeting our goals in the President Trump’s Strategy to ensure a reliable supply of critical minerals,” said USGS director Jim Reilly. “It provides information supporting American manufacturers’ planning and sound supply-chain management decisions.”

The methodology evaluated the global supply of and U.S. demand for 52 mineral commodities for the years 2007 to 2016. It identified 23 mineral commodities, including some rare earth elements, cobalt, niobium and tungsten, as posing the greatest supply risk for the U.S. manufacturing sector. These commodities are vital for mobile devices, renewable energy, aerospace and defense applications, among others.

“Manufacturers of new and emerging technologies depend on mineral commodities that are currently sourced largely from other countries,” said USGS scientist Nedal Nassar, lead author of the methodology. “It’s important to understand which commodities pose the greatest risks for which industries within the manufacturing sector.”

The supply risk of mineral commodities to U.S. manufacturers is greatest under the following three circumstances: U.S. manufacturers rely primarily on foreign countries for the commodities, the countries in question might be unable or unwilling to continue to supply U.S. manufacturers with the minerals; and U.S. manufacturers are less able to handle a price shock or from a disruption in supply.

A graph showing the net import reliance of the United States for more than 90 different mineral commodities. Credit: USGS

“Supply chains can be interrupted for any number of reasons,” said Nassar. “International trade tensions and conflict are well-known reasons, but there are many other possibilities. Disease outbreaks, natural disasters, and even domestic civil strife can affect a country’s mineral industry and its ability to export mineral commodities to the U.S.”

Risk is not set in stone; it changes based on global market conditions that are specific to each individual mineral commodity and to the industries that use them. However, the analysis indicates that risk typically does not change drastically over short periods, but instead remains relatively constant or changes steadily.

“One thing that struck us as we were evaluating the results was how consistent the mineral commodities with the highest risk of supply disruption have been over the past decade,” said Nassar. “This is important for policymakers and industries whose plans extend beyond year-to-year changes.”

For instance, between 2007 and 2016, the risk for rare earth elements peaked in 2011 and 2012 when China halted exports during a dispute with Japan. However, the supply of rare earth elements consistently remained among the highest risk commodities throughout the entire study period.

In 2019, the U.S. Department of Commerce, in coordination with the Department of the Interior and other federal agencies, published the interagency report entitled “A Federal Strategy to Ensure a Reliable Supply of Critical Minerals,” in response to President Trump’s Executive Order 13817. Among other things, the strategy commits the U.S. Department of the Interior to improve the geophysical, geologic, and topographic mapping of the U.S.; make the resulting data and metadata electronically accessible; support private mineral exploration of critical minerals; make recommendations to streamline permitting and review processes enhancing access to critical mineral resources.

The methodology is entitled “Evaluating the Mineral Commodity Supply Risk of the U.S. Manufacturing Sector,” and is published in Science Advances.

See the full article here .

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Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Science X community members enjoy access to many personalized features such as social networking, a personal home page set-up, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.
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On March 3, 1879, we were established by the passing of the Organic Act through Congress. Our main responsibilities were to map public lands, examine geological structure, and evaluate mineral resources. Over the next century, our mission expanded to include the research of groundwater, ecosystems, environmental health, natural hazards, and climate and land use change.

From National Geographics: “Brazil’s Best Kept Secret: The Pantanal”

From National Geographics

PHOTOGRAPH BY MARKUS MAUTHE, LAIF/REDUX

2.22.20
Avery Stonich

The Amazon rain forest may get all the attention, but when it comes to wildlife, South America’s biggest biodiversity star is the Pantanal.

I get my first hint of the Pantanal’s impressive biodiversity as soon as I get off the plane in Corumbá, Brazil. White splotches cover the tarmac like some sort of Rorschach test on steroids. Bird droppings, I come to realize. The tropical heat drapes over me like a wool blanket; the thick air carries the raw scents of nature, a mix of earthy and sour.

Part national park, part UNESCO World Heritage site, the Pantanal is the world’s largest tropical wetland, covering over 70,000 square miles—an area the size of Washington State—in the smack-dab center of South America.

Brazil can lay claim to most of the region, but, as nature recognizes no political boundaries, the Pantanal spills into neighboring Paraguay and Bolivia. And though it’s often overshadowed by the Amazon rain forest to the north, the Pantanal quietly boasts the highest concentration of wildlife on the continent.

Life in the Pantanal follows the ebb and flow of an epic ecosystem that pulses with the seasons like a beating heart.

Each year torrential rains fill the Pantanal’s giant basin, creating a vast flooded landscape. When the downpour subsides, water slowly drains into the Paraguay River, leaving behind fish- and snail-filled pools that attract huge flocks of egrets, storks, and spoonbills. Even pantaneiros, the local cowboys, move their cattle herds in sync with the water.

But the local fauna isn’t limited to birdlife. Some of the Pantanal’s most lively inhabitants include jaguars, giant anteaters, piranha, howler and capuchin monkeys, and green anacondas—the world’s largest snakes, which prowl swamps and lazy rivers in search of wild pigs, deer, and other prey.

Green anacondas—the world’s largest snakes. Size: 20 to 30 feet. Weight: Up to 550 pounds. Dave Lonsdale

And, unlike the Amazon, where the thick jungle obscures the view, the Pantanal lays out its wild kingdom like a Broadway stage packed with high-kicking dancers.

“The Pantanal is such an open environment,” says Photo in Natura founder Daniel De Granville, who has led tours in the area for more than 20 years. “You can see [so] far.”

I visit in April, during the flooded season, and board a ship that slowly chugs down the Paraguay River from Corumbá. Tangles of hyacinth plants crowd the shore, periodically releasing large chunks that float down the river like rafts in the swift current. Sipping a cool caipirinha—a Brazilian cocktail made with fresh lime and a sugarcane-based liquor called cachaça—I watch the descending sun transform into a glowing orb that gives our once yellow wake a rose-colored hue.

After dinner, I am among a small group who joins a guide on a smaller boat to explore a narrow channel in search of caimans, alligator-like reptiles that lurk along the shallow riverbanks.

Caimans.Lea Maimone

Nightfall brings no relief from the day’s humidity, and the still thick air shows up as fog in the beam of our flashlights as we drift amid a symphony of buzzing insects and croaking frogs.

We shine our lights in swooping arcs along the shore, and suddenly two eyes sparkle like diamonds in the darkness. “There’s one!” several of us shout in unison. We paddle through the reeds at the water’s edge until we come upon the caiman. Submerged except for its beady eyes and the tip of its spiny tail, the prehistoric-looking creature remains completely still, confident in its camouflage.

The next day, we wake up in Porto da Manga and set out on land, bumping along a dirt road in an open truck. Suddenly the driver grinds to a halt. “Capybaras, there, coming out of the shrubs,” our guide says.

Capybaras. Photograph by Joel Sartore, National Geographic Photo Ark

Up ahead I see the blunt-faced snout of what looks a lot like a massive hamster. Up to two feet tall and 175 pounds, capybaras are the world’s largest rodents. An adult scampers across the road, trailed by several youngsters. Before the traffic jam has a chance to clear, a furry creature pops its head out of a marsh in the distance. “A giant otter,” notes our guide. “Look, there are two of them!”

A few miles on, we encounter another hurdle: a caracara—a bird of prey resembling a buzzard—hops in front of us in pursuit of roadkill.

Northern Caracara (also called Northern Crested Caracara). MAULI

I admire its black cap, fleshy orange face, and white neck before my gaze drifts to a placid pond and the puffy clouds and leafy trees reflected in its still surface. A quiet scene, or so it would seem; the longer I look, the more the water comes to life.

A caiman lies in wait among the lilypads. A marsh deer pauses to nibble in the brush. Bright green parakeets flit past, announcing themselves with excited chirps. A heron stands sentinel on the shore, ready to strike.

At that moment it occurs to me that the Pantanal springs to life the moment you learn to sit quietly and observe.

Sure you’ll see plenty motoring along in a boat, pedaling a mountain bike on a dirt road, or riding a horse through the flooded fields. But the true heart of this place reveals itself slowly. And then bowls you over with its stunning vitality.

Just like the rains that fill this vast basin and the floodwaters that slowly ebb away, the perpetual fluctuations of the Pantanal invite visitors to pause and take it all in.

Each day brings a new landscape—a river rises, a pool disappears, and the circle of life continues in an unending loop.

See the full article here .

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The National Geographic Society has been inspiring people to care about the planet since 1888. It is one of the largest nonprofit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, and the promotion of environmental and historical conservation.

From Eos: “‘Glacial Earthquakes’ Spotted for the First Time on Thwaites”

From AGU

From Eos

17 February 2020
Katherine Kornei
hobbies4kk@gmail.com

These seismic events, triggered by icebergs capsizing and ramming into Thwaites, reveal that the glacier has lost some of its floating ice shelf.

Icebergs calving off Thwaites Glacier occasionally capsize and launch seismic waves that travel hundreds of kilometers. Credit: David Vaughan, British Antarctic Survey.

Icebergs calve off glaciers all the time. But most don’t pitch backward, capsize, and send seismic waves radiating out for thousands of kilometers.

New research reports that such “glacial earthquakes” have now been detected for the first time on Antarctica’s Thwaites Glacier. These observations confirm that Thwaites’s floating ice shelf is degrading. That’s bad news, scientists agree, because the glacier helps hold back the West Antarctic Ice Sheet from flowing into the sea.

Flipping Icebergs

Scenarios for iceberg calving at fast tidewater glaciers. Buoyancy-driven calving is likely to produce icebergs with small width-to-height ratios that will capsize against the terminus front. The generated iceberg-to-terminus contact force is responsible for the production of glacial earthquakes. Credit: Sergeant et al., 2019, Annals of Geology

Thwaites Glacier, roughly the size of the state of Florida, is one of the largest sources of ice loss in Antarctica and is responsible for about 4% of global sea level rise.

It regularly sheds icebergs hundreds of meters on a side into the Amundsen Sea, but some of these chunks of ice aren’t just drifting away, said J. Paul Winberry, a geophysicist at Central Washington University in Ellensburg who led the new study. Thanks to their shape, they’re capsizing. “They’re taller than they are wide. They’re top-heavy, and they want to flip over,” said Winberry.

Over several tens of seconds, these icebergs roll backward and collide with the new edge of Thwaites. “They bang the front of the glacier,” said Winberry.

Those collisions launch seismic waves that can be picked up by detectors hundreds and even thousands of kilometers away. Last year, Winberry was combing through seismic data and serendipitously discovered two of these collisions. “We got really lucky,” said Winberry.

By triangulating the signals recorded by seven seismic stations spread across West Antarctica, he and his colleagues determined that the events had occurred on the front of Thwaites.

Using optical and radar satellite imagery acquired within minutes of the seismic events, both of which took place 8 November 2018, the team confirmed that calving had indeed occurred. The researchers counted five capsized icebergs, their icy undersides now exposed. (In radar imagery, such icebergs appear dark—ice reflects radio waves more poorly than snow.)

Seismology complements satellite imagery when it comes to studying glaciers, said Lucas Zoet, a glaciologist at the University of Wisconsin–Madison not involved in the research. Satellites can obtain high-resolution imagery but typically pass over the same spot on Earth only every few days or, at best, every few hours, Zoet said. Seismological instruments, on the other hand, are always listening. That’s important, he said, because “the real interesting part might happen in just a couple minutes.”

All About Ice Shelves

These glacial earthquakes shed light on Thwaites’s geometry and therefore its future stability.

For icebergs to capsize, they must be taller than they are wide. That’s common in Greenland [Annals of Geology above] because most glaciers there don’t contain floating ice shelves, said Winberry. “The edge of a glacier is grounded or close to touching the bedrock.” That ice thickness translates into icebergs being taller than they are wide, which renders them unstable in the water.

But Antarctic glaciers tend to have floating ice shelves, so their iceberg progeny are typically wider than they are tall and, accordingly, don’t produce glacial earthquakes. Thwaites appears to be an anomaly.

“This portion of Thwaites Glacier is distinct from the rest of Antarctica in that it’s lost most of its floating ice shelf,” said Winberry. “We think that’s what’s going to happen to the rest of Thwaites going forward.” Ice shelves, by literally getting hung up on islands and underwater ridges, help stabilize glaciers by acting like buttresses.

Tiny Temblors, Too

The seismological data that Winberry and his colleagues analyzed revealed more than just two glacial earthquakes—there were also over 600 tiny temblors in the 6 days leading up to the calving.

“We think we’re hearing the accelerating failure of the ice before it calves off,” said Winberry.

That’s an important window into how Thwaites is changing, he said. These observations can be used to inform models of calving, Winberry and his colleagues suggest.

These results were published last month in Geophysical Research Letters.

In the future, Winberry and his team plan to do a more systematic search for glacial earthquakes on Thwaites. They’re interested in determining possible triggering events that might drive calving, like big storms or moving sea ice.

See the full article here .

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From Harvard Gazette: “Going where the diversity is”

Harvard University

From Harvard Gazette

February 12, 2020
Deborah Blackwell
Photos by Ben Goulet-Scott/Harvard University Department of Organismic and Evolutionary Biology

Panamanian field expeditions examine how species persevere in face of climate change.

Student researchers Ben Goulet-Scott (left), Sylvia Kinosian, and Jacob Suissa, reach the crest of a hill overlooking the Mamoní Valley Preserve while carrying 90 species of ferns on their backs.

Last month, two graduate students from the Arnold Arboretum of Harvard University traveled to one of the most species-rich landscapes in the world: a remote strip of tropical rainforest at the narrowest point in the Central American country of Panama.

Ben Goulet-Scott, a Ph.D. candidate in the Graduate School of Arts and Sciences’ Department of Organismic and Evolutionary Biology (OEB) and a fellow in the Arboretum’s Hopkins Lab, and Jacob Suissa, OEB Ph.D. candidate in the Friedman Lab at the Arboretum, hope their research in the Mamoní Valley Preserve in Panama will increase our understanding of how biodiversity can persevere in the face of climate change, deforestation, and human disturbance.

The 20-square-mile land conservancy on the isthmus separating Central and South America teems with life, making the condensed rainforest habitat a perfect location for their research project because of the vast number of known and potentially undiscovered species living there, Goulet-Scott said.

Student members of the Mamoní Valley Preserve Natural History Project, Jacob Suissa (left), Sylvia Kinosian, Brian Vergara, Jose Palacios, and Christian López examine the rhizome vasculature of a fern species during their first collection trip in the rainforest.

“New England has twice the land area of Panama, but half the number of bird species, and 10 times fewer reptiles and amphibians,” he said. “This particular location contains species that migrate or move from north to south and get funneled into this very narrow area, concentrating an incredible amount of biodiversity.”

The Mamoní Valley Preserve (MVP) Natural History Project is an ongoing series of student-led field expeditions, organized by Goulet-Scott in 2017. The project is designed to establish a baseline understanding of how the different land-use conditions within the preserve — from fully deforested cattle pasture to recovering secondary forest and intact primary forest — affect patterns of diversity.

By bringing early career biologists like himself to the site for fieldwork, Goulet-Scott is building a list of species and observations to eventually make available in a central repository for scientists and researchers focused on conservation.

Ferns stems are collected. University of Panama student Brian Vergara examines a species of Selaginella through a magnifying glass.

Gabriel Salazar, a Mamoní Valley Preserve guide (left), and student members of the expedition Jose Palacios, Ben Goulet-Scott, and Jacob Suissa stop to rest after a long day of hiking through the Mamoní Valley Preserve.

“Identifying every species there is actually probably not possible, but that’s how we think about the mission of these trips,” he said. “By bringing groups of students who have expertise in identifying different types of organisms, we work to document all the different species we see in each type of habitat.”

Creating a baseline is vital because it will help determine which areas are of high priority for conserving certain species, and which species might already be threatened.

“It’s an interesting exploration,” Goulet-Scott said. “The more frequently we do biodiversity studies, the better we are able to track how conservation is going in this area.”

The MVP Natural History Project intrigued Robert Brooker ’89, M.B.A. ’97, who learned about Goulet-Scott’s research and funded this expedition.

“I met Ben on a trip there a year ago and was excited about what he was doing and wanted to support it,” said Brooker, the chairman of WIN-911 Software in Austin, Texas. “Ben and his colleagues are very interested in this work and I want to help a group of creative and intelligent students to accomplish whatever they want to accomplish to make the world a better place.”

The trip in January was Goulet-Scott’s third expedition for the project. The first, in 2017, included four doctoral students from Harvard, with a taxonomic focus on reptiles and amphibians. During the second trip in 2018, seven Harvard Ph.D. students and one from the University of Texas collected data on insects, specifically butterflies and moths.

“Identifying every species there is actually probably not possible, but that’s how we think about the mission of these trips,” said Ben Goulet-Scott.

This year’s team — two Harvard Ph.D. students, one Harvard undergraduate, a Ph.D. student from the University of Utah, and three undergraduates from the University of Panama — investigated ferns, the second-most-diverse lineage of vascular plants behind flowering plants. Ferns are a focal point for Suissa, who investigated an ancient lineage of fern relatives as a research technician at the Smithsonian Institution Museum of Natural History in Washington, D.C. At Harvard he studies the evolution of the water transport system in ferns, which is a building block for the downstream analysis of climate change.

“Studying ferns in locations like the preserve furthers our understanding of global patterns of biodiversity and can help inform conservation practices in the future,” he said. “We need to know what is where in order to protect it.”

Suissa has done fieldwork in Costa Rica four times, but this was his first time in Panama, where there may be as many as 700 different species of plant in a 100 square kilometer region. He said this intense diversity in such a small space is an important educational opportunity for students studying tropical biology. Survey findings from each MVP expedition are also used to create educational materials such as field guides and brochures for the preserve, as well as for youth environmental education.

Christian Lopez, a graduate student in botany from the University of Panama, said he appreciated being part of this MVP Natural History Project expedition, on which he was able to find species he had never previously seen in the wild.

Arboretum Arboretum Fellows explore biodiversity in Panama. Video produced by Ben Goulet-Scott.

“This collaboration with Harvard University and its doctoral students has been a great learning opportunity for me, and the exchange of knowledge went both ways,” he said.

Other team members included Jon Hamilton ’20, environmental science and public policy; Sylvia Kinosian, Ph.D. candidate in biology, Utah State University; and Jose Palacios and Brian Vergara, undergraduate students studying biology at the Universidad de Panama. Goulet-Scott said one of the most exciting things about the MVP Natural History Project is that it is student-run.

“There’s no one more experienced than a grad student involved, so it’s all about being self-organized,” he said. “We are in charge of figuring out all the logistics and planning how we’re going to spend our day, what the goals of the trip are, and what equipment we need to bring.”

Student researchers Jose Palacios (back), Jacob Suissa, and Sylvia Kinosian, hike through the rainforest carrying bags of ferns collected in Cerro Brewster (Dianmayala) in the Mamoní Valley Preserve. The team traveled over unpaved, bumpy roads and through 15 river crossings.

Conducting field work in the rainforest is not for the weak of body or spirit. Sweltering heat and humidity, unpredictable weather, potential for infection, deadly snakes and spiders, and even the chiggers that burrow into waistbands and armpits can impact the best-prepared researcher. The team traveled in the beds of pickup trucks over unpaved, bumpy roads and through 15 river crossings. One of their trucks slid off of a riverbank and got stuck, partially submerged. Once a fallen tree blocked their passage until they helped local farmers chop it up with machetes.

The weeklong expedition included challenging hikes in pouring rain while carrying heavy packs full of equipment and trash bags full of plant specimens. The students hiked up a 900-meter mountain, felt their way through the wet cloud mist of an elfin forest, and bathed in a pristine waterfall. Suissa avoided stepping on a deadly fer-de-lance viper thanks only to one of the local guides. But his first trip to the neotropics as an undergraduate was enough to change the trajectory of his career.

Guide Gabriel Salazar takes a moment of rest overlooking the top of Cerro Brewster (Dianmayala) after a three-hour intense uphill hike.

On this expedition, Suissa collected more than 100 fern stems, spanning their evolutionary tree. The group’s efforts yielded 170 specimens and an estimated 160 species, including rare and hybrid ferns and lycophytes — unexpected and exciting findings for the researchers, Goulet-Scott said.

Lider Sucre, M.B.A. ’97, CEO of Mamoní 100 (one of the three organizations involved in protecting the Mamoní Valley), said the MVP History Project is a catalyst to bigger and deeper opportunities for the future of global science.

“For three years now we’ve been seeing that the Mamoní Valley Natural History Project that Harvard University students have led and been engaged with is an incredibly important part of how we give greater substance to the biodiversity that lives here,” he said. “It is a unique keystone location matched by nothing else, a crossroads to so many lifeforms, and they have been incredibly lucky with their exceptionally rare finds with wildlife that is not usually seen.”

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Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

From University of Washington: “Polar bears in Baffin Bay skinnier, having fewer cubs due to less sea ice”

From University of Washington

February 12, 2020
Hannah Hickey

A polar bear in Baffin Bay, West Greenland in 2012 seen from the air.Kristin Laidre/University of Washington.

Polar bears are spending more time on land than they did in the 1990s due to reduced sea ice, new University of Washington-led research shows. Bears in Baffin Bay are getting thinner and adult females are having fewer cubs than when sea ice was more available.

The new study, recently published in Ecological Applications, includes satellite tracking and visual monitoring of polar bears in the 1990s compared with more recent years.

“Climate-induced changes in the Arctic are clearly affecting polar bears,” said lead author Kristin Laidre, a UW associate professor of aquatic and fishery sciences. “They are an icon of climate change, but they’re also an early indicator of climate change because they are so dependent on sea ice.”

The international research team focused on a subpopulation of polar bears around Baffin Bay, the large expanse of ocean between northeastern Canada and Greenland. The team tracked adult female polar bears’ movements and assessed litter sizes and the general health of this subpopulation between the 1990s and the period from 2009 to 2015.

The study compared the movements of adult female polar bears during two time periods. In the 1990s (left), sea ice in mid-July still spanned Baffin Bay, providing polar bears with a large area to hunt and travel. In more recent summers (right), Baffin Bay was mostly open water in mid-July, and polar bears were stuck closer to shore.Joshua Stevens, NASA Earth Observatory/National Snow & Ice Data Center.

Polar bears’ movements generally follow the annual growth and retreat of sea ice. In early fall, when sea ice is at its minimum, these bears end up on Baffin Island, on the west side of the bay. They wait on land until winter when they can venture out again onto the sea ice.

When Baffin Bay is covered in ice, the bears use the solid surface as a platform for hunting seals, their preferred prey, to travel and even to create snow dens for their young.

“These bears inhabit a seasonal ice zone, meaning the sea ice clears out completely in summer and it’s open water,” Laidre said. “Bears in this area give us a good basis for understanding the implications of sea ice loss.”

Satellite tags that tracked the bears’ movements show that polar bears spent an average of 30 more days on land in recent years compared to in the 1990s. The average in the 1990s was 60 days, generally between late August and mid-October, compared with 90 days spent on land in the 2000s. That’s because Baffin Bay sea ice retreats earlier in the summer and the edge is closer to shore, with more recent summers having more open water.

The authors compared the movements of 43 adult female polar bears with tags that recorded their positions from 1991 to 1997 (left) with those of 38 adult females tracked from 2009 to 2015 (right). With less sea ice, the bears’ movements are restricted to a smaller area and they spend more time close to shore, especially in Greenland.Joshua Stevens/NASA Earth Observatory and Kristin Laidre/Uiversity of Washington.

“When the bears are on land, they don’t hunt seals and instead rely on fat stores,” said Laidre. “They have the ability to fast for extended periods, but over time they get thinner.”

To assess the females’ health, the researchers quantified the condition of bears by assessing their level of fatness after sedating them, or inspecting them visually from the air. Researchers classified fatness on a scale of 1 to 5. The results showed the bears’ body condition was linked with sea ice availability in the current and previous year — following years with more open water, the polar bears were thinner.

The body condition of the mothers and sea ice availability also affected how many cubs were born in a litter. The researchers found larger litter sizes when the mothers were in a good body condition and when spring breakup occurred later in the year — meaning bears had more time on the sea ice in spring to find food.

The authors also used mathematical models to forecast the future of the Baffin Bay polar bears. The models took into account the relationship between sea ice availability and the bears’ body fat and variable litter sizes. The normal litter size may decrease within the next three polar bear generations, they found, mainly due to a projected continuing sea ice decline during that 37-year period.

“We show that two-cub litters — usually the norm for a healthy adult female — are likely to disappear in Baffin Bay in the next few decades if sea ice loss continues,” Laidre said. “This has not been documented before.”

Laidre studies how climate change is affecting polar bears and other marine mammals in the Arctic. She led a 2016 study [The Cryosphere] showing that polar bears across the Arctic have less access to sea ice than they did 40 years ago, meaning less access to their main food source and their preferred den sites. The new study uses direct observations to link the loss of sea ice to the bears’ health and reproductive success.

“This work just adds to the growing body of evidence that loss of sea ice has serious, long-term conservation concerns for this species,” Laidre said. “Only human action on climate change can do anything to turn this around.”

Co-authors of the study are Eric Regehr and Harry Stern at the UW; Stephen Atkinson and Markus Dyck at the Government of Nunavut in Canada; Erik Born at the Greenland Institute of Natural Resources; Øystein Wiig at the Natural History Museum in Norway; and Nicholas Lunn of Environment and Climate Change Canada. Main funders of the research include NASA and the governments of Nunavut, Canada, Greenland, Denmark and the United States.

For more information, contact Laidre at klaidre@uw.edu or 206-616-9030.

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From Yale University: “Predicting 50,000 years of bird migrations”

From Yale University

February 18, 2020
Jim Shelton

Snow geese in flight.

Neither wind, nor rain — nor massive sheets of ice — have kept Earth’s birds from their appointed rounds of migrating to better climes, according to a new study.

That’s the conclusion of a new study from the Max Planck-Yale Center for Biodiversity Movement and Global Change (MPYC), which simulated global bird migrations during scenarios of past climate conditions. The researchers said that, in the Americas in particular, migrating birds successfully maneuvered vastly changing landscapes in the past 50,000 years.

“Our simulations predict that bird migration worldwide has remained relatively constant over this period, suggesting an origin for this phenomenon that is older than the glacial cycles of recent Earth history,” said first author Marius Somveille, a former MPYC researcher who is starting a postdoctoral position at Colorado State University.

Yet there has been regional variation in migrating birds’ response to climate change, the researchers said. In the Americas, for example, there has been a larger increase in the distances that birds have migrated over the past 50,000 years, compared with other parts of the world.

“In the last ice age, up to about 18,000 years ago, North America had an ice sheet that covered a large part of the continent and prevented bird species from living there,” said Yale’s Walter Jetz, senior author of the study, professor of ecology and evolutionary biology, and co-director of MPYC.

“This ice sheet retreated and birds colonized the land — and those birds were likely highly migratory, as seasonality in this area was pronounced. Our simulations suggest that toward the present this part of the world has seen both migratory distances and migration activity significantly increase,” he said.

The study appears in the journal Nature Communications.

Using existing data about the global distribution of migratory birds, the researchers created a model that predicted migrations based on energy efficiency: They positioned each species’ breeding and non-breeding ranges in a way that accounted for the availability of food and how much energy birds would reasonably expend during migration.

To estimate migration activity far in the past, the researchers applied their model to reconstructions of past climate conditions.

Co-author and MPYC co-director Martin Wikelski of the Max Planck Institute of Animal Behavior said the findings may be of use to conservationists and policymakers because the simulations “have the potential to inform predictions of how future climate change will impact bird migrations.”

Additional co-authors of the study were Robert Beyer and Andrea Manica of the University of Cambridge, and Ana Rodrigues of the Université de Montpellier.

Support for the research came from MPYC, the Knobloch Family Foundation and grants from the National Science Foundation and NASA.

See the full article here .

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Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

From University of Exeter: “South American volcano showing early warning signs of ‘potential collapse,’ research shows”

From University of Exeter

One of South America’s most prominent volcanoes is producing early warning signals of a potential collapse, new research has shown [Earth and Planetary Science Letters].

Credit: CC0 Public Domain

Tungurahua volcano in Ecuador – known locally as “The Black Giant” – is displaying the hallmarks of flank instability, which could result in a colossal landslide.

New research, led by Dr James Hickey from the Camborne School of Mines, has suggested that the volcano’s recent activity has led to significant rapid deformation on the western flank.

The researchers believe that the driving force causing this deformation could lead to an increased risk of the flank collapsing, causing widespread damage to the surrounding local area.

The research recommends the volcano should be closely monitored to watch for stronger early warning signs of potential collapse.

The study is published in the journal Earth & Planetary Science Letters.

Dr Hickey, who is based at the University of Exeter’s Penryn Campus, Cornwall, said: “Using satellite data we have observed very rapid deformation of Tungurahua’s west flank, which our research suggests is caused by imbalances between magma being supplied and magma being erupted”.

Tungurahua volcano has a long history of flank collapse, and has also been frequently active since 1999. The activity in 1999 led to the evacuation of 25,000 people from nearby communities.

A previous eruption of Tungurahua, around 3,000 years ago, caused a prior, partial collapse of the west flank of the volcanic cone.

This collapse led to a wide-spread debris avalanche of moving rock, soil, snow and water that covered 80 square kilometres – the equivalent of more than 11,000 football fields.

Since then, the volcano has steadily been rebuilt over time, peaking with a steep-sided cone more than 5000 m in height.

However, the new west flank, above the site of the 3000 year old collapse, has shown repeated signs of rapid deformation while the other flanks remain stable.

The new research has shown that this deformation can be explained by shallow, temporary magma storage beneath the west flank. If this magma supply is continued, the sheer volume can cause stress to accumulate within the volcanic cone – and so promote new instability of the west flank and its potential collapse.

Dr Hickey added: “Magma supply is one of a number of factors that can cause or contribute to volcanic flank instability, so while there is a risk of possible flank collapse, the uncertainty of these natural systems also means it could remain stable. However, it’s definitely one to keep an eye on in the future.”

See the full article here .

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The University of Exeter is a public research university in Exeter, Devon, South West England, United Kingdom. It was founded and received its royal charter in 1955, although its predecessor institutions, St Luke’s College, Exeter School of Science, Exeter School of Art, and the Camborne School of Mines were established in 1838, 1855, 1863, and 1888 respectively.[5][6] In post-nominals, the University of Exeter is abbreviated as Exon. (from the Latin Exoniensis), and is the suffix given to honorary and academic degrees from the university.

The university has four campuses: Streatham and St Luke’s (both of which are in Exeter); and Truro and Penryn (both of which are in Cornwall). The university is primarily located in the city of Exeter, Devon, where it is the principal higher education institution. Streatham is the largest campus containing many of the university’s administrative buildings[7] The Penryn campus is maintained in conjunction with Falmouth University under the Combined Universities in Cornwall (CUC) initiative. The Exeter Streatham Campus Library holds more than 1.2 million physical library resources, including historical journals and special collections.[8]

Exeter was named the Sunday Times University of the Year in 2013[9] and was the Times Higher Education University of the Year in 2007.[10] It has maintained a top ten position in the National Student Survey since the survey was launched in 2005.[11] The annual income of the institution for 2017–18 was £415.5 million of which £76.1 million was from research grants and contracts, with an expenditure of £414.2 million.[1]

Exeter is a member of the Russell Group of leading research-intensive UK universities[12] and is also a member of Universities UK, the European University Association, and the Association of Commonwealth Universities and an accredited institution of the Association of MBAs (AMBA).

From Eos: “Fluid Pressure Changes Grease Cascadia’s Slow Aseismic Earthquakes”

From AGU

From Eos

2.18.20
Mary Caperton Morton

Twenty-five years’ worth of data allows scientists to suss out subtle signals deep in subduction zones.

Cascadia subduction zone

Cascadia plate zones

The study region followed the coast of Vancouver Island in British Columbia, one of the source regions for slow earthquakes along the Cascadia Subduction Zone. Credit: NASA

Not all earthquakes make waves. During slow “aseismic” earthquakes, tectonic plates deep in subduction zones can slide past one another for days or even months without producing seismic waves. Why some subduction zones produce devastating earthquakes and tsunamis while others move benignly remains a mystery. Now a new study is shedding light on the behavior of fluids in faults before and after slow-slip events in the Cascadia Subduction Zone.

Aseismic earthquakes, also known as episodic tremor and slip, were discovered about 20 years ago in the Cascadia Subduction Zone, where oceanic plates are descending beneath the North American plate at a rate of about 40 millimeters per year.

Vancouver profile

Oregon profile

This 1,000-kilometer-long fault has a dangerous reputation but has not produced a major earthquake since the magnitude 9.0 megathrust earthquake and tsunami that struck on 26 January 1700. Scientists think that some of Cascadia’s energy may be dissipated by regular aseismic events that take place deep in the fault zone roughly every 14 months.

Episodic tremor and slip occur deep in subduction zones, and previous studies have suggested that these slow-slip events may be lubricated by highly pressurized fluids. “There are many sources of fluids in subduction zones. They can be brought down by the descending plate, or they can be generated as the downgoing plate undergoes metamorphic reactions,” said Pascal Audet, a geophysicist at the University of Ottawa in Ontario and an author on the new study, published in Science Advances.

“At depths of 40 kilometers, the pressure exerted on the rocks is very high, which normally tends to drive fluids out, like squeezing a sponge,” Audet said. “However, these fluids are trapped within the rocks and are virtually incompressible. This means that fluid pressures increase dramatically, weakening the rocks and generating slow earthquakes.”

This 1,000-kilometer-long fault has a dangerous reputation but has not produced a major earthquake since the magnitude 9.0 megathrust earthquake and tsunami that struck on 26 January 1700. Scientists think that some of Cascadia’s energy may be dissipated by regular aseismic events that take place deep in the fault zone roughly every 14 months.

Eavesdropping on Slow Quakes

To study how fluid pressures change during slow earthquakes, lead author Jeremy Gosselin, also at Ottawa, and Audet and colleagues drew upon 25 years of seismic data, spanning 21 slow-earthquake events along the Cascadia Subduction Zone. “By stacking 25 years of data, we were able to detect slight changes in the seismic velocities of the waves as they travel through the layers of oceanic crust associated with slow earthquakes,” Audet said. “We interpret these changes as direct evidence that pore fluid pressures fluctuate during slow earthquakes.”

Audet and colleagues are still working to identify the cause and effect of the pore fluid pressure changes. “Is the change in fluid pressure a consequence of the slow earthquake? Or is it the opposite: Does an increase in pore fluid pressure somehow trigger the slow earthquake? That’s the next big question we’d like to tackle.”

“I’m surprised and impressed they were able to isolate these signals,” said Michael Bostock, a geophysicist at the University of British Columbia in Vancouver who was not involved in the new study. “They’re very subtle, but they’re all pointing in the same direction.”

Theoretical models, as well as other seismic studies on subduction zones in Japan and New Zealand, have offered supporting lines of evidence that pore fluids are redistributed at the boundaries of tectonic plates during slow-slip events, Audet said. “Other studies have offered somewhat indirect evidence for this idea, but our study offers the first direct evidence that fluid pressures do in fact fluctuate during slow earthquakes.”

The next steps will be to conduct similar seismic studies on other subduction zones, Bostock said. It’s too soon to say whether this fluid behavior is universal to all slow-earthquake zones, but “there may be other factors at play as well, such as temperature and pressure, that create a sweet spot where slow earthquakes are more likely to occur,” he said. The right combination of overlapping factors may help explain why some fault zones record more aseismic events than others.

Whether these changes in fluid pressures could be used to predict where and when a slow-slip event might occur is unknown, Bostock said, although “slow earthquakes are already more predictable than regular earthquakes.” In Cascadia, for example, they’re known to occur about every 14 months, give or take, for reasons that remain unclear. “Prediction is the holy grail of earthquake science, but it’s fraught with difficulties. Tectonic faults, despite their grand scale, are very sensitive to perturbations in ways we don’t clearly understand yet.”

See the full article here .

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Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

From AGU GeoSpace Blog: “Climate change could trigger more landslides in High Mountain Asia”

From AGU GeoSpace Blog

11 February 2020
Jessica Merzdorf

More frequent and intense rainfall events due to climate change could cause more landslides in the High Mountain Asia region of China, Tibet and Nepal, according to the first quantitative study of the link between precipitation and landslides in the region.

High Mountain Asia stores more fresh water in its snow and glaciers than any place on Earth outside the poles, and more than a billion people rely on it for drinking and irrigation. The study team used satellite estimates and modeled precipitation data to project how changing rainfall patterns in the region might affect landslide frequency. The study team found that warming temperatures will cause more intense rainfall in some areas, and this could lead to increased landslide activity in the border region of China and Nepal.

More landslides in this region, especially in areas currently covered by glaciers and glacial lakes, could cause cascading disasters like landslide dams and floods that affect areas downstream, sometimes hundreds of miles away, according to the new study in AGU’s journal Geophysical Research Letters.

A landslide in Randa, Switzerland. Credit: Wandervogel.

High Mountain Asia stretches across tens of thousands of rugged, glacier-covered miles, from the Himalayas in the east to the Hindu Kush and Tian Shan mountain ranges in the west. As Earth’s climate warms, High Mountain Asia’s water cycle is changing, including shifts in its annual monsoon patterns and rainfall.

The model shows landslide risk for High Mountain Asia increasing in the summer months in the years 2061-2100, thanks to increasingly frequent and intense rainfall events. Summer monsoon rains can destabilize steep mountainsides, triggering landslides. Credit: NASA’s Earth Observatory/Joshua Stevens.

Heavy rain, like the kind that falls during the monsoon season in June through September, can trigger landslides on the steep terrain, creating disasters that range from destroying towns to cutting off drinking water and transportation networks. In summer 2019, monsoon flooding and landslides in Nepal, India and Bangladesh displaced more than 7 million people. In order to predict how climate change might affect landslides, researchers need to know what future rainfall events might look like. But until now, the research making the landslide predictions has relied on records of past landslides or general precipitation estimate models.

“Other studies have either addressed this relationship very locally, or by adjusting the precipitation signal in a general way,” said Dalia Kirschbaum, a research scientist at NASA’s Goddard Space Flight Center. “Our goal was to demonstrate how we could combine global model estimates of future precipitation with our landslide model to provide quantitative estimates of potential landslide changes in this region.”

The study team used a NASA model that generates a “nowcast” estimating potential landslide activity triggered by rainfall in near real-time. The model, called Landslide Hazard Assessment for Situational Awareness (LHASA), assesses the hazard by evaluating information about roadways, the presence or absence of nearby tectonic faults, the types of bedrock, change in tree cover and the steepness of slopes. Then, it integrates current precipitation data from the Global Precipitation Measurement mission and Tropical Rainfall Measuring Mission. If the amount of precipitation in the preceding seven days is abnormally high for that area, then the potential occurrence of landslides increases.

The study team first ran LHASA with NASA precipitation data from 2000-2019 and NOAA climate model data from 1982-2017. They compared the results from both data sets to NASA’s Global Landslide Catalog, which documents landslides reported in the media and other sources. Both data sets compared favorably with the catalog, giving the team confidence that using the modeled precipitation data would yield accurate forecasts.

NASA’s Global Landslide Catalog contains more than 1,000 records of landslides in High Mountain Asia between 2007 and 2017. Some of these events caused hundreds or thousands of fatalities. Credit: NASA’s Earth Observatory/Joshua Stevens.

Finally, the study team used NOAA’s model data to take LHASA into the future, assessing precipitation and landslide trends in the future (2061-2100) versus the past (1961-2000). They found that extreme precipitation events are likely to become more common in the future as the climate warms, and in some areas, this may lead to a higher frequency of landslide activity.

Most significantly, the border region of China and Nepal could see a 30-70% increase in landslide activity. The border region is not currently heavily populated, Kirschbaum said, but is partially covered by glaciers and glacial lakes. The combined impacts of more frequent intense rainfall and a warming environment could affect the delicate structure of these lakes, releasing flash floods and causing downstream flooding, infrastructure damage, and loss of water resources.

The full human impact of increasing landslide risk will depend on how climate change affects glaciers and how populations and communities change. When they evaluated their model projections in the context of five potential population scenarios, the team found that most residents in the area will be exposed to more landslides in the future regardless of the scenario, but only a small proportion will be exposed to landslide activity increases greater than 20%.

The study demonstrates new possibilities for research that could help decision-makers prepare for future disasters, both in High Mountain Asia and in other areas, said Kirschbaum.

“Our hope is to expand our research to other areas of the world with similar risks of landslides, including Alaska and Appalachia in the United States,” said Sarah Kapnick, physical scientist at NOAA’s Geophysical Fluid Dynamics Laboratory and co-author on the study. “We’ve developed a method, figured out how to work together on a specific region, and now we’d like to look at the U.S. to understand what the hazards are now and in the future.”

See the full article here .

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GeoSpace is a blog on Earth and space science, managed by AGU’s Public Information staff. The blog features posts by AGU writers and guest contributors on all sorts of relevant science topics, but with a focus on new research and geo and space sciences-related stories that are currently in the news.

Do you have ideas on topics we should be covering? Would you like to contribute a guest post to the blog? Contact Peter Weiss at pweiss@agu.org.

From Nature: “30 years of the iron hypothesis of ice ages”

From Nature

17 February 2020

In 1990, an oceanographer who had never worked on climate science proposed that ice-age cooling has been amplified by increased concentrations of iron in the sea — and instigated an explosion of research.

Thirty years ago this month, John Martin proposed a solution to one of the biggest mysteries of Earth’s climate system: how was nearly one-third of the carbon dioxide in the atmosphere (about 200 gigatonnes of carbon) drawn into the ocean as the planet entered the most recent ice age, then stored for tens of thousands of years, and released again as the ice sheets melted? These large natural cycles in atmospheric CO2 levels (Fig. 1a) were revealed in 1987 by an analysis of ancient air bubbles trapped in the first long ice cores taken from the Antarctic ice sheet [1]. Martin recognized that iron was a key ingredient that could have transformed the surface ocean during glacial times. His landmark iron hypothesis [2], published in Paleoceanography, described a feedback mechanism linking climatic changes to iron supply, ocean fertility and carbon storage in the deep ocean.

Figure 1 | The anti-correlated data that inspired the iron hypothesis. a, Measurements of air bubbles trapped in cores drilled from the Antarctic ice sheet show that atmospheric levels of carbon dioxide were significantly lower during the coldest periods (shaded regions) than during modern times (data from ref. [16]; CO2 concentrations are shown in parts per million by volume; p.p.m.v.). b, The ice-core records also reveal that more iron was transported to the Southern Ocean in wind-blown dust during the coldest periods than during warmer times (data from ref. [17]; iron flux is measured in micrograms per square metre per year). In 1990, Martin2 hypothesized that the increased levels of iron in the Southern Ocean during the coldest periods fertilized the growth of photosynthetic microorganisms in the surface Southern Ocean, which therefore produced more biomass from CO2. This, in turn, would have increased the strength of the biological pump, a mechanism that sequesters some of the biomass (and the carbon within it) in the deep ocean. Martin proposed that the stronger biological pump explains why so much atmospheric CO2 is drawn into the ocean during cold times.

Two hundred gigatonnes is a lot of carbon to periodically withdraw from and release to the atmosphere. In the 1980s, a handful of models (see ref. [3], for example) had shown that an increase in biomass production in polar ocean regions was the most effective process for removing so much atmospheric carbon. Photosynthetic organisms in the surface ocean convert CO2 from the atmosphere into biomass, much of which is subsequently broken down into CO2 again by other organisms and returned to the atmosphere. But part of the biomass sinks into the deep ocean, which therefore effectively serves as a large storage reservoir of dissolved CO2. This mechanism of CO2 removal is called the biological pump.

However, biomass production requires not only CO2, but also other nutrients to build lipids, proteins and enzymes. Researchers were struggling to ascertain how the ocean’s abundance of key nutrients, such as nitrates or phosphates, might have increased during glacial times to fuel a stronger biological pump.

Martin argued that iron is another nutrient that limits the biological pump. He suggested that the modern marine ecosystem of the Southern Ocean around Antarctica is starved of iron, and therefore relatively low in biomass, despite having abundant nitrates and phosphates. But during glacial times, strong winds over cold, sparsely vegetated continents could have transported large amounts of iron-bearing dust into this ocean (Fig. 1b). Martin reasoned that this dust could have fertilized marine ecosystems and strengthened the biological pump, so that more carbon was transferred into the deep ocean, lowering atmospheric CO2 levels.

Around the time of publication, evidence for high dust delivery during glacial periods had just emerged from studies of deep Antarctic ice cores [4]. But there were no reliable measurements of dissolved iron in the Southern Ocean that could confirm that its surface waters are iron-starved in modern times, or data supporting the proposal that delivery of iron-rich dust would make a difference to ocean productivity. It was clear, however, that large patches of the world’s ocean had much lower quantities of biomass than would be expected on the basis of the concentrations of key nutrients such as nitrates and phosphates. But many researchers argued that this was due to natural overgrazing of algae by herbivores [5].

The idea that modern algal growth is limited by iron availability had, in fact, been proposed [6] in the 1930s, but had been incorrectly discounted by oceanographers — who had measured plenty of iron in seawater samples collected from the waters around their iron ships [7]. Martin was one of the first oceanographers to implement painstaking procedures to avoid the contamination of samples and to determine that iron concentrations in the north Pacific Ocean were extremely low [7], certainly low enough to curtail biomass production.

Despite the initial scepticism that greeted the iron hypothesis, 12 separate experiments [8] were carried out between 1993 and 2005 in which around 300–3,000 kilograms of dissolved iron were injected into small patches of the Southern Ocean, the equatorial Pacific Ocean and the north Pacific. The biomass of algae increased wherever iron was added, as biological production surged.

Unfortunately, Martin died mere months before the first of these experiments, and did not witness the ocean-scale confirmation of his hypothesis, nor the internationally coordinated campaign to measure iron geochemistry throughout the world’s oceans [9] — which confirmed iron limitation and revealed the intricate strategies used by marine ecosystems to acquire and recycle iron [10].

Earth scientists also tried to test the iron hypothesis computationally using simple ocean models. They used the changes in the dust-accumulation rate recorded in ice cores as input to simulate changes in iron delivery to the Southern Ocean, and data from the experimental iron fertilizations to calculate how this iron could affect algal growth and the biological pump. Such models could reproduce the timing and magnitude of about half of the observed decrease in atmospheric CO2 levels during glacial periods [11]. Iron fertilization is therefore clearly an important process that causes atmospheric changes, but might not be the only one.

Finding data to prove that biological production had been higher during glacials was a harder task — after all, the ecosystem during the most recent glacial period (about 20,000 years ago) is long dead. One possible solution was to extract cores from sediments piled on the sea floor, to see whether the mineral skeletons of algae accumulated faster during glacial times than in the modern era. However, the results were often ambiguous12, for several reasons: many algae don’t produce a preservable skeleton; numerous factors determine what proportion of biological remains is preserved on the sea floor; and the location of biological production changes through time as ocean fronts and sea-ice positions migrate.

Fortunately, Martin [2] and others [13] had anticipated an alternative, global-scale test of the biological pump during glacial times. If more biomass reached the deep ocean during glacials, then deep-sea microorganisms would use up more oxygen as they consumed it, decreasing the concentration of oxygen in deep waters. Evidence of deep-ocean oxygen depletion would therefore be indicative of a strong biological pump.

Martin recognized that the presence of certain microfossils in glacial-age sediments meant that the deep ocean had not become completely devoid of oxygen during glacials. But although this evidence crudely constrained estimates of the degree to which iron fertilization might have enhanced productivity during glacials, it could not be used to determine whether levels of deep-ocean oxygen were lower than during modern times. Since then, analysis of more-sensitive geochemical records indicates that the oxygen concentration in bottom waters did decrease during glacial times [14]. This provides the strongest confirmation yet of the large-scale accumulation of carbon in the deep ocean during glacial periods owing to a stronger biological pump.

Slower rates of mixing between the deep and shallow oceans could also have enhanced the biological pump during glacials. The latest generation of climate models in which the ocean and atmosphere are coupled can test the contribution of the multiple processes that could have resulted in a reduction in bottom-water oxygen levels. Such models indicate that mixing rates can account for only half of the observed deep-ocean storage of CO2 during the glacial period, and that iron fertilization of the Southern Ocean is the major cause of the extra CO2 storage observed [15].

Martin concluded his paper by saying that iron availability “appears to have been a player” in strengthening the biological pump during glacial cycles, but that the size of its role remained to be determined. Thirty years later, the evidence convincingly shows that iron fertilization of the Southern Ocean was indeed a leading actor in this global-climate feedback.

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Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.