Large-scale fossil study reveals origins of modern-day biodiversity gradient 15 million years ago

Peer-Reviewed Publication

UNIVERSITY OF OXFORD

 

IMAGE: DEPICTIONS OF PRESENT-DAY PLANKTONIC FORAMINIFERA FLOATING IN THE DEEP SEA. IMAGE CREDIT: RICHARD BIZLEY, BIZLEYART. view more 

CREDIT: DEPICTIONS OF PRESENT-DAY PLANKTONIC FORAMINIFERA FLOATING IN THE DEEP SEA. IMAGE CREDIT: RICHARD BIZLEY, BIZLEYART.

• Today, species richness peaks in equatorial regions but until now there has been no clear explanation for this.
• By analysing fossil records, researchers found that a key driver of the modern biodiversity gradient was a global cooling event that occurred 15 million years ago.
• This produced a steeper temperature gradient between low and high latitudes, and within the water column, causing tropical regions to support a greater number of ecological niches for species to inhabit.

Researchers have used nearly half a million fossils to solve a 200-year-old scientific mystery: why the number of different species is greatest near the equator and decreases steadily towards polar regions. The results – published today in the journal Nature – give valuable insight into how biodiversity is generated over long timescales, and how climate change can affect global species richness.

It has long been known that in both marine and terrestrial systems species (including animals, plants, and single-celled organisms) show a ‘latitudinal diversity gradient’, with biodiversity peaking at the equator. But until now, limited fossil data has prevented researchers from thoroughly investigating how this diversity gradient first arose.

In this new study, researchers at the Universities of Oxford, Leeds and Bristol, used a group of unicellular marine plankton called planktonic foraminifera. The team analysed 434,113 entries in a global fossil database, covering the last 40 million years. They then investigated the relationship between the number of species over time and space, and potential drivers of the latitudinal diversity gradient, such as sea surface temperatures and ocean salinity levels.

Key findings:

• The modern-day latitudinal diversity gradient first started to emerge around 34 million years ago, as the Earth began to transition from a warmer to cooler climate.
• This gradient initially remained shallow, until around 15–10 million years ago, when it steepened significantly. This coincides with a significant increase in global cooling.
• Peak richness for planktonic foraminifera occurred at higher latitudes from 40–20 million years ago. By around 18 million years ago, however, peak richness shifted to between 10° to 20° latitude, consistent with the diversity pattern observed today.
• There was a strong positive relationship between species richness and sea surface temperatures – both when modelled over time at specific locations, or at different locations at a specific time.
• There was also a positive relationship between species richness and the strength of the thermocline: the temperature gradient that exists between the warmer mixed water at the ocean's surface and the cooler deep water below.

According to the researchers, these results indicate that the modern-day distribution of species richness for planktonic foraminifera could be explained by the steepening of the latitudinal temperature gradient from the equator to the poles over the last 15 million years. This may have opened up more ecological niches in tropical regions within the water column, compared with higher latitudes, promoting greater rates of speciation.

To test this hypothesis, the researchers examined the extent to which modern species of planktonic foraminifera live at different depths within the vertical water column. They found that in low latitudes closer to the equator, species today are more evenly distributed vertically within the water column, compared with high latitudes.

This suggests that a key driver of the modern-day diversity gradient was a significant increase in the difference in sea surface temperatures between low- and high-latitude regions, and within the water column, from 15 million years onwards. The warmer waters at the tropics were able to support a broader range of different temperature habitats and ecological niches within the vertical water column, encouraging higher numbers of species to evolve.

This is supported by the fact that the tropics today are richer than the tropics of warmer time periods in the past (such as the Eocene and Miocene) when there was little or no vertical temperature gradient in the oceans.

In addition, cooling sea temperatures at high latitudes likely caused many regional populations of species to become extinct, contributing to the modern diversity gradient.

Planktonic foraminifera originate from the Early to Middle Jurassic period (around 170 million years ago). They are found in oceans all over the world – from polar regions to the equator – and occupy a range of ecological niches in the upper two kilometers of the oceans. Because they produce hard outer shells, they can be preserved in large numbers. The global abundance of planktonic foraminifera and their exceptional fossil record from the last 66 million years made them an ideal group for this study.

Dr Erin Saupe (Department of Earth Sciences, University of Oxford), lead author for the study, said: ‘By resolving how spatial patterns of biodiversity have varied through deep time, we provide valuable information crucial for understanding how biodiversity is generated and maintained over geological timescales, beyond the scope of modern-day ecological studies.’

Associate Professor Tracy Aze (School of Earth and Environment, University of Leeds), a co-author for the study, added: ‘Although they are small enough to fit on the head of a pin, planktonic foraminifera have one of the most complete species-level fossil records known to science. Our research builds on 60 years of deep-sea sample collection and the diligent counting and recording of hundreds of thousands of specimens by research scientists. It’s fantastic to be able to produce such important results about the drivers of species distributions through time and to do justice this wonderful fossil archive.’

Study co-author Dr Alex Farnsworth, Senior Research Associate at the Department of Geographical Sciences, University of Bristol, said: ‘Understanding why species in ancient history were more diverse and plentiful nearer the equator and less so nearer the poles can give important insights how marine species, such as plankton, might respond in future. These tiny single-celled organisms are a vital link in the marine food chain, so studying their reactions to changing climates may help us better predict how they will likely be affected as temperatures continue to warm with the increasing onset of climate change. This has potentially large implications for marine food webs, such as fish and aquatic mammals like seals and whales, and could be used to inform future measures to protect sea life and preserve biodiversity.’

A scanning electron microscope image of the shell of the planktonic foraminifera species Globigerinella adamsi. This specimen was collected from sea floor sediments in the Southwest Indian Ocean aboard the GLOW Cruise.

A light microscope image of a planktonic foraminifera (bottom right) surrounded by thin strands of its cytoplasm that extend into the surrounding environment. This living specimen had recently been collected from the water in the Southwest Indian Ocean aboard the GLOW Cruise. 

Image credit: Tracy Aze, University of Leeds.

Notes to editors:

The paper ‘Origination of the modern-style diversity gradient 15 million years ago’ will be published in Nature.

After the embargo lifts, the paper will be available at: https://www.nature.com/articles/s41586-023-05712-6

For interview requests and to view a pre-embargo copy of the paper, contact Dr Caroline Wood: caroline.wood@admin.ox.ac.uk

A range of images are available of planktonic foraminifera. To request these, contact Dr Caroline Wood: caroline.wood@admin.ox.ac.uk

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Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the seventh year running, and ​number 2 in the QS World Rankings 2022. At the heart of this success are the twin-pillars of our ground-breaking research and innovation and our distinctive educational offer.

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About the University of Bristol 

The University is ranked within the top 10 universities in the UK and 61st in the world (QS World University Rankings 2023); it is also ranked among the top five institutions in the UK for its research, according to analysis of the Research Excellence Framework (REF) 2021; and is the 3rd most targeted university by top UK employers. 

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JOURNAL

Nature

DOI

10.1038/s41586-023-05712-6 

ARTICLE TITLE

Origination of the modern-style diversity gradient 15 million years ago

ARTICLE PUBLICATION DATE

15-Feb-2023

Late Cenozoic climate cooling biogeographically shifted marine plankton communities

Peer-Reviewed Publication

HARVARD UNIVERSITY, DEPARTMENT OF ORGANISMIC AND EVOLUTIONARY BIOLOGY

 

IMAGE: FORAMS ARE SMALL AND SHELLY. THIS FORAM BELONGS TO THE SPECIES DENTOGLOBIGERINA ALTISPIRA, WHICH WENT EXTINCT ABOUT 3 MILLION YEARS AGO, POTENTIALLY DUE TO NORTHERN HEMISPHERE ICE SHEET EXPANSION. view more 

CREDIT: ADAM WOODHOUSE

Studying changes in marine biogeographic patterns, and the factors impacting these patterns over geological time, can help scientists understand current responses­ in organisms due to human-driven climate change. For instance, researchers know that marine organisms are shifting geographically towards the Earth’s poles in response to human-driven climate change. However, predicting the extent to which the species will shift and how such shifts are intertwined with extinction events has not been easy to discern.

One group of organisms though, the planktonic foraminifera, have recently helped researchers answer how the Late Cenozoic climatic events restructured global marine plankton communities, which may aid in predicting Earth’s current climate change’s impact on all ocean organisms.

Planktonic foraminifera are unicellular marine eukaryotic organisms that have calcareous (calcium carbonate) shells. Their calcitic shells help to preserve these tiny organisms, which get buried on the seafloor as micro fossils. Their physiology, including their shells, are sensitive to alterations in their surrounding environment, making their calcareous remains useful as climatic tracers of both past and present environmental conditions within the ocean’s water column.

In a new study in Nature, researchers examined planktonic foraminifera (forams) fossils and found a global clade-wide shift in marine latitudinal zones towards the Equator, likely driven by the development of bipolar ice sheets. The study further showed that the shift was not tied to a coupling of functional traits and species diversity, but rather the combination of ecological and morphological traits of the organisms.

“In modern ecology we consider species diversity and functional traits synonymous,” said co-lead author Anshuman Swain, postdoctoral researcher in the Department of Organismic and Evolutionary Biology and Junior Fellow of the Society of Fellows at Harvard University. “But, looking back in time we found that this correlation breaks down after two million years, so our assumption that we can use that to predict future climate change might be misguided.”

Swain and co-lead author Adam Woodhouse, postdoctoral researcher at the Institute for Geophysics, The University of Texas Austin, examined the fossil data of Late Cenozoic planktonic forams, specifically the last eight million years, to see how their relative distribution changed in response to climatic events. Rather than focus on species diversity though, Swain and Woodhouse classified the data by ecological characteristics of ecogroups (where they live in the water column) and morphogroups (morphological categories of their shells).

There are benthic and planktonic types of forams. Planktonic forams are found floating in the upper reaches of the ocean. This placing is important as the global distributions of many other organisms correlate with forams due to their low placement in the food chain. Many marine organisms (such as predatory fish, squid, krill, sharks, and cetaceans) rely on stable food chains, so how the forams respond to climate change can be a predictor for these and other organisms. Another bonus of studying these organisms is the incomparable quality of fossil data available. The researchers applied network science methods to Triton, a global dataset of planktonic foraminiferal records with more than 500,000 individual species occurrences. The specimens were collected by the International Ocean Drilling Program from across the Earth’s oceans during more than 50 years of scientific ocean drilling.

“The fossil record of the planktonic foraminifera represents an incredible biological archive, and exhibits a better Cenozoic species-level record than even the best genus-level record of any macroinvertebrate group – making them the perfect solution for our study,” said Woodhouse.

The researchers looked at seventeen morphogroups and six ecogroups of forams. Most studies examine how species are emerging and changing. For this study, the researchers asked how are the organisms responding to climate change and environmental factors ecologically. “Ecogroups and morphogroups are more consistent groups throughout the Cenozoic era,” said Swain, “so they have advantages over species studies, which are inconsistent groups. This makes it easier to make predictions from traits rather than species.”

They gathered a large dataset of traits and plotted the biogeographical distribution patterns in the ecogroups and morphogroups during the late Cenozoic (0-15 million years). Their findings showed a global latitudinal shift towards the Equator regions within clade-wide communities in both ecological and morphological groups, especially during the past eight million years.

“Once we saw the results we said this is wild,” said Swain. “Before this shift, everything was kind of random, there was no discernible strong pattern. But then, there was a strong shift that coincided with the formation of the ice sheets.”

The study showed dynamic biogeography among planktonic foraminifera in the last eight million years, including large-scale spatial rearrangements of biodiversity patterns that appear to be coupled with the emergence of bipolar ice sheets. The expansion of polar ice caps impacted the latitudes where the ecological groups were most happy, causing them to shift due to a number of factors including where oxygen was most available. Surprisingly, this trend was not visible when looking at only species data.

“We don’t know the exact reason for this,” said Swain, “but you can have an equal abundance of species without having a sense of the different ecosystems. What we did see was that ecogroups showed this trend. Meaning this climatic event affected the distribution of foraminifera and in turn the distribution of other organisms. The foram’s correlation with anthropogenically important marine animal groups may lead us to predict more alterations to their ranges and community structure driven by ongoing climate change.”

"Earth’s current biosphere has slowly evolved over millions of year to be adapted to a world of ice ages,” Woodhouse said, “so the trends we document are potentially worrying because if human-driven climate change suddenly switches us to an Earth of eight million years ago [before glaciation], we may be detrimentally restructuring the marine communities of the entire ocean."

The left panel illustrates the shift of the latitudinal region where all groups were equally abundant and were present in the highest diversity (in blue). The bands shifted from high to mid-latitudes (8 million years ago) to low latitudes today due to increased particulate organic carbon and oxygen availability with depth as well as the presence of bipolar ice sheets, which increased the gradient of temperature between high and low latitudes. (SML in the right panel refers to the surface mixed layer, where the turbulence is generated by winds, and processes such as evaporation or sea ice formation cause an increase in salinity).

CREDIT

Anshuman Swain

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JOURNAL

Nature

DOI

10.1038/s41586-023-05694-5 

ARTICLE TITLE

Late Cenozoic cooling restructured global marine plankton communities

Astrophysicists discover the perfect explosion in space

Peer-Reviewed Publication

UNIVERSITY OF COPENHAGEN - FACULTY OF SCIENCE

 

IMAGE: DARACH WATSON AND ALBERT SNEPPEN view more 

CREDIT: DARACH WATSON

When neutron stars collide they produce an explosion that, contrary to what was believed until recently, is shaped like a perfect sphere. Although how this is possible is still a mystery, the discovery may provide a new key to fundamental physics and to measuring the age of the Universe. The discovery was made by astrophysicists from the University of Copenhagen and has just been published in the journal Nature.

Kilonovae - the giant explosions that occur when two neutron stars orbit each other and finally collide - are responsible for creating both great and small things in the universe, from black holes to the atoms in the gold ring on your finger and the iodine in our bodies. They give rise to the most extreme physical conditions in the Universe, and it is under these extreme conditions that the Universe creates the heaviest elements of the periodic table, such as gold, platinum and uranium.

But there is still a great deal we do not know about this violent phenomenon. When a kilonova was detected at 140 million light-years away in 2017, it was the first time scientists could gather detailed data. Scientists around the world are still interpreting the data from this colossal explosion, including Albert Sneppen and Darach Watson from the University of Copenhagen, who made a surprising discovery.

"You have two super-compact stars that orbit each other 100 times a second before collapsing. Our intuition, and all previous models, say that the explosion cloud created by the collision must have a flattened and rather asymmetrical shape," says Albert Sneppen, PhD student at the Niels Bohr Institute and first author of the study published in the journal Nature.

This is why he and his research colleagues are surprised to find that this is not the case at all for the kilonova from 2017. It is completely symmetrical and has a shape close to a perfect sphere.

"No one expected the explosion to look like this. It makes no sense that it is spherical, like a ball. But our calculations clearly show that it is. This probably means that the theories and simulations of kilonovae that we have been considering over the past 25 years lack important physics," says Darach Watson, associate professor at the Niels Bohr Institute and second author on the study.

The spherical shape is a mystery

But how the kilonova can be spherical is a real mystery. According to the researchers, there must be unexpected physics at play:

"The most likely way to make the explosion spherical is if a huge amount of energy blows out from the center of the explosion and smooths out a shape that would otherwise be asymmetrical. So the spherical shape tells us that there is probably a lot of energy in the core of the collision, which was unforeseen," says Albert Sneppen.

When the neutron stars collide, they are united, briefly as a single hypermassive neutron star, which then collapses to a black hole. The researchers speculate whether it is in this collapse that a large part of the secret is hidden:

"Perhaps a kind of 'magnetic bomb' is created at the moment when the energy from the hypermassive neutron star's enormous magnetic field is released when the star collapses into a black hole. The release of magnetic energy could cause the matter in the explosion to be distributed more spherically. In that case, the birth of the black hole may be very energetic," says Darach Watson.

However, this theory does not explain another aspect of the researchers' discovery. According to the previous models, while all elements produced are heavier than iron, the extremely heavy elements, such as gold or uranium, should be created in different places in the kilonova than the lighter elements such as strontium or krypton, and they should be expelled in different directions. The researchers, on the other hand, detect only the lighter elements, and they are distributed evenly in space.

They therefore believe that the enigmatic elementary particles, neutrinos, about which much is still unknown, also play a key role in the phenomenon.

"An alternative idea is that in the milliseconds that the hypermassive neutron star lives, it emits very powerfully, possibly including a huge number of neutrinos. Neutrinos can cause neutrons to convert into protons and electrons, and thus create more lighter elements overall. This idea also has shortcomings, but we believe that neutrinos play an even more important role than we thought," says Albert Sneppen.

Illustration of spherical explosion

CREDIT

Albert Sneppen

A New Cosmic Ruler

The shape of the explosion is also interesting for an entirely different reason:

"Among astrophysicists there is a great deal of discussion about how fast the Universe is expanding. The speed tells us, among other things, how old the Universe is. And the two methods that exist to measure it disagree by about a billion years. Here we may have a third method that can complement and be tested against the other measurements," says Albert Sneppen.

The so-called "cosmic distance ladder" is the method used today to measure how fast the Universe is growing. This is done simply by calculating the distance between different objects in the universe, which act as rungs on the ladder.

"If they are bright and mostly spherical, and if we know how far away they are, we can use kilonovae as a new way to measure the distance independently – a new kind of cosmic ruler," says Darach Watson and continues:

"Knowing what the shape is, is crucial here, because if you have an object that is not spherical, it emits differently, depending on your sight angle. A spherical explosion provide much greater precision in the measurement.”

He emphasizes that this requires data from more kilonovae. They expect that the LIGO observatories will detect many more kilonovae in the coming years.

Artistic illustration of kilonova

CREDIT

Robin Dienel/Carnegie Institution for Science)

FACT BOX: ABOUT KILONOVAE

• Neutron stars are extremely compact stars that consist mainly of neutrons. They are typically only about 20 kilometers across, but can weigh one and a half to two times as much as the Sun. A teaspoon of neutron star matter would weigh about as much as Mount Everest.
   
• When two neutron stars collide, the phenomenon of a kilonova occurs. This is the name of the gigantic explosion that the merger creates. It is a radioactive fireball that expands at enormous speed and consists mostly of heavy elements formed in the merger and its aftermath — both the lighter and the very heavy elements — which are ejected into space.
   
• The phenomenon was predicted in 1974 and first clearly observed and identified in 2013. In 2017, detailed data from a kilonova was obtained for the first time, when the detectors LIGO (in the USA) and Virgo (in Europe) sensationally succeeded in measuring gravitational waves from the kilonova AT2017gfo, which was in a galaxy 140 million light years away.

 

FACT BOX: ABOUT THE STUDY

• The analyses have been carried out on data from the kilonova AT2017gfo from 2017. Those data are the ultraviolet, optical, and infrared light from the X-shooter spectrograph on the Very Large Telescope at the European Southern Observatory, combined with previous analyses of gravitational waves, radio waves and data from the Hubble Space Telescope.
   
• The scientific article about the study has been published in the journal Nature.
   
• The study is an important early result of the HEAVYMETAL collaboration, which was recently awarded an ERC Synergy grant.
   
• The following researchers contributed to the work: Albert Sneppen and Darach Watson from the Cosmic Dawn Center / Niels Bohr Institute, University of Copenhagen; Andreas Bauswein and Oliver Just, GSI Helmholtzzentrum für Schwerionenforschung, Germany; Rubina Kotak from the University of Turku, Finland; Ehud Nakar and Dovi Poznanski from Tel Aviv University, Israel; and Stuart Sim from Queen's University Belfast, UK.

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JOURNAL

Nature

ARTICLE TITLE

Spherical symmetry in the kilonova AT2017gfo/GW170817

ARTICLE PUBLICATION DATE

15-Feb-2023

Engineered magic: Wooden seed carriers mimic the behavior of self-burying seeds

Geometric design and engineering of biodegradable materials could improve versatility, efficiency of aerial seeding

Peer-Reviewed Publication

CARNEGIE MELLON UNIVERSITY

 

IMAGE: THIS TIME-LAPSE SHOWS AN E-SEED CARRIER DRILLING INTO THE GROUND AFTER EXPOSURE TO MOISTURE. view more 

CREDIT: CARNEGIE MELLON UNIVERSITY

How seeds implant themselves in soil can seem magical. Take some varieties of Erodium, whose five-petalled flowers of purple, pink or white look like geraniums.

The seed of these plants is carried inside a thin, tightly wound stalk. During rain or high humidity, the corkscrew-like stalk unwinds and twists the seed into the soil, where it can take root and is safe from hungry birds and harsh environmental conditions. 

Inspired by Erodium's magic, Lining Yao, the Cooper-Siegel Assistant Professor of Human-Computer Interaction at Carnegie Mellon University, worked with a team of collaborators to engineer a biodegradable seed carrier referred to as E-seed. Their seed carrier, fashioned from wood veneer, could enable aerial seeding of difficult-to-access areas, and could be used for a variety of seeds or fertilizers and adapted to many different environments. It's an idea that Yao, the daughter of part-time farmers, has pondered since she was a Ph.D. student at MIT in the mid-2010s.

"Seed burial has been heavily studied for decades in terms of mechanics, physics and materials science, but until now, no one has created an engineering equivalent," said Yao, director of the Morphing Matter Lab in the School of Computer Science's Human-Computer Interaction Institute. "The seed carrier research has been particularly rewarding because of its potential social impact. We get excited about things that could have a beneficial effect on nature."

The team's research appeared in the February issue of Nature.

Danli Luo, a former research assistant at the Morphing Matter Lab and the lead author of the Nature paper, said design and construction of the seed carrier were inspired by the self-burying mechanism that Erodium evolved as it adapted to arid climates.

Erodium's stalk forms a tightly wound, seed-carrying body with a long, curved tail at the top. When it begins to unwind, the twisting tail engages with the ground, causing the seed carrier to push itself upright. Further unwinding creates torque to drill down into the ground, burying the seed.

But Erodium's one-tailed carrier only works well on soils with crevices. To employ their E-seed carriers in a broader range of environments, the research team developed a three-tailed version that is more efficient at pushing itself upright. 

"Geometry can enhance the functionality of the materials beyond what nature offers us. It also makes the design versatile to be applied to other materials," said Shu Yang, a materials scientist and co-author from the University of Pennsylvania.

The researchers considered a number of possible materials for their carriers, including hydrogels, paper and other forms of processed cellulose. They ultimately chose veneers of white oak — a species of tree abundant in Schenley Park adjacent to the CMU campus in Pittsburgh — and widely used in furniture. Like Erodium, veneers respond to moisture.

"Seeds have a magic response to rain," Yao said. 

Growing up in Inner Mongolia, Yao learned early from her parents the importance of timing the seeding process with the prospect of rain. Her appreciation for that timing grew during this project, as the researchers did plenty of field testing of the carriers, rather than just lab tests. That meant they had to keep their eyes on the weather, rushing the carriers to a test field when rain was in the offing.

The team developed a five-step process including both chemical washing and mechanical molding to manufacture the seed carriers. Although the carriers are currently fabricated in the lab, the researchers anticipate adapting the process to an industrial scale.

"Making E-seed through digital design and fabrication methods is crucial for our long-term goals," said Guanyun Wang, a former postdoctoral researcher in the Morphing Matter Lab who continued on the project after assuming a faculty position at Zhejiang University. 

In addition to seeds, the researchers demonstrated they could use the carriers to deliver nematodes (worms used as natural pesticides), fertilizers and fungi. Work is also underway to adapt them for planting seedlings. 

"Gaining insight into the mechanics of wood and seed drilling dynamics leads to improved design and optimization," said Teng Zhang, associate professor of mechanical and aerospace engineering at Syracuse University, who performed modeling and simulations to explain the working mechanism of the wood actuators and the benefits of E-seed's three-tailed design. 

These applications were possible thanks to a user study conducted by Aditi Maheshwari and Andreea Danielescu from ​Accenture Labs, who interviewed subject matter experts in reforestation, agriculture and soil health management to inform the applicability of E-seed in the real world.

"Understanding real-world applications of bioengineered technologies like E-seed is crucial for advancing ecological design," said Maheshwari, research and development principal at Accenture Labs, who works on sustainable materials and environments.

Danielescu, director of the Future Technologies R&D group at Accenture Labs, said E-seed can improve ecological resilience. 

"Technologies like E-seed can help us address real-world problems — helping us avoid landslides, reducing the impact of invasive species and improving reforestation of hard-to-reach places," Danielescu said. 

The carriers also could be used to implant sensors for environmental monitoring. They might also assist in energy harvesting by implanting devices that create current based on temperature fluctuations.

"The interest in the research from agriculture, forestry and other disciplines has been encouraging," Yao said. But perhaps one of the most important endorsements came from a source close to her: her father, the part-time farmer.

"When I mentioned the idea to him, he got it immediately."

E-seeds are dropped from a drone during a field test of the engineered seed carriers.

E-seeds on the ground near Hangzhou, China, after being dropped from a drone.

A vegetable plant growing next to its E-seed carrier. This seed was planted in a garden on Carnegie Mellon University’s campus in Pittsburgh, Pennsylvania.

CREDIT

Carnegie Mellon University

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JOURNAL

Nature

DOI

10.1038/s41586-022-05656-3 

ARTICLE TITLE

Autonomous self-burying seed carriers for aerial seeding

ARTICLE PUBLICATION DATE

15-Feb-2023

Before global warming, was the Earth cooling down or heating up?

Peer-Reviewed Publication

NORTHERN ARIZONA UNIVERSITY

Accurate climate models play a critical role in climate science and policy, helping to inform policy- and decision-makers throughout the world as they consider ways to slow the deadly effects of a warming planet and to adapt to changes already in progress.

To test their accuracy, models are programmed to simulate past climate to see if they agree with the geologic evidence. The model simulations can conflict with the evidence. How can we know which is correct?

A review article published today in Nature addresses this conflict between models and evidence, known as the Holocene global temperature conundrum. Lead author Darrell Kaufman, a Regents’ professor in the School of Earth and Sustainability, and University of Arizona postdoctoral researcher Ellie Broadman, a co-author who worked on this study while earning her Ph.D. at NAU, analyzed a broad swath of available data from the last 12,000 years to break down the conundrum. The study builds on work Kaufman did that was included in the latest major climate report by the Intergovernmental Panel on Climate Change (IPCC) and looks at whether the global average temperature 6,500 years ago was warmer, as indicated by proxy evidence from natural archives of past climate information, or colder, as simulated by models, in comparison to the late 19th century, when the Industrial Revolution led to a significant increase in human-caused warming.

This comprehensive assessment concludes that the global average temperature about 6,500 years ago was likely warmer and was followed by a multi-millennial cooling trend that ended in the 1800s. But, they cautioned, uncertainty still exists despite recent studies that claimed to have resolved the conundrum.

“Quantifying the average temperature of the earth during the past, when some places were warming while others were cooling, is challenging, and more research is needed to firmly resolve the conundrum,” Kaufman said. “But tracing changes in global average temperature is important because it’s the same metric used to gauge the march of human-caused warming and to identify internationally negotiated targets to limit it. In particular, our review revealed how surprisingly little we know about slow-moving climate variability, including forces now set into motion by humans that will play out as sea level rises and permafrost thaws over coming millennia.”

What we know

We know more about the climate of the Holocene, which began after the last major ice age ended 12,000 years ago, than any other multi-millennial period. There are published studies from a variety of natural archives that store information about historical changes that occurred in the atmosphere, oceans, cryosphere and on land; studies that look at the forces that drove past climate changes, such as Earth’s orbit, solar irradiance, volcanic eruptions and greenhouse gases; and climate model simulations that translate those forces into changing global temperatures. All these types of studies were included in this review.

The challenge up to now has been that our two significant lines of evidence point in opposite directions. Paleo-environmental “proxy” data, which includes evidence from oceans, lakes, and other natural archives, point to a peak global average temperature about 6,500 years ago and then a global cooling trend until humans started burning fossil fuels. Climate models generally show global average temperatures increasing in the last 6,500 years.

If the proxy data are correct, that points to deficiencies in the models and specifically suggests that climate feedbacks that can amplify global warming are underrepresented. If the climate models are correct, then the tools for reconstructing paleotemperatures need to be sharpened.

We also know that, whether the numbers trend up or down, the change in global average temperature in the past 6,500 years has been gradual—probably less than 1 degree Celsius (1.8 degrees Fahrenheit). This is less than the warming already measured in the last 100 years, most of which humans have caused. However, because global temperature change of any magnitude is significant, especially in response to changing greenhouse gases, knowing whether temperatures were higher or lower 6,500 years ago is important to our knowledge of the climate system and improving forecasts of future climate.

What we don’t know

This study highlighted uncertainties in the climate models. If the authors’ preferred interpretation—that recent global warming was preceded by 6,500 years of global cooling—is correct, then scientists’ understanding of natural climate forcings and feedbacks, and how they are represented in models, needs improvement. If they’re incorrect, then scientists need to improve their understanding of the temperature signal in proxy records and further develop analytical tools to capture these trends on a global scale.

Attempting to resolve the Holocene global temperature conundrum has been a priority for climate scientists in the last decade; Broadman remembers reading the initial paper on this topic when she started her Ph.D. in 2016. All the studies since have added to the understanding of this issue, which gets scientists in the field closer to a comprehensive understanding. Recent studies on this topic have tried adjusting proxy data to account for their presumed weaknesses, inserting plausible forcings into climate models and blending proxy data with climate-model output, all arriving at different conclusions about the cause of the conundrum. This review takes a step back to revisit the issue with a comprehensive global-scale assessment, showing that we don’t yet know the solution to this conundrum.

Developing widely applicable methods of quantifying past temperature is a high priority for climate scientists already. For example, Kaufman’s lab is testing the use of chemical reactions involving amino acids preserved in lake sediment as a new method for studying past temperature changes. Combined with new radiocarbon dating technology from the Arizona Climate and Ecosystem lab at NAU, this technique could help determine whether global warming reversed a long-term cooling trend.

Why it matters

Broadman, whose work includes a focus on science communication, created the figures that accompany the research. This is a critical way of communicating hard-to-understand results to audiences—and in climate science, the audiences are diverse and include educators, policymakers, nonprofits and scientists throughout the world.

“One interesting takeaway is that our findings demonstrate the impact that regional changes can have on global average temperature. Environmental changes in some regions of the Earth, like declining Arctic sea ice or changing vegetation cover in what are now vast deserts, can cause feedbacks that influence the planet as a whole,” Broadman said. “With current global warming, we already see some regions changing very quickly. Our work highlights that some of those regional changes and feedbacks are really important to understand and capture in climate models.”

Additionally, Kaufman said, accurately reconstructing the details of past temperature change offers insights into climate’s response to various causes of both natural and anthropogenic climate change. The responses serve as benchmarks to test how well climate models simulate the Earth’s climate system.

“Climate models are the only source of detailed quantitative climate predictions, so their fidelity is critical for planning the most effective strategies to mitigate and adapt to climate change,” he said. “Our review suggests that climate models are underestimating important climate feedbacks that can amplify global warming.”

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JOURNAL

Nature

DOI

10.1038/s41586-022-05536-w 

METHOD OF RESEARCH

Systematic review

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Revisiting the Holocene global temperature conundrum

ARTICLE PUBLICATION DATE

15-Feb-2023

New compound that withstands extreme heat and electricity could lead to next-generation energy storage devices

Flexible polymers made with a new generation of the Nobel-winning “click chemistry” reaction find use in capacitors and other applications

Peer-Reviewed Publication

DOE/LAWRENCE BERKELEY NATIONAL LABORATORY

 

IMAGE: A NEW TYPE OF POLYSULFATE COMPOUND CAN BE USED TO MAKE POLYMER FILM CAPACITORS THAT STORE AND DISCHARGE HIGH DENSITY OF ELECTRICAL ENERGY WHILE TOLERATING HEAT AND ELECTRIC FIELDS BEYOND THE LIMITS OF EXISTING POLYMER FILM CAPACITORS. view more 

CREDIT: YI LIU AND HE (HENRY) LI/BERKELEY LAB

– By Rachel Berkowitz

Society’s growing demand for high-voltage electrical technologies – including pulsed power systems, cars and electrified aircraft, and renewable energy applications – requires a new generation of capacitors that store and deliver large amounts of energy under intense thermal and electrical conditions. Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Scripps Research have now developed a new polymer-based device that efficiently handles record amounts of energy while withstanding extreme temperatures and electric fields. The device is composed of materials synthesized via a next-generation version of the chemical reaction for which three scientists won the 2022 Nobel Prize in Chemistry.

Polymer film capacitors are electrical components that store and release energy within an electric field using a thin plastic layer as the insulating layer. They make up 50% of the global high voltage capacitor market and offer advantages including light weight, low cost, mechanical flexibility, and robust cyclability. But state-of-the-art polymer film capacitors decrease dramatically in performance with increasing temperature and voltages. Developing new materials with improved tolerance for heat and electric fields is paramount; and creating polymers with near-perfect chemistry offers a way to do so.

“Our work adds a new class of electrically robust polymers to the table. It opens many possibilities to the exploration of more robust, high performing materials,” said Yi Liu, a chemist at Berkeley Lab and senior author on the Joule study reporting the work. Liu is the Facility Director of Organic and Macromolecular Synthesis at the Molecular Foundry, a DOE Office of Science user facility at Berkeley Lab.

In addition to remaining stable when subjected to high temperatures, a capacitor needs to be a strong “dielectric” material, meaning that it remains a strong insulator when subjected to high voltages. However, few known materials systems exist that deliver both thermal stability and dielectric strength. This scarcity is due to a lack of reliable and convenient synthesis methods, as well as a lack of fundamental understanding of the relationship between polymer structure and properties. “Improving the thermal stability of existing films while retaining their electrical insulating strength is an ongoing materials challenge,” said Liu.

A long-term collaboration between researchers at the Molecular Foundry and Scripps Research Institute has now met that challenge. They used a simple and quick chemical reaction developed in 2014 that swaps out fluorine atoms in compounds that contain sulfur-fluoride bonds, to yield long polymer chains of sulfate molecules called polysulfates. This Sulfur-Fluoride Exchange (SuFEx) reaction is a next-generation version of the click chemistry reaction pioneered by K. Barry Sharpless, a chemist at Scripps Research and two-time Nobel laureate in Chemistry, along with Peng Wu, also a chemist at Scripps Research. The near-perfect yet easy-to-run reactions join separate molecular entities through strong chemical bonds that form between different reactive groups. Liu’s team had originally used a variety of thermal analysis tools to examine the basic thermal and mechanical properties of these new materials.

As part of a Berkeley Lab program to synthesize and identify novel materials that could be useful in energy storage, Liu and his colleagues now find that, surprisingly, the polysulfates have outstanding dielectric properties, especially at high electric fields and temperatures. “Several commercial and lab-generated polymers are known for their dielectric properties, but polysulfates had never been considered. The marriage between polysulfates and dielectrics is one of the novelties here,” said He Li, a postdoctoral researcher in the Molecular Foundry and in Berkeley Lab’s Materials Sciences Division, and lead author of the study. 

Inspired by the excellent baseline dielectric properties offered by polysulfates, the researchers deposited extremely thin layers of aluminum oxide (Al2O3) onto thin films of the material to engineer capacitor devices with enhanced energy storage performance. They discovered that the fabricated capacitors exhibited excellent mechanical flexibility, withstood electric fields of more than 750 million volts per meter, and performed efficiently at temperatures up to 150 degrees Celsius. In comparison, today’s benchmark commercial polymer capacitors only function reliably at temperatures lower than 120 degrees Celsius. Above that temperature, they can only withstand electric fields smaller than 500 million volts per meter, and the energy efficiency severely drops by over half. 

The work opens new possibilities for exploring robust, high performing materials for energy storage. “We have provided deep insight into the underlying mechanisms that contribute to the material’s excellent performance,” said Wu.

The polymer strikes a balance of electrical, thermal, and mechanical properties, likely due to the sulfate linkages introduced by the click chemistry reaction. Because modular chemistry accommodates extraordinary structural diversity and scalability, the same route could offer a viable path to new polymers with higher performance that meet even more demanding operational conditions.

The polysulfates are strong contenders to become new state-of-the-art polymer dielectrics. Once researchers overcome barriers in large-scale manufacturing processes for thin film materials, the devices could greatly improve the energy efficiency of integrated power systems in electric vehicles and enhance their operational reliability. 

“Who could have imagined that a wispy sulfate polymer film could fend off lightning and fire, two of the most destructive forces in the universe?!” said Sharpless. 

“We’re continuously pushing the envelope of thermal and electrical properties, and accelerating the lab-to-market transition,” Liu added.

The technology is now available for licensing by contacting ipo@lbl.gov.

The work received funding from the Department of Energy’s Office of Science, the National Science Foundation, and the National Institute of Health. The work was carried out at the Molecular Foundry. 

Polysulfates with excellent thermal properties are casted into flexible free-standing films. High-temperature, high-voltage capacitors based on such films show state-of-the-art energy storage properties at 150 oC. Such power capacitors are promising for improving the energy efficiency and reliability of integrated power systems in demanding applications such as electrified transportation.

CREDIT

Credit: Yi Liu and He (Henry) Li/Berkeley Lab

Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams, Lawrence Berkeley National Laboratory and its scientists have been recognized with 16 Nobel Prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the Lab’s facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy’s Office of Science.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.

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JOURNAL

Joule

DOI

10.1016/j.joule.2022.12.010 

ARTICLE TITLE

High-performing polysulfate dielectrics for electrostatic energy storage under harsh conditions