Monday, January 06, 2025

Marked decrease in Arctic pressure ridges

Analysis of three decades of aerial survey data reveals major changes

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

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Close-up of a newly formed pressure ridge in the Arctic Ocean.
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Credit: Alfred-Wegener-Institut / Andreas Preusser

In the Arctic, the old, multiyear ice is increasingly melting, dramatically reducing the frequency and size of pressure ridges. These ridges are created when ice floes press against each other and become stacked, and are a characteristic feature of Arctic sea ice, an obstacle for shipping, but also an essential component of the ecosystem. In a recently released study in the journal Nature Climate Change, experts from the Alfred Wegener Institute report on this trend and analyse observational data from three decades of aerial surveys.

Satellite data from the last three decades documents the dramatic changes in Arctic sea ice due to climate change: the area covered in ice in summer is declining steadily, the floes are becoming thinner and moving faster. Until recently, it was unclear how the characteristic pressure ridges had been affected, since it’s only been possible to reliably monitor them from space for the past few years.

Pressure ridges are produced by lateral pressures on sea ice. Wind or ocean currents can stack floes up, forming metre-thick ridges. The part of the ridges – which break up the otherwise smooth surface of the ice every few hundred metres – extending above the water is called the sail and measures between one and two metres. Even more impressive is the keel below the water line, which can extend down to 30 metres and create an impassable obstacle for shipping. Pressure ridges affect not only the energy and mass balance of the sea ice, but also the biogeochemical cycle and the ecosystem: when their sails catch the wind, floes can be driven all across the Arctic. Polar bears use pressure ridges as a source of protection for overwintering or birthing their young. In addition, the structures offer ice-associated organisms at various trophic levels protection and promote the turbulent mixing of water, which increases nutrient availability.

A team of researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), has now reprocessed and analysed laser-based readings gathered in 30 years of research flights over the Arctic ice. The survey flights, which cover a total distance of roughly 76,000 kilometres, show for the first time that the frequency of pressure ridges north of Greenland and in Fram Strait is decreasing by 12.2%, and their height by 5%, per decade. Data from the Lincoln Sea, an area where particularly old ice is known to accumulate, paints a similar picture: here, the frequency is declining by 14.9% and the height by 10.4% per decade.

“Until now, it’s remained unclear how pressure ridges were changing,” says Dr Thomas Krumpen, a sea-ice expert at the AWI and the study’s main author. “More and more of the Arctic consists of ice that melts in the summer and is no more than a year old. This young, thin ice can more readily be deformed and more rapidly forms new pressure ridges. So you might expect their frequency to increase. The fact that pressure ridges are nonetheless in decline is due to the dramatic melting of older floes. Ice that has survived several summers is characterised by a particularly high number of pressure ridges, since it has been subjected to high pressures over a longer timeframe. The loss of this multiyear ice is so severe that we’re observing an overall decline in pressure-ridge frequency, even though the thin young ice is easier to deform.”

In order to draw conclusions regarding Arctic-wide changes, the researchers combined all observational data to develop a metric. Then, with the aid of satellite data, they applied it to the Arctic as a whole: “We tend to see the greatest decline in pressure ridges in those places where the ice’s age has decreased most,” summarises Prof Christian Haas, Head of Sea-ice Physics at the AWI. “Major changes can be seen in the Beaufort Sea, but also in the Central Arctic. Both regions are now partly ice-free in summer, though they were once dominated by ice that was at least five years old.”

For the study, individual pressure ridges and their heights were precisely measured and analysed during survey flights. This was possible thanks to the low-level flights (less than 100 metres above the surface) and the laser sensors’ high scanning rate, which allowed terrain models to be created. The AWI began scientific flights over the sea ice in the early 1990s, launching from Svalbard. Back then, the institute relied on two Dornier DO228s, Polar 2 and Polar 4; they have since been succeeded by two Basler BT-67s, Polar 5 and Polar 6. Specially equipped for flights under the extreme conditions found in the polar regions, they can be fitted with a range of sensors. Using these aircraft, researchers survey the ice north of Greenland, Svalbard and Canada twice a year. But the icebreaker Polarstern’s onboard helicopters are also part of the monitoring programme.

In order to estimate the direct effects of the observed changes on the Arctic ecosystem, models need to be developed that can reflect both physical and biological processes in sea ice of various ages. Although we know that pressure ridges are home to a range of organisms, we still lack a deeper understanding of the role of pressure-ridge age. Yet this aspect is especially important, as the percentage of ridges that don’t survive their first summer is on the rise. Another riddle: although the size and frequency of ridge sails have decreased, the drift speed of Arctic ice has generally increased. As AWI sea-ice physicist Dr Luisa von Albedyll, who contributed to the study, explains: “Actually, the ice should drift more slowly when the sails shrink, since there’s less area for the transfer of momentum. This indicates that there are other changes producing just the opposite effect. Stronger ocean currents or a smoother ice underside due to more intensive melting could be contributing factors. To answer these open questions and gain a better grasp of the complex interrelationships, we have made the entire dataset available in a public archive, (Link zu PANGAEA), ensuring that other researchers can use it and integrate it into their studies.”

An expedition with the research vessel Polarstern is planned for next summer, with a focus on investigating the biological and biogeochemical differences between floes and pressure ridges of different ages and provenances. At the same time, there will be extensive aerial survey flights with the research aircraft. According to Thomas Krumpen: “By combining ship-based and aerial observations, we hope to gain better insights into the complex interactions between the sea ice, climate and ecosystem – since we’ll only be able to devise effective strategies for the preservation and sustainable use of the Arctic once we better understand the region’s environmental system.”

Journal

Nature Climate Change

DOI

10.1038/s41558-024-02199-5

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Smoother ice with fewer pressure ridges in a more dynamic Arctic

Article Publication Date

6-Jan-2025

ANIMAL EXPERIMENTATION AS TORTURE

Singapore and Japan scientists develop technology to control cyborg insect swarms

Nanyang Technological University

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*Illustration of how multiple cyborg insects will follow a single leader (swarm navigation)*
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Credit: NTU Singapore

Scientists from Nanyang Technological University, Singapore (NTU Singapore), Osaka University, and Hiroshima University have developed an advanced swarm navigation algorithm for cyborg insects that prevents them from becoming stuck while navigating challenging terrain.

Published in Nature Communications, the new algorithm represents a significant advance in swarm robotics. It could pave the way for applications in disaster relief, search-and-rescue missions, and infrastructure inspection.

Cyborg insects are real insects equipped with tiny electronic devices on their backs - consisting of various sensors like optical and infrared cameras, a battery, and an antenna for communication - that allow their movements to be remotely controlled for specific tasks.

The control of a single cyborg insect was first demonstrated by Professor Hirotaka Sato from NTU Singapore’s School of Mechanical and Aerospace Engineering in 2008[1].

However, a single insect is insufficient for operations such as search-and-rescue missions, where earthquake survivors are spread out and there is an optimal 72-hour window for locating them.

In 2021[2] and 2024[3], Prof Sato and his partners from Singapore’s Home Team Science & Technology Agency (HTX) and Klass Engineering and Solutions demonstrated how cyborg insects may be used for search and rescue operations in future.

This latest paper on the new swarm system uses a leader-follower dynamic, where one cyborg insect acts as a group leader guiding 19 others.

Co-corresponding authors of the paper, Professor Masaki Ogura[4] from Hiroshima University and Professor Wakamiya Naoki from Osaka University, developed the swarm control algorithm and computer programmes, while NTU Professor Hirotaka Sato and his team prepared the cyborg insect swarm, implemented the algorithm on the insects’ electronic backpacks, and conducted the physical experiments in Singapore.

The scientists noted several benefits to their new swarm algorithm during lab experiments. Allowing the cyborg insects to move more freely reduced the risk of the cyborgs getting stuck in obstacles, and nearby cyborgs could also help free those stuck or flipped over.

How the cyborg insect swarm works

Earlier research demonstrated control of a single cyborg or a group that was controlled by algorithms that provided detailed and complex instructions for individual insects, an approach that would not coordinate movement for a big group.

With the new method, the leader insect is first appointed by the algorithm, then notified of the intended destination, and its control backpack will coordinate with the backpack of others in the group to guide the swarm.

This “tour leader” approach allows the swarm to adapt dynamically, as the insects can assist each other to overcome obstacles, adjusting their movements if one member becomes trapped.

The insects used are Madagascar hissing cockroaches equipped with a lightweight circuit board, sensors and a rechargeable battery on their backs – which forms an autonomous navigation system that helps them navigate their surroundings and nudges them towards a target.

These cyborgs consume significantly less energy than traditional robots, which rely on power-intensive motors for movement. The insect’s legs provide the locomotion needed to move the backpack, as the backpack nudges the insect by applying tiny electrical stimulations, guiding it towards a particular direction.

When combined with the swarm control algorithm, the insects’ instincts enable them to navigate complex terrains and respond rapidly to environmental changes.

In experiments, the new algorithm reduced the need to nudge the insects by about 50 per cent compared to earlier approaches, thus allowing the insects to have more independent navigation over obstacles and resolving issues such as insects becoming stuck or trapped.

NTU Prof Hirotaka Sato said the technology is envisioned to be helpful in search and rescue missions, infrastructure inspection, and environmental monitoring, where narrow spaces and unpredictable conditions render conventional robots ineffective.

“To conduct search and inspection operations, large areas must be surveyed efficiently, often across challenging and obstacle-laden terrain. The concept involves deploying multiple swarms of cyborg insects to navigate and inspect these obstructed regions. Once the sensors on the backpack of a cyborg insect detect a target, such as humans in search-and-rescue missions or structural defects in infrastructure, they can wirelessly alert the control system.” explains Prof Sato.

Prof Sato is renowned for his pioneering work in cyborg insects. He had previously received global recognition when his research was named one of TIME magazine’s 50 Best Inventions of 2009 and one of the 10 Emerging Technologies of 2009 (TR10) by MIT Technology Review.

Co-corresponding author of the paper, Professor Masaki Ogura, Graduate School of Advanced Science and Engineering at Hiroshima University, said: “Our swarm control algorithm represents a significant breakthrough in coordinating groups of cyborg insects for complex search-and-rescue missions. This innovation has the potential to greatly enhance disaster response efficiency while also opening new avenues for research in swarm control. It underscores the importance of developing control methods that perform effectively in real-world scenarios, going beyond theoretical models and simulations.”

Co-corresponding author, Professor Wakamiya Naoki, Graduate School of Information Science and Technology, Osaka University, explained: “Unlike robots, insects do not behave as we intend them to. However, instead of forcibly trying to control them precisely, we found that taking a more relaxed and rough approach not only worked better but also led to the natural emergence of complex behaviours, such as cooperative actions, which are challenging to design as algorithms. This was a remarkable discovery. While their actions may appear haphazard at first glance, there seems to be a great deal we can still learn from the sophisticated and intricate behaviours of living organisms.”

Their latest advance underscores the practical potential of biohybrid systems in addressing real-world challenges and the importance of global interdisciplinary research collaborations.

Looking ahead, the joint team aims to develop algorithms that enable coordinated swarm actions beyond simple movements, such as collaboratively transporting large objects.

They also plan to conduct experiments in outdoor environments, including rubble piles commonly found in disaster zones, to validate the algorithm’s effectiveness in more complex and real-world scenarios.

[1] Hirotaka Sato et al., "A cyborg beetle: Insect flight control through an implantable, tetherless microsystem," 2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, Tucson, AZ, USA, 2008, pp. 164-167, doi: 10.1109/MEMSYS.2008.4443618.

[2] Chong, C. (2021, December 6). S'pore team turning cockroaches into life-saving cyborg bugs at disaster sites. The Straits Times. https://www.straitstimes.com/singapore/spore-team-turning-cockroaches-into-life-saving-cyborg-bugs-at-disaster-sites

[3] Sun, D. (2024, April 5). Singapore’s cyborg cockroaches on display at homeland security event at MBS. The Straits Times. https://www.straitstimes.com/singapore/singapore-s-cyborg-cockroaches-on-display-at-homeland-security-event-at-mbs

[4] Masaki Ogura, Professor in the Graduate School of Advanced Science and Engineering, Hiroshima University