Monday, October 20, 2025

Did marine life in the palaeocene use a compass?

Based on a sophisticated method, an international team has succeeded in mapping magnetic domains in giant fossilised magnetic microparticles: these may have served as compasses for ancient organisms

Helmholtz-Zentrum Berlin für Materialien und Energie

Some ancient marine organisms produced mysterious magnetic particles of unusually large size, which can now be found as fossils in marine sediments. An international team has succeeded in mapping the magnetic domains on one of such ‘giant magnetofossils’ using a sophisticated method at the Diamond X-ray source. Their analysis shows that these particles could have allowed these organisms to sense tiny variations in both the direction and intensity of the Earth’s magnetic field, enabling them to geolocate themselves and navigate across the ocean. The method offers a powerful tool for magnetically testing whether putative biological iron oxide particles in Mars samples have a biogenic origin.

A few years ago, mysterious particles of magnetite were discovered in marine sediments. These magnetite particles were exceptionally large – about 10-20 times larger than the ‘conventional magnetite magnetofossils’ that are made by magnetotactic bacteria for the purposes of passive orientation in the Earth’s field. Giant magnetofossils are observed in a variety of shapes, including needles, spindles, bullets and spearheads. To date, it is unknown which organisms were able to form these gigantic magnetite particles and for what purpose they were used. Although some giant magnetofossils resemble conventional magnetofossils in shape, their unusually large size was though to make them poorly optimised for the purpose of magnetic alignment alone. Instead, an accepted option is that some living beings used such magnetite particles primarily as a protective shield against predators due to their mechanical hardness, meaning that their magnetic properties did not play a major role. However, not all researchers are convinced by this theory.

A compass for sea creatures?

Sergio Valencia, a physicist at HZB, and palaeomagnetism researcher Richard J. Harrison from the University of Cambridge, UK, have now investigated an alternative hypothesis. They suspect that these creatures did indeed use the magnetic properties of these particles to help them navigate using the Earth's magnetic field by detecting small variations in intensity and direction of the field – a kind of in-built magnetic GPS system. To test this idea, it was necessary to map the three dimensional magnetic structure of the magnetofossils, enabling the magnetic energy and associated forces on the particle in the local Earth's magnetic field to be estimated.

Non-destructive investigation

Harrison and Valencia examined a particle shaped like a spearhead, with a diameter of 1.1 µm and a length of 2.25 µm. It came from the team of Liao Chang, University Beijing, and was found in a marine sediment in the North Atlantic that is around 56 million years old. A major challenge was to examine the internal magnetic structure of this rather thick sample without slicing and destroying it as this modifies the magnetic domain structure. This could be achieved at the Diamond X-ray source in Oxford, UK, using a newly developed technique devised by Claire Donnelly at the Max Planck Institute for the Chemical Physics of Solids (MPI CPfS) in Dresden, Germany. The so-called pre-edge phase X-ray magnetic circular dichroism (XMCD) ptychography allowed them to visualise the magnetic domain structure within the full volume of the sample in a non-destructive way. "This was a truly international collaboration involving experts from different fields, all working together to shed light on the possible functionality of these magnetofossils," says Sergio Valencia, the principal investigator who initiated and coordinated the effort.

3D mapping of the sample

The team was able to map the entire sample volume in three dimensions and at high resolution. ‘With the help of magnetic vector tomography, all three components of the magnetisation could be reconstructed and spatially resolved throughout the entire volume of the grain with a resolution of a few 10 nm,’ says Valencia, emphasising: ‘Once we have set up the successor source BESSY III, such measurements could also be carried out in Berlin.’

Magnetic vortex detected

The results show that the magnetite particle contains a single magnetic vortex that reacts to spatial fluctuations in the Earth's magnetic field with strong forces and could thus provide an organism with an accurate way to map the Earth’s magnetic field intensity, enabling magnetic navigation.

‘Marine organisms, for example a fish, may have used this property for magnetic navigation,’ says Harrison. Even if the particles studied here originally developed as protective armour, it is possible that, in the course of evolution, its descendants also used these particles as a navigational tool.

Use of the Earth's magnetic field to navigate is a widespread phenomenon today, observed in molluscs, amphibians, fish, reptiles, birds and mammals. Giant magnetofossils have been found in sediments dating back as far as 97 Million years, providing fossil evidence that magnetoreceptive navigation developed at least that long ago.

Outlook on particles from Mars

‘Iron-oxide particles resembling those made by some bacteria on Earth have been discovered on the Martian meteorite ALH84001, although their biological origin is strongly disputed. As we continue the search for evidence of life on Mars through sample return missions, we now have a method to investigate any new potential magnetofossils found and provide evidence to support or refute their biological origin,’ says Richard Harrison. ‘It would be very exciting to use this experimental technique to evaluate the morphological and magnetic fingerprints of those iron oxide particles. This could help in the search for evidence of past life,’ says Valencia.

Journal

Communications Earth & Environment

Cuts of the 3D magnetic volume of the fossil in three different heights: The blue/red colour indicates the in-plane component of the magnetisation, with magnetic moments swirling around a central line, forming a vortex pattern much like a tornado (see projections at the bottom). The 3D reconstruction has been obtained based on 140 individual images at different angles.

Credit

Jeffrey Neethirajan/ MPI CPfs and Sergio Valencia / HZB

DOI

10.1038/s43247-025-02721-3

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Magnetic vector tomography reveals giant magnetofossils are optimised for magnetointensity reception

Article Publication Date

20-Oct-2025

Important phenomenon discovered in the Arctic – could boost marine life

University of Copenhagen

image:
*Measurements of nitrogen fixation in the Arctic Ocean aboard RV Polarstern (photo: Rebecca Duncan)*
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Credit: Rebecca Duncan

The shrinking sea ice in the Arctic Ocean is, overall, a disaster. But paradoxically, the melting of the ice can also fuel the engine of the Arctic food chains: algae.

Algae are the main food source for life in the sea, but they need nitrogen to grow. And nitrogen is in short supply in the Arctic Ocean. However, a new international study led by the University of Copenhagen indicates therewill probably be more of it in the future than previously thought. This could change the future prospects for marine life in the High North and possibly for the carbon budget.

The researchers are the first to discover that the phenomenon of nitrogen fixation occurs beneath sea ice even in the central Arctic Ocean. Nitrogen fixation is a process in which special bacteria convert nitrogen gas (N2) dissolved in seawater into ammonium. Ammonium helps the bacteria to grow, but it also benefits algae and the rest of the food chain in the sea.

"Until now, it was believed that nitrogen fixation could not take place under the sea ice because it was assumed that the living conditions for the organisms that perform nitrogen fixation were too poor. We were wrong," says Lisa W. von Friesen, lead author of the study and former PhD student at the Department of Biology.

Less ice could mean more algae

Whereas in most other oceans it is cyanobacteria that perform nitrogen fixation, the study shows that in the Central Arctic Ocean it is a completely different type of bacteria that converts nitrogen: the so-called non-cyanobacteria.

The researchers have measured the highest rates of nitrogen fixation at the ice edge, where the ice melts most actively. Although the bacteria can perform nitrogen fixation under the ice, it is easier for them to do so along the ice edge. So as the sea ice retreats and the area of melting expands, larger amounts of nitrogen are expected to be added through nitrogen fixation.

"In other words, the amount of available nitrogen in the Arctic Ocean has likely been underestimated, both today and for future projections. This could mean that the potential for algae production has also been underestimated as climate change continues to reduce the sea ice cover," says Lisa W. von Friesen.

‘Because algae are the primary food source for small animals such as planktonic crustaceans, which in turn are eaten by small fish, more algae can end up affecting the entire food chain’ adds Lisa W. von Friesen.

May affect the ocean's CO2 uptake

In addition, the newly discovered source of nitrogen could also be beneficial for the uptake of CO2 – at least regionally. More algae make the ocean better at absorbing CO2.

"For the climate and the environment, this is likely good news. If algae production increases, the Arctic Ocean will absorb more CO2 because more CO2 will be bound in algae biomass. But biological systems are very complex, so it is hard to make firm predictions, because other mechanisms may pull in the opposite direction," says Lasse Riemann, professor at the Department of Biology and senior author of the study.

Nevertheless, the researchers believe that nitrogen fixation should be included in forecasts for the Arctic Ocean.

‘We do not yet know whether the net effect will be beneficial for the climate. But it is clear that we should include an important process such as nitrogen fixation in the equation when we try to predict what will happen to the Arctic Ocean in the coming decades as sea ice declines,’ says Lasse Riemann.

***

HOW IT WORKS

In the Arctic Ocean, nitrogen fixation is carried out by so-called non-cyanobacteria. These bacteria feed on dissolved organic matter released by algae, among other things. In return, the bacteria release fixed nitrogen, which helps algae in the surrounding water to grow.

In addition to being the first link in the marine food chain, algae also act as the ocean's little CO2 vacuum cleaners. As they grow, they absorb CO2 from the atmosphere, which can then sink as algal biomass into the deep sea.

ABOUT THE STUDY

• The scientific article about the study has just been published in the journal Communications Earth & Environment.

• The researchers behind the study come from: University of Copenhagen, Denmark; Linnaeus University, Sweden; Alfred Wegener Institute, Germany; Aix Marseille University, France; National Oceanography Centre, United Kingdom; Max Planck Institute for Chemistry, Germany; Stockholm University, Sweden and Swedish University of Agricultural Sciences, Sweden.

• The study is based on two scientific expeditions with the ships IB Oden and RV Polarstern. Measurements were taken at 13 different locations across the central Arctic Ocean, in the sea off northeast Greenland and north of Svalbard.

Measurements were taken at 13 different locations in the Arctic Ocean (credit: Lisa W. von Friesen).

Credit

Lisa W. von Friesen