Mysterious magnetic fossils provide earlier climatic clues

There are fossils found in ancient marine sediments and not just more than a few magnetic nanoparticles, which can tell us a lot about the climate of the past, especially episodes of abrupt global warming. Now researchers, including doctoral student Courtney Wagner and associate professor Peter Lippert of the University of Utah, have found a way to gather the valuable information in the fossils without crushing the rare specimens into a fine powder. Their results are in Proceedings of the National Academy of Sciences.

“It’s so fun to be a part of a discovery like this, something that could be used by other researchers studying magnetofossils and intervals of planetary change,” says Wagner. “This work can be used by many other scientists, inside and outside our specialized community. It is very exciting and fulfilling.”

The name “magnetofossil” may make one think the images of the X-Men, but the reality is that magnetofossils are microscopic bacterial iron fossils. Some bacteria make magnetic particles 1/1000 of the width of a hair which, when joined together in a chain in the cell, acts like a compass on a nano-scale. The bacteria, called ‘magnetotactic bacteria’, can then use this compass to align themselves with the Earth’s magnetic field and move efficiently to their favorite chemical conditions in the water.

Some of these biologically-produced magnets have grown to ‘giant’ sizes, about 20 times larger than typical magnetic fossils, during some periods in the past, at the beginning and middle of the Eocene period from 56 to 34 million years ago. , and into exotic shapes such as needles, pivots, spearheads and giant bullets. Because the bacteria used their magnetic supersens to find their preferred levels of nutrients and oxygen in the ocean water, and because the giant magnetofossils are associated with periods of rapid climate change and rising global temperatures, they can tell us much about ocean during that rapid warming, and especially how conditions have changed over time.

Previously, extraction and analysis of these fossils had to crush the samples into a fine powder for electron microscopy imaging. “The extraction process can be time consuming and unsuccessful, electron microscopy can be expensive, and the destruction of samples means that it is no longer useful for most other experiments,” says Wagner. “The collection and storage of these samples requires specialized personnel, equipment and planning, so we want to preserve as much material as possible for additional studies.”

So Wagner, Lippert and colleagues, including Ramon Egli of the Central Institute for Meteorology and Geodynamics and Ioan Lascu at the National Museum of Natural History, found another way. Using sediment samples collected in New Jersey, they designed a new way to perform an analysis called FORC (first order reversal curve) measurements. With these high-resolution magnetic measurements, they found that the magnetic signature of giant magnetofossils was characteristic – enough to use the technique in other samples to identify the presence of the fossils. “FORC measurements examine the reaction of magnetic particles to magnetic fields applied from the outside, and make it possible to distinguish different types of iron oxide particles without actually seeing them,” says Egli.

“The ability to quickly find giant magnetofossil compositions in the geological record will help identify the origin of these unusual magnetofossils,” the researchers write, as well as the ecology of the organisms that formed them. This is important, says Wagner, because no known living organisms today form giant magnetofossils and we still do not know which organisms formed them in the past. “The organisms that produced these giant magnetofossils are completely mysterious, but they leave exciting research paths open for the future,” Lascu adds.

But in addition, the information in magnetofossils helps scientists understand how oceans have responded to climate change in the past – and how our current oceans can respond to continuous warming.