About Magnetofossils:

• These are the fossilised remains of magnetic particles created by magnetotactic bacteria, also known as magnetobacteria, and found preserved within the geological records.
• What are Magnetotactic bacteria?
  • These are mostly prokaryotic organisms that arrange themselves along the earth’s magnetic field.
  • These organisms were believed to follow the magnetic field to reach places that had optimal oxygen concentration.
  • These bacteria contained “novel structured particles, rich in iron” in small sacs that essentially worked as a compass.
  • These magnetotactic bacteria create tiny crystals made of the iron-rich minerals magnetite or greigite. The crystals help them navigate the changing oxygen levels in the water body they reside in.

What did the study find?

• The three-metre-long sediment core from the southwestern Bay of Bengal consisted mainly of “pale green silty clays,”. Researchers reported finding abundant benthic and planktic foraminifera — single-celled organisms with shells found near the sea bed and free-floating in water.
• At a depth of around 1,000-1,500 m, the Bay of Bengal has a distinctively low oxygen concentration. Analysis of the sediment sample confirmed fluctuations in the monsoon took place as the scientists found particles of magnetic minerals from the two distinct geological periods.
• The rivers Godavari, Mahanadi, Ganga-Brahmaputra, Cauvery, and Penner, which empty into the Bay of Bengal, played a crucial role in the formation of the magnetofossils.
• The nutrient-rich sediment carried in by these rivers provided a sufficient supply of reactive iron, which combined with the available organic carbon in the suboxic conditions of the Bay of Bengal to create a favourable environment for the growth of magnetotatic bacteria.
• The freshwater discharge from these rivers along with the other oceanographic processes, like eddy formation, rendered the oxygen content in these waters that isn’t usually found in other low-oxygen zones.
• The scientists also said the presence of the magnetofossils showed that the suboxic conditions of the Bay of Bengal persisted for a long time, allowing the bacteria to thrive.