Scientists have recently made a groundbreaking discovery by uncovering colossal magnetofossils in the Bay of Bengal. These are sizable magnetic crystals left behind by microorganisms found in sediment dating back 50,000 years. The findings mark the most recent giant magnetofossils ever documented.
Magnetotactic bacteria produce tiny crystals made of magnetite or greigite, which they use to navigate the changing conditions of water columns or saturated sediment. When these microorganisms die, the crystals remain as magnetofossils, vital in recording magnetic signatures in sediment layers and providing valuable insights into past environmental changes.
Researchers from the CSIR-National Institute of Oceanography in Goa made this discovery by extracting a sediment core nearly 3 metres long from the southwestern Bay of Bengal. The region is continuously replenished by sediment-laden waters from the Godavari, Krishna, and Penner rivers, and the core consists mainly of silty clays, revealing a diverse array of foraminifera - minute single-celled organisms encased in shells - both benthic (living on the seafloor) and planktic (drifting in water).
Through careful magnetic analysis and electron microscopy of core samples, the team identified a range of giant magnetofossils with unique shapes, including needle, spindle, bullet, and spearhead morphologies. These magnetofossils were found ubiquitously throughout the sediment core, spanning a time frame of the last 42,700 years.
The researchers suggest that the influx of reactive iron and organic carbon from riverine sources into the oxygen-depleted waters of the Bay of Bengal created favourable conditions for the organisms responsible for producing giant magnetofossils. Bioavailable iron and organic carbon likely acted as a nutrient source, promoting the growth of these microorganisms.
The authors emphasise that as long as such favourable environmental conditions persist, the organisms responsible for generating giant magnetofossils will continue to thrive, leaving their mark on the sedimentary record of the Bay of Bengal.
Magnetofossils are the remains of magnetic particles that were created by magnetotactic bacteria. These bacteria are organisms that align themselves with the Earth's magnetic field. Magnetotactic bacteria have the unique ability to biomineralise extremely small magnetic crystals, which are made of magnetite or greigite. These magnetic crystals aid the bacteria in navigating changing redox conditions in the water column or saturated sediment. Magnetofossils have emerged as a promising tool for studying paleoenvironmental change and the history of the Earth's geomagnetic field. Scientists have even discovered giant magnetofossils in sediments from approximately 56 to 46 million years ago.
