Magnetofossils in the Northern Indian Ocean

Magnetofossils are potential recorder of paleoenvironmental conditions that control the abundance and diversity of magnetotactic bacteria and giant iron biomineralizing organisms in marine sediments. In this study, we conducted suite of rock magnetic and transmission electron microscope analyses on marine (modern, fossil) sediments deposited during different climatic events to characterize the magnetofossil contribution and establish the magnetofossil records in the diverse regions of the northern Indian Ocean. First-order reversal curve diagrams of the representative samples confirmed the presence of non-interacting single domain magnetofossils. High-resolution electron microscope observations results indicate that conventional and giant type magnetofossils are more abundant, widespread, and spatially distributed within northern Indian Ocean. Electron diffraction and energy dispersive spectrometry confirmed their distinctive morphologies and magnetite crystal structure. Magnetic hysteresis and isothermal remanent magnetization curves, first-order reversal curve diagrams, and low-temperature magnetic measurements revealed large variations in magnetic properties of magnetofossils (conventional and giant), which mainly relate to the specific region, climatic events, and time periods. Our findings on the existence of conventional and giant magnetofossils, their abundance, morphological signatures and bulk magnetic measurements expands our understanding of modern and paleoenvironmental conditions (oxygenation, productivity, weathering and sedimentation patterns, nutrient supply, `influx of reactive iron, organic carbon content) that controlled the growth and preservation of magnetofossils in the modern and ancient sediments in the northern Indian Ocean.