Hyderabad: Sediments lying on the floor of the Bay of Bengal near the Andaman Islands may appear local, but scientists have found that much of this mud and sand actually began its journey in the Himalayas, travelling thousands of kilometres through one of the world’s largest river systems before settling deep beneath the ocean.A team from the CSIR-National Geophysical Research Institute (NGRI), Hyderabad, and the CSIR-National Institute of Oceanography (NIO), Goa, studied samples of seabed material collected at various depths, ranging from shallow waters near the islands at 110 metres to the deep ocean floor at 3,177 metres.The study’s findings were published in a recent edition of the ‘Journal of Earth System Science’ in a research paper titled ‘Provenance and weathering of surface sediments along an Andaman-Bay of Bengal depth transect.’“This is interesting because one might naturally expect the sediments closest to the Andaman Islands to be dominated by material eroded from those islands. Instead, the evidence we found indicates a strong Himalayan sediment signature even in locations close to the Andaman margin,” said Pavan Miriyala, one of the researchers from CSIR-NGRI.By analysing the chemical composition, particle size and clay mineral content of the samples, the researchers found that deeper sediments contained more aluminium and potassium and less silica, indicating that the material becomes finer with increasing depth and distance from shore.When compared with sediments from known geological sources, the samples showed a much stronger resemblance to material carried by the Ganga-Brahmaputra river system than to rocks from the Andaman Islands.The reason, researchers say, lies in the enormous volume of sediment transported annually by the Ganga and Brahmaputra rivers, estimated at around 1,000 million tonnes. Monsoon-driven currents and ocean circulation spread this fine Himalayan material across the Bay of Bengal, allowing it to travel vast distances before settling on the seabed.The study also highlights the role of the Andaman Trench, a subduction zone where one tectonic plate moves beneath another. Over geological timescales, sediments from the Bengal Fan are drawn toward the trench and accumulated near the islands, reinforcing the Himalayan signature even in sediments found close to the Andaman coast.The findings show that the seafloor around the Andaman Islands is shaped not only by local geological processes but also by events occurring thousands of kilometres away. Understanding where seabed sediments originate helps scientists reconstruct ocean circulation patterns, monsoon behaviour and the geological evolution of the region, all of which influence marine ecosystems and nutrient distribution.One sample from the deepest location, however, stood out for being coarser and compositionally distinct, which researchers believe could be linked to underwater landslides near the trench. They suggest that wider sampling and more advanced geochemical analyses could provide an even clearer picture of sediment transport across the region.Quote“Our study highlights an important source-to-sink connection: What happens in the Himalayas can leave a geological signature thousands of kilometres away in the Bay of Bengal and near the Andaman margin. Understanding these sediment pathways is important not only for reconstructing the geological history of the region, but also for interpreting marine sediment records used to study past changes in climate, monsoon activity, erosion and tectonic processes.” — Pavan Miriyala, researcher
