Deep fossil freshwater in coastal Bangladesh

Deep fossil freshwater in coastal Bangladesh | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Deep fossil freshwater in coastal Bangladesh Huy Le, Kerry Key, Michael Steckler, Nafis Sazeed, Mark Person, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5290787/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Nov, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Aquifer overexploitation and saltwater intrusion threaten freshwater resources in coastal regions worldwide 1,2 . In Bangladesh, arsenic contamination and droughts further impact shallow freshwater availability in parts of the country 3,4 . In the coastal zone, much of the shallow groundwater is saline while availability of deeper fresh groundwater is poorly understood. Here, we utilize deep-sensing magnetotelluric soundings to image the contrast in electrical resistivity between resistive fresh and conductive saline groundwater along a 120 km profile adjacent to the Pusur River in the Ganges-Brahmaputra Delta, Bangladesh. Our data reveal two distinct deep freshwater bodies: a seaward-dipping wedge extending to 600 m depth in the northern transect, and a smaller fresh-to-brackish zone located near the coastline. We propose that these aquifers are remnants of preserved Pleistocene groundwater, supported by 14C ages up to 30,000 years 5 . An intervening high-salinity zone between the two freshwater bodies likely formed by Ganges paleovalley incision during the last glacial maximum, followed by marine transgression and deposition of conductive muddy sediments. Our results provide a framework for location and distribution of fossil groundwater reserves in Bangladesh’s riverine coastline, offering a potential resource for this water-stressed region. The interplay between past sea-level cycles, sedimentation, and hydrogeological processes may also control the distribution of deep fresh groundwater at other deltas. Earth and environmental sciences/Solid Earth sciences/Geophysics Earth and environmental sciences/Solid Earth sciences/Hydrogeology Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Published Journal Publication published 28 Nov, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5290787","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":369230162,"identity":"3350185a-6523-417f-b861-cb3676ad5a66","order_by":0,"name":"Huy 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In Bangladesh, arsenic contamination and droughts further impact shallow freshwater availability in parts of the country\u003csup\u003e3,4\u003c/sup\u003e. In the coastal zone, much of the shallow groundwater is saline while availability of deeper fresh groundwater is poorly understood. Here, we utilize deep-sensing magnetotelluric soundings to image the contrast in electrical resistivity between resistive fresh and conductive saline groundwater along a 120 km profile adjacent to the Pusur River in the Ganges-Brahmaputra Delta, Bangladesh. Our data reveal two distinct deep freshwater bodies: a seaward-dipping wedge extending to 600 m depth in the northern transect, and a smaller fresh-to-brackish zone located near the coastline. We propose that these aquifers are remnants of preserved Pleistocene groundwater, supported by 14C ages up to 30,000 years\u003csup\u003e5\u003c/sup\u003e. An intervening high-salinity zone between the two freshwater bodies likely formed by Ganges paleovalley incision during the last glacial maximum, followed by marine transgression and deposition of conductive muddy sediments. Our results provide a framework for location and distribution of fossil groundwater reserves in Bangladesh’s riverine coastline, offering a potential resource for this water-stressed region. 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