Where the river turns old: Urbanized deltas imprint a fossil signature on black carbon exported to the ocean

Where the river turns old: Urbanized deltas imprint a fossil signature on black carbon exported to the ocean | 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 Where the river turns old: Urbanized deltas imprint a fossil signature on black carbon exported to the ocean Gan Zhang, Xin Yi, Xiaofei Geng, Guangcai Zhong, Bolong Zhang, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8021964/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Black carbon (BC) from biomass burning is a key component of the global carbon cycle, and radiocarbon (14C) age of riverine BC is used to constrain its terrestrial residence time. However, whether 14C-free BC from fossil fuel combustion significantly contributes to riverine BC and biases these ages remains arguable. Here, we track dissolved and particulate BC (DBC, PBC) along a river continuum from forested headwaters to the urbanized estuary. Such a gradient allowed us to distinguish fossil BC from pre-aged biomass-derived BC. We estimate that fossil sources contribute 18 ± 3% of DBC and 24 ± 6% of PBC in the urban zone, causing the apparent 14C ages to be older by 1,475–1,972 years for DBC and 1,619–2,877 years for PBC. The aging effect on DBC was primarily linked to less-condensed aromatics, while that of PBC—especially pronounced during the dry season—was driven by highly condensed aromatics. Our findings reveal that urbanized deltas are critical conduits of fossil BC to the ocean, necessitating land-use contextualized assessments when applying riverine 14C ages to estimate terrestrial residence times. Earth and environmental sciences/Biogeochemistry/Carbon cycle Earth and environmental sciences/Environmental sciences/Environmental impact riverine black carbon carbon cycle benzene polycarboxylic acids radiocarbon age urban fossil sources Full Text Additional Declarations There is NO Competing Interest. Supplementary Files SIsubmit1.pdf Supporting Information Cite Share Download PDF Status: Under Review 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. 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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-8021964","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":546509688,"identity":"f9fdd9bf-932b-4dc6-8d9d-89bbefae19f9","order_by":0,"name":"Gan 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