Determining rainfall seasonality from high-resolution carbon isotope profiles in evergreen wood and charcoal

Determining rainfall seasonality from high-resolution carbon isotope profiles in evergreen wood and charcoal | 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 Determining rainfall seasonality from high-resolution carbon isotope profiles in evergreen wood and charcoal Gemma Poretti, Alisoun House, Justin Pargeter, Vincent Hare This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7132671/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 Rainfall seasonality is a critical parameter in palaeoclimate reconstructions, both for improving climate models, and understanding past human-environment relationships. One promising approach is to infer rainfall seasonality from sub-annual variations in the stable carbon isotope composition (δ¹³C) of evergreen growth rings. Here, we test this proxy using modern samples of Protea (angiosperm) and Podocarpus (gymnosperm) collected across South Africa’s three major rainfall zones. High-resolution δ¹³C profiles from wood show consistent seasonal patterns that broadly correspond to rainfall seasonality, while comparable – though dampened – signals are retained in charcoal. We further show that isotopic boundaries can substitute for visible ring increments, enabling proxy application even when ring structure is absent, as is often the case in archaeological material. Well-dated charcoal fragments from Boomplaas Cave, an archaeological site in the Southern Cape, indicate the presence of winter-rainfall in the Last Glacial Maximum, aligning with climate models and other proxies. The results support the use of a new proxy for rainfall seasonality in evergreen wood and charcoal, but also highlight the need for local calibration, especially under water stressed conditions. This approach offers new potential for reconstructing seasonal rainfall from archaeological charcoal. Earth and environmental sciences/Climate sciences/Palaeoclimate Earth and environmental sciences/Climate sciences/Biogeochemistry/Carbon cycle Full Text Additional Declarations There is NO Competing Interest. Supplementary Files RS459.pdf Reporting Summary 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. 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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-7132671","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":494705228,"identity":"fd274ff1-d0f0-41de-8427-2ca9e7a190c7","order_by":0,"name":"Gemma Poretti","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA10lEQVRIiWNgGAWjYFADZuYDQFJChmgNEjzMbAlgmgQtDDwGIAZhLfLu3WkPPu6xqbNn5/n86kaNBQ8D++GjG/BpMTxzdrvhjGdpQIfxbrPOOQayLS3tBl4tM3K3SfMcOAzWYpzDBtQiwWOGX8v8tyAt/4FaeJ4Z5/wjQou8BC9IywGQFubHuW1EaDHgyQX65UCyZM9hNjPm3D4JHjZCfpFvP7vtwYcDdvzs/Ycff875VifHz374GH5bDjCwwdhsEmASn3KwLQ0INcwfCKkeBaNgFIyCkQkAkKRBhI+AVFkAAAAASUVORK5CYII=","orcid":"","institution":"University of Cape Town","correspondingAuthor":true,"prefix":"","firstName":"Gemma","middleName":"","lastName":"Poretti","suffix":""},{"id":494705229,"identity":"2d2acf2f-883d-424f-873b-c8e3502404dc","order_by":1,"name":"Alisoun House","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Alisoun","middleName":"","lastName":"House","suffix":""},{"id":494705230,"identity":"089b5ae5-8860-490d-a11d-0aa5c561f711","order_by":2,"name":"Justin Pargeter","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Justin","middleName":"","lastName":"Pargeter","suffix":""},{"id":494705231,"identity":"4d295554-bc09-467d-a3cc-182a52b1d325","order_by":3,"name":"Vincent Hare","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Vincent","middleName":"","lastName":"Hare","suffix":""}],"badges":[],"createdAt":"2025-07-15 16:32:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7132671/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7132671/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88578670,"identity":"c73c9930-e584-4c9a-ade6-7948bb1cd0b1","added_by":"auto","created_at":"2025-08-08 02:26:00","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6413392,"visible":true,"origin":"","legend":"Article File","description":"","filename":"PorettiCEEmanuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7132671/v1_covered_5b03a1c9-befd-4e3d-9340-7d63a70d49ed.pdf"},{"id":88577651,"identity":"a26461f9-0104-4c84-bb8e-6507e466fd2e","added_by":"auto","created_at":"2025-08-08 02:17:52","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4359436,"visible":true,"origin":"","legend":"Reporting Summary","description":"","filename":"RS459.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7132671/v1/458da860792b47d8bc5fc818.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Determining rainfall seasonality from high-resolution carbon isotope profiles in evergreen wood and charcoal","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7132671/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7132671/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Rainfall seasonality is a critical parameter in palaeoclimate reconstructions, both for improving climate models, and understanding past human-environment relationships. 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