Applied Geochemistry最新文献

{"title":"Potassium isotope fractionation of potassium-bearing mineral fertilizers and its implications for global potassium cycle","authors":"Shanke Liu ,&nbsp;Benxun Su ,&nbsp;Wenjun Li ,&nbsp;Jianming Liu","doi":"10.1016/j.apgeochem.2025.106343","DOIUrl":"10.1016/j.apgeochem.2025.106343","url":null,"abstract":"<div><div>Potassium (K) isotopes are increasingly recognized as promising tracers for evaluating the impact of anthropogenic activities on the biogeochemical K cycle, particularly given the widespread use of K fertilizers in agriculture to mitigate soil K depletion. Understanding K isotope behavior in soil is essential because soil acts both as a carrier of fertilizers and as a source of K from weathered rocks. In this study, we determined the K isotopic compositions of K-bearing mineral fertilizers (KMFs), which were produced from K-feldspar through artificial hydrothermal alteration, exhibiting physicochemical properties similar to those of soil. The δ⁴¹K values of bulk K in KMFs range from −0.755 ± 0.023 ‰ to −0.095 ± 0.020 ‰. The K isotopic compositions of 0.5 mol/L acid-soluble K are close to those of bulk K in KMFs, in the range of −0.751 ± 0.043 ‰ to −0.103 ± 0.035 ‰. The observation of isotopically heavier water-soluble K compared to bulk sample K confirms the preferential enrichment of heavy K isotopes in aqueous solutions, consistent with observations in weathered rocks. A combined mechanism involving K–O bond-driven and diffusion-mediated K isotope fractionation offers a plausible explanation for the discrepancy between theoretical models and experimental observations. The application of K-bearing fertilizers has the potential to impact δ⁴¹K values in rivers and seas due to interactions among soil, plants, and water. Our findings contribute to a more comprehensive understanding of K cycling in ecosystems.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106343"},"PeriodicalIF":3.1,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143621030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mercury isotope signatures in soils reveal degassing from fault zones on the eastern margin of the Tibetan Plateau","authors":"Lei Zhang ,&nbsp;Lishuang Guo ,&nbsp;Deyang Shi ,&nbsp;Chuang Bao","doi":"10.1016/j.apgeochem.2025.106341","DOIUrl":"10.1016/j.apgeochem.2025.106341","url":null,"abstract":"<div><div>Mercury isotopic fractionations in soils have been widely studied, but the mercury isotopic compositions in soils in earthquake fault zones are poorly understood. Here we investigated the fractionation characteristics of mercury isotopes in soils along the Anninghe-Zemuhe fault zone on the eastern margin of the Tibetan Plateau, Southwest China. The results showed that the δ²⁰²Hg values of soils ranged from −1.23‰ to 0.39‰ with an average of −0.86‰ ± 0.38‰, and the Δ¹⁹⁹Hg values ranged from −0.46‰ to −0.02‰ with an average of −0.27‰ ± 0.12‰ (1SD, n = 22). The Δ¹⁹⁹Hg values in deep soils were more negative than those in surface soils. The fault gouge had a more negative Δ¹⁹⁹Hg value and was different from the geological source with near-zero Δ¹⁹⁹Hg value. The characteristics of mercury isotope variations reveal that mercury-containing gas degasses from terrestrial and geological reservoirs in the Anninghe-Zemuhe fault zone. We demonstrate that mercury isotopes can reveal mercury sources from degassing in soils in active fault zones.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106341"},"PeriodicalIF":3.1,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143580515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Applied geochemistry presents its 2024 excellence-in-review awards","authors":"Zimeng Wang,&nbsp;Philippe Van Cappellen,&nbsp;Yanxin Wang","doi":"10.1016/j.apgeochem.2025.106342","DOIUrl":"10.1016/j.apgeochem.2025.106342","url":null,"abstract":"","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106342"},"PeriodicalIF":3.1,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143715268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deep carbon degassing from strike-slip fault and rift system in India-Asia collision zone: Insights from fluid geochemistry in hydrothermal systems","authors":"Wenbin Zhao ,&nbsp;Zhengfu Guo ,&nbsp;Wenjing Liu ,&nbsp;Antonio Caracausi ,&nbsp;Dario Buttitta ,&nbsp;Yutao Sun ,&nbsp;Jujing Li ,&nbsp;Xiangang Xie ,&nbsp;Chunqing Sun ,&nbsp;Zhifang Xu","doi":"10.1016/j.apgeochem.2025.106340","DOIUrl":"10.1016/j.apgeochem.2025.106340","url":null,"abstract":"<div><div>Degassing of carbon-rich fluids through hydrothermal activities in continental fault systems represents one of the dominant ways within global carbon cycle. Complex phase transitions and geochemical transformations occur during their ascent to the surface, leading to chemical and isotopic composition alterations of fluids. Here, we present a combined dataset of chemical and isotopic data of spring water and bubbling gas samples collected from strike-slip Karakoram fault (KKF) and northern Xaniza rift (NXR) region in southern Tibetan Plateau, aiming to provide comprehensive constrain on the provenance and inventory of carbon-rich fluids in hydrothermal systems. The carbon isotopic compositions of dissolved inorganic carbon (DIC) positively correlate with dissolved values of CO₂, suggesting significant hydrothermal degassing in the system. The initial concentrations and carbon isotopic compositions of pre-degassing DIC, as well as the degrees of degassing, are determined based on the fractionation modeling between gaseous CO₂ and residual DIC. In order to provide a quantitative constraint on the pristine DIC inventory in hydrothermal waters, we conducted an integrated modeling method involving calcite precipitation, hydrothermal degassing, and mixing between deep-sourced carbon and organic matter. The modeling suggests that hydrothermal fluids from the NXR region exhibit slightly higher proportions of endogenic carbon (91.0%–95.9%) but lower contribution of subsurface organic matter (1.5%–6.8%) compared to the KKF region (75.1%–88.1% and 4.6%–24.9%). Our study emphasizes the substantial role of extensional continental rifting in deep carbon degassing through hydrothermal activities within the India-Asia collision zones.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106340"},"PeriodicalIF":3.1,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143593108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Human-induced eutrophication Alters mercury accumulation and speciation in sediments: A comparative analysis of Dianchi and Fuxian Lake, Southwestern China","authors":"Ke Zhang ,&nbsp;Ying Li ,&nbsp;Haiquan Yang","doi":"10.1016/j.apgeochem.2025.106320","DOIUrl":"10.1016/j.apgeochem.2025.106320","url":null,"abstract":"<div><div>Lake sediments have served as essential reservoirs and sinks for mercury (Hg), providing critical historical records of Hg deposition. However, insufficient research on the accumulation patterns of sedimentary Hg in lakes with diverse trophic states and depositional environments has posed a significant barrier to advancing our understanding of long-term environmental impacts of Hg deposition. This study examined historical trends in Hg concentrations and changes in Hg speciation within sediment cores from two ecologically contrasting lakes on the Yunnan-Guizhou Plateau, China: Dianchi Lake (shallow, hypereutrophic) and Fuxian Lake (deep, oligotrophic). The results showed that Hg concentrations and accumulation rates in all four sediment cores have accelerated since the 1980s, with average Hg concentrations in Dianchi Lake (583 ppb in DC1 and 211 ppb in DC4) significantly higher than those in Fuxian Lake (132 ppb in FX1 and 96 ppb in FX2). Mercury speciation analysis revealed that higher primary productivity in Dianchi Lake favored Hg-organic matter (Hg-OM) complexes, while prolonged anaerobic conditions and lower primary productivity in Fuxian Lake promoted the formation of Hg sulfide (HgS). Strong positive correlations between Hg, total organic carbon (TOC), and total nitrogen (TN) highlighted the pivotal role of organic matter in Hg accumulation and retention. Additionally, C/N and δ¹³C analyses indicated that organic matter in Dianchi Lake originated from a mix of endogenous, exogenous, and anthropogenic sources, whereas it remained primarily endogenous in Fuxian Lake. The synchronous increase in both Hg concentrations and Hg/TOC ratios observed in the DC1 sediment core demonstrated the significant influence of anthropogenic eutrophication on Hg enrichment. In contrast, this effect was less pronounced in the DC4 core, where Hg speciation analysis revealed HgS as the dominant species in surface sediments. These findings highlight the critical role of lake eutrophication and its induced environmental changes in governing Hg speciation and accumulation in lacustrine sediments. This study emphasizes the need to incorporate lake trophic status evaluation and sediment matrix characterization as essential methodological prerequisites when interpreting lacustrine sediment records for reconstructing historical Hg contamination patterns and predicting bioavailability-related ecological risks.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"182 ","pages":"Article 106320"},"PeriodicalIF":3.1,"publicationDate":"2025-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry and mineralogy of the late Neogene alkaline megalake sediments in the Qaidam Basin (China): Implications for provenance, tectonics, paleoclimate, paleoenvironment and organic matter accumulation","authors":"Jinqi Qiao ,&nbsp;Qingyong Luo ,&nbsp;Xianglu Tang ,&nbsp;Dandan Wang ,&nbsp;Imran Khan ,&nbsp;Ludmila Kopaevich","doi":"10.1016/j.apgeochem.2025.106339","DOIUrl":"10.1016/j.apgeochem.2025.106339","url":null,"abstract":"<div><div>The late Neogene is widely regarded as a suitable analogy for future climate scenarios, but the paleoclimatic conditions of this period on the Qinghai-Tibet Plateau remain poorly understood. This study investigates the mineralogical composition and elemental geochemistry of 24 shale samples from two wells in the Yiliping Depression of the Qaidam Basin to reconstruct the paleodepositional conditions of the sediments and the late Neogene paleoclimate conditions. The results indicate that the chemical composition of the late Neogene alkaline lacustrine sediments was little affected by sediment recycling, sorting, diagenesis and metasomatism. Provenance analysis indicates a predominantly felsic source with minor contributions from intermediate volcanic rocks, formed under a tectonic setting similar to continental island arc tectonic settings in geochemistry. Paleoclimate reconstructions reveal consistently arid and cold conditions on the Qinghai-Tibet Plateau, characterized by weak chemical weathering. These climatic conditions were colder than those achieved in most contemporaneous regions globally, with a distinct cooling trend from the late Neogene to the Pleistocene. The deposition occurred predominantly in hypersaline environments, with localized transitions to brackish conditions. The redox conditions of the water column varied spatially, i.e., oxic waters dominated in the central depression (the H 1 well area), while the margins of the depression (the Y 3 well area) experienced fluctuations between oxic to anoxic conditions. The primary paleoproductivity in the Y 3 well exhibited similarities to that in the Holocene lakes of Peru and Brazil, whereas the H 1 well showed resemblances to most marine sediments. Notably, the primary paleoproductivity of the studied samples was lower than that of typical upwelling systems. Organic matter preservation was principally controlled by depositional conditions, with little effects from primary paleoproductivity and sedimentation rate/detrital input. This work provides valuable insights into the late Neogene climate dynamics on the Qinghai-Tibet Plateau and enhances the understanding of the formation of microbial gas source rocks.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106339"},"PeriodicalIF":3.1,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143580465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An experimental and modeling study of CaCO3 nucleation and inhibition by PAPEMP under a regime of increasing oversaturation with implications for crystallization and scale formation","authors":"Amit G. Reiss,&nbsp;Xin Wang,&nbsp;Yuqing Ye,&nbsp;Amy T. Kan,&nbsp;Mason B. Tomson","doi":"10.1016/j.apgeochem.2025.106322","DOIUrl":"10.1016/j.apgeochem.2025.106322","url":null,"abstract":"<div><div>Rising saturation causes nucleation in natural and engineered environments. As the saturation increases, nucleation begins, forming a scale that is detrimental to energy production, desalination, and other industrial procedures. Inhibitor addition for scale prevention is a common practice with significant economic and environmental costs. Traditional experiments to determine induction times (<em>t</em>_<em>ind</em>) and evaluate inhibitor efficiency are performed under constant oversaturation. Similarly, constant oversaturation is used in both the empirical and the classical nucleation theory modeling schemes used for scale prediction. Subsequently, experiments and models do not address the dynamic nature of oversaturation increase during energy production.</div><div>We developed an experimental system for quantitative investigation of nucleation kinetics under a regime of dynamic oversaturation and a simple algorithm for determining <em>t</em>_<em>ind</em> from laser measurements. Using our system, we studied the precipitation kinetics of CaCO₃ minerals at a pH of ∼6.76, ionic strength of I = 1 m, temperature range of 50–90 °C, and varying rates of oversaturation increase (i.e., characteristic times). We quantified the effect of a potent inhibitor (Polyamino Polyether Methylene Phosphonate; PAPEMP) on the <em>t</em>_<em>ind</em> and the forming solid phase. Finally, we show that the characteristic time controls <em>t</em>_<em>ind</em> in systems with rising supersaturation and developed a numerical model that explicitly accounts for this key parameter.</div><div>Here, we present our experimental system, results, and modeling scheme. We show that for a given set of conditions, calcite induction occurs at a similar oversaturation, regardless of the rate at which oversaturation increases. Moreover, we show that PAPEMP retards CaCO₃ nucleation at below ppm levels and that it has a temperature-dependent effect on polymorphism. Lastly, we suggest that expanding existing models such that:</div><div><span><math><mrow><msub><mi>t</mi><mrow><mi>i</mi><mi>n</mi><mi>d</mi></mrow></msub><mo>=</mo><mi>f</mi><mrow><mo>(</mo><mrow><mo>Δ</mo><mi>S</mi><mi>I</mi></mrow><mo>)</mo></mrow><mo>∗</mo><mi>f</mi><mrow><mo>(</mo><msub><mi>t</mi><mrow><mi>i</mi><mi>n</mi><mi>d</mi><mo>,</mo><mi>c</mi><mi>o</mi><mi>n</mi><mi>s</mi><mi>t</mi><mi>a</mi><mi>n</mi><mi>t</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span></div><div>where <em>f(ΔSI)</em> is a function of oversaturation with time and <em>f(t</em>_{<em>ind, constant</em>}<em>)</em> are existing modeling schemes, adequately describe the dynamic nature of oversaturation and show a form of <em>f(ΔSI)</em> that provides an excellent fit with measured <em>t</em>_<em>ind</em>.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106322"},"PeriodicalIF":3.1,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143580467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiometric dating and biodegradation assessment of Light Non-Aqueous Phase Liquids (LNAPL): Results from two case studies","authors":"A. Briganti ,&nbsp;M. Voltaggio ,&nbsp;M. Resitano ,&nbsp;C. Cruz Viggi ,&nbsp;F. Aulenta ,&nbsp;C. Carusi ,&nbsp;E. Rainaldi","doi":"10.1016/j.apgeochem.2025.106334","DOIUrl":"10.1016/j.apgeochem.2025.106334","url":null,"abstract":"<div><div>This study introduces a comprehensive methodology that integrates radiometric dating with gas chromatographic (GC) analyses of light non-aqueous phase liquids (LNAPL) recovered from monitoring wells at different filling stations. The aim is to evaluate the temporal evolution of LNAPLs in two distinct scenarios: natural attenuation (at site 1) and ongoing remediation activities (at site 2). The study period spans one year and four months, from June 2020 to October 2021. Throughout this time frame, the study monitored the progress of petroleum hydrocarbon biodegradation by analysing selected compounds: Total Petroleum Hydrocarbons (TPH), Σ <em>n</em>-alkanes (C₁₃ to C₁₈), Σ isoprenoids (C₁₅ to C₂₀), C₁₇/Pristane and C₁₈/Phytane ratios, and a specific biodegradation diagnostic index. The age determination provided reliable results for a single-point model release scenario (site 1). However, at site 2, where multiple LNAPL spills occurred, the age determination resulted in only an apparent age, due to the mixing of different fluids. Nevertheless, the unlike spatial distribution of the fluids offers some chances to estimate the age of the end members. The trend of the biodegradation in LNAPLs recovered from the two sites seems similar, pointing to a nearly complete removal of isoprenoids, independent of the initial values and whether or not there is an active remediation process. The main difference between the sites is the apparent tendency to the reduction of the heaviest (TPH) and more persistent compounds (such as pristane and phytane), probably triggered by the electrokinetic oxidation system taking place in the second site. The importance of these initial experimental findings lies in their ability to evaluate the site-specific response to pollutants, thereby enhancing the effectiveness of remediation efforts over time.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106334"},"PeriodicalIF":3.1,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143621032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Determination of CO2 and DIC in high-CO2 waters: An application for the analysis of coal mine waters","authors":"Dorothy J. Vesper ,&nbsp;Charles A. Cravotta III ,&nbsp;Lili Lei ,&nbsp;Morgan Wallace ,&nbsp;Camille R. Schaffer","doi":"10.1016/j.apgeochem.2025.106336","DOIUrl":"10.1016/j.apgeochem.2025.106336","url":null,"abstract":"<div><div>The impact of sulfuric-acid weathering on the global carbon cycle is increasingly being recognized as important in both recent and deep time estimates yet remains poorly constrained. Global-scale estimates of CO₂ fluxes are hampered by the lack of data, especially for acidic waters. Mining-impacted groundwaters and associated discharges, which can be acidic and contain CO₂ orders of magnitude greater than atmospheric equilibrium, are chemically unstable at the Earth surface and are often difficult to sample and accurately analyze. The direct CO₂ method used herein is accurate and precise with holding times up to 25 days. This modified method allows for the determination of CO₂ and DIC in samples lacking measurable alkalinity or having high CO₂ pressures; these samples may otherwise be excluded from estimates of regional carbon fluxes. To demonstrate the method, natural and CO₂-treated mine waters with pHs ranging from 3.1 to 7.1 were sampled and found to contain between 2 and 13 mM CO₂ (88–572 mg CO₂/L, 24–154 mg C/L) and 2–21 mM dissolved inorganic carbon, DIC (24–252 mg C/L). In comparison to standard DIC estimation methods, the direct method for analyzing CO₂ and determining corresponding concentrations of DIC is more accurate and reproducible over holding times of several weeks for water samples containing low-to-high CO₂ and with acidic-to-circumneutral pH.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"183 ","pages":"Article 106336"},"PeriodicalIF":3.1,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143628109","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A 3.5-year rainfall isotope records from northwestern Madagascar featuring 17Oexcess and implication for paleoclimate research","authors":"Ny Riavo G. Voarintsoa","doi":"10.1016/j.apgeochem.2025.106335","DOIUrl":"10.1016/j.apgeochem.2025.106335","url":null,"abstract":"<div><div>The lack of modern rainfall stable isotope datasets can leave a knowledge gap in paleoclimate reconstructions using climate sensitive archivers like stalagmites. This is the case of the growing number of paleoclimate records from Anjohibe Cave, where no local rainfall data has been available. This paper reports the first modern rainfall stable isotopes of hydrogen (δ²H and <em>d-</em>excess) and oxygen (δ¹⁷O and δ¹⁸O), highlighting a novel ¹⁷O_excess proxy, spanning 3.5 years of collection from Mahajanga, the closest city of Anjohibe. These data are compared to the only prior existing rainfall isotope data from Madagascar, which was collected from the capital, Antananarivo. Interpretation of the results was helped with model simulations using ERA5T reanalysis and HYSPLIT back trajectory models. Overall, the rainfall data provide better insights on hydrological processes in Mahajanga, including a better constrain on the latitudinal migration of the Inter-Tropical Convergence Zone (ITCZ) and its impact on the kinetic and equilibrium isotopic effect that is best observed in both <em>d</em>-excess and ¹⁷O_excess.</div><div>Results show that rainfall δ¹⁸O (ranging between −7.9 and + 3.9‰, vs. VSMOW) and δ²H (ranging between −49.8 and + 19.7 ‰, vs. VSMOW) from Mahajanga fit within the Global Meteoric Water Line, and they are best explained by the amount effect. However, both <em>d</em>-excess and ¹⁷O_excess are kinetically affected by evaporation for months receiving &lt;1000 mm of rainfall. These months represents the onset and termination of a rainy summer season, when the ITCZ is positioned further north. Above 1000 mm, both values plateaued at ∼15 ‰ and at ∼20 per meg, respectively, regardless of the amount. These values seem to represent the regional equilibrium value for <em>d</em>-excess and ¹⁷O_excess in Mahajanga, when the air is moist during the southward visit of the ITCZ. It is also noted that Mahajanga ¹⁷O_excess values are at the lower spectrum relative to the global ¹⁷O_excess values (20–30 per meg), which are currently biased toward more northern hemisphere datasets. Anjohibe Cave drip waters (varying between −5.6 and −2.1‰ vs. VSMOW for δ¹⁸O and between −33.9 and −8.3 ‰ vs. VSMOW for δ²H), on the other hand, reflect more mixing of the rainfall values due to epikarst storage effects. Calculation of the isotopic fractionation factor between stalagmite and the drip waters in Anjohibe Cave also suggests a good fit with the global fractionation value, 1000ln¹⁸α = 16.89 ± 0.62 × 10³/T(K) – 27.41 ± 2.14, and serves as an excellent motivation to develop future ¹⁷O_excess records from stalagmites in the region.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"184 ","pages":"Article 106335"},"PeriodicalIF":3.1,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}