Geochimica et Cosmochimica Acta最新文献

{"title":"Diffusion of Eu, Ce and Lu in orthopyroxene","authors":"Maria A. Dias, Ralf Dohmen, Nils Hartmann","doi":"10.1016/j.gca.2025.09.038","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.038","url":null,"abstract":"We have measured diffusion coefficients for Eu, Lu and Ce in single crystal orthopyroxene (opx) using thin film diffusion couples produced by pulsed laser deposition. The diffusion experiments were conducted in CO-CO<ce:inf loc=\"post\">2</ce:inf> vertical gas mixing furnaces in the temperature range of <ce:italic>T</ce:italic> = 950–1100 °C and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> = 10<ce:sup loc=\"post\">−7</ce:sup> to 10<ce:sup loc=\"post\">−11</ce:sup> Pa. The microstructure of a subset of samples was investigated by scanning transmission electron microscopy (STEM) and backscattered secondary electron microscopy (BSE) in lamellae prepared using a focused ion beam – scanning electron microscope (FIB-SEM). The results were used for the interpretation of depth profiles acquired using time of flight – secondary ion mass spectrometry. This analytical approach allowed to identify low-concentration regions of the diffusion profiles, unaffected by artefacts, that could be fit to determine diffusion coefficients of Eu, Lu, and Ce. We found faster diffusion rates for Lu, Eu and Ce than previously reported for orthopyroxene and diopside. The obtained activation energies are comparable to previous studies of Lu diffusion in diopside and Nd diffusion in opx, along the iron-wüstite buffer. Our results suggest that Lu diffusion is seemingly dependent on Lu concentration and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2,</ce:inf> indicating a different diffusion mechanism than for Eu and Ce. Assuming that Eu is mostly in the trivalent state, we observed a trend of decreasing diffusivity with increasing ionic radii. The experimental data defines the following Arrhenius equations for Lu, Ce and Eu:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"17 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145229095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Silicon isotope variations of ocean island basalts: the effect of recycled materials on Si isotopes in the mantle","authors":"Yu-Chao Lin, Hui-Min Yu, Matthew G. Jackson, Elisabeth Widom, David Kuentz, Fang Huang","doi":"10.1016/j.gca.2025.09.032","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.032","url":null,"abstract":"To investigate the effect of recycled slab materials on the Si isotopes of the mantle, we analyzed the Si isotopes of 80 ocean island basalts (OIB) from five hotspots around the world, including Azores, Iceland, Samoa, St. Helena, and Cook-Austral Islands. These samples have a wide range of radiogenic isotope signatures, representing various mantle sources including EM Ⅱ (enriched mantle Ⅱ) and HIMU (high μ, μ = <ce:sup loc=\"post\">238</ce:sup>U/<ce:sup loc=\"post\">204</ce:sup>Pb). After evaluating the influences of chemical weathering, seawater alteration, partial melting, and fractional crystallization on Si isotopes in these OIB, which are negligible, the Si isotopic characteristics of OIB could reflect their original mantle compositions. The δ<ce:sup loc=\"post\">30</ce:sup>Si of EM Ⅱ-type samples range from −0.37 ± 0.03 ‰ to −0.17 ± 0.05 ‰ with an average of −0.28 ± 0.08 ‰ (2SD, N = 27), and HIMU-type samples range from −0.39 ± 0.05 ‰ to −0.22 ± 0.05 ‰ with an average of −0.29 ± 0.09 ‰ (2SD, N = 37). Additionally, we employed the parameter Δ<ce:sup loc=\"post\">30</ce:sup>Si (defined as δ<ce:sup loc=\"post\">30</ce:sup>Si<ce:inf loc=\"post\">sample</ce:inf> – δ<ce:sup loc=\"post\">30</ce:sup>Si<ce:inf loc=\"post\">Igneous Array</ce:inf>), which effectively corrects for magmatic differentiation processes while preserving source-related Si isotopic signatures. All analyzed samples exhibit Δ<ce:sup loc=\"post\">30</ce:sup>Si values below 0.10 ‰, further demonstrating the limited Si isotopic variation.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"32 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145229096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zircon records carbonatite fractional crystallization and hydrothermal metasomatism during REE mineralization","authors":"Yan Yu, Yang Li, Lan Yang, Li-Guang Wu, Xian-Hua Li","doi":"10.1016/j.gca.2025.09.035","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.035","url":null,"abstract":"Carbonatites and associated alkali fluids are vital for the enrichment of rare earth elements (REE). However, genesis of the Bayan Obo REE deposit remains debated after a century of exploration and study, mainly due to an apparent conflict between the Mesoproterozoic carbonatites dated at ∼1.3 Ga and a dominant Paleozoic REE mineralization age peaking at ∼0.43 Ga, and the inability of two commonly assumed ore-forming fluids (i.e., subduction-derived fluids and metamorphic fluids) to mobilize/transport REE. Here we address this paradox by conducting petrographic, Hf concentration and oxygen isotope studies using zircon grains from Bayan Obo carbonatites dated at ∼1.32 Ga and ∼0.43 Ga (<ce:cross-ref ref>Li et al., 2025</ce:cross-ref>, Science Advances). Zircons from the Mesoproterozoic carbonatites are weakly zoned with a mean δ<ce:sup loc=\"post\">18</ce:sup>O value of 4.9 ± 0.4 ‰ (2SD), while intensively altered zircons from a coeval carbonatite dike bear chaotic textures with an elevated δ<ce:sup loc=\"post\">18</ce:sup>O value of 7.0 ± 0.9 ‰ (2SD). Zircons from the Paleozoic carbonatites exhibit extreme δ<ce:sup loc=\"post\">18</ce:sup>O variability ranging from 5 ‰ to 11 ‰, which is correlated with zircon HfO<ce:inf loc=\"post\">2</ce:inf> concentrations (1.6–4.7 wt%) and the compositional transition of hosting carbonatites from Ca-rich to Mg-rich. We infer that these zircons were crystallized from highly fractionated carbonatitic melts. For the Paleozoic carbonatites, the presence of alkali- and REE-rich brines/fluids is evidenced by abundant riebeckite and monazite inclusions hosted in zircon rims. In line with the fenite alteration zones associated with the Paleozoic carbonatites, and the dominant mineralization age of ∼0.43 Ga, our results highlight that alkali brines/fluids derived from the Paleozoic carbonatites are critical for generating the world’s largest REE deposit.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"48 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145311745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Partitioning of Nb and Ta between rutile and carbonatitic melts: Implications for genesis of arc magmas and carbon cycle at subduction zones","authors":"Wei Chen ,&nbsp;Massimo Tiepolo ,&nbsp;Guo-Liang Zhang","doi":"10.1016/j.gca.2025.09.037","DOIUrl":"10.1016/j.gca.2025.09.037","url":null,"abstract":"<div><div>Carbonatitic melts are crucial media in element transfer at subduction zones, however, their role in Nb/Ta fractionation is unclear. Here we experimentally determined the rutile-carbonatitic melt partition coefficients (D values) of Nb and Ta at 2.5–8.0 GPa and 1000–1300 ℃. The results show that D_Nb ranges from 17 to 79, D_Ta from 39 to 393, and D_Nb/D_Ta from 0.20 to 0.27. D_Nb and D_Ta strongly depend on pressure and temperature, decreasing initially and then increasing as pressure/temperature rises. Conversely, the narrow range of D_Nb/D_Ta suggests that this ratio is insensitive to either pressure or temperature. Using these new partition coefficients, we modeled behaviors of Nb and Ta in carbonatitic melts and residual rutile-bearing eclogites during slab melting. Our results demonstrate that slab melting imparts lower Nb/Ta ratios to rutile-bearing eclogites and higher Nb/Ta ratios to carbonatitic melts than their protoliths. Consequently, deeply subducted rutile-bearing eclogites cannot serve as a superchondritic Nb/Ta reservoir that could explain Earth’s Nb paradox. We quantify the contribution of slab-derived carbonatitic melts on the Nb/Ta variations of natural carbonatite assuming that their mantle sources have been impregnated by such melts. The results indicate slab-derived carbonatitic melts explain less than two orders of magnitude of Nb/Ta variation in carbonatites. After fully clarifying the Nb/Ta fractionation in various types of slab-derived liquids, we identify that the mantle source of silica-undersaturated, high Nb/Ta arc magmas is metasomatized by slab-derived carbonatitic melts, while those of silica-saturated magmas are by silicic melts originating from the basaltic part of the slab.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 71-83"},"PeriodicalIF":5.0,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fate of iodate on adsorbed/coprecipitated ferrihydrite-organic matter complexes","authors":"Shilin Zhao ,&nbsp;Junxia Li ,&nbsp;Xianjun Xie ,&nbsp;Yanxin Wang","doi":"10.1016/j.gca.2025.09.034","DOIUrl":"10.1016/j.gca.2025.09.034","url":null,"abstract":"<div><div>The mobility of iodate in soils and sediments is significantly related to the states of iron minerals and natural organic matter (NOM). However, the influences of associated processes (adsorption versus coprecipitation) between iron minerals and NOM on the fate of iodate remain unclear. In this study, the iodate behavior on adsorbed or coprecipitated ferrihydrite (HFO)-humic acid (HA) complexes was investigated through batch experiments under varying conditions (pH, ionic strength, and co-existing anions). Mechanisms insights were obtained using attenuated total reflectance Fourier transform infrared spectroscopy and density functional theory. The results show that compared to pure HFO, iodate adsorption decreases in the presence of adsorbed or coprecipitated HA, due to the reduced inner-sphere adsorption sites occupied by HA. The reduction degree in iodate adsorption is greater for coprecipitated HFO-HA (HFO-cHA) complexes than for adsorbed HFO-HA (HFO-aHA) complexes. The adsorbed iodate is more prone to combine with adsorbed HA to form organic iodine compared to coprecipitated HA. With increasing pH and co-existing anions, the decreasing in iodate adsorption was observed in pure HFO and HFO-aHA/HFO-cHA complexes, but interestingly, the decreased degree in iodate adsorption follows the order of HFO-cHA complexes &gt; pure HFO &gt; HFO-aHA complexes. The dominant outer-sphere species of iodate on the complexes leads to the more sensitive surface of HFO-cHA complexes, and as the coprecipitated HA increases, the percentage of inner-sphere species of iodate was decreasing. Compared to the coprecipitated HA, the adsorbed HA can be more easily dissolved as the pH rising or as co-existing ions replace HA on the adsorption sites. Iodate can sorb and occupy sites vacated by HA desorption. The findings of this study provide new insights to understand the mobilization of soil/sediment iodate, which plays a vital role in the cycling of iodine in nature.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 28-39"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Isolating the light dependence of carbon isotope fractionation in Gephyrocapsa (Emiliania) huxleyi","authors":"Ann Pearson ,&nbsp;Pratigya J. Polissar ,&nbsp;Susan J. Carter ,&nbsp;Elida Kocharian ,&nbsp;Samuel R. Phelps ,&nbsp;Oscar D. Hover ,&nbsp;Raquel P. Reis ,&nbsp;Emily Kuang ,&nbsp;Lorelei M. Wolf","doi":"10.1016/j.gca.2025.09.033","DOIUrl":"10.1016/j.gca.2025.09.033","url":null,"abstract":"<div><div>Estimates of past atmospheric carbon dioxide content (<em>p</em>CO₂) derived from geochemical archives are critical to the advancement of climate science. One of the most frequently used marine proxies is the biological discrimination of stable carbon isotopes (<em>ε</em>_p) recorded in long-chain ketones of the haptophyte algae, a method known as alkenone paleobarometry. In its conventional application, the fractionation of carbon isotopes is assumed to reflect the kinetic isotope effect (KIE) of the carbon-fixing enzyme Rubisco, and the cellular carbon budget is assumed to be governed by the ratio of demand by carbon fixation to diffusive CO₂ supply (demand:supply). Changes in this budget cause variation in the expression of <em>ε</em>_p, with the smallest <em>ε</em>_p values reflecting the highest ratio of demand:supply, i.e., the lowest relative CO₂ concentrations. However, prior work indicates that photosynthetic irradiance also influences expression of <em>ε</em>_p. To isolate the influence of the photosynthetic effect, we cultivated a calcifying strain of <em>Gephyrocapsa</em> (<em>Emiliania</em>) <em>huxleyi</em> in nitrate-limited chemostat culture under conditions of constant growth rate and CO₂ supply, but six different levels of irradiance. The resulting values of <em>ε</em>_p varied between 16 ‰ at photon flux density (PFD) &lt; 50 μmol m⁻² s⁻¹ to 20 ‰ at PFD &gt; 150 μmol m⁻² s⁻¹. The low-light cultures exhibited slightly decreased carbon uptake at steady-state, and as such, the smallest values of <em>ε</em>_p were recorded under the highest in-situ CO₂ concentrations, opposite to <em>ε</em>_p vs. demand:supply expectations. The data are consistent with prior batch-culture studies of <em>G. huxleyi</em> and other <em>Gephyrocapsa</em> strains, suggesting that while those experiments used different cultivation approaches, a light-dependent effect on cell carbon budgets may be universal, perhaps through direct influence on the efficiency of carbon concentrating mechanisms (CCMs). These results point toward future strategies to improve the physiological accuracy of <em>ε</em>_p models and refine <em>p</em>CO₂ reconstructions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 105-115"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218056","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stable carbon isotope fractionation during the transformation of amorphous CaCO3 at low water–solid ratios: impact of humidity and temperature","authors":"Maria P. Asta ,&nbsp;Sarah Bonilla-Correa ,&nbsp;Aurélie Pace ,&nbsp;Martin Dietzel ,&nbsp;Antonio García-Alix ,&nbsp;Torsten Vennemann ,&nbsp;Anders Meibom ,&nbsp;Arthur Adams","doi":"10.1016/j.gca.2025.09.029","DOIUrl":"10.1016/j.gca.2025.09.029","url":null,"abstract":"<div><div>The isotopic composition of carbonates has been widely used as a proxy for reconstructing Earth’s past environmental conditions, which requires the preservation of the isotope composition of the primary precipitate or knowledge about its transformation pathway. In this context, the formation of crystalline carbonates via amorphous precursors has been identified as a common formation process for natural carbonates, where the impact to the isotopic composition of the final CaCO₃ products is insufficiently known to date. This study focusses on the stable carbon isotope fractionation during the transformation of amorphous calcium carbonate (ACC) into crystalline carbonate in the presence/absence of atmospheric CO₂ induced by (i) humidity (from 33 to 95 % RH) at a temperature of 5 and 20 °C and (ii) solid-state transformation of ACC to calcite induced by heating up to 500 °C. During the crystallization of ACC at very low water ratios, induced by humidity, and in the presence of CO₂, δ¹³C values of the solids increased with reaction time, where the crystalline carbonate-ACC enrichment factors (¹³ε_cc−ACC) range between 2.0 and 8.4 ‰ at the final stage. This ¹³ε_cc−ACC evolution reflects the incorporation of ambient CO₂(g) alongside carbonate ions released during ACC dissolution. In contrast, without CO₂(g) the crystalline CaCO₃ almost matches the isotope composition of the ACC (¹³ε_c_c_−ACC = −0.4 ± 0.3 ‰), thus indicating non-significant CO₂ degassing and/or subsequent re-equilibration trend. The solid-state transformation of ACC to calcite during heat-induced dehydration yields a slightly negative enrichment factor (¹³ε_c_alcite_−ACC = −0.8 ± 0.3 ‰) that may reflect carbon isotope fractionation due to rapid recrystallization-rate kinetics. Our results suggest that the carbon isotope compositions of carbonates formed via an amorphous precursor at low water/solid ratios (e.g., in caves, soils or biominerals) may not accurately reflect the original conditions of the carbonate formation, hence paleoenvironmental conditions should be interpreted with care.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 56-70"},"PeriodicalIF":5.0,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantifying the origins of labile estuarine particulate organic matter of varying reactivity using a fatty acid isotope model based on a genetic algorithm","authors":"Tengteng Wang, Han Zhang, Jiachen Li, Nengwang Chen, Lifang Wang, Wei-lei Wang, Jie Liu, Junhui Chen, Jiaheng Shen, Tiantian Tang","doi":"10.1016/j.gca.2025.09.030","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.030","url":null,"abstract":"As a major link between oceanic and terrestrial carbon reservoirs, estuarine particulate organic matter (POM) exhibits highly dynamic molecular and isotope compositions due to intensive mixing and selective decomposition of compounds with a wide range of reactivity. It is thus challenging to quantitatively predict the geochemical fate of estuarine POM, particularly more labile compounds. In this study, we investigated the stable carbon isotope distribution of fatty acids in suspended particles from two subtropical estuaries in southeast China, the Pearl River Estuary and the Zhangjiang Estuary. Three major short-chain fatty acids, 14:0, 16:0, and 18:0 show progressive but varied increases in δ<ce:sup loc=\"post\">13</ce:sup>C values along the estuaries as a response to the dissolved inorganic carbon δ<ce:sup loc=\"post\">13</ce:sup>C gradient. Accordingly, a lability model using genetic algorithm parameter optimization was established based on the isotope mass balance of individual fatty acids, which quantified POM from three origins with distinctive molecular composition and isotopic values: locally produced phytoplankton, decomposed phytoplankton, and terrestrial materials. A dominant contribution of phytoplankton and its decomposed products ranging from 63 % to 99 % was found higher in regions with more phytoplankton biomass. Relatively higher terrestrial input was found in upstream estuaries as well as areas influenced by tidal exchange with mangroves. The modeled fatty acid composition of decomposed phytoplankton can be best described by a first-order decomposition reaction. Elevated labile POM from phytoplankton may exacerbate coastal hypoxia and reduce burial efficiency in areas with amplified anthropogenic perturbation, whereas more recalcitrant POM exported from mangroves favors long-term preservation in the adjacent coastal ocean.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"126 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145311746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Linking source-to-sink processes, organic matter composition, and oxygen consumption on a shallow passive margin shelf sustained by small mountainous rivers","authors":"Yu-Shih Lin ,&nbsp;Chih-Lin Wei ,&nbsp;Yuan-Pin Chang ,&nbsp;Jih-Terng Wang ,&nbsp;Shu-Ying Chuang ,&nbsp;Liang-Chi Wang ,&nbsp;James T. Liu ,&nbsp;Hong-Chun Li ,&nbsp;Chieh-Wei Hsu","doi":"10.1016/j.gca.2025.09.031","DOIUrl":"10.1016/j.gca.2025.09.031","url":null,"abstract":"<div><div>Continental shelf sediments are a focal point for research on the transport, degradation, and burial of organic matter (OM), yet OM reactivity has rarely been examined within an integrated source-to-sink framework. This study investigates the relationships among source-to-sink processes, surface sediment OM composition, and oxygen consumption rates—used as a proxy for OM reactivity—of the northeastern Taiwan Strait, a passive margin shelf influenced by small mountainous rivers (SMRs). Distinct zonation of OM types was observed across the shelf. Petrogenic OM, the most abundant component, was concentrated in the depocenter, likely transported by hyperpycnal flows. Its association with low total oxygen uptake (TOU) underscores its refractory character. In contrast, fresh terrestrial OM, enriched in nearshore muds via hypopycnal flows or resuspension-advection processes, elevated TOU by nearly threefold compared to petrogenic OM-dominant sediments. As a minor component, marine OM exhibited a spatial distribution consistent with vertical delivery by the biological pump. High benthos-mediated oxygen consumption was found in silty and sandy sediments with the maximum marine OM proportion. Dissolved oxygen uptake showed a strong positive correlation with total hydrolyzable amino acids, derived from both marine and terrestrial sources. The observed connection between OM composition and oxygen consumption is attributed to the high-fidelity delivery of fresh and refractory OM from SMRs, followed by spatial partitioning driven by transport dynamics. The burial efficiency of terrestrial OM on this passive margin shelf was lower than on adjacent active margins, highlighting the critical role of shelf morphology in regulating carbon burial efficiency in SMR-sustained systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 40-55"},"PeriodicalIF":5.0,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145156603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"NanoSIMS mapping of skeletal organic matrix relative to aragonite formation in a scleractinian cold-water coral","authors":"A.M. Gothmann ,&nbsp;J. Daniel ,&nbsp;Y. Chan ,&nbsp;P. Diaz ,&nbsp;J.B. Cliff ,&nbsp;L. Polerecky ,&nbsp;J. Granger ,&nbsp;J.L. Mottram ,&nbsp;M. Prokopenko ,&nbsp;L. Boehm Vock ,&nbsp;A. Logan ,&nbsp;N. Mersy ,&nbsp;T. Smith ,&nbsp;J. Stolarski","doi":"10.1016/j.gca.2025.09.025","DOIUrl":"10.1016/j.gca.2025.09.025","url":null,"abstract":"<div><div>Organic matrix (OM) molecules are found in coral skeletons and make up ∼ 1 % of the coral skeleton by weight. These molecules play an important role in the coral biomineralization process and can be used as environmental archives. In this study, we visualize the presence and formation of OM in coral skeletons using NanoSIMS imaging of samples from cold-water corals (CWCs) fed with a ¹⁵N-enriched diet and incubated in elementally-enriched seawater. We estimate extension rates of 0.8–2.8 μm/day for our samples, consistent with other estimates of skeletal extension in this species, suggesting that our experimental conditions did not have a noticeable deleterious impact on calcification in this study. While NanoSIMS maps reveal that N, S and organic C are mainly concentrated in thin bands parallel to the growth front of the skeleton, these elements are sometimes enriched in distinct patches and/or diffusely present throughout the skeleton. Quantitative analysis reveals that the areas enriched in N, S, and organic C overlap in space, suggesting that these regions are enriched in organic matter. Our NanoSIMS maps may be useful when considering the potential impact of OM contamination on trace element proxies. Analysis of the level and patterns of ¹⁵N enrichment in our coral skeletons indicates that part of the N source that forms the organic matrix may exist as a discrete N pool that is either small or has a short turnover rate. Our ¹⁵N data, interpreted in the context of the timing of experimental growth, also suggest that heterotrophic feeding may trigger the formation of organic-rich layers within the skeleton, implying that feeding may support biomineralization by encouraging the synthesis of organic bands.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"408 ","pages":"Pages 116-131"},"PeriodicalIF":5.0,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145218057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}