Organic Geochemistry最新文献

{"title":"Optimized method for sequential extraction and analysis of polycyclic aromatic hydrocarbons, anhydrosugars and lipid biomarkers in speleothem carbonate and drip waters","authors":"Zhao Wang ,&nbsp;Jonathan D. Smolen ,&nbsp;Michael T. Hren ,&nbsp;Yuval Burstyn ,&nbsp;Isabel P. Montañez ,&nbsp;Jessica L. Oster ,&nbsp;Aida Zyba ,&nbsp;Erica A. Scarpitti","doi":"10.1016/j.orggeochem.2025.104961","DOIUrl":"10.1016/j.orggeochem.2025.104961","url":null,"abstract":"<div><div>Organic molecules such as <em>n</em>-alkyl lipids, terpenoids, anhydrosugars (AHs), and polycyclic aromatic hydrocarbons (PAHs) are found in karst systems, including cave deposits and drip waters, and provide a potential record of surface climate, ecosystem, and fire. However, it is analytically challenging to separate and measure multiple classes of organic compounds in these low-abundance matrices. Here, we present a simple, solid-phase sequential extraction method for the separation and purification of organic matter in carbonates (∼0.5 g, powder) and drip waters (300 mL, freeze-dried). This method offers efficient extraction and separation of hydrocarbons (<em>F_H</em>) (saturated and PAHs) (hexane/dichloromethane; 70/30; v/v) and polar lipid compounds (<em>F_P</em>) (e.g., AHs, sterols, and diterpenoids) (acetone) with a high recovery of standards in <em>F_H</em> (78 ± 7 %, on average) and <em>F_P</em> (90 ± 6 %, on average) across multiple matrices (i.e., speleothems and waters). Acid digestion was applied to the post-initial sequential extraction speleothem samples to fully liberate any remaining molecules trapped in the calcite crystals. We found that ∼10% of <em>n</em>-alkanes (C₂₀-C₃₂) and the smallest PAHs (naphthalene, methylated naphthalene, and fluorene) of total extractable hydrocarbons were left in the acid digestion, indicating that modification of the sequential extraction could be applied based on the target of interests. In total, this sequential solid-phase extraction method provides reliable separation of geochemically significant compound classes across different matrices within karst systems.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104961"},"PeriodicalIF":2.6,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143520529","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":"Study on the main controlling factors on the differential accumulation of natural gas in multiple (ultra-)deeply-buried marine strata","authors":"Zezhang Song ,&nbsp;Ziyu Zhang ,&nbsp;Bing Luo ,&nbsp;Wenjin Zhang ,&nbsp;Changqi Liu ,&nbsp;Xingwang Tian ,&nbsp;Dailin Yang ,&nbsp;Luya Wu ,&nbsp;Bingfei Ge ,&nbsp;Shigui Jin ,&nbsp;Jiutao Yuan","doi":"10.1016/j.orggeochem.2024.104918","DOIUrl":"10.1016/j.orggeochem.2024.104918","url":null,"abstract":"<div><div>Ultra-deep natural gas is characterized by significant burial depth, high maturity, limited biomarkers, and complicated gas-source relationships. Ultra-deep gas accumulations generally underwent complex modifications during their long evolution, making it challenging to clarify the controlling factors of gas accumulation. This study focuses on gas accumulations in multiple (ultra-)deep marine carbonate strata, ranging from the Sinian Dengying (Z₂dn) to the Permian Maokou (P₂m) formations, in the Penglai gas area of the central Sichuan Basin. Using unsupervised machine learning algorithms, we conducted clustering analysis on natural gas composition and isotopes (δ¹³C and δ²H). Furthermore, we combined reservoir microscopic analysis, isotope data (δ¹³C of kerogen and solid bitumen; and δ¹⁸O, δ¹³C, and ⁸⁷Sr/⁸⁶Sr of dolomite), and fluid inclusion analysis to determine the main controlling factors that differentiate gas accumulation in multiple marine carbonate strata. The results indicate that: (1) Natural gases from Z₂dn-P₂m strata in the Penglai gas area are mainly dry gas (dryness &gt; 0.996). Specifically, Z₂dn natural gas exhibits high non-hydrocarbon content, low C₂H₆, δ¹³C_C₂H₆, and δ²H_CH₄. Conversely, the Cambrian (Є) natural gas demonstrates the opposite characteristics. The natural gas in P₂m has relatively high C₂H₆, greater δ¹³C_C₂H₆ and δ²H_CH₄ values. (2) The natural gas from Z₂dn-P₂m in the Penglai gas area is oil-cracking gas and mainly sourced from Є₁q. Due to maturity, hydrocarbon gases are dominated by CH₄. He and N₂ are from inorganic, deep Earth sources and show differential enrichment. Influenced by hydrothermal alteration and TSR, H₂S and CO₂ are enriched in Z₂dn. The δ¹³C_C₂_H₆ in natural gas follows the order: Z₂dn &gt; P₂m &gt; Cambrian. The δ¹³C_CH₄ in natural gas follows the order: Z₂dn ≥ P₂m &gt; Cambrian. (3) Overall, the Z₂dn-P₂m differential accumulation in the Penglai gas area is primarily influenced by various factors, including multiple source rocks, deep hydrothermal transformation, and strike-slip faults.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104918"},"PeriodicalIF":2.6,"publicationDate":"2025-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378489","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":"Study on hydrocarbon retention and expulsion of kerogen based on centrifugal swelling method","authors":"Tian Liang ,&nbsp;Feng Zhu ,&nbsp;Zhao-Wen Zhan ,&nbsp;Xiao-Hui Lin ,&nbsp;Yan-Rong Zou ,&nbsp;Ping’an Peng","doi":"10.1016/j.orggeochem.2024.104921","DOIUrl":"10.1016/j.orggeochem.2024.104921","url":null,"abstract":"<div><div>Centrifugal swelling experiments using <em>n</em>-hexadecane and 1-methylnaphthalene were carried out to explore the connection between hydrocarbon retention and expulsion in type Ⅰ kerogen. A driving force-hydrocarbon expulsion model was innovatively established through the results of differential centrifugation experiments and low field nuclear magnetic resonance. Additionally, the hydrocarbon expulsion process of kerogen was categorized into three distinct stages based on the driving force, including free, intergranular state and immovable state (adsorption and swelling) hydrocarbon expulsion. A linear correlation also was established between the T₁/T₂ signal and the liquid hydrocarbon content during the swelling process, revealing that low-field NMR technology could effectively detect the retention of alkane compounds in kerogen. The study revealed that when the driving force is greater than 647.4 g N, most of the shale oil retained in the kerogen is in an immobile state, which cannot be exploited. Additionally, the hydrocarbon expulsion model based on the centrifugal experiment presents several advantages, including low equipment requirements, straightforward operation, and a broad range of applications. This model can effectively support various types of laboratories conducting shale oil retention assessment work, especially those in oilfields with relatively simple experimental setups.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104921"},"PeriodicalIF":2.6,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143373026","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":"Biomarker signatures in host rocks and their co-occurring fossil plants from northern Scotland","authors":"Olumuyiwa T. Akinsanpe ,&nbsp;Adebola O. Akinsanpe ,&nbsp;Solomon A. Adekola ,&nbsp;Oluwaseye P. Oyetade ,&nbsp;Waheed G. Akande ,&nbsp;Musa B. Usman ,&nbsp;Abdulwahab M. Bello ,&nbsp;Uzochukwu K. Benjamin ,&nbsp;Adeniyi O. Olusanya ,&nbsp;Chikezie Emele","doi":"10.1016/j.orggeochem.2025.104948","DOIUrl":"10.1016/j.orggeochem.2025.104948","url":null,"abstract":"<div><div>The Devonian Period paleogeographic setting fostered the growth of diverse terrestrial and marine organisms, enhancing organic matter production and preserving terrestrial organic matter (TOM). Northern Scotland shows rock sequences with well-preserved TOM, including distinctive fossil plant fragments. The biomarker record of host rock-fossil plant system is notably fragmented. Nonetheless, the exposed outcrops of Old Red Sandstone in northern Scotland allow detailed sampling and biomarker analysis of the Devonian rocks and their co-existing fossil plants. The biomarker record of the host rocks and the co-occurring plant fossils show that the organic matter of the Rhynie Chert, Newton of Kinkell and Kerrera siltstones were derived from vascular plants. The plant biomarkers detected in the Rhynie Chert includes tetracyclic diterpenoids (kaurane and beyerane), cadalene and methylnaphthalene. These biomarkers except cadalene were also present in Den of Morphie samples, Achanarras Quarry, Kerrera plant and Newton of Kinkell siltstone-plant samples. The similarity in biomarker signatures between fossil plants and host rocks in Achanarras suggested a shared origin of organic matter. Also, the sulfur-rich euxinic conditions in the studied areas, the hydrothermal permineralization and presence of pyrite framboids in the Rhynie Chert preserved the organic matter. This was indicated by low Pr/Ph ratios and high sulfur content, enhancing preservation and reducing organic matter degradation. The study concluded that the biomarker record of the host rock-plant fossil system in northern Scotland aids the understanding of terrestrialization process and higher plant evolution in the Devonian.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104948"},"PeriodicalIF":2.6,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143373025","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":"Protocols to assist deconvolution of co-eluting 5β– and 5α–steranes by gas chromatography–mass spectrometry","authors":"Luke M. Brosnan,&nbsp;Paul F. Greenwood,&nbsp;Peter Hopper,&nbsp;Kliti Grice","doi":"10.1016/j.orggeochem.2024.104916","DOIUrl":"10.1016/j.orggeochem.2024.104916","url":null,"abstract":"<div><div>Molecular parameters based on the relative abundance of various sterane isomers contribute valuable information about sources and thermal history of organic-matter-rich sediments. However, this application is limited for 5β– and 5α–steranes due to their co-elution on common gas chromatography (GC) columns: e.g., relative retention index of 5β20<em>R</em> and 5α20<em>S</em> cholestanes on Agilent DB1 columns = 28.081 and 28.065, respectively. Selected ion monitoring (SIM) and tandem (MS/MS) mass spectral protocols were developed to improve the analytical resolution of these compounds, exploiting slight differences in mass fragmentation patterns. Protocols were optimised on a 1:1 mixture of authentic 5α20<em>R</em> and 5β20<em>R</em> cholestane standards (5α20<em>R</em> in place of 5α20<em>S</em>). Parameters offering 5α:5β selectivity (e.g., SIM: 149/151 Da; MRM: [149 → 79]/[151 → 79]) were tested on a suite of 5α20<em>R</em>:5β20<em>R</em> standards and show an excellent correlation (<em>R</em>² &gt; 0.99) with substrate composition. The capacity to quantify the relative contribution of co-eluting 5α20<em>S</em> and 5β20<em>R</em> in more complex samples was tested by analyses of a crude oil (Blina-4, Canning Basin, Western Australia) known to have high abundances of C_27-29 5α20<em>S</em> steranes (20<em>S</em>/[20<em>S</em> + 20<em>R</em>] ≈ 0.5) and spiked with 5β20<em>R</em> cholestane. The relative proportions of 5α20<em>S</em> and 5β20<em>R</em> were determined using 5α20<em>R</em>:5β20<em>R</em> calibration curves with good consistency and accuracy. Values deviated from the target when either analyte was particularly dominant (≥80 %), probably due to differences in ion density compared to the resolved standards. This issue may be improved with further method refinement and the true sterane deconvolution value offered by this approach will become apparent with further application to a diverse range of samples.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104916"},"PeriodicalIF":2.6,"publicationDate":"2025-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143373039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing tetraether lipids as a paleotemperature proxy on western edge of the Chinese Loess Plateau: A cautionary tale","authors":"Jingjing Guo ,&nbsp;Louise Fuchs ,&nbsp;Martin Ziegler ,&nbsp;Youbin Sun ,&nbsp;Francien Peterse","doi":"10.1016/j.orggeochem.2025.104947","DOIUrl":"10.1016/j.orggeochem.2025.104947","url":null,"abstract":"<div><div>The 130,000-year long, high-resolution paleotemperature record obtained from branched glycerol dialkyl glycerol tetraethers (brGDGTs) stored in a loess-paleosol sequence from Yuanbao on the western Chinese Loess Plateau (CLP) does not follow global temperature variations, whereas these are recorded by traditional loess proxy records from the same section. Specifically, reconstructed temperatures are lowest during Marine Isotope Stage 5 (MIS5), even indicating colder interstadials than stadials, which contradict brGDGT-based records from other sections on the CLP. The overall low temperatures during wet periods may be explained by an increase in soil moisture availability, which dampens land surface temperatures by increasing the soil heat capacity. However, comparison of brGDGT distributions at Yuanbao with those in modern surface soils from the CLP and the global soil calibration dataset reveals a lack of modern analogues during the interval from ∼73 to 63 ka. Notably, the Isomer Ratio (IR) rapidly increases from 0.2 to 0.6 (corresponding to a pH shift of ∼2 units) during this period, indicating a drastic shift in the composition of the bacterial community that in turn may have influenced the MBT′_5Me-temperature relationship. This community shift occurs after Chinese Stadial-20 around 73 ka, a weak monsoon event tentatively linked to oceanic reorganizations after the Toba eruption, suggesting that this drastic change in (hydro)climate might have impacted brGDGT producers. We thus recommend thoroughly assessing brGDGT distributions and understanding the environmental background prior to interpretating brGDGT-based temperatures in a paleoclimatic context.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104947"},"PeriodicalIF":2.6,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143145071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On-line hydropyrolysis gas chromatography-mass spectrometry (HyPy-GC–MS) for kerogen-bound biomarkers","authors":"Fu Wang ,&nbsp;Yuhong Liao ,&nbsp;Chang Samuel Hsu","doi":"10.1016/j.orggeochem.2024.104927","DOIUrl":"10.1016/j.orggeochem.2024.104927","url":null,"abstract":"<div><div>Flash pyrolysis gas chromatography-mass spectrometry (Py-GC–MS) is seldom used to release bound biomarkers, because its hydrogen-poor pyrolysis conditions usually result in a low yield of bound biomarkers and high concentrations of olefins. In this study, by using a Py-GC–MS system and immature kerogen/coal samples, we investigated the effects of heating rate (flash versus 30 °C/min), carrier/reaction gas (He versus H₂), hydrogen pressure, and catalyst [(NH₄)₂MoO₂S₂] on the yields and distributions of bound biomarkers. Also, the bound biomarkers obtained by different pyrolysis conditions were compared with those from catalytic offline hydropyrolysis (HyPy) and free biomarkers from extracted organic matter (EOM). We propose a new technology of hydropyrolysis-gas chromatography-mass spectrometry (HyPy-GC–MS) to be used to release bound biomarkers. HyPy-GC–MS using low-pressure H₂ at slow heating rate can increase the yield of bound biomarkers by 3–9 times, minimize the cracking of the hopanes side chain, better preserve the original sterane and terpane distributions, and have characteristics<!--> <!-->of lower maturity, compared with conventional flash Py-GC–MS without H₂. Additionally, the steroidal and terpenoid yields by HyPy-GC–MS using low-pressure H₂ at slow heating rate from immature kerogens were 3–6 times that by HyPy. Compared with EOM, biomarker maturity parameter derived from HyPy-GC–MS may not fully represent the actual maturity of samples. Higher hydrogen pressure can significantly facilitate the hydrogenation of unsaturated hydrocarbons into saturated hydrocarbons, but it can also decrease the yields of pyrolysates with higher carbon numbers (i.e., &gt;C₂₅), leading to a change in the biomarker ratios related to carbon numbers (e.g., the proportion of C₂₇-C₂₈-C₂₉ ααα20R steranes and TT₂₃/H₃₀ ratio).</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"200 ","pages":"Article 104927"},"PeriodicalIF":2.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143176264","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":"Controlling factors and geological applications of the drimane-skeleton compound content and composition of crude oils in complex petroleum systems: New insights from the Western Pearl River Mouth Basin, South China Sea","authors":"Peng Cheng ,&nbsp;Yuhao Ren ,&nbsp;Haifeng Gai ,&nbsp;Shangli Liu ,&nbsp;Tao Cheng ,&nbsp;Hui Tian","doi":"10.1016/j.orggeochem.2024.104925","DOIUrl":"10.1016/j.orggeochem.2024.104925","url":null,"abstract":"<div><div>Crude oils generally contain drimane-skeleton compounds, but the uncertainty of the main factors controlling drimane distributions limits their effective geological applications, especially in complex petroleum systems. In this study, the drimane-skeleton compound composition and the relative content of each drimane-skeleton compound to C₃₀ hopane (C_DSC) were systematically studied for crude oils in different structural regions of the Western Pearl River Mouth (WPRM) Basin, South China Sea. The results show that the C_DSC of crude oil is mainly controlled by its organic sources. Higher C_DSC values in crude oil indicates a greater contribution from terrigenous organic matter to their source rocks. For crude oils from source rocks with similar biotic inputs, the C_DSC values are controlled mainly by the depositional environment. Higher C_DSC values in crude oil correspond to higher concentrations of clay minerals and lower salinities. In addition, the drimane-skeleton compound composition of crude oil is largely controlled by its maturity. The ratios of drimane to homodrimane (Dr/HDr), total rearranged drimane to total drimane and homodrimane (TRDr/TDr), and 8-rearranged drimane to 9-rearranged drimane (8RDr/9RDr) synchronously increase with increasing maturity. These ratios can effectively characterize the maturity of various types of crude oils. The maturity range characterized by the drimane maturity parameters is greater than that characterized by conventional maturity parameters. Correlation diagrams based on drimane parameters and other organic geochemical parameters can be used to classify crude oils and reveal their sources and origins, which has great application potential in complex petroliferous basins, especially in deep and ultra-deep petroleum systems with abundant light oil/condensate.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"200 ","pages":"Article 104925"},"PeriodicalIF":2.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143175325","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":"Constraining the sources of archaeal tetraether lipids in multiple cold seep provinces of the Cascadia Margin","authors":"Katherine J. Keller ,&nbsp;Mark M. Baum ,&nbsp;Xiao-Lei Liu ,&nbsp;Kemi Ashing-Giwa ,&nbsp;Isabel R. Baker ,&nbsp;Jerome Blewett ,&nbsp;Ann Pearson","doi":"10.1016/j.orggeochem.2024.104882","DOIUrl":"10.1016/j.orggeochem.2024.104882","url":null,"abstract":"<div><div>Archaeal isoprenoid glycerol dialkyl glycerol tetraether lipid (iGDGT) abundance profiles and carbon isotopic compositions reflect the relative distributions of archaeal sources, including planktonic, benthic, and methane-cycling contributions. Here, we analyze the carbon isotope ratios of iGDGTs purified from sediments of three different cold seep sites in Cascadia Margin, off the coast of Washington, USA. Together with relative abundance and glycerol configurations, we use the carbon isotope ratios to estimate the contributions of multiple archaeal sources to the sedimentary iGDGT assemblages and their impact on values of the TEX₈₆ and methane indices. Using a Bayesian mixing model, we robustly characterize three potential endmembers by determining their characteristic lipid distributions, inferred contributions to the total sediment inventory, and carbon isotopic signatures. Despite the geographic proximity of the sample locations, we find site-specific heterogeneity in relative iGDGT abundances and δ¹³C values. Planktonic and benthic methane-cycling sources predominate in all cases (contributing &gt; 98% of iGDGTs), while benthic non-methane cycling archaea contribute minimally to the sedimentary lipid pool. Environments with higher methane influence show an increased presence of anti-parallel iGDGTs, indicating that methane-cycling archaea may dominantly or exclusively synthesize iGDGTs in this configuration. Our results quantify the relationship between the methane index (MI) and methane impact in systems dominated by planktonic and benthic methane-cycling archaea. Within the framework of the TEX₈₆ temperature proxy, this permits a quantitative demonstration that it is overly simplistic to apply a MI cutoff threshold as a binary indicator to determine methane influence, and caution is needed when taking this approach in paleoclimate reconstructions.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"200 ","pages":"Article 104882"},"PeriodicalIF":2.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143176249","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":"Contrasting particulate organic carbon and sediment trophic status in two Antarctic fjords: Hope Bay and Collins Bay","authors":"Stefanie Martínez ,&nbsp;Luis Cerpa ,&nbsp;Pablo Muniz ,&nbsp;Natalia Venturini","doi":"10.1016/j.orggeochem.2024.104926","DOIUrl":"10.1016/j.orggeochem.2024.104926","url":null,"abstract":"<div><div>Fjords of the Antarctic Peninsula are sensitive to climate change and important carbon sinks, due to their high sedimentation rates. We used several biogeochemical markers to establish sediment trophic status, origin, and sources of suspended and sedimentary organic carbon (OC) in two fjords, Hope Bay (HB) and Collins Bay (CB). Water samples at different depths and bottom sediments were collected in 2019/20 on board the R/V BAP Carrasco. Distinct glacier runoff settings between the two studied fjords were reflected in different physico-chemical water column conditions. Based on its isotopic and biopolymeric composition suspended particulate organic carbon (POC) in both HB and CB, can be considered fresh with high nutritional and energetic quality. Also, POC is derived from recent phytoplankton production, subjected to little bacterial degradation and zooplankton grazing. The predominance of muddy sediments and high total proteins (PRT) concentrations (2.88–3.04 mg g⁻¹) in CB, contrasting with sandy sediments and low PRT concentrations (1.37–1.55 mg g⁻¹) in HB, were consistent with a higher sedimentation rate in CB than in HB. The predominance of PRT-rich and fresh marine sedimentary OC in bottom sediments of the two fjords denoted the occurrence of an important benthic-pelagic coupling. Sedimentary C/N and δ¹³C indicated a main autochthonous marine origin of OC in bottom sediments of the two fjords. Biopolymeric carbon (BPC) concentrations showed that HB sediments are mesotrophic, whereas CB sediments are eutrophic, with a high organic load. Our results show the relevance of getting an integrated vision of both the pelagic and the benthic systems, for a better understanding of OC pathways and fate in Antarctic fjords undergoing rapid environmental changes linked to climate change.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"200 ","pages":"Article 104926"},"PeriodicalIF":2.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143175351","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}