Climate-driven ecosystem change in Antarctica is reshaping carbon dynamics and influencing global climate. Under sustained warming, mobilization and reburial of organic carbon (OC) in coastal Antarctica may represent an important carbon sink, yet regional OC burial and oxidation remain poorly quantified. Here, we apply ramped pyrolysis/oxidation analysis and isotopic end-member mixing models to investigate sedimentary OC along two Western Antarctic Peninsula (WAP) fjords underlain by contrasting bedrock types. We show that the fjord underlain by sedimentary rocks exhibits ten-fold higher burial flux of petrogenic OC (OCpetro) than that dominated by volcanic rocks. We estimate burial fluxes of 6.1-8.8 Gg C yr-1 for biospheric OC (OCbio) and 0.3-3.1 Gg C yr-1 for OCpetro in WAP fjords, respectively, with regional OCbio burial likely exceeding OCpetro oxidation. Model simulations indicate that future ecosystem change may increase regional OC burial flux by 2-4 times, which is critical for predicting the long-term carbon-climate feedback.

Resin production is a major innovation in land plants, signaling the evolution of specialized secretory systems, complex terpenoid biosynthesis, and defensive and wound-sealing functions. Yet its origin remains poorly constrained because fossilized resin (amber) is exceedingly rare in Paleozoic deposits, with the earliest widely accepted amber record from the Late Carboniferous. Here we report the earliest known amber from the Middle Devonian of China (~385 million years old), extending the geological record of amber by ~65 million years. Fourier transform infrared spectroscopy and gas chromatography-triple quadrupole mass spectrometry reveal chemical signatures comparable to conifer-type amber. These data indicate that some Middle Devonian vascular plants-most plausibly progymnosperms or arborescent lycopsids-had already evolved biosynthetic capacity consistent with terpene synthase. The early emergence of resin production may have promoted the ecological success of Devonian-Carboniferous terrestrial floras by enhancing protection and wound sealing.

Earthquakes and storms can trigger extensive landslides, enhancing the erosion and transport of fluvial sediments and organic carbon, thereby affecting carbon cycle processes across multiple timescales. However, due to the stochastic nature of these extreme events and the scarcity of long-term observational data, coupled with the limitations of traditional methods for tracing particulate organic carbon (POC) sources, the mechanisms underlying the impacts of earthquakes and storms on POC sources and fluxes remain poorly understood. In particular, decadal-scale monitoring of earthquake impacts on riverine POC remains absent, limiting a systematic understanding of POC dynamics under extreme events. In this study, the ramped pyrolysis/oxidation (RPO) technique was applied to analyze the organic carbon composition of suspended sediment, vegetation, soil, and rock samples from the upper Min Jiang. RPO results demonstrate that organic carbon in vegetation and soils exhibits lower oxidation temperatures (<530 °C) and correspondingly lower activation energy (Ea<200 kJ mol−1), whereas rock-derived petrogenic organic carbon (POCpetro) is characterized by higher activation energy (Ea>200 kJ mol−1). Based on these significant differences in thermal stability, and the observed correlation between the 14C activity of organic carbon in suspended sediments and the proportion of the Ea<200 kJ mol−1 fraction, RPO analysis is considered an effective approach for distinguishing biospheric POC (POCbio) derived from vegetation and soils, and POCpetro in the Min Jiang basin. Using this approach, the study quantifies the variations in POC sources and fluxes before and after storms in the upper Min Jiang. Results show that storms mobilized more POCbio into the river, with only two days of storms contributing approximately 30

The modern carbon cycle in Arctic fjords is being disrupted by Arctic warming as permafrost thaw and glacier retreat intensify. Consequently, the erosion and export of terrestrial organic carbon (OC) to the ocean have accelerated. However, it is still largely unknown how this carbon cycle perturbation impacts the fate of mobilized OC in sediments. Here, we applied the ramped-temperature pyrolysis oxidation (RPO) technique to investigate the thermochemical decomposition potential of sedimentary OC in Svalbard fjords. The thermochemically labile, moderate, and refractory OCs are classified by specific energy thresholds. Our results show that sedimentary OC in Svalbard fjords exhibits overall high thermochemical heterogeneity. Fractions of refractory OC, as defined thermochemically, increase on a per-fjord basis from northern to southern fjords and are generally higher near the head of each fjord. The spatial pattern of refractory OC is most likely attributed to the delivery and sorting of petrogenic OC derived from bedrock erosion. By compiling published data sets with our results, we estimate an OC burial rate of 7.3 +/- 6.2 & times; 1011 gC yr-1 in Svalbard fjords, with 1.2 +/- 1.1 & times; 1011 gC yr-1 and 2.7 +/- 2.4 & times; 1011 gC yr-1 attributed to labile and refractory components, respectively. Although a thermochemical moderate fraction still dominates the sediment OC pool, this work highlights that Svalbard fjords also serve as significant reservoirs of both labile and refractory sedimentary OC.

Microbialites preserve crucial records of early life and geobiological processes, yet interpreting their formation mechanisms remains challenging. Here we analyze Oligocene oncolites from the Junggar Basin that retain exceptional lipid biomarkers due to limited diagenetic alteration. These spheroidal structures exhibit alternating calcite-rich laminae with Fe-Mn coatings, revealed through petrographic and elemental mapping. Lipid analysis identifies prokaryote-dominated communities, particularly phototrophs and heterotrophs, with carbonate-associated biomarkers indicating continuous microbial activity during growth. The release of saturated fatty acid derivatives through acid treatment further confirms exceptional organic preservation. We demonstrate that oncoid formation involved complex microbial consortia mediating calcification. These deposits correlate with accelerated Tianshan Mountain uplift, which triggered lake shallowing and turbulent conditions that enhanced benthic microbial productivity prior to Central Asian aridification. Our findings establish microbialites as sensitive indicators of coupled tectonic and environmental changes during the Oligocene-Miocene transition. Oligocene-aged microbialites preserved intact lipid biomarkers, revealing microbial activity and oncolite growth. Advanced geochemical and imaging techniques decoded these microbial “time capsules” at unprecedented resolution.

The Carnian Pluvial Episode (CPE) was an interval of prominent hydroclimatic perturbations during the early Late Triassic. The causes of these changes have been widely attributed to intensified greenhouse forcing. However, the temporal dynamics of the hydrological cycle across low-latitude regions during the CPE remain poorly constrained. In this study, we present high-resolution organic geochemical data from the Erguan section of the Nanpanjiang Basin (South China) that record three distinct, globally correlated negative excursions in carbonate carbon isotope composition (S13C). New biomarker data, including synchronous increases in the relative abundance of C30 moretane (relative to its a,(3-isomer), dibenzofuran-based proxies, and the relative concentration of C29 steranes (C29/C27-29 steranes), document three discrete episodes of enhanced terrestrial organic matter input. Notably, the first pulse aligns with a pronounced negative S13C excursion, whereas the subsequent two events occurred significantly later, postdating the S13C shifts. These episodes, coinciding with intervals of increased siliciclastic deposition, were attributed to increased runoff, suggesting dynamic and episodic perturbations of the hydroclimatic regime in eastern Tethys. Collectively, our data reveal a complex interplay between the perturbations in hydrological and carbon cycles during the CPE, providing insight into the dynamics of climate change and its consequences.

Emerging viewpoints suggest dynamic oceanic redox states and notable biotic turnovers in the early Paleozoic, but these aspects remain controversial and require further investigation. The Tarim Basin, which harbors significant marine hydrocarbon source rocks, records a typical phase of marine deposition of the early Paleozoic. In this study, we investigated biomarker compositions and patterns of selected rocks and crude oils of Early Cambrian to Late Ordovician ages from the Tarim Basin, China. Of particular importance are fossilized C40 aromatic carotenoids and their biogenic aryl isoprenoid derivatives, which originate specifically from phototrophic sulfur bacteria inhabiting the euxinic photic zone and are indicative of redox conditions of ancient oceans. The prevalence of 2,3,6-aryl isoprenoids and isorenieratane indicates a biological origin of green sulfur bacteria, implying that the Tarim Basin witnessed euxinia in the subsurface photic zone during a certain period of the early Paleozoic. Along with other biomarker-based proxies, especially steroids and hopanoids, our results from the Tarim Basin suggest the dominance of reducing oceanic water column in the early Cambrian and the late evolution of partially oxygenated water column.

Ramped-temperature pyrolysis/oxidation (RPO) analysis has emerged as a powerful analytical technique for characterizing sedimentary organic carbon (OC) provenance and reactivity, bridging the knowledge gap between bulk carbon isotopic measurement and molecular-level biomarker analyses. While acid pretreatment is routinely employed to remove carbonates prior to RPO analysis, its methodological impacts remain poorly constrained compared to other geochemical measurements (e.g., delta C-13). Given the widespread utilization of RPO analysis in recent studies, a comparative examination of pretreatment conditions is timely to ensure unbiased acquisition of thermochemical results. This study systematically evaluates how decarbonation protocols influence RPO results through comparative analyses of different pretreatment approaches. We demonstrate that both acidification method (rinsing vs. fumigation) and HCl concentration significantly affect RPO thermograms, with observed differences attributed to the alteration of organic-inorganic associations and selective leaching of acid-soluble OC. Generally, results from diluted acid rinsing are more similar to the raw material. Based on comprehensive testing, we recommend diluted (i.e., 1 N) HCl rinsing with moderate reaction times (similar to 12 h) as the optimal pretreatment conditions for most samples, while acknowledging that specific sample characteristics (e.g., organic lean, protein rich) may necessitate adjustments to the protocol. These finding highlight the importance of pretreatment conditions in thermochemical decomposition studies.

Abstract. Acidification is frequently adopted to remove carbonates preceding particulate organic carbon (POC) measurements. In practice, acid rinsing and acid fumigation are two typical and well-established acidification methods eliminating inorganic carbon. However, detailed protocols therein are most likely adopted based on conventional laboratory practices, assuming that the measurement precision is unaffected by experiment conditions. In fact, acidification can cause mineral dissolution and leaching of organic components, and therefore impacts the quantity and composition of residual POC considerably. Nonetheless, the effect of acidification on POC properties and the underlying mechanisms are ambiguous when relying solely on bulk measurements. In this study, we investigated POC properties following acidification using ramped temperature pyrolysis/oxidation (RPO) technique, in combination with bulk carbon analyses, to assess the impact of different decarbonation pretreatments on the sedimentary organic carbon (OC) measurements. Our results reveal that both acidification method (rinsing or fumigation) and HCl concentrations under acid rinsing are main factors dictating OC properties measured. Notably, despite negligible differences in bulk measurements, RPO results show distinct variations between these two acidification methods. In combination with other evidence, our study suggests that the alteration of organic-inorganic associations, which is ubiquitous during acidification, drives the behaviour of POC properties that measured. Furthermore, we demonstrate that the characteristics of residual POC in acid-rinsed samples are more proximal to pristine, natural states of the raw materials, whereas the strikingly discrepant differences between two acidification methods can be attributed mainly to the perturbation caused by calcium chlorides after acid fumigation.

Hydrocarbon biomarkers, diagnostic fossil molecules tied to specific organisms, are essential for classify crude oils and associated paleoenvironments. While previous studies on Tertiary crude oils and source rocks from the western Qaidam Basin emphasized uniform depositional environments, recent discoveries of Eocene marine incursions and H2S-rich gas reservoirs complicate these interpretations. Organic sulfur compounds (OSCs) in Qaidam Tertiary crude oils, though unexplored, offer new insight into genetic affinities and depositional histories. However, the structural complexity of OSCs posts challenges for direct detection. Catalytic desulfurization, which release sulfurized biomarkers, provides an alternative approach to understanding OSCs and sulfurization mechanisms. Herein, sulfurized biomarkers from crude oils across the western Qaidam Basin were investigated using Raney nickel desulfurization. The new biomarker inventories after desulfurization exhibiting lower thermal maturity than their free hydrocarbon counterparts, indicating early sequestration of organic molecules via natural sulfurization. The exceptional abundance of desulfurized C37 and C38 alkanes likely originates from previously sulfurized C37 and C38 long-chain alkenones. Higher abundances of sulfurized homohopanes, gammacerane and carotenoids in the Qigequan and Gasikule Oilfields highlight distinctive anoxic and stratified environments in the westernmost Qaidam Basin. In contrast, anomalously over-matured signatures in the Yingzhong Oilfield reveal unusual thermal evolution. Overall, sulfurized biomarkers confirm compositional heterogeneities and genetic affinities among oilfields, providing primitive information that enhances oil-source rock correlations and paleoenvironment reconstruction. This study underscores the need to evaluate both free and sulfurized lipids to fully understand petroleum systems.

Tracing sources of organic carbon (OC) is a critical aspect of studying surface carbon cycling. Previous methods, such as carbon and nitrogen isotopes, have struggled to separate different sources in some case studies. This study introduces a new approach for quantifying OC sources by using ramped pyrolysis/oxidation (RPO) thermograms without RPO-fraction radiocarbon analysis. We applied matrix calculations to decompose thermograms into different endmembers contributions. This method was tested on two-, three-, and four-endmember systems. The results show that the deviation in source contribution estimates is within 5%. The method was applied in tracing sources of particulate organic carbon (POC) of the Buha River, northeastern Tibetan Plateau. By analyzing the thermograms of riverine suspended sediments and their potential sources, the RPO-based mixing model estimated that soil, vegetation, and rocks contributed approximately 89 +/- 3%, 4 +/- 3%, and 6 +/- 3% of the POC, respectively. This study highlights the applicability of RPO in tracing OC sources.

Weathering of rock-derived organic carbon (OC) is an important source of atmospheric CO2 in the global carbon cycle, contributing to the long-term regulation of climates. Despite numerous investigations on clastic rocks, weathering behaviors of OC in calcareous rocks remain poorly constrained due to their conventional recognition of organic-lean features. Here, we analyzed bulk OC and biomarkers along weathering profiles of organic-rich calcareous rocks from the Green River Formation. Total OC and ramped-temperature pyrolysis/oxidation results reveal a minimal degradation of OC. Given a substantial fraction of bulk OC and a rich pool of biomolecules preserved in carbonate matrix, our results suggest that the limited bulk-level degradation is attributed to the shielding of OC in carbonate matrix. Furthermore, contrasting biomarker proxies are observed between free and associated forms, implying that carbonate-associated lipids are resistant to degradation during weathering; whereas clearly decreasing patterns of free lipids at the molecular level correspond to weathering-induced microbial degradation of excluded OC. Overall, our findings reveal that calcareous rocks might be an overlooked, yet understudied, carbon pool involved in the global organic carbon cycle.

The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil side, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from pelagophyte marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition. During the break-up of Gondwana, a marine invasion from the proto-South Atlantic Ocean about 116 million years ago transformed the paleoecosystem of the Campos Basin, as revealed by the analysis of lipid biomarkers and carbonate isotopes from the east coast of Brazil

Reactive iron (FeR) serves as an important sink of organic carbon (OC) in marine surface sediments, which preserves approximately 20% of total OC (TOC) as reactive iron-bound OC (FeR-OC). However, the fate of FeR-OC in subseafloor sediments and its availability to microorganisms, remain undetermined. Here, we reconstructed continuous FeR-OC records in two sediment cores of the northern South China Sea encompassing the suboxic to methanic biogeochemical zones and reaching a maximum age of ~100 kyr. The downcore FeR-OC contributes a relatively stable proportion of 13.3 ± 3.2% to TOC. However, distinctly lower values of less than 5% of TOC, accompanied by notable 13C depletion of FeR-OC, are observed in the sulfate-methane transition zone (SMTZ). FeR-OC is suggested to be remobilized by microbially mediated reductive dissolution of FeR and subsequently remineralized, the flux of which is 18–30% of the methane consumption in the SMTZ. The global reservoir of FeR-OC in microbially active Quaternary marine sediments could be 19-46 times the size of the atmospheric carbon pool. Thus, the FeR-OC pool may support subseafloor microorganisms and contribute to regulating Earth’s carbon cycle. This study shows that iron-bound organic carbon (FeR-OC) is generally persistent but can be remobilized during iron reduction and utilized by microbes in subseafloor sediments. This sedimentary FeR-OC pool may contribute to regulating Earth’s carbon cycle.

Sedimentary rocks from the early Eocene Green River Formation comprise the largest known lacustrine oil shale deposits, contain remarkably well-preserved fossils, and provide a unique record of climate evolution across the Early Eocene Climate Optimum, a period of high atmospheric CO2. The depositional environment of these intermountain lakes spanned from relatively fresh and fluvially influenced to expanded and stratified saline closed basin lakes under the influence of the Laramide orogeny and alternating humid and arid climatic conditions. As the surface area of the lakes expanded, alkalinity and salinity increased, with depositional cycles that linked to evaporative cycles and marked by an increasing abundance of organic matter-rich shales (TOC > 10 wt%). Simultaneously, an intriguing 20 parts per thousand positive shift in the sulfur isotope composition of sulfide minerals and organic sulfur is observed. Given that this trend cannot be simply explained by a change in the source of sulfate delivered to the basin, the evolution of biogeochemical sulfur cycling and the balance of fluxes in response to basin evolution remain unresolved. Here, we combine the sulfur isotope compositions of pyrite, organic sulfur, and carbonate-associated sulfate and molecular proxies of euxinia in samples from the Uinta basin's depocenter. We find that organic matter-rich sediments reflect deposition in a stratified water column with enhanced burial of pyrite and sulfurized organic matter, while organic-lean facies present evidence of, at least transiently, euxinic conditions reaching the photic zone during arid conditions presumably because of evaporation. As the lake became both saline-stratified and euxinic, we observe that delta S-34 values of all measured sulfur-bearing sedimentary proxies increase and evolve along a 1:1 line, a trend independent of facies that we interpret as reflecting a sulfate-limited system despite saline conditions. The isotopic mass balance of sulfur fluxes implies the existence of a sink of sulfur depleted in S-34 that is spatially decoupled from burial in the depocenter. Modeling sulfur biogeochemical processes in a saline stratified lake system allows us to estimate that at least 50 % of the sulfur entering the lake could have been lost from the upper part of the euxinic water column where the fractionation factor imparted by microbial sulfate reduction is expressed. We propose that the overall isotopic enrichment of the system was caused by H2S degassing during arid climate intervals, presumably enhanced by transient water column mixing events. Further, episodic intrusion of euxinic bottom waters into the upper part of the water column might have triggered mass fish and plankton mortality, consequently facilitating the formation of these exceptionally fossiliferous and organic matter-rich rocks. Our study finds that volatile outgassing may be an underappreciated mechanism for the sulfur mass balance of stratified lacustrine systems.

Anoxygenic phototrophic bacteria (green and purple sulfur bacteria) thrive in anoxic environments where light penetrates a sulfide-containing (euxinic) water column. Genomic data and photosynthetic bacterial carotenoid pigments should provide complementary information on the spatio-temporal dynamics of anoxygenic phototrophs in modern euxinic environments. In turn, these contemporary depositional settings often serve as analogues for ancient counterparts. However, in some modern environments, DNA-informed patterns of phototrophic sulfur bacteria occurrence do not match distributions of their carotenoid inventories. One possible explanation for these seemingly incompatible observations is that the rapid sulfurization of carotenoids and incorporation into macromolecules via multiple carbon-sulfur bonds prevents or confounds their detection by conventional means. Here, to evaluate this conundrum, we revisit some representative contemporary euxinic environments where anoxygenic phototrophic bacteria have mostly been detected based on genomic analyses. Although free intact carotenoids are sporadically detected in surface sediments, their distributions do not reveal a complete picture. Exogenously sourced fossil carotenoids (e.g., paleorenieratane) is an additional complication. Carotenoid inventories obtained by desulfurization with Raney nickel, on the other hand, stand in stark contrast to those present as free lipids. In particular, sulfur-linked carotenoids present in euxinic lake sediments provide a more complete picture of compositions of anoxygenic sulfur bacterial communities and account for discrepancies reported in previous studies. We observe a closer alignment between genomic data and patterns of sulfurized carotenoids and, importantly, our results highlight how sulfurization serves as a pathway for the rapid modification of highly functionalised lipids and their sequestration into the macromolecular component of sediment extracts.

Elucidating the formation mechanism of organic-rich shale holds significant implications for hydrocarbon exploration, carbon sequestration, and carbon cycling. In recent years, the relationship between organic matter and clay minerals in shale has attracted widespread attention. This study aims to comprehensively overview the interactions between organic matter and clay minerals during deposition and diagenesis. Through sedimentation processes, climate and provenance control the composition of clay minerals in sediments jointly. Meanwhile, clay minerals exhibit selective adsorption of organic matter, thereby influencing the abundance and type of organic matter in sediments. In modern marine depositional environments, the interaction between clay minerals and organic matter significantly impacts the overall activity and burial efficiency of organic carbon. During the diagenesis stage, the presence of organic matter dramatically affects the transformation of smectite into illite. Conversely, the process of smectite illitization also exerts a significant influence on hydrocarbon generation. Furthermore, this study introduces state-of-the-art techniques to investigate the interactions between organic matter and clay minerals.

The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil margin, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition.