Marine Carbonate Research Articles

Hydrocarbon charging process of Ordovician strike‐slip fault zones in the Shunbei area, Tarim Basin, NW China

Ultra‐deep marine carbonate reservoirs is an important field for oil and gas exploration, and it is also a hot research topic in recent years. However, their hydrocarbon episodic charging model is still under debate up to now. A great breakthrough has been made in the newly discovered ultra‐deep fault‐karst oil reservoir in the Shunbei area of Tarim Basin. Based on quantitative gas chromatogram‐mass spectrometry, stable carbon isotopes of reservoir oils, microthermometry and confocal laser scanning analyses of fluid inclusions, the reservoir oil origin and hydrocarbon charging history in Shunbei No. 1, No. 5 and No. 7 strike‐slip fault zones are expounded. The results showed that the Ordovician reservoir oil derives from the source rocks within the Cambrian Yuertusi Formation deposited in a highly anoxic bottom water environment. There were four stages of hydrocarbon charging in the study area, in the late Caledonian, late Hercynian–Indosinian, middle Yanshanian and late Himalayan. During this period, the force‐field strength of the charged oil gradually decreased, and the early‐stage charged crude oil with low maturity and high force‐field strength preferentially accumulated in the Yijianfang Formation, while the late‐stage charged crude oil with high maturity and low force‐field strength preferentially accumulated in the Yingshan Formation. This study reveals the history and differences of petroleum accumulation in the Shunbei fault zones, which is significance for understanding the hydrocarbon distribution in ultra‐deep marine carbonate reservoirs.

PRE‐, SYN‐ AND POST‐TECTONIC DIAGENETIC EVOLUTION OF A CARBONATE RESERVOIR: A CASE STUDY OF THE LOWER CRETACEOUS FAHLIYAN FORMATION IN THE DEZFUL EMBAYMENT, ZAGROS FOLDBELT, SW IRAN

Lower Cretaceous carbonates of the Fahliyan Formation form prolific reservoir rocks at oilfields in the Dezful Embayment, central Zagros fold‐thrust belt, SW Iran. The carbonates have undergone significant diagenetic alteration in phases which can in general be linked to the pre‐, syn‐ and post‐tectonic evolution of the fold‐thrust belt. This paper investigates the impact of diagenetic processes on the reservoir quality of the carbonates using integrated petrographic, geochemical and sedimentological analyses of subsurface and outcrop samples of the formation. Diagenetic alterations include:(i) pre‐tectonic eogenesis in the marine and shallow‐burial realm, which resulted in micritization of allochems and cementation by equant and isopachous calcite rims and framboidal pyrite together with limited dolomitization and dissolution of metastable bioclasts. The isotopic compositions of micrite and early calcite cement depart from postulated values of Lower Cretaceous marine carbonates, signifying early stabilization of precursor metastable carbonate minerals and the possible effects of the incursion of meteoric waters and/or increasing burial temperatures;(ii) mesogenesis during the subsequent syn‐tectonic phase, which included Late Cretaceous ophiolite obduction at the northern margin of the Arabian Plate and the later Zagros orogeny in the Miocene‐Pliocene. Diagenetic modifications included the emplacement of hydrocarbons, the development of stylolites and fractures, and the precipitation of saddle dolomite, replacive rhombic dolomite, discrete pyrite, microcrystalline quartz, kaolin and anhydrite. The average stable isotope compositions of saddle dolomite (δ18O: ‐6.9 ‰ ± .9 and δ13C 0.5 ‰ ± 1.6, respectively) also reflects the influence of high temprature basinal fluids;and (iii) “late” (telogenetic, post‐tectonic) uplift‐related modification starting in the Pliocene, when the incursion of meteoric waters resulted in the formation of vugs, the calcitization of dolomite, and cementation by fracture‐filling blocky calcite. The negative δ18O and δ13C stable isotope values (average: ‐5.5 ‰ ± 1.5; and ‐3.6 ‰ ± 5.9, respectively) of late blocky calcite cement suggest the incursion of meteoric water into the system.This study demonstrates that diagenetic processes in carbonates in the Fahliyan Formation, which exerted a significant control on the distribution of secondary porosity, can be related to the tectonic evolution of the central Zagros fold‐thrust belt. Thus, constraining the diagenetic history of carbonate successions within the context of their wider tectonic evolution is important for the prediction of the spatial and temporal distribution of reservoir quality.

On the occurrence of Neoplanorbulinella Matsumaru, 1976 (Foraminifera) from the late Oligocene of Central Iran (Qom Formation): Palaeobiogeographic implications

The shallow marine carbonates of the upper Oligocene Qom Formation yielded several occurrences of the foraminiferan genus Neoplanorbulinella Matsumaru. Neoplanorbulinella saipanensis Matsumaru has so far been recorded from the late Eocene–early Miocene of Japan and late Oligocene of NE Italy whereas N. malatyaensis Gedik is only reported from the Oligocene from its type locality in the Malatya Basin, eastern Turkey. The new records reported here from the Qom Formation indicate that both species occur in the Dobaradar section, ca. 10 km south of the city of Qom in North–Central Iran. The palaeogeographic distribution of these two species therefore has to be extended as far as the palaeolongitude of current Central Iran. The accompanying larger benthic foraminifers, including Miogypsinoides complanatus (Schlumberger), M. formosensis Yabe and Hanzawa, Spiroclypeus margaritatus (Schlumberger), Operculina complanata (Defrance), and Risananeiza pustulosa Boukhary et al., indicate the upper Chattian SBZ 23 Zone. The co-existence of the N. saipanensis and N. malatyaensis points to suitable palaeobiogeographic conditions of Central Iran to host Western and Eastern Tethyan taxa.

Estimating marine carbon uptake in the northeast Pacific using a neural network approach

Abstract. The global ocean takes up nearly a quarter of anthropogenic CO2 emissions annually, but the variability in this uptake at regional scales remains poorly understood. Here we use a neural network approach to interpolate sparse observations, creating a monthly gridded seawater partial pressure of CO2 (pCO2) data product from January 1998 to December 2019, at 1/12∘ × 1/12∘ spatial resolution, in the northeast Pacific open ocean, a net sink region. The data product (ANN-NEP; NCEI Accession 0277836) was created from pCO2 observations within the 2021 version of the Surface Ocean CO2 Atlas (SOCAT) and a range of predictor variables acting as proxies for processes affecting pCO2 to create nonlinear relationships to interpolate observations at a spatial resolution 4 times greater than leading global products and with better overall performance. In moving to a higher resolution, we show that the internal division of training data is the most important parameter for reducing overfitting. Using our pCO2 product, wind speed, and atmospheric CO2, we evaluate air–sea CO2 flux variability. On sub-decadal to decadal timescales, we find that the upwelling strength of the subpolar Alaskan Gyre, driven by large-scale atmospheric forcing, acts as the primary control on air–sea CO2 flux variability (r2=0.93, p<0.01). In the northern part of our study region, divergence from atmospheric CO2 is enhanced by increased local wind stress curl, enhancing upwelling and entrainment of naturally CO2-rich subsurface waters, leading to decade-long intervals of strong winter outgassing. During recent Pacific marine heat waves from 2013 on, we find enhanced atmospheric CO2 uptake (by as much as 45 %) due to limited wintertime entrainment. Our product estimates long-term surface ocean pCO2 increase at a rate below the atmospheric trend (1.4 ± 0.1 µatm yr−1) with the slowest increase in the center of the subpolar gyre where there is strong interaction with subsurface waters. This mismatch suggests the northeast Pacific Ocean sink for atmospheric CO2 may be increasing.

Genomic potential for inorganic carbon sequestration and xenobiotic degradation in marine bacterium Youngimonas vesicularis CC-AMW-ET affiliated to family Paracoccaceae.

Ecological studies on marine microbial communities largely focus on fundamental biogeochemical processes or the most abundant constituents, while minor biological fractions are frequently neglected. Youngimonas vesicularis CC-AMW-ET, isolated from coastal surface seawater in Taiwan, is an under-represented marine Paracoccaceae (earlier Rhodobacteraceae) member. The CC-AMW-ET genome was sequenced to gain deeper insights into its role in marine carbon and sulfur cycles. The draft genome (3.7Mb) contained 63.6% GC, 3773 coding sequences and 51 RNAs, and displayed maximum relatedness (79.06%) to Thalassobius litoralis KU5D5T, a Roseobacteraceae member. While phototrophic genes were absent, genes encoding two distinct subunits of carbon monoxide dehydrogenases (CoxL, BMS/Form II and a novel form III; CoxM and CoxS), and proteins involved in HCO3- uptake and interconversion, and anaplerotic HCO3- fixation were found. In addition, a gene coding for ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, form II), which fixes atmospheric CO2 was found in CC-AMW-ET. Genes for complete assimilatory sulfate reduction, sulfide oxidation (sulfide:quinone oxidoreductase, SqrA type) and dimethylsulfoniopropionate (DMSP) cleavage (DMSP lyase, DddL) were also identified. Furthermore, genes that degrade aromatic hydrocarbons such as quinate, salicylate, salicylate ester, p-hydroxybenzoate, catechol, gentisate, homogentisate, protocatechuate, 4-hydroxyphenylacetic acid, N-heterocyclic aromatic compounds and aromatic amines were present. Thus, Youngimonas vesicularis CC-AMW-ET is a potential chemolithoautotroph equipped with genetic machinery for the metabolism of aromatics, and predicted to play crucial roles in the biogeochemical cycling of marine carbon and sulfur.

Early marine carbonate cementation in a relict shelf-edge coral reef North of Miami, Florida: Pseudo-coupled depositional and diagenetic modeling

Carbonate depositional and early diagenetic processes overlap in time because of the high chemical reactivity of calcite. Previous studies have modeled early diagenesis in a static depositional framework. They followed a rule-based modeling approach instead of applying rigorous thermodynamics and reaction kinetics.This study has developed a pseudo-coupled approach based on a dynamic depositional framework and reactive transport modeling for diagenesis. It has been tested for the “Pompano” reef north of Miami, Florida. The model includes five reef parasequences deposited over 9.0 kyr with five facies zones. After deposition of the first parasequence, diagenetic processes are modeled. The resulting framework forms the starting condition for depositing the next parasequence. Subsequently, its diagenetic overprint and the continued overprint in the underlying parasequence(s) are modeled. These workflow steps are repeated until all five parasequences are covered.The results show the spatial and temporal development of calcite cementation and porosity distribution. During the reef catch-up phase, cement mainly developed at the depositional surface (up to 10% of the total sediment volume). During the keep-up phase, cement abundance increases to a maximum value of ∼17%. After the reef's demise, cement forms a crust at the sediment-water interface with up to 38% of the total sediment volume. In general, controlling factors of cement distribution include facies-specific flow velocities, reef facies, relative sea-level changes, depositional gaps, and seawater salinity.The modeling results of this study are well aligned with the actual cement and porosity distribution in the Pompano reef and with other sub-recent and ancient examples described in the literature. Pseudo-coupled depositional-diagenetic modeling represents a suitable approach for quantitative porosity prediction in comparable depositional and diagenetic settings. It reduces uncertainties in prediction at inter-well to prospect scale for oil and gas exploration, geothermal exploration, and subsurface storage of CO2.

Distribution and isotopic compositions of phenanthrene and methylphenanthrenes in crude oils: Implications for source input delineation and grouping oil families

This study aimed to identify the origins of crude oils by analyzing the δ13C values of phenanthrene (Phen) and methylphenanthrenes (9-MP and 1-MP) in some selected oils from the Tarim Basin (NW China), Termit Basin (Niger), Bongor Basin (Chad), and Fushan Depression (South China Sea). The study showed that oils with low 9-MP/1-MP ratios (<2.0), phenanthrene (Phen) δ13C values below −30.0‰, and Δ13C(9MP-Phen) and Δ13C(1MP-Phen) values above zero are marine-originated oils, while oils with high 9-MP/1-MP ratios (>2.0), phenanthrene (Phen) δ13C values above −20.0‰, and Δ13C(9MP-Phen) and Δ13C(1MP-Phen) values below zero are terrestrial-originated oils. Oil samples with high 9-MP/1-MP ratios (>2.0), phenanthrene (Phen) δ13C values ranging from −30.0‰ to −20.0‰, and Δ13C(9MP−Phen) and Δ13C(1MP-Phen) plots below zero are mixed-originated oils with higher terrestrial contribution. In contrast, oils with low 9-MP/1-MP ratios, phenanthrene (Phen) δ13C values ranging from −30.0‰ to −20.0‰, and plotting above and below Δ13C(9-MP−Phen) and Δ13C(1-MP−Phen) vice versa, are mixed-originated oils with higher contribution from marine sources.In combination with the geological settings, the results indicated that the oils from the Tarim Basin have three distinct origins. The majority of the oils are marine-sourced oils derived from the Lower-Paleozoic marine carbonate rocks. Oil samples *T2, *T3, and *T4 are mixed-originated oils with higher terrestrial contribution generated from the Mesozoic lacustrine shales/mudstones in the Tarim Basin. The oil samples *T1 (XH1) and *T9 (S94) are from a mixed origin with higher marine material, are derived from Upper-Paleozoic marine shale source rocks in the Tarim Basin. In Termit Basin, most of the selected oils are mixed oils with higher marine organism contribution from YSQ1 and YSQ2 source rocks from the Mesozoic Yogou Shale Formations, except for *T27 oil sample (Douwani-1), which is a mixed oil with higher terrestrial contribution from YSQ3 source rocks of the Mesozoic Yogou Shale Formations. As for the selected oils from Bongor Basin and Fushan Depression, they are mixed oils with higher contributions from aquatic organisms generated from the Mesozoic and Cenozoic lacustrine shale rocks, respectively.This approach allowed to identify for the first time the mixed origin with higher contribution of marine organic matter of the oil samples *T1 (XH1) and *T9 (S94) from the Tarim Basin, and the mixed origin with higher contribution of terrestrial organic matter of the oil sample *T27 (Douwani-1) from the Termit Basin.

Elemental and Sr–Nd isotopic evidence for unravelling the origin of the low-temperature geothermal fluids of Tivoli Terme (Latium, central Italy) between erosional S4 and S3 phases (upper Pleistocene) and neotectonics implications

Sr and Nd isotopic ratios along with (REE + Y) and other trace elements were measured in bedded travertines from three quarries at Tivoli Terme, Latium, aimed at deciphering their chemical and isotopic characteristics for the origin and evolution of fluids. Travertines, which were deposited between ∼81 and ∼54 ka BP, display high Sr and low REY contents along with REYPAAS patterns, supporting their fluid origin mainly from marine rocks, in particular the Upper Triassic Burano Evaporite Fm. This has been confirmed by the narrow ranges of δ87Sr and εNd values, close to those of that formation and other Mesozoic marine carbonates from central Italy. A sample of today's thermal water from Tivoli Terme provided a REYPAAS pattern and a δ87Sr value comparable with travertines, both features supporting that today's water is analog to past hydrothermal fluids. The overlap of the chemical and Sr–Nd isotopic compositions of coeval travertines and thermal waters from Tivoli and Acquasanta Terme, Marche, suggests a common fluid origin, ruling out any significant contribution from magmatic fluids/rocks to Tivoli travertines, yet deposited at the periphery of the Alban Hills volcano. Lastly, the geochemical results provide implications for regional neotectonics and the role of CO2-rich fluid pressure in fault activation, even in mildly active to almost inactive tectonic domains.

Continental Thermal Structure and Carbonate Storage of Subducted Sedimentary Origin Control on Different Increases in Atmospheric CO2 in Late Ediacaran and Jurassic

AbstractCarbon release during continental rifting is thought to regulate atmospheric CO2 levels. Supercontinent dispersal‐induced extensional tectonics is similar during the Late Ediacaran and Jurassic, while they exhibit different increases in atmospheric CO2 concentration. The underlying mechanism of distinct CO2 emissions remains to be understood. Here, we conduct petrological‐thermomechanical modeling to show that metamorphic decarbonation and melting of carbonates that are derived from subducted sediments are ubiquitous during continental extension. We find that the hotter lithosphere and deeper storage of these carbonates cause more significant amounts of rift‐related CO2 release through volcanoes and faults. They may cause ∼12%–77% larger decarbonation efficiency, providing an efficient driving mechanism for a ∼31% larger increase in atmospheric CO2 levels during the Late Ediacaran than throughout the Jurassic. The rapid eruption and deposition of recycled carbonatite volcanic ash may contribute to the production of Late Ediacaran marine carbonates with the largest negative δ13C (−12‰).

The Paleocene Hangu formation: A key to unlocking the mysteries of Paleo-Tethys tectonism

The sedimentary rocks of the Paleocene Hangu Formation in the Yadgaar Section of the Upper Indus Basin in northern Pakistan, have been the subject of an integrated field, petrographical, and sedimentological investigation. The goals of this study are to improve our understanding of the sedimentary environment, facies shifts, and the impact of tectonism on the genesis of the investigated sedimentary facies. A better understanding of the intricate relationships between the aforementioned factors will clarify whether the regional tectonic drive has partial control over or complete command of the sedimentation processes. The results of this study shows that the Hangu Formation consists of four facies: bauxite, sandstone, coal, and limestone. The bauxite deposits formed in a karst environment with severe chemical weathering in a humid to extremely humid climatic setting. Thin coal laminae indicate a peatland environment that formed within a humid tropical climate. Sub-arkose, arenite, and arkose sandstone facies mark deltaic (sub-humid), coastal–near shore (humid to hot-humid), and high-energy fluvial (arid to semi-arid) sedimentary environments, respectively. Finally, the occurrence of marly limestone points towards deposition on a shallow marine carbonate platform within a coastal-brackish environment. The facies shift of the sediments provides evidence for a gradual transition from continental to marine conditions within the study area, together with episodic transgressive and regressive cycles as well as changing climatic and geomorphological conditions. In consequence, all these changes are controlled and shaped by the effects of Paleo-Tethys tectonism during the Indo-Eurasian intra-oceanic subduction. This advancement through the current work helps in understanding tectonic-sedimentary mechanics, i.e., how regional tectono-sedimentological processes influence the formation of sedimentary sequences.

Coral-based rare earth element proxy for hydrothermal fluid on the Yongxing Island, South China Sea

Coral reefs play an important role in the high-resolution paleoclimate and paleoenvironment records. In particular, the contents, distribution patterns and elemental anomalies of the rare earth elements can reflect the paleoceanic conditions and sedimentary environments. In this study, we focus on the SSZK1 core in the Coral Reef of Yongxing Island, South China Sea (SCS). The sediments of this core can be divided into two stages: P1 (18.00–24.95 m) and P2 (24.95–55.92 m), based on the dating results. The results show that the coral reefs of P1 and P2 stages have slightly different REE contents, but similar REE + Y patterns. In general, the REE + Y patterns of both P1 and P2 stages are similar to those of normal marine carbonates (rocks), showing LREE depletion, negative Ce anomaly and high Y/Ho ratios. This indicates that the REEs of coral preserved their pristine geochemical features although they have experienced the diagenetic alteration to some degree. However, the samples, such as the YX-2300 coral bone formed at 114 ka, have obvious positive Eu anomalies except the similar REE + Y characteristics as the normal marine carbonates (rocks). The positive Eu anomalies indicate that some hydrothermal fluids may be input into the surrounding water at the time of coral bone formation. Based on the model calculations, at least 0.1% of hydrothermal fluids were added to the surrounding seawater during the growth of YX-2300 coral bone. By comparing the data and ages, it is suggested that these hydrothermal fluids could be associated with volcanic activities on Gaojishi Island or Hainan Island. This evidence is important to trace the occurrence of modern worldwide volcanism or deep faults activity in the deep-sea.

Unraveling the photochemical reactivity of dissolved organic matter in the Yangtze river estuary: Integrating incubations with field observations

Dissolved organic matter (DOM) sustains a substantial part of the organic matter transported seaward in large estuaries, where photochemical reactions significantly influence its transformation and fate. Irradiation experiments can provide valuable information on the photochemical reactivity (photo-labile, photo-resistant, and photo-product) of molecules. However, previous research paid less attention to exploring the controls of the initial DOM chemistry to irradiation experiments and examining the applicability of their further integration with field research. Here, we conducted irradiation experiments for samples from the freshwater and seawater endmember of the Yangtze River Estuary (YRE), which receives organic matter transport from the largest river in China, the Yangtze River. Molecules that occurred before and after irradiation experiments were characterized by the Fourier transform ion cyclotron resonance mass spectrometry. Results show that both post-irradiation samples have the lower aromaticity degree and reduced oxidation state, while the freshwater endmember sample exhibits more dramatic changes, indicating the controls of parent molecules to the effect of irradiation experiments. Integrating with the “molecular matching” approach, we compared the molecules occurring in field samples with the classified molecules (photo-resistant, photo-labile, and photo-product) acquired from performed irradiation experiments and correlated the relative intensity of photochemical reactivity types with salinity. When applying results from different experiments to conduct “molecular matching”, the photo-resistant and photo-labile relative intensity possess consistently positive and negative trends with increasing salinity, respectively. This suggests their reliability for molecular matching applications, while the inconsistent trends for the photo-product relative intensity with salinity suggest its uncertainty in assessing the photo-induced effects. Moreover, the molecular composition within the photochemical reactivity types in field samples also evolved along the salinity gradient and showed similar trends with the DOM changes after experimental irradiation. Despite various factors influencing estimations, it is revealed that a fraction of aromatic molecules and majority of carboxyl-rich alicyclic molecules considered with biologically persistent nature in the YRE freshwater zone are simultaneously not susceptible to photochemical transformation to potentially constitute a long-term marine carbon sink. This study emphasizes the importance and limitations of the combination of field research and laboratory-controlled experiments to provide a better understanding of the crucial role of photochemical reactions in affecting carbon cycling in large estuaries.

Alkalinity biases in CMIP6 Earth system models and implications for simulated CO2 drawdown via artificial alkalinity enhancement

Abstract. The partitioning of CO2 between atmosphere and ocean depends to a large degree not only on the amount of dissolved inorganic carbon (DIC) but also on alkalinity in the surface ocean. That is also why ocean alkalinity enhancement (OAE) is discussed as one potential approach in the context of negative emission technologies. Although alkalinity is thus an important variable of the marine carbonate system, little knowledge exists on how its representation in models compares with measurements. We evaluated the large-scale alkalinity distribution in 14 CMIP6 Earth system models (ESMs) against the observational data set GLODAPv2 and show that most models, as well as the multi-model mean, underestimate alkalinity at the surface and in the upper ocean and overestimate it in the deeper ocean. The decomposition of the global mean alkalinity biases into contributions from (i) physical processes (preformed alkalinity), which include the physical redistribution of biased alkalinity originating from the soft tissue and carbonates pumps; (ii) remineralization; and (iii) carbonate formation and dissolution showed that the bias stemming from the physical redistribution of alkalinity is dominant. However, below the upper few hundred meters the bias from carbonate dissolution can gain similar importance to physical biases, while the contribution from remineralization processes is negligible. This highlights the critical need for better understanding and quantification of processes driving calcium carbonate dissolution in microenvironments above the saturation horizons and implementation of these processes into biogeochemical models. For the application of the models to assess the potential of OAE to increase ocean carbon uptake, a back-of-the-envelope calculation was conducted with each model's global mean surface alkalinity, DIC, and partial pressure of CO2 in seawater (pCO2) as input parameters. We evaluate the following two metrics: (1) the initial pCO2 reduction at the surface ocean after alkalinity addition and (2) the uptake efficiency (ηCO2) after air–sea equilibration is reached. The relative biases of alkalinity versus DIC at the surface affect the Revelle factor and therefore the initial pCO2 reduction after alkalinity addition. The global mean surface alkalinity bias relative to GLODAPv2 in the different models ranges from −85 mmol m−3 (−3.6 %) to +50 mmol m−3 (+2.1 %) (mean: −25 mmol m−3 or −1.1 %). For DIC the relative bias ranges from −55 mmol m−3 (−2.6 %) to 53 mmol m−3 (+2.5 %) (mean: −13 mmol m−3 or −0.6 %). All but two of the CMIP6 models evaluated here overestimate the Revelle factor at the surface by up to 3.4 % and thus overestimate the initial pCO2 reduction after alkalinity addition by up to 13 %. The uptake efficiency, ηCO2, then takes into account that a higher Revelle factor and a higher initial pCO2 reduction after alkalinity addition and equilibration mostly compensate for each other, meaning that resulting DIC differences in the models are small (−0.1 % to 1.1 %). The overestimation of the initial pCO2 reduction has to be taken into account when reporting on efficiencies of ocean alkalinity enhancement experiments using CMIP6 models, especially as long as the CO2 equilibrium is not reached.

Effects of oxygen availability on mycobenthic communities of marine coastal sediments

In coastal marine sediments, oxygen availability varies greatly, and anoxic conditions can develop quickly over low spatial resolution. Although benthic fungi are important players in the marine carbon cycle, little is known about their adaptation to fluctuating availability of oxygen as terminal electron acceptor. Here, we study which part of a mycobenthic community from oxic coastal sediments can thrive under temporarily anoxic conditions. We test whether phylogeny or certain fungal traits promote plasticity in respect to changes in oxygen availability. Therefore, we incubated mycobenthos under oxic and anoxic conditions, performed ITS2 Illumina tag-sequencing and an additional meta-analysis on a literature survey. Half of all OTUs showed a plasticity towards changing oxygen availability and exhibited different strategies towards anoxic conditions, with rapid response within hours or a delayed one after several days. The strategy of dimorphism and facultative yeasts were significantly linked to OTU occurrence in anoxic conditions, while phylogeny and other traits had less effect. Our results suggest that different fungal niches are formed over the duration of prolonged anoxic conditions. The taxon-specific proliferation seems to be regulated by the fine-tuning of various traits and factors. It is essential to take these results into account when conducting conceptual work on the functionality of the marine benthos.

Biological carbon pump responses to multiscale physical processes: a review of sediment trap studies in the South China Sea

Accurately assessing the capacity of the modern ocean to photosynthetically fix and sequester atmospheric CO2, termed the biological carbon pump (BCP), is a key component in studies on the marine carbon cycle and the global climate system. Particulate organic carbon (POC) flux into the ocean interior is an important indicator of the BCP strength, and it can be directly measured by sediment traps on time scales from days to years. This study has been conducted in the South China Sea (SCS) for over three decades. The SCS is one of the largest tropical marginal seas, located in the Asian monsoon region with frequent occurrence of dynamic physical processes and anthropogenic perturbations. It hosts an ideal natural laboratory to investigate the response of the BCP to multiscale physical processes. In this mini review, we briefly introduce the study history of mooring sediment traps in the SCS, synthesize the processes that regulate the temporal variability in mesopelagic POC flux, and how it is sensitive to climate changes. The time-series characteristics of the POC flux are clearly linked to primary production, as well as the key physical processes in the upper layer. The seasonal East Asian monsoon, intraseasonal eddies, aerosol deposition and interannual El Niño Southern Oscillation (ENSO) events are the main controlling factors over weekly to yearly timescales. Together, they suggest that the multiscale physical forcing in the upper layer regulates the mesopelagic POC export flux by controlling nutrient supplementation and subsequent POC production.

Dissolved organic matter cycling revealed from the molecular level in three coastal bays of China

As the widespread distributed and critical zones connecting the land and ocean systems, coastal bays are special units with semi-enclosed landforms to accommodate and process dissolved organic matter (DOM) in the context of increasing anthropogenic effects globally. However, compared to other common systems that have been paid much attention to (e.g., large river estuaries, wetlands), the roles of the coastal bays in coastal carbon cycling are less explored. To fill this knowledge gap, here we combined optical techniques and ultra-high-resolution mass spectrometry to systematically investigate the DOM chemistry of the three typical coastal bays in different nutrient levels, Xiangshan Bay, Jiaozhou Bay, and Sishili Bay, in China. Results show that terrestrial signals and anthropogenic imprints were observed in these three bays to various extents. Besides, Xiangshan Bay with a higher nutrient level had the DOM characterized by lower humification and aromaticity degree than Jiaozhou Bay and Sishili Bay, which not likely mainly resulted from the differences in the primary production or photochemical processing. Further examination reveals that microbial processing likely contributes to the differences in DOM chemistry among the three bays, as indicated by different proportions of potentially transformed nitrogen-containing molecules and relative abundances of the island of stability molecules. Considering the nutrient levels in different bays, we speculate that the lower nutrient concentrations would promote the efficiency of the microbial carbon pump (MCP), which hypothesized that heterotrophic microorganisms might contribute to the formation of marine recalcitrant organic carbon. Additionally, the enrichment of oxygen-rich compounds in the unique carboxyl-rich alicyclic molecule pool of Jiaozhou Bay and Sishili Bay suggests that the efficient MCP might preferentially form them in these two bays. This study emphasizes the importance of coordinating the land and ocean systems and controlling the nutrient discharge to coastal bays, thus, to potentially promote long-term marine carbon sequestration.

Carbon budget and evaluation of marine industry in Jiangsu Province, China.

The measurement and evaluation of carbon budget of marine industry is the basis for promoting green and efficient development of marine economy under the goal of carbon neutrality. We constructed a carbon accounting system for the marine industry in Jiangsu Province, and assessed carbon efficiency and neutrality. The results showed that from 2016 to 2020, the total amount of marine carbon sinks in Jiangsu Province were 894.8 to 2773.2 thousand tons, while carbon emissions of major marine industries were 3538.4 to 4350.6 thousand tons. The net emissions of marine industries ranged from 1478.7 to 2906.1 thousand tons. Both of carbon sinks and emissions were significantly increased in this period. In terms of carbon sinks, the offshore wind power accounted for the largest contribution, followed by ecosystem carbon sequestration, and mariculture carbon sequestration was the smallest. In terms of carbon emissions, the marine transportation industry played a dominant role, followed by coastal tourism and marine fisheries, while the marine engineering and construction industry and marine shipping industry accounted for a small proportion. In general, the carbon neutral status showed that marine industry in Jiangsu Province was in carbon deficit from 2016-2020, but the net emissions were decreasing year by year. The net carbon sink efficiency of mariculture in Jiangsu Province was lower than the national level, and carbon efficiency of offshore wind power was stable.

Research on the game of fishermen's cooperative behavior in developing marine carbon sink fisheries from a complex network perspective

The development of marine carbon sink fisheries is both an important support to achieve the goal of net zero emissions as well as a hot topic concerning the livelihood of fishermen. Although it has been shown that there is great potential for carbon sinks in terms of environmental benefits, the lack of economic benefits in the short term is a hindrance that prevents marine carbon sink fisheries from being accepted by practitioners, especially fishermen groups. There is need to stimulate fishermen's enthusiasm for cooperative development of marine carbon sink fisheries and to promote marine carbon sink fisheries in order to achieve high efficiency and effectiveness. This paper adopts a complex network evolutionary game, based on the assumptions of WS small-world model on social network relationships, focuses on fishermen groups, and explores the dynamic evolutionary law of cooperative behavior diffusion in development of marine carbon sink fisheries. The results of the study show that (1) the government can accelerate the diffusion of cooperative behavior in the pre-development stage of marine carbon sink fisheries through subsidies, supplemented by certain punishments to curb the betrayal behavior, with the strength of the rewards and punishments dynamically adjusted according to the changes in the risks of implementation of marine carbon sink fisheries. (2) In the long term, higher value of marine carbon sink fisheries and their derived products is the essential demand of fishermen, which can effectively improve the depth of diffusion of fishermen's cooperation in developing marine carbon sink fisheries. (3) To avoid the spread of betrayal in the later stages of marine carbon sink fisheries development, the government can gradually reduce production subsidies and convert them into environmental subsidies in the sale process.

Nutritional Status Regulates Bacteria‐Virus Interactions in the Northern South China Sea

AbstractHeterotrophic bacteria play a vital role in the marine carbon cycle and viruses are an important regulator of bacterial metabolism and community composition. It remains unclear about how bacteria‐virus interactions vary with environmental conditions in oceans. In this study, bacterial metabolic activity and community composition were examined in three treatments with different viral pressure (control, virus‐rich and virus‐reduced) through bioassay experiments at three stations with different environmental conditions in the shelf of the northern South China Sea. Our results showed that bacteria‐virus interactions varied with environmental conditions. Viral lysis mediated bacterial growth rate (BGR) and production by shaping bacterial community composition. Furthermore, the effect of viral lysis on bacterial growth rate and production was reduced in substrate‐rich waters compared to substrate‐low waters. However, the opposite pattern occurred for viral regulation on bacterial respiration and carbon demand, likely since viral lysis dramatically mitigated the maintenance respiration of bacteria. Consequently, viral lysis to greater extent mitigated bacterial carbon processing in substrate‐rich environments than in substrate‐low environments. Our findings provided new insights into bacteria‐virus interactions, and improved our understanding of the role microbial processes in carbon cycling in oceans.

Does marine ecological compensation policy have improved marine carbon emission efficiency? Evidence from coastal areas in China.

The marine ecological compensation (MEC) policy is a scheme for protecting and restoring marine ecology. The previous studies have verified that the policy has improved the marine environment, ignoring the comprehensive performance of the economy and environment. Is the MEC policy actually effective for reducing marine carbon emission considering resource input and economy output? To address the question, this paper evaluates the impact of MEC policy on marine carbon emission efficiency by introducing the multi-stage difference-in-difference with propensity score matching. The results show that the MEC policy significantly improves marine carbon emission efficiency, and the positive effects dynamically enhance over time. Low-carbon technology innovation is confirmed to play a mediating role by which the MEC policy improves marine carbon emission efficiency. Therefore, gradually popularizing the MEC policy and accelerating low-carbon technology innovation are crucial measures to improve marine carbon emission efficiency and achieve sustainable marine development.