Significant Carbon Sink Research Articles

Drought offsets the vegetation greenness-induced gross primary productivity from 1982 to 2018 in China

Recent studies have shown that climate stress may cause asynchronous changes between greenness and productivity, but the mechanism how greenness and productivity respond to drought remains unclear. The significant greening of vegetation in China has attracted worldwide attention; nevertheless, it is unclear whether large-scale greening will translate into productivity in the context of recent droughts. In this study, we used the vegetation index dataset to extract long-term trends in vegetation greenness and productivity from 1982 to 2018, and then chose the multi-scale Standardized Precipitation Evapotranspiration Index (SPEI) index to measure how vegetation greenness and productivity change in response to drought. The results show that significant vegetation greening did not cause a simultaneous increase in productivity during 1982–2018. Vegetation greenness and productivity trends were relatively consistent before 2000 and diverged after 2000, especially during the prolonged drought of 2000–2009. The opposite trend between greenness and productivity in humid ecosystems during drought periods mainly caused this trend difference. In humid ecosystems, short-term drought promotes vegetation greening, while long-term drought has no significant impact on greenness. However, the inhibitory effect of drought on productivity deepens with an increase in drought duration. Therefore, prolonged droughts offset vegetation greenness-induced gross primary productivity. We also found that prolonged drought causes a significant decrease in greenness but has little effect on productivity in arid ecosystems, possibly because vegetation productivity is more sensitive to soil water than atmospheric drought. Our results highlight the complexity of vegetation growth in the context of climate change. Furthermore, it is crucial to pay attention to the impact of climate stress on regional carbon sequestration functions, considering the significant carbon sink potential of forest areas in southern China.

Enhancement of carbon sink in the main marginal sea ice zone by cold season Arctic cyclones

The Arctic Ocean, as a significant carbon sink, is attracting increased attention within the scientific community. This study focused on the main marginal sea ice zone, which has been the most sensitive to environmental changes in recent decades. Using data from reanalysis, models, and on-site observations, the changes in air–sea CO2 flux (FCO2) were analyzed during the influence of Arctic cyclones (ACs) in 2021–2022. Results indicated that the passage of ACs tended to increase the average carbon sink in the main marginal ice zone, with a more pronounced effect during the cold season. During ACs, the average FCO2 could reach −6.95 mmolC m−2 d−1. This was mainly associated with the stronger and more concentrated distribution of ACs where there was lower pCO2 (air–sea gradient of CO2 partial pressure) in the cold season. Additionally, the change in FCO2 during ACs was primarily affected by the sea surface wind and sea-ice concentration in the cold season, while it was influenced by a variety of environmental factors in the warm season, including the sea surface wind, sea-ice concentration, and ecological factors.

Carbon storage in mollusk shells: An overlooked yet significant carbon sink in terrestrial ecosystems

Mollusks, the second largest animal family, are found in a variety of ecosystems. As they grow, their shells absorb carbon and form calcium carbonate, making them an important storage place for carbon. However, the amount of carbon deposited in the carbonate shells of terrestrial mollusks throughout modern and geological history has not been quantified. In this study, we first conducted an investigation of carbon deposits in shells from various mollusk species at 470 modern surface soil sample sites across diverse terrestrial ecosystems in China. The deciduous broadleaf forest and shrublands exhibited a higher carbon deposition rate of ∼1.37 ± 2.15 and ∼1.56 ± 2.92 g C m−2/yr−1, while croplands and grasslands displayed a rate of ∼1.11 ± 1.95 and 1.07 ± 1.78 g C m−2/yr−1, respectively. Using geostatistical methods, we estimated the total shell carbon deposition of grassland, forest, shrublands, and croplands in China to be ∼3.39–5.45 × 106 t C yr−1, constituting ∼1.68–2.71 % of China's terrestrial carbon sink, an overlooked portion in previous studies. Additionally, we provided quantitative data on shell carbon fluxes spanning a remarkable 20,000-year period through over ten fossil sequences from loess deposits. The results underscore the continuous and abundant carbon deposition in mollusk shells across various locations for at least 20,000 years, highlighting the persistence and substantial accumulation of shell carbon deposits over time. Remarkably, we estimated that the total shell carbon deposition of loess sediments in China and the world over the past 20,000 years may reach 1.10 × 108 t C and 1.29 × 109 t C, roughly equivalent to an afforestation area of 2.32 × 106 km2 and 2.72 × 107 km2, respectively.

Remote sensing, allometry, and carbon stocks of Phyllostachys aurea in the Western Highlands of Cameroon

The fight against climate change is one of the major concerns of the international community and has led to a search to identify cost-effective ways to manage ecosystems in a way that removes atmospheric carbon-dioxide while providing essential societal benefits. As bamboo ecosystems in Cameroon are poorly known, this study sought to evaluate the distribution of bamboo, develop allometric equations for it and estimate carbon stocks associated with bamboo in the Western Highlands of Cameroon. Landsat 8 OLI imagery was used to increase data on the distribution and carbon stocks of Phyllostachys aurea Carrière ex Rivière & C. Rivière in the study area. P. aurea is reportedly the most exploited species for ecological, socioeconomic and cultural activities in the region, posing a challenge for the sustainability of the species. Twelve circular plots were established in P. aurea stands in the Western Highlands. Five per cent of the bamboo stems were harvested. Every stem was sorted into leaves, branches, and culms. These were weighed, and sub-samples taken to the laboratory. Sub-samples were oven-dried for biomass estimation. Regression analysis was used to develop the allometric equations. The best equation was used to estimate the carbon stocks. The Western Highlands region of Cameroon is estimated to have 241,296 ha of bamboos. The dominant bamboo species identified in the study area include Oldeania alpina (K.Schum.) Stapleton (syn. Yushania alpina K.Schum.), Bambusa vulgaris Schrad. ex J.C.Wendl. and P. aurea. Focusing on P. aurea the best fit equation with a bias of − 6.98%, Adj.R² = 0.711, AIC = 17 and RSE = 0.262, was selected. The mean density of P. aurea was 38,017 ± 4510 culms.ha−1. The mean culm aboveground biomass was 3.15 ± 0.94 kg. The AGB of P. aurea was estimated at 119.05 ± 3.63 t.ha−1, mean AGC was 55.95 ± 5.81 t C.ha−1 and mean aboveground carbon dioxide equivalence (AGCO2eq) was 205.35 ± 58.01.22 t CO2.ha−1. P. aurea constitutes a significant carbon sink in the Western Highlands of Cameroon. Policymakers and development planners should therefore recommend this species for carbon markets, international initiatives such as AFR100, and the Nationally Determined Contribution addressing the United Nations Sustainable Development Goal 13 (SDG13) to combat climate change.

Comparative Analysis of Peatland Emission Factors: Unravelling the Need for Standardized Measurement and Reporting

Abstract Peatlands have a crucial role in the global carbon cycle, acting as significant carbon sinks, but become a significant source of greenhouse gas (GHG) emissions when peatlands are drained, and during peat extraction. This article presents a comprehensive overview of peatland ecosystems, emphasizing their classification across various climatic zones and the complex set of different characteristics that determine contribution to GHG emissions. Currently, inconsistencies exist in the definition of emission factors used between countries leading to varied approaches in estimating peatland emissions and posing significant challenges in the comparison and aggregation of global data on peat extraction related GHG. The aim of the study is to analyse the disparities in emission factors and calculation methodologies employed by different countries. Data from national GHG emission reports are submitted under the UNFCCC and the Kyoto Protocol. Emissions report data calculations and emission factors can be based on either nationally determined data or data specified in the IPCC guidelines. Consequently, emission factor data for four countries - Latvia, Finland, Sweden and Germany - are collected and processed, which was compared with IPCC guidelines data. The data was compared by equating units of measurement. The results show there is a pronounced difference between the emission factors of each country, however, all of these factors are lower than the maximum values specified in the IPCC guidelines. The study concludes that emission factors are predetermined differently for each country, and it is not possible to determine the differences among assumptions for parameters included in the specification of the emission factors. The results suggest there is a need for development of a more transparent accounting for emissions with regard to the diverse environmental and anthropogenic factors influencing peatland ecosystems. Factors like composition, depth of peat, water table levels, and local land-use practices further compound this variability in emission accounting. Addressing these challenges is crucial for enhancing the accuracy and reliability of GHG emission reporting under international frameworks like the United Nations Framework Convention on Climate Change and the Kyoto Protocol.

Ecosystem carbon exchange across China's coastal wetlands: Spatial patterns, mechanisms, and magnitudes

Coastal wetlands are of great importance for global carbon cycle and climate mitigation because of their strong carbon uptake capacity. However, the national-scale ecosystem carbon exchange dynamics in coastal wetlands, including magnitudes, spatial patterns, and controlling mechanisms, remains poorly understood. In this study, we utilized eddy covariance measurements from China's coastal wetlands to quantify carbon fluxes, assess their spatial patterns, and explore the controlling mechanisms. Integrating climate, vegetation, and soil factors, we constructed a cascaded relationship network to reveal the potential controlling mechanisms of spatial variations in carbon fluxes. The results revealed that gross primary production (GPP) and ecosystem respiration (ER) were 1405 ± 656 (mean ± sd) gC m−2 yr−1and 893 ± 465, respectively. Net ecosystem production (NEP) in coastal wetlands (567 ± 348 gC m−2 yr−1) exceeded China's terrestrial and marine ecosystems by 2–8 times, highlighting their significant carbon sink capacity. The carbon sink capacity in mangroves was significantly higher than salt marsh, exhibiting a twofold difference in NEP. Spatially, carbon fluxes displayed negative correlations with latitude, indicating the influence of climate features. Although tropical climate zone exhibited significantly higher carbon fluxes than temperate zone, no differences were observed between subtropics zone with others due to the distribution of mixed plants and largest area. The structural equation model (SEM) showed that the climate factors, including temperature, precipitation, and net radiation indirectly promoted GPP and ER through regulating the physiological process of mangrove and salt marsh, as well as soil carbon production and consumption. The cascaded relationship of climate-vegetation-soil showed in SEM explained 71–85 % of the spatial variations in GPP and ER, and ultimately accounted for 85 % of NEP. The carbon consumption efficiency (ER/GPP) in coastal vegetations was of 0.6, lower than that of global and China's terrestrial ecosystems, suggesting their strong efficiency in carbon fixation in coastal wetlands. Lastly, the scenario simulation results implied the importance of coastal vegetation restoration on enhancing blue carbon benefits.

Hydrogen transport options for a large industrial user: Analysis on costs, efficiency, and GHG emissions in steel mills

The planned steel industry shift from fossil-based production to low carbon alternatives will require millions of tons of hydrogen. Hydrogen delivery to large users calls for building of new infrastructures. This study analyses five different hydrogen delivery pathways including mill-site electrolysis, pipeline transport of hydrogen in new and repurposed pipelines, pipeline transport of synthetic methane, and shipping of various products. Costs, energy efficiency, and greenhouse gas (GHG) emissions are evaluated using a steel mill consuming 144 kt of hydrogen as an example. The results suggest that mill-site electrolysis and both the hydrogen pipeline transport alternative seemed to be the best performers among the studied cases. Pipeline transport of synthetic methane and shipping have around 130 % and 40 % higher costs in comparison to mill-site hydrogen production and pipeline transport of hydrogen. Their energy efficiencies were the least appealing. Greenhouse gas emissions of the studied cases varies between 7.7 and 13.7 kgCO2-eq/kgH2. The synthetic methane could provide a significant carbon sink, if only renewables are utilized in hydrogen production, but due to high cost and poor energy efficiency it can still be regarded as an unfeasible route. It can be concluded that there are notable differences between transport options, and significant uncertainties on how large-scale hydrogen demand should be handled exist.

Machine Learning-Based examination of recent mangrove forest changes in the western Irrawaddy River Delta, Southeast Asia

Mangrove forests serve as a significant carbon sink and provide effective shoreline protection against devastating winds. However, these forests are facing an unprecedented decline in tropical and subtropical large deltas due to human activities and climate change. This study focuses on quantifying the dynamic changes of mangrove forests in the Western Irrawaddy River Delta (WIDR), which is part of Myanmar’s largest delta in Southeast Asia, Remote sensing images from 1988 to 2022 were utilized alongside a machine learning approach to analyze these changes. The findings demonstrate a significant decline of mangrove forests within the WIRD, with a reduction in area by 45.35% over the past 35 years. Additionally, the patches of mangrove forests have become increasingly fragmented. Losses predominantly occurred in the inland regions, while gains were observed along the seaward edges, suggesting progradation towards the sea, which compensated for a net loss of 2,812.32 ha during the study period. The intensification of human activities, specifically deforestation and aquaculture pond utilization, appears to be the leading cause of catastrophic internal degradation within the WIRD’s mangrove forests. Contrary to the influence of local sea level rise or variations in suspended sediment discharge into the WIRD, this study suggests that the persistent retreat of mangrove forest fringes is controlled by large waves generated by the southwest monsoon. Estuarine barriers situated in the WIRD act as buffers, dissipating wave energy and facilitating seaward growth. of mangrove forests. Our study reveals a significant pattern in the WIRD, where landward mangrove forest loss coincided with seaward mangrove forest gain. This work underscores the importance of addressing landward mangrove forest loss and recognizing the emergence of seaward gains in the WIRD, providing valuable insights for fostering successful and sustainable mangrove management and protection initiatives.

Carbon emissions from Australian Sphagnum peatlands increase with feral horse (Equus caballus) presence

Peatlands are globally significant carbon sinks, but when disturbed, have the potential to release carbon back to the atmosphere as greenhouse gases. Feral horse populations in the Australian Alps degrade Sphagnum peatlands, which are highly sensitive to disturbance. However, the link between this degradation and peatland carbon cycling is not understood. Here, we compared the autumn daytime carbon dioxide (CO2) and methane (CH4) fluxes of 12 alpine and subalpine Sphagnum peatlands in Kosciuszko National Park, Australia. The presence of feral horses at these sites was correlated with higher carbon loss: sites with horses were losing carbon to the atmosphere (4.83 and 8.18 g CO2-e m−2 d−1 in areas of Sphagnum moss and bare soil, respectively), whereas sites without horses were removing carbon from the atmosphere (−6.39 g CO2-e m−2 d−1). Sites with feral horses also had higher soil bulk density, temperature, and electrical conductivity (EC), and higher water pH, EC, and turbidity, than sites without horses. Our findings suggest that excluding feral horses from peatland areas could reduce rates of carbon loss to the atmosphere, in addition to improving overall site condition, peat soil condition, and water quality. We discuss potential management applications, further research, and restoration opportunities arising from these results.

Forest Carbon Storage and Carbon Sequestration Potential in Shaanxi Province, China

The carbon storage of forest vegetation plays a crucial role in the terrestrial carbon budget. The objective of this study is to elucidate the current biomass carbon storage and sequestration capacity, as well as the future carbon sequestration potential of forest ecosystems in Shaanxi Province of China, thus providing data support and policy references for sustainable forest management and the response of carbon sequestration to climate change. Based on the data obtained from the seventh and ninth forest resource inventories, the regional biomass conversion factors, and carbon measurement parameters, the biomass conversion factor method is employed to estimate the biomass storage and carbon sequestration capacity of forest ecosystems. (1) The total carbon storage of forest lands in Shaanxi Province was 285.20 Tg. The carbon storage of arbor forests, sparse woodlands, scattered forests, four-side trees, shrub woodland, and bamboo forests were 237.09 Tg, 2.93 Tg, 12.30 Tg, 5.98 Tg, 26.35 Tg, and 0.56 Tg, respectively. (2) Over the 10 years from the seventh (2005) to the ninth (2015) forest resource inventories, the carbon storage of forests increased from 207 Tg to 285 Tg, with a total increase of 78.01 Tg (37.65%), demonstrating a significant carbon sink function. (3) From 2015 to 2060, the carbon density of arbor forests will increase from 33.53 Mg/ha to 46.90 Mg/ha, and the carbon storage will increase from 237 Tg to 432 Tg. These results indicate that forests have significant net carbon sequestration capacity and can play an important role in achieving China’s carbon peak and carbon neutrality goals. Aiming for carbon neutrality, improving forest management, along with protecting and utilizing forest resources through technological innovation, will become the driving force for increasing carbon storage in Shaanxi Province in the future.

Microbial Responses to Carbon Sequestration Soil Amendment and Productivity

Soil a significant carbon sink, plays a pivotal role in mitigating climate change. This review underscores the potential of soil amendments for enhancing carbon sequestration, focusing on the intricate relationship between these amendments and soil microbial communities. Soil amendments, ranging from biochar and organic compost to mineral additives, have been identified as viable strategies to boost soil carbon stocks. Concurrently, these amendments influence the diversity, structure, and functional roles of microbial communities, which in turn, are integral to soil carbon dynamics. Tools like 16S rRNA sequencing, metagenomics, and isotope tracing techniques have propelled our understanding of microbial responses, shedding light on the complex microbial networks and their roles in carbon cycling. While promising, the application of soil amendments presents challenges. Variability arising from different soil types, climates, and microbial dynamics poses a consistent research challenge. Potential risks like reduced sequestration over time and economic considerations for large-scale application necessitate attention. Future directions hinge on innovations in soil amendment products, harnessing microbial inoculants for synergistic effects, and fostering interdisciplinary collaborations. This convergence of science, technology, and collaborative research heralds a future where soils are not just seen as substrates but as active, dynamic entities in the fight against climate change.

An dataset of carbon and water fluxes over the reed wetlands in Panjin City (2018–2020)

With significant carbon sink capacity, active water vapor exchange and heat regulation capacity, wetlands are key ecosystems for stabilizing greenhouse gas emissions and mitigating climate change. Despite Liaohe Delta wetland being the largest warm temperate coastal wetland in Asia, its long-term carbon and water fluxes of the wetland are still not thoroughly examined, which limits the accuracy of simulating CO2 fluxes and regional carbon sinks. As a result, it is urgent to carry out long-term data monitoring and sorting in this area. This dataset is the flux data of the reed wetland ecosystem in Liaohe Delta from 2018 to 2020, collected from the Panjin Reed Wetland Research Station of the Northeast Ecological and Agrometeorological Field Experimental Base of China Meteorological Administration. Based on the data processing system of China Flux Observation and Research Network (ChinaFLUX), we established the standardized dataset of ecosystem carbon and key meteorological elements, including data files at half-hourly, daily, monthly and yearly scales. This dataset is of great significance in accurately evaluating the status and roles of carbon and water fluxes in the reed wetland ecosystem of Liaohe Delta in the regional and global carbon and water cycles.

Complementary use of thermogravimetric analysis and oven to assess the composition and bound CO2 content of recycled concrete aggregates

The carbonation of recycled concrete aggregates (RCA) has emerged as a possible significant carbon sink to mitigate the increase of CO2 concentration in atmosphere and global warming. A reliable determination of bound CO2 content is thus needed to optimize carbonation processes but there is no real consensus on the existing quantification methods, mainly based on thermal decomposition of calcium carbonate. With the aim of developing a relevant quantification method of bound CO2 during the carbonation of RCA, an experimental study based on the combination of two main techniques – thermogravimetric analysis (TGA) and high-temperature oven – was performed at different scales: paste, mortar, and concrete. XRD analyses allowed highlighting the overlaps between the decomposition of portlandite and calcium carbonate polymorphs during linearly increasing temperatures. Oven and TGA with isothermal steps were found to provide consistent and complementary data on RCA composition and their bound CO2 content from initially dried specimens.

Asymmetry of carbon sequestrations by plant and soil after forestation regulated by soil nitrogen

Forestation is regarded as an effective strategy for increasing terrestrial carbon sequestration. However, its carbon sink potential remains uncertain due to the scarcity of large-scale sampling data and limited knowledge of the linkage between plant and soil C dynamics. Here, we conduct a large-scale survey of 163 control plots and 614 forested plots involving 25304 trees and 11700 soil samples in northern China to fill this knowledge gap. We find that forestation in northern China contributes a significant carbon sink (913.19 ± 47.58 Tg C), 74% of which is stored in biomass and 26% in soil organic carbon. Further analysis reveals that the biomass carbon sink increases initially but then decreases as soil nitrogen increases, while soil organic carbon significantly decreases in nitrogen-rich soils. These results highlight the importance of incorporating plant and soil interactions, modulated by nitrogen supply in the calculation and modelling of current and future carbon sink potential.

Community Forests of Rogho and Boala, Significant Carbon Sinks in the Center-West Region of Burkina Faso

This study aimed to evaluate the carbon stock potential of the community forests of Rogho and Boala. The indirect method was adopted to estimate the above and below-ground woody biomass, while the integral collection method was chosen to estimate the herbaceous biomass. Data was collected from 77 circular plots with a radius of 18m, which included the diameter and height of plant species within these plots. The data analysis that the Boala community forest produced 2,150.7 t/ha of biomass, which corresponded to 1,075.35 t/ha of carbon, while the Rogho community forest produced 402.81 t/ha of biomass, which corresponded to 201.41 t/ha of carbon. The G1 group had the highest amount of carbon sequestered with 2,327.61 t/ha of biomass, which corresponded to 1,163.80 tC/ha. The CCEN unit had the lowest amount with 262.49 t/ha of biomass, which corresponded to 131.24 tC/ha. The proportion of herbaceous biomass in the carbon stock in the Rogho and Boala sites was 4.49% and 0.8%, respectively. Therefore, there is a need to strengthen the management of these forest areas to further improve their carbon storage potential.

Carbon-sink potential of continuous alfalfa agriculture lowered by short-term nitrous oxide emission events

Alfalfa is the most widely grown forage crop worldwide and is thought to be a significant carbon sink due to high productivity, extensive root systems, and nitrogen-fixation. However, these conditions may increase nitrous oxide (N2O) emissions thus lowering the climate change mitigation potential. We used a suite of long-term automated instrumentation and satellite imagery to quantify patterns and drivers of greenhouse gas fluxes in a continuous alfalfa agroecosystem in California. We show that this continuous alfalfa system was a large N2O source (624 ± 28 mg N2O m2 y−1), offsetting the ecosystem carbon (carbon dioxide (CO2) and methane (CH4)) sink by up to 14% annually. Short-term N2O emissions events (i.e., hot moments) accounted for ≤1% of measurements but up to 57% of annual emissions. Seasonal and daily trends in rainfall and irrigation were the primary drivers of hot moments of N2O emissions. Significant coherence between satellite-derived photosynthetic activity and N2O fluxes suggested plant activity was an important driver of background emissions. Combined data show annual N2O emissions can significantly lower the carbon-sink potential of continuous alfalfa agriculture.

Substantial role of check dams in sediment trapping and carbon sequestration on the Chinese Loess Plateau

Understanding the processes governing lateral terrestrial organic carbon transfer is confounded by the fact that organic carbon deposits on land have not yet been fully explored. Despite recent advances in understanding organic carbon deposition in aquatic ecosystems, the burial of organic carbon in dry depositional environments remains unclear. Here, combining large-scale field surveys and remote sensing techniques, we provide a robust estimate for sediment retention and organic carbon burial of check dams on the Chinese Loess Plateau. We find that the 50,226 active check dams have intercepted 10.2 ± 0.6 Pg eroded sediment during 1970-2020, which equals to 46% of the sediment load of Yellow River. Based on 86 deep sediment cores, we estimate that 21.6 ± 9.9 Tg of organic carbon was buried over the past 50 years by check dams with a burial rate of 468 ± 204 g C m−2 yr−1, approximately one order of magnitude higher than that of global lakes/reservoirs. We also find that the organic carbon burial efficiency of check dams (~80%) is significantly higher than in other depositional environments. We argue that organic carbon burial by check dams represents a significant terrestrial carbon sink and must be accounted for in global carbon budget.

Quantifying an Overlooked Deciduous‐Needleleaf Carbon Sink at the Southern Margin of the Central‐Siberian Permafrost Zone

AbstractWith over 700 million km2 Siberia is the largest expanse of the northern boreal forest—deciduous‐needleleaf larch. Temperatures are increasing across this region, but the consequences to carbon balances are not well understood for larch forests. We present flux measurements from a larch forest near the southern edge of Central‐Siberia where permafrost degradation and ecosystem shifts are already observed. Results indicate net carbon exchanges are influenced by the seasonality of permafrost active layers, temperature and humidity, and soil water availability. During periods when surface soils are fully thawed, larch forest is a significant carbon sink. During the spring‐thaw and fall‐freeze transition, there is a weak signal of carbon uptake at mid‐day. Net carbon exchanges are near‐zero when the soil is fully frozen from the surface down to the permafrost. We fit an empirical ecosystem functional model to quantify the dependence of larch‐forest carbon balance on climatic drivers. The model provides a basis for ecosystem carbon budgets over time and space. Larch differs from boreal evergreens by having higher maximum productivity and lower respiration, leading to an increased carbon sink. Comparison to previous measurements from another northern larch site suggests climate change will result in an increased forest carbon sink if the southern larch subtype replaces the northern subtype. Observations of carbon fluxes in Siberian larch are still too sparse to adequately determine age dependence, inter‐annual variability, and spatial heterogeneity though they suggest that boreal larch accounts for a larger fraction of global carbon uptake than has been previously recognized.

The dispersal of fluvially discharged and marine, shelf-produced particulate organic matter in the northern Gulf of Mexico

Abstract. Rivers play a key role in the global carbon cycle by transporting terrestrial organic matter (TerrOM) from land to the ocean. Upon burial in marine sediments, this TerrOM may be a significant long-term carbon sink, depending on its composition and properties. However, much remains unknown about the dispersal of different types of TerrOM in the marine realm upon fluvial discharge since the commonly used bulk organic matter (OM) parameters do not reach the required level of source- and process-specific information. Here, we analyzed bulk OM properties, lipid biomarkers (long-chain n-alkanes, sterols, long-chain diols, alkenones, branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs and isoGDGTs)), pollen, and dinoflagellate cysts in marine surface sediments along two transects offshore the Mississippi–Atchafalaya River (MAR) system, as well as one along the 20 m isobath in the direction of the river plume. We use these biomarkers and palynological proxies to identify the dispersal patterns of soil–microbial organic matter (SMOM), fluvial, higher plant, and marine-produced OM in the coastal sediments of the northern Gulf of Mexico (GoM). The Branched and Isoprenoid Tetraether (BIT) index and the relative abundance of C32 1,15-diols indicative for freshwater production show high contributions of SMOM and fluvial OM near the Mississippi River (MR) mouth (BIT = 0.6, FC321,15 > 50 %), which rapidly decrease further away from the river mouth (BIT < 0.1, FC321,15 < 20 %). In contrast, concentrations of long-chain n-alkanes and pollen grains do not show this stark decrease along the path of transport, and especially n-alkanes are also found in sediments in deeper waters. Proxy indicators show that marine productivity is highest close to shore and reveal that marine producers (diatoms, dinoflagellates, coccolithophores) have different spatial distributions, indicating their preferred niches. Close to the coast, where food supply is high and waters are turbid, cysts of heterotrophic dinoflagellates dominate the assemblages. The dominance of heterotrophic taxa in shelf waters in combination with the rapid decrease in the relative contribution of TerrOM towards the deeper ocean suggest that TerrOM input may trigger a priming effect that results in its rapid decomposition upon discharge. In the open ocean far away from the river plume, autotrophic dinoflagellates dominate the assemblages, indicating more oligotrophic conditions. Our combined lipid biomarker and palynology approach reveals that different types of TerrOM have distinct dispersal patterns, suggesting that the initial composition of this particulate OM influences the burial efficiency of TerrOM on the continental margin.

Geochemistry and organic petrography of the Middle Permian Lucaogou alkaline lacustrine oil shale in the southern Junggar Basin, China: Implications for formation conditions and organic matter accumulation

Organic matter (OM) accumulation in terrestrial sediments shows not only a significant carbon sink in the Earth's carbon cycle but an important origin of fossil fuels, which is closely associated with the complex and diverse depositional environments and climate conditions. The Junggar Basin developed the most laterally extensive and thickest alkaline lacustrine sediments as well as the richest hydrocarbon source rock/oil shale interval of all the world during the deposition of the Lucaogou Formation and equivalent units. In this study, the sedimentary succession of 564 m with a mudstone and dolomite matrix of the Lucaogou oil shale from the Qi 1 well located in the southern Junggar Basin was investigated, which can be divided into two members based on lithology. This paper is a synthetic use of major element oxides, trace, and rare-earth elements as well as organic petrography data as proxies to evaluate the provenance, paleotectonic setting, paleoclimate and weathering conditions, paleoenvironment, and paleoproductivity as well as origin and accumulation of OM of the Lucaogou sediments.It is suggested that no recycling sediments in all the studied samples, based on parameters including the Th/Sc vs. Zr/Sc plot, the Chemical Index of Alteration (CIA) being linearly dependent on Weathering Index of Parker (WIP), and the high Index of Compositional Variability. The provenance mainly from intermediate-felsic volcanic rocks (e.g., granodiorite, andesite and dacite) is supported by the bivariate plots of Euanom vs. Th/Sc, La/Th vs. Hf, La/Sc vs. Co/Th, Cr/Th vs. Sc/Th, Y/Ni vs. Cr/V, and Nb/Y vs. Zr/TiO2 as well as triangular diagrams of mafic–felsic–weathering, M+–4Si–R2+ and Rb/V–Zr/Zn–Sc/Nb. The continental island arc is inferred from paleotectonic setting discrimination diagrams (i.e., the La–Th–Sc, Th–Co–Zr/10 and Th–Sc–Zr/10 ternary as well as Ti/Zr vs. La/Sc binary diagrams). The chemical weathering indices (i.e., the CIA, WIP, weathering index (W), Weathering Intensity Scale, Sodium Depletion Index, and Ga/Rb vs. K2O/Al2O3 binary diagram) indicate the paleoclimate conditions were cold/arid with weak chemical weathering in a warming and/or enhanced continental weathering episode. Besides, the Sr/Ba ratios and gallium concentrations indicate the paleosalinity was brackish to hypersaline and was higher in the lower member in relation to that in the upper member. However, the suboxic environment of the benthic water (inferred from the MoEF vs. UEF co-variations and Corg/P ratios as well as large sizes of framboidal pyrites) and the moderate paleoproductivity (evaluated via the Sibio, Babio, and Pbio values, as well as Ni/Al and Cu/Al ratios) caused by predominate algae and bacteria (inferred from the organic petrography) kept stable in the paleolake during this period. The OM accumulation was mainly controlled by the preservation conditions rather than the paleoproductivity and limited detrital inputs/low deposition rates, which was indicated by the plot of Co × Mn values vs. Cd/Mo ratios and the total organic carbon contents being negatively related to stable carbon isotope compositions of OM.