Carbon In Sediments Research Articles

Lake Surface Water Temperature in high altitude lakes in the Pyrenees: Combining satellite with monitoring data to assess recent trends

Lake Surface Water Temperature (LSWT) influences critical bio-geological processes in lake ecosystems, and there is growing evidence of rising LSWT over recent decades worldwide and future shifts in thermal patterns are expected to be a major consequence of global warming.At a regional scale, assessing recent trends and anticipating impacts requires data from a number of lakes, but long term in situ monitoring programs are scarce, particularly in mountain areas. In this work, we propose the combined use of satellite-derived temperature with in situ data for a five-year period (2017–2022) from 5 small (<0.5km2) high altitude (1880–2680 masl) Pyrenean lakes. The comparison of in situ and satellite-derived data in a common period (2017–2022) during the summer season showed a notably high (r = 0.94, p < 0.01) correlation coefficient, indicative of a robust relationship between the two data sources. The root mean square errors ranged from 1.8 °C to 3.9 °C, while the mean absolute errors ranged from 1.6 °C to 3.6 °C.We applied the obtained in situ-satellite eq. (2017–2022) to Landsat 5, 7 and 8/9 data since 1985 to reconstruct the summer surface temperature of the five studied lakes with in situ data and to four additional lakes with no in situ monitoring data. Reconstructed LSWT for the 1985–2022 showed an upward trend in all lakes. Moreover, paleolimnological reconstructions based on sediment cores studies demonstrate large changes in the last decades in organic carbon accumulation, sediment fluxes and bioproductivity in the Pyrenean lakes.Our research represents the first comprehensive investigation conducted on high mountain lakes in the Pyrenees that compares field monitoring data with satellite-derived temperature records. The results demonstrate the reliability of satellite-derived LSWT for surface temperatures in small lakes, and provide a tool to improve the LSWT in lakes with no monitoring surveys.

Sediment carbon storage in subtidal beds of the invasive seagrass Halophila stipulacea along an extreme water depth gradient, St. Thomas, U.S. Virgin Islands

Blue carbon ecosystems such as mangroves, salt marshes, and seagrass beds are found globally and are fundamental to fisheries production, storm surge protection, and carbon sequestration. The contribution of seagrass ecosystems to global carbon stocks is still not well understood, including in the United States Virgin Islands (USVI). No study has been published to-date assessing the sediment carbon density (SCD) in seagrass beds in the USVI. This study focused on the carbon storage ability of the invasive species, Halophila stipulacea, which is compact in size compared to common native seagrasses and has spread rapidly to become a dominant seagrass in the USVI. This species forms dense mats across a wide depth range (<1 m to 50 m) typically uninhabitable to its native counterparts (Syringodium filiforme and Thalassia testudinum). Several biotic and abiotic factors influence the carbon storage ability of seagrass, yet little is known about carbon storage sequestration along a depth gradient for H. stipulacea. This study provides the first assessment of the biological characteristics (shoot density, leaf area, leaf height, and percent cover) and carbon storage ability of H. stipulacea across a depth gradient (shallow: 5–10 m; medium: 15–20 m; deep: 25–30 m) at two sites in St. Thomas, USVI. Mean sediment carbon density (SCD) values per core reported for H. stipulacea in this study ranged from 3.88 to 15.67mgC/cm3; these were comparable to regional and global seagrass studies. Biological characteristics were not an accurate predictor of SCD. A significant interaction between water depth and site was found to affect mean SCD of H. stipulacea beds. It is likely that site-specific factors most likely account for variations seen within the data. Although carbon values in this study compared to values reported in the literature, other factors such as land use, proximity to carbon sources, sediment microbial community, and water current patterns may be driving SCD values. These findings highlight the need for site and species-specific carbon storage assessments on local to regional scales to accurately estimate current and forecasted blue carbon stocks.

Application of remote sensing methods for monitoring extent, condition and blue carbon storage in salt marshes

Salt marshes are fragile coastal ecosystems that provide a wide range of ecosystem services, including carbon sequestration and storage. Despite the importance of salt marshes for blue carbon sequestration, few studies have been done on blue carbon monitoring using satellite remote sensing techniques. This study arose to fill this knowledge gap, and aimed to determine the amount of blue carbon sequestered in salt marshes by analyzing the particular case of the Pancas salt marsh (Tagus Estuary, Portugal). To achieve this, the extent and condition of the Pancas salt marsh were assessed using remote sensing methods, by establishing a methodology that effectively identified and validated its extent based on Sentinel-2 imagery from 2016 to 2022. This method involves generating a reference salt marsh extent map followed by mapping salt marsh extent through four Vegetation Indices (VI) from Sentinel-2 data to compare and thus validate the salt marsh extent based on the information provided by the satellite. Considering the extent of the salt marsh and the changes it has undergone over the 7 years studied, together with reference values for sequestered carbon in the salt marsh sediments, approximate values for sequestered blue carbon were determined. The results highlighted the validation of Normalised Difference Vegetation Index (NDVI) as the best-performing VI for this study and as a proxy for the condition of the salt marsh in terms of the spatial and temporal distribution of its aboveground biomass. It was also verified that the salt marsh expanded its frontal region by 0.22 km2 between 2016 and 2022, while certain areas of high marsh have suffered dieback. Concerning sequestered carbon, an increase of 508.2 tonnes since 2016 was quantified, corresponding to 66500 tonnes of blue carbon stored for 2022. Our study revealed the intrinsic relationship between the extent of a salt marsh and its carbon sequestration capacity highlighting the importance of future application of more remote sensing techniques, to emphasize the significant role of these ecosystems in carbon sequestration and climate change mitigation.

The inputs of autochthonous organic carbon driven by mangroves reduce metal mobility and bioavailability in intertidal regions

The significance of mangroves in carbon storage is widely acknowledged. However, the potential role of carbon enhancement driven by mangroves in mitigating the risk of metal exposure remains unclear. In this study, a natural mangrove reserve located in Futian was selected to investigate the potential role of autochthonous organic carbon on metal bioavailability. The presence of mangroves seemed to have little effect on the accumulations of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) in surface sediments. Metal mobility and bioavailability, however, were found to be directly influenced by the presence of mangroves. Compared with mudflat, mangrove sediments exhibited an obvious in the bioavailability of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) by 19–79 %, with the highest reduction occurring in the interior of mangroves dominated by K. obovata. Mangroves also significantly enhanced the accumulation of organic carbon in sediments, regardless of carbon components. Moreover, the results from random forest analysis further showed that autochthonous organic carbon was the most important carbon component that negatively related to metal bioavailability. In summary, this is the first study to provide a linkage between mangrove cover and increased autochthonous organic carbon input, which decreases metal bioavailability. The present data also suggest that mangroves are an efficient natural barrier to alleviate the risk of metal exposure in intertidal regions.

Hydrothermal alteration and geochemical proximity indicators to ore at the Metsämonttu Zn–Pb–Cu–Au–Ag deposit, Uusimaa belt, southern Finland

The Paleoproterozoic Metsämonttu Zn–Pb–Cu–Ag–Au deposit (1.5 Mt at 3.5 wt% Zn, 0.8 wt% Pb, 0.3 wt% Cu, 13.2 wt% S, 25 g/t Ag, and 1.4 g/t Au, production 1952–1974) is the largest past-producing mine in the Aijala–Orijärvi area (Orijärvi formation, Aijala member) within the Uusimaa belt, southern Finland. The Aijala member is characterized by 1.9–1.88 Ga felsic-dominated volcanic-sedimentary supracrustal rocks with intercalated sedimentary carbonates and iron formations. The area is underexplored, and little deposit-scale research has been carried out, despite the lateral continuum to the world-class ore district of Bergslagen in south-central Sweden. To better understand the Metsämonttu VMS-related alteration system, we reassessed the previously described metamorphic mineral assemblages and their protolith rock compositions by using mobile and immobile element geochemistry. This resulted in the definition of four metamorphosed alteration mineral assemblages and eight chemostratigraphic rock units. The chemostratigraphic results suggest that the lithological and/or structural setting of the Metsämonttu succession is more complex than previously considered. The stratigraphic footwall is mainly characterized by an extensive cordierite + anthophyllite ± biotite ± phlogopite + pyrite ± pyrrhotite (Mg–Fe–S) assemblage dominated by mafic rocks, designated Mafic B1 and Mafic B2, and Andesite A1. The main sulfide mineralization is hosted by tremolite + diopside ± biotite ± phlogopite ± chlorite skarn (Ca–Mg–K). A sericite-bearing muscovite + quartz ± biotite ± phlogopite + pyrite (K–Si–S) assemblage is composed of felsic to mafic protoliths (Mafic B1–B2, Andesite A1, Dacite A1, Dacite B1, Dacite C1) and extends several tens of meters into the stratigraphic hanging-wall. A quartz + pyrite ± muscovite (Si–S) assemblage represents the immediate ore-proximal alteration and is derived from rocks with a rhyolitic composition (Rhyolite A1).Limited drill core samples near Metsämonttu mineralization, along with restricted surface alteration, pose challenges in studying geochemical variations from distal to ore proximal areas and limits the ability to model the shape and size of the alteration zone. Large mass changes suggest that the alteration was hydrothermal, and due to several protolith compositions, the alteration is interpreted to be predominantly discordant to stratigraphy. A 60-m-wide alteration halo surrounds the Metsämonttu deposit. Major and trace elements, namely MgO, Na2O, K2O, SiO2, Fe2O3, Cu, Zn, Pb, S, Ag, Tl, Hg, Se, Te, Sn, Sb, Rb, and Sr, and the indices modified alteration index (MAI), Ishikawa alteration index (AI), chlorite‑carbonate-pyrite index (CCPI), S/Na2O can be used for chemical vectoring, which can assist regional or near-mine exploration. Elements MnO, Ba, Cd, Bi, As, Ni, Co, W, Ga, Mo, and indices Hashigushi index and advance argillic alteration index (AAAI) were less useful as geochemical exploration indicators.

History of human activity in South China since 7 cal ka BP: Evidence from a sediment record in the South China Sea

Human modifications of the Earth System have been getting increasing attention and this has resulted in the concept of the “Anthropocene”. A complete sequence of human-environment interactions needs to be reconstructed to define the onset of the Anthropocene. To address the chronological gaps and provide a general history of human impact in South China during the Holocene, we present a comprehensive reconstruction of the vegetation, chemical weathering, and heavy metal emissions in the Pearl River and Hainan catchments since 7.0 cal ka BP, using a continuous record of black carbon, clay minerals, and major and trace element concentrations of sediment in Core ZK001 taken from the northwestern South China Sea. Based on high-resolution sediment records, combined with archaeological and historical documents, we propose that human impact in South China can be divided into three stages: a hunting-gathering age (7.0–2.9 cal ka BP), a transitional period (2.9–2.0 cal ka BP) and an intensive farming age (<2.0 cal ka BP). Climate controlled both the vegetation and chemical weathering intensity before 2.9 cal ka BP, after which forest clearance by human-induced fire became significant. Along with population growth and technological progress, enhanced human activities including deforestation, cultivation, and metallurgical activities, gradually superseded natural processes and profoundly impacted the environment in South China, especially after 2.0 cal ka BP. Combined with previous studies from the Pearl River catchment, the Anthropocene likely commenced at 2−3 cal ka BP at least in South China.

Quantification and isotopic characterization of benzene polycarboxylic acids (BPCA)-derived black carbon in deep oceanic sediments: Towards assessing pyrogenic inputs from marine sources

Methodologies based on benzene polycarboxylic acids (BPCA) selectively target the polymeric aromatic fraction of black carbon (BC) and are considered adequate to quantify pyrogenic inputs in environmental samples such as soils, lakes, and marine dissolved organic carbon. However, the usefulness of these methodologies to quantify BPCA-derived BC in deep-sea sediments has not been fully evaluated. In this manuscript we describe and validate a procedure to quantify BPCAs in deep oceanic sediments with very low organic carbon content. The resulting analytical procedure has produced reproducible quantitative data for BPCAs over a period of 10 months (coefficient of variation, CV = 6.4 − 6.6%). The stable carbon isotopes (δ13C) of BC_BPCA have been characterized using an LC Isolink™-irMS system with an accuracy better than 0.5‰. The quantitative and isotopic composition of several marine sediments has been characterized to investigate the relative contributions of marine/diagenetic and continental/pyrogenic sources to the BC accumulated in oceanic sediments from different contexts, ranging from upwelling systems to remote oceanic locations. Overall, a significant fraction of the sedimentary BC is of marine origin and should be considered in inventories of pyrogenic materials accumulated in the world oceans. However, the continental/pyrogenic sources can be largely dominant in marine settings with large inputs of pyrogenic materials.

Shallow mantle cycle of subducted sedimentary limestone indicated by carbonate xenoliths

In the subduction zone, carbon (C) release from the subducted plate into the mantle wedge takes place by various mechanisms, including metamorphic degassing, carbonate dissolution, and hydrous melting. Recent studies have highlighted the significant role of buoyant limestone diapirs in facilitating C recycling during subduction processes. Here, we report that the Hannuoba carbonate xenoliths of eastern China were introduced into the shallow mantle in the form of sedimentary limestone diapirs. We conducted a comprehensive study of the Hannuoba carbonate xenoliths using petrological analysis, major- and trace-element analysis, in situ zircon dating, and C-O isotopic analysis techniques. The whole-rock major and trace elements, along with high δ18OSMOW values (22.8‰−23.2‰), indicate that the protolith of Hannuoba carbonate xenoliths consists of sedimentary limestones. The spectral age peaks of detrital zircons (400−100 Ma, 500−450 Ma, 2.0−1.6 Ga, and 2.8−2.2 Ga) suggest that the primary source of the protolith is the North China Craton. When sedimentary limestone diapirs enter into the mantle wedge, they undergo partial melting under high-temperature conditions. This process results in the melting of low-melting point pelitic components, while leaving behind resistant minerals such as pure calcite. Due to its low density and viscosity, this pure limestone component will continue to migrate upward and assimilate with the mantle peridotite. In this process, the pure calcites are preserved in the shallow mantle in a solid-state form rather than as carbonatitic melts. The discovery of graphite and spinel in the Hannuoba carbonate xenoliths indicates that the depth of formation of the sedimentary limestone diapirs does not exceed 2.5 GPa (&amp;lt;70 km). The calcite in Hannuoba carbonate xenoliths exhibits extremely low δ13CVPDB (−11.8‰ to −11.0‰) and high δ18OSMOW (22.8‰−23.2‰) contents. This characteristic C-O isotopic signature can be explained by the Rayleigh decarbonation of sedimentary limestones under upper-mantle conditions (&amp;lt;3 GPa). Based on calculations, the Hannuoba carbonate xenoliths are a product of subducted sedimentary limestone experiencing 99% volume decarbonation. Through this metamorphic decarbonation process, limestone diapirs release a significant amount of CO2 into the arc magma system. During subduction processes, sedimentary carbonate rocks can be recycled to the mantle wedge of island arcs as solid limestone diapirs. The C flux released by this mechanism cannot be ignored.

Estimation of Mariculture Carbon Sinks in China and Its Influencing Factors

The scientific assessment of mariculture carbon sinks is crucial to recognize its potential as a significant component of marine blue carbon in global climate change mitigation. Therefore, the objective of the research was to estimate the seaweed and shellfish mariculture carbon sink of different varieties in various sea areas. The paper emphasized the distinction between short-term carbon sequestration in seaweed and shellfish that can be removed and long-term carbon sequestration that is deposited. Methodologically, the evaluation was based on the carbon sequestration mechanism and systematic pathways in shellfish and seaweeds. Additionally, the carbon sequestration of shellfish and seaweed aquaculture over the last decade was evaluated by the carbon sink assessment model, and the reasons for the differences in the carbon sink capacity of mariculture in China’s coastal provinces were discussed by using the LMDI decomposition model. The results indicated the carbon sequestration of offshore seaweeds and shellfish mariculture in China was huge. From 2010 to 2020, offshore seaweed aquaculture in China amounted to 7.959 Mt C/a, while shellfish aquaculture contributed 33.542 Mt C/a to the carbon sinks. Sedimentary carbon sequestration by shellfish accounted for 51% of the total carbon sequestration in mariculture involving shellfish and seaweeds. Especially noteworthy is the sedimentary carbon sequestration by shellfish, which is an indispensable and crucial component of mariculture carbon sequestration estimation. It is concluded that improvements in farming efficiency exerted the greatest influence on the variations of the mariculture carbon sink, while adjustments in farming structure had a relatively minor impact in the case of little change in aquaculture yield. Enhancing farming efficiency emerges as a practical approach to bolstering the carbon sink potential of marine aquaculture fisheries in the future.

Sources and pathways of carbon and nitrogen of macrophytes and sediments using stable isotopes in Al-Kharrar Lagoon, eastern Red Sea coast, Saudi Arabia.

Elemental ratios (δ13C, δ15N and C/N) and carbon and nitrogen concentrations in macrophytes, sediments and sponges of the hypersaline Al-Kharrar Lagoon (KL), central eastern Red Sea coast, were measured to distinguish their sources, pathways and see how they have been influenced by biogeochemical processes and terrestrial inputs. The mangroves and halophytes showed the most depleted δ13C values of -27.07±0.2 ‰ and -28.34±0.4 ‰, respectively, indicating their preferential 12C uptake, similar to C3-photosynthetic plants, except for the halophytes Atriplex sp. and Suaeda vermiculata which showed δ13C of -14.31±0.6 ‰, similar to C4-plants. Macroalgae were divided into A and B groups based on their δ13C values. The δ13C of macroalgae A averaged -15.41±0.4 ‰, whereas macroalgae B and seagrasses showed values of -7.41±0.8 ‰ and -7.98 ‰, suggesting uptake of HCO3- as a source for CO2 during photosynthesis. The δ13C of sponges was -10.7±0.3 ‰, suggesting that macroalgae and seagrasses are their main favoured diets. Substrates of all these taxa showed δ13C of -15.52±0.8 ‰, suggesting the KL is at present a macroalgae-dominated lagoon. The δ15N in taxa/sediments averaged 1.68 ‰, suggesting that atmospheric N2-fixation is the main source of nitrogen in/around the lagoon. The heaviest δ15N (10.58 ‰) in halophytes growing in algal mats and sabkha is possibly due to denitrification and ammonia evaporation. The macrophytes in the KL showed high C %, N %, and C/N ratios, but this is not indicated in their substrates due possibly to a rapid turnover of dense, hypersaline waters carrying most of the detached organic materials out into the Red Sea. The δ13C allowed separation of subaerial from aquatic macrophytes, a proxy that could be used when interpreting paleo-sea level or paleoclimatic changes from the coastal marine sediments.

Rapid and sensitive determination of trace Cd in carbonate samples using direct solid sampling electrothermal vaporization atomic absorption spectrometry

The accurate determination of cadmium (Cd) hosted and accumulated in sedimentary carbonate remains challenging due to its low concentration (ng·g−1) and complex matrix. Conventional methods, such as inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GF-AAS), which typically rely on liquid sampling and sample digestion, are tedious, labor-intensive and time-consuming. In this study, a rapid and sensitive method for the direct determination of carbonate-hosted Cd was developed based on solid sampling electrothermal atomic absorption spectrometry (SS-ETV-AAS). This method eliminates the need of acid digestion procedure, allowing the entire analysis, including sample preparation, to be completed within 10 min. To minimize the carbonate matrix effect, ethylene diamine tetra acetic acid disodium salt (EDTA-2Na) was proposed as matrix modifier to facilitate the release of Cd, enabling fast and accurate determination of trace Cd in carbonate samples. Under optimized conditions, the Cd detection limits was found to be as low as 0.17 ng·g−1, and repeatability (relative standard deviation, RSD) was better than 8 % (n = 7). The accuracy of the proposed SS-ETV-AAS was verified by analyzing five carbonate certified reference materials (GBW07127, GBW07129, GBW07130, GBW07135 and JDo-1), two soil certified reference materials (GBW07404a, GBW07405), as well as several actual carbonate samples. All these results demonstrate that the proposed SS-ETV-AAS method provides a simple, rapid and sensitive approach for measuring trace Cd in carbonates.

Recommended centrifuge method: Specific grain size separation in the

The isolation of specific grain size classes of lithogenic samples and biogenic carbonate from the <63 µm fraction (i.e. clay and silt) of marine sediment is often a prerequisite to further pre-treatments and/or analytical measurements for palaeoceanographic studies. Established techniques employed have included sieving, settling and micro-filtration (and/or a combination of these). However, these methods often use significant amounts of bulk sediment (often up to ∼3 g) and/or require considerable amounts of time during sediment processing (ranging from 48 h to 3 weeks) to isolate a size specific class for further analyses. Here, we build on previous approaches to isolate three grain size classes (e.g. <2 µm, clay; 2–10 µm, fine silt; and 10–63 µm, coarse silt) from the <63 µm fraction of marine sediment with the aid of a centrifuge at varying revolutions per minute using Stokes’ Law. We show the utility of our approach using two common sediment types dominated by (i) lithogenic and (ii) biogenic carbonate (specifically coccoliths) components of marine sediment cores. Our method reduces the amount of sample material required to 1–2 g to provide an isolated clay fraction (or other targeted size fraction) and decreases the sample processing time (to ∼1 hour) to enable high throughput of analysis, when compared to previous techniques for palaeoceanographic proxy measurements.•We recommend a more straightforward grain size isolation method for lithogenic sediment and biogenic carbonate sediment types•Isolating commonly targeted grain size fractions for palaeoceanographic studies using a centrifuge

Factors controlling long-term carbon sequestration in the paleo-Yellow River delta: Implications for future delta management

River deltas have contributed to the regulation of atmospheric CO2 concentrations throughout Earth's history, but the capacity and controlling factors for deltas to serve as permanent carbon sinks over the long term are unclear. To address this issue, we carried out a high-resolution assessment of carbon burial in a well-dated sediment core (BXZK13) from the paleo-Yellow River delta on the west coast of the Bohai Bay. We found that the sedimentary environments in core BXZK13 since the Late Pleistocene (∼84 k cal yr B.P.) were divided into seven depositional units. The apparent mass accumulation rate (AMAR) of total organic carbon (TOC) and total inorganic carbon (TIC) varied significantly between depositional units. The average rates were highest in delta front deposits (TOC: 135 g m−2 yr−1, TIC: 333 g m−2 yr−1). Notably, the rates of carbon accumulation were dominated by TIC. The differences in the characteristics of TIC in the borehole compare to those of carbonates in Yellow River sediments and the positive correlation between TIC and Fe suggested that authigenic carbonate contributed significantly to long-term carbon burial in the delta. The apparent sedimentation rate (ASR) dominated the variations of the carbon AMAR, and the high clay and Fe content in the sediment enhanced TOC preservation and authigenic carbonate precipitation. Low concentrations of TIC were associated with several cold events, and there was a positive correlation between the chemical index of alteration and TIC. The implication was that climate may have affected the dynamics of inorganic carbon burial by regulating authigenic carbonate precipitation. These results enable a more thorough understanding of the factors that control long-term carbon sequestration, which is critical for both management purposes as well as assessment of the role of deltas in past and future climate change.

Mixed siliciclastic-carbonate-tuffaceous sedimentation in a rift lacustrine basin: A case study of the Lower Cretaceous Jiufotang Formation in the Luxi sag, Songliao basin

The Lower Cretaceous Jiufotang Formation lacustrine successions in the rift Luxi sag, Songliao Basin are characterized by mixed siliciclastic-carbonate-tuffaceous and organic-rich deposits. Ten facies were recognized and were formed in fan delta, delta, littoral-sublittoral lacustrine and deep lacustrine environments. A depositional sequence characterized by significant changes in facies and lake regime has been defined, and is divided into lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) that are separated by sequence boundaries, initial flooding surfaces, and maximum flooding surfaces, respectively. During the LST, the delta and fan delta deposits covered the marginal area and extended into littoral-sublittoral lacustrine and deep lacustrine environments, respectively. During the TST, the areas of delta and fan delta decreased and lake areas increased, and the carbonate-dominated shoals and mixed siliciclastic-carbonate shorelines occupied the edge of the Majiapu highland belt. During the HST, the lake areas further expanded, and the fan delta deposits extended into deep lacustrine environments and formed deposits of underflows and turbidites. A depositional model in the rift lacustrine Luxi sag is proposed, incorporating the effects of tectonics and sediment supply, climate and carbonate production, hydrodynamic conditions, and lake-level fluctuations. During the LST, the active tectonic movement, high input of siliciclastic sediments, and subaerial volcanic eruptions resulted in the wide distribution of mixed siliciclastic-tuffaceous sedimentation. During the TST, the brackish lake water controlled by periodic dry and hot climate facilitated the carbonate deposition in shallow water, and tractional currents onto the lake shore carried sediments to form the mixed siliciclastic-carbonate-tuffaceous facies. During the HST, more humid climate and increased runoff allowed formation of widely distributed, mostly oil shale-rich deposits, and the gravity flows carried the sediments into the deeper part of basin to form the mixed siliciclastic-carbonate-tuffaceous facies. The depositional model of mixed deposits in this rift lacustrine basin has been proposed here in order to encourage comparison with other similar basins.

Trends in estuarine pyrite formation point to an alternative model for Paleozoic pyrite burial

The early Paleozoic Era (∼540–420 Ma) was an interval of profound biogeochemical changes including increasing oxygen (O2) and the onset of bioturbation (sediment mixing by animals). It is hypothesized that incipient bioturbation caused a monotonic decrease in sedimentary burial of pyrite (FeS2), which would have slowed atmospheric O2 accumulation. However, pyrite accumulation can exhibit complex responses to dynamic, low-O2 environmental conditions. To assess pyrite burial in a potential modern analogue to early Paleozoic environments, we collected sediment cores from the Chesapeake Bay, an estuary with multiple gradients in sulfate concentration, hypoxia intensity, organic carbon flux and lability, and bioturbation. Results indicate that pyrite accumulation is maximized not under strong sulfate depletion in highly reducing sediments, but rather in sediments that occupy the mid-range of sulfate–chloride ratios. This probably occurs through efficient replenishment of pore water sulfate and/or through the generation of sulfur redox intermediates, which promote pyrite formation via the polysulfide reaction pathway. In light of these results and in contrast to earlier models, we hypothesize that mild early Paleozoic bioturbation temporarily increased pyrite burial efficiency by stimulating higher sulfate reduction rates and increasing sedimentary sulfide retention. Compiled sulfur and carbon data from a geochemical database indicate that median sulfur-carbon ratios of fine-grained marine siliciclastic rocks increased from the Ediacaran through the Ordovician, then decreased and became much less variable from the Silurian onward. Thus, the Cambrian and Ordovician Periods may constitute a distinct interval of the Proterozoic-Phanerozoic transition in which bioturbation temporarily accelerated O2 buildup. This transition probably ended in the Silurian, when pO2 rose to sufficient levels to homogenize sedimentary carbon–sulfur cycling.

Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves on local and global scales

Mangrove soils are highly enriched in organic carbon. Tidal pumping drives seawater and oxygen into mangrove soils during flood tide and releases carbon-rich porewater during ebb tides. Here, we resolve semi-diurnal (flood/ebb tides), diel (day/night) and weekly (neap/spring tides) drivers of porewater-derived CO2 fluxes in two mangroves and update global estimates of CO2 emissions building on earlier observations from other sites. Tidal pumping controlled pCO2 variability within the two mangrove creeks. The highest values of pCO2 (2,585–6,856 µatm) and 222Rn (2,315–6,159 dpm m−3) and lowest values of pH (6.8–7.1) and dissolved oxygen (1.7–3.7 mg L−1) at low tides were due to enhanced porewater export. 222Rn and pCO2 in mangrove porewater were 4–15 and 38–41 times greater than surface waters, respectively. pCO2 increased by 50 ± 30 % from high to low tide, 9 ± 22 % from day to night and 57 ± 5 % from neap to spring tide with clear changes in hourly, diel, and weekly time scales. Combining our new estimates with literature data, global porewater-derived (16 sites) and water-atmosphere (52 sites) CO2 fluxes in mangroves would upscale to 45 ± 12 and 41 ± 10 Tg C y−1, respectively. These fluxes represent 25 % of net primary production and are twice as high as the sediment carbon burial rates in global mangroves. Overall, our local observations and global compilation suggest that porewater-derived CO2 exchange is a major but often unaccounted source of CO2 in mangroves. The porewater-derived CO2 can be emitted to the atmosphere or laterally exported to the ocean and should be included in carbon budgets to solve global imbalances.

Distribution Patterns of Sediment Organic Carbon Stocks in Shallow Lakes and the Significance for Sustainable Lake Management: Chaohu Lake in Eastern China as a Case Study

Shallow lake sediments have huge potential for carbon storage, but they are vulnerable to various environmental changes and are highly susceptible to becoming a source of carbon emissions. Understanding the amount of sediment carbon storage can provide information about the potential of shallow lakes in mitigating climate change. In this study, sediment sampling was conducted at 12 study sites in Chaohu Lake, China, and sediment water content, grain size, bulk density, and sediments organic carbon (SOC) content were examined in five layers along the vertical direction, respectively, and the distribution and storage of SOC were estimated. The results showed that the surface sediments in the west lake area of Chaohu Lake would release 66,300 t of SOC to the overlying water body in the future. The sediments in the middle lake area and the east lake area will absorb another 15,900 t and 17,300 t of TOC from the water body in the future, respectively. Overall, the lake-wide sediments will release 33,100 t of SOC into the water body in the future. In addition, the results of the study also indicate that human activities are another major influence on the change in organic carbon stocks in lake sediments, and therefore, proactive measures for the restoration and protection of lake sediments are essential because increasing the SOC stocks in the sediments and maintaining the lakes in a sustainable manner can contribute to the crucial role they play in mitigating climate change.

Sounding out horse mussel sediment thickness: an integrated data approach

Horse mussel beds are listed as a Priority Marine Feature (PMF) in Scotland for their influence in the creation of diverse benthic communities and provision of ecosystem services. In Scotland, horse mussel beds are also recognised for their importance in marine carbon sequestration. Unfortunately, there is a paucity of data on horse mussel bed carbon stocks and sediment thickness. There are also significant financial and logistical barriers with which to address these data gaps. This study investigates the robustness of Sub-Bottom Profiling (SBP) as a cost-effective method to quantify horse mussel sediment thickness across a landscape. Integrating SBP and Drop-Down Video (DDV) data, this study also details an integrated approach to investigate the links between horse mussel habitat condition and sediment thickness. With the addition of abiotic data, this study uses Structural Equation Modelling (SEM) to elucidate key relationships between abiotic factors, biotic variables, and sediment thickness. There is a significant positive correlation of horse mussel habitat condition and sediment thickness. Average horse mussel total sediment thickness, across all measures of habitat condition, was 1.37m. These findings substantially increase previous estimates of horse mussel sediment thickness, and potential value to climate change mitigation through blue carbon frameworks. This study highlights the importance of both abiotic and biotic factors on marine carbon sediment quantification.

Molecular composition and characteristics of Sediment-adsorbed Dissolved Organic Matter (SDOM) along the coast of China

Sediment-adsorbed Dissolved Organic Matter (SDOM) in coast plays a crucial role in the terrestrial and marine carbon cycle processes of the global environment. However, understanding the transport dynamics of SDOM along the coast of China, particularly its interactions with sediments, remains elusive. In this study, we analyzed the δ13C and δ15N stable isotopic compositions, as well as the molecular characteristics of SDOM collected from coastal areas spanning the Bohai Sea (BS), Yellow Sea (YS), East China Sea (ECS), and South China Sea (SCS), by using isotope ratio mass spectrometry and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). We identified the predominant sources of carbon and nitrogen in coastal sediments, revealing terrigenous origins for most C and N, while anthropogenic sources dominated in the SCS. Spatial variations in SDOM chemodiversity were observed, with diverse molecular components influenced by distinct environmental factors and sediment sources. Notably, lignins and saturated compounds (such as proteins/amino sugars) were the predominant molecular compounds detected in coastal SDOM. Through Mantel tests and Spearman's correlation analysis, we elucidated the significant influence of spatial environmental factors (temperature, DO, salinity, and depth) and sediment sources on SDOM molecular chemodiversity. These findings contribute to a more comprehensive understanding of the carbon cycle dynamics along the Chinese coast.

Mangrove ecosystems’ role in climate change mitigation

Mangrove forests are crucial to ecosystems for their benefits, and role in climate change mitigation. Across marine and terrestrial boundaries, they shield coastal areas from tidal waves and storms, with dense roots that dissipate wave energy effectively. These roots also trap carbon-rich particles from the water, storing them in sediments and fostering sediment accretion and carbon burial. Mangrove ecosystems have declined over the past five decades, largely due to aquaculture. This decline reduces coastal resilience, exacerbating risks from storms, sea-level rise, and erosion, while releasing stored carbon as CO2 emissions. Mangrove degradation is crucial for climate mitigation. Mitigation strategies should prioritize conserving ecosystems with high carbon sequestration rates, reducing anthropogenic CO2 emissions, and rehabilitating mangrove habitats converted for aquaculture. We must expand our knowledge and understanding of the significance of mangroves in delivering coastal protection, how mangrove ecosystems serve as carbon sinks, how future changes could impact them, and how anthropogenic activities and climate change can impact their carbon storage.