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Burial of organic carbon and pyrite sulfur in the modern ocean: Its geochemical and environmental significance
Abstract
It is possible to estimate the present-day rate of burial of organic carbon in marine sediments from a knowledge of the suspended load carried by rivers and the organic carbon content of resultant deltaic-shelf sediments. This is done here for a number of the world's major rivers. Extrapolation of results to all remaining rivers indicates that the total burial rate of organic carbon in shelf-deltaic muds is 130 Mt (megatons = 10/sup 12/ gm) of carbon per y. This value is decidedly lower than the rate by which organic carbon is added to the oceans by rivers, which indicates that continentally-derived organic matter must undergo appreciable biological decomposition in the marine environment. The low carbon burial also indicates that much less than 10 percent of the missing anthropogenic CO/sub 2/ produced over the past 100 yrs is present as organic carbon in marine sediments. The average organic carbon concentration calculated from this data for modern terrigenous muds is lower than that found for ancient shales, and this can be best explained in terms of dilution of carbon in modern sediments by excess river-borne mineral matter resulting from man-induced soil erosion or Pleistocene continental glaciation. The worldwide burial rate of pyritic sulfur in marine sediments, 39 Mt S per y, is obtained by dividing the organic carbon burial rate in anoxic, terrigenous, fine-grained sediments by the constant ratio of C/S found, at depth, in such sediments. The average concentration of pyrite sulfur in modern muds (0.22 percent) is somewhat lower than that estimated for ancient shales (0.35 percent), and this can be best explained in terms of dilution of the sulfur in modern muds by river-borne silicate mineral matter, from glaciation or soil erosion, in the same manner as hypothesized for organic carbon.
... More detailed analysis of the results of kNN and random forests are provided in the supplementary information. The correlation plot between measured and predicted data shows similar errors for are also consistent with the early work on TOC distributions by Berner (1982) and Emerson and Hedges (1988) marginal seas that promotes TOC preservation (Hedges and Keil, 1995). The map published by Lee et al. (2019) shows several large areas in the open Pacific that have unusually high TOC concentrations. ...
... However, TOC concentrations in shelf surface sediments are diminished by a number of factors: i. frequent biological and physical reworking that accelerates TOC degradation processes (Song et al., 2022), ii. dilution of TOC by inorganic material (clay, silt, sand) in delta deposits and other shelf regions with high sedimentation rates (Berner, 1982), ...
... Regions with fine sand, with the grain size between 0.05 mm and 0.5 mm(1, being the higher feature value) has low impact on the TOC concentration. Higher sediment thickness in the earth's crust lead to lower TOC concentration because of dilution (Berner, 1982). Higher sea surface POC and absorption of 443 nm ocean color wave length results in higher TOC concentration, while lower values of the features do not impact the model output greatly. ...
Spatial predictions of total organic carbon (TOC) concentrations and stocks are crucial for understanding marine sediments’ role as a significant carbon sink in the global carbon cycle. In this study, we present a geospatial prediction of TOC concentrations and stocks at a 5 x 5 arc minute grid scale, using a deep learning model — a novel machine learning approach based on a new compilation of over 22,000 global TOC measurements and a new set of predictors, such as seafloor lithologies, grain size distribution, and an alpha-chlorophyll satellite data. In our study, we compared the predictions and discuss the limitations from various machine learning methods. Our findings reveal that the neural network approach outperforms methods such as k Nearest Neighbors and random forests, which tend to overfit to the training data, especially in highly heterogeneous and complex geological settings. We provide estimates of mean TOC concentrations and total carbon stock in both continental shelves and deep sea settings across various marine regions and oceans. Our model suggests that the upper 10 cm of oceanic sediments harbors approximately 171 Pg of TOC stock and has a mean TOC concentration of 0.68 %. Furthermore, we introduce a standardized methodology for quantifying predictive uncertainty using Monte Carlo dropout and present a map of information gain, that measures the expected increase in model knowledge achieved through in-situ sampling at specific locations which is pivotal for sampling strategy planning.
... warming temperatures and increasing erosion than does the removal of atmospheric CO 2 via silicate weathering, suggesting that POC bio burial will be the dominant atmospheric carbon sink during modern climate warming Hilton, 2017). In this context, the source and fate of POC influence the storage and release of carbon over both shorter, human-relevant timeframes and geologic timescales (Berner, 1982;Hilton, 2017). ...
... Mineral association of POC in rivers or estuaries (Hemingway et al., 2019) and deposition with large number of sediments can substantially slow the mineralization of POC particularly under anoxic conditions (Peter et al., 2016;Repasch et al., 2021;Richardson et al., 2013). Long-term sedimentation of OC in coastal environments is a critical pathway of carbon sequestration over geologic timescales (Berner, 1982;Hilton, 2017). Glacier-containing fjords in northern Southeast Alaska have high sedimentation rates, with upper Lynn Canal experiencing a mass accumulation rate of 0.58 ± 0.15 g cm −2 yr −1 and other glacierized fjords reaching 33.5 ± 18 g cm −2 yr −1 (Walinsky et al., 2009). ...
... The understanding of erosion as a global thermostat, by way of silicate weathering, carbonate precipitation, and POC burial that act as carbon sinks on geologic timescales (Berner, 1982;Galy et al., 2015), has been complicated by the realization that substantial petrogenic OC release as CO 2 can occur during mountain glaciation, weathering, and erosion (Blattmann, 2022;Horan et al., 2017). In mountainous watersheds in New Zealand, for example, enhanced oxidation rates of OC petro during weathering were observed in a watershed with 58% glacier coverage compared with a watershed with 10% glacier coverage, suggesting that glacier recession could result in a net increase in carbon storage in fjords, although this effect is likely dependent on the bedrock lithology and OC content (Horan et al., 2017). ...
Biospheric particulate organic carbon (POCbio) burial and rock petrogenic particulate organic carbon (POCpetro) oxidation are opposing long‐term controls on the global carbon cycle, sequestering and releasing carbon, respectively. Here, we examine how watershed glacierization impacts the POC source by assessing the concentration and isotopic composition (δ¹³C and Δ¹⁴C) of POC exported from four watersheds with 0%–49% glacier coverage across a melt season in Southeast Alaska. We used two mixing models (age‐weight percent and dual carbon isotope) to calculate concentrations of POCbio and POCpetro within the bulk POC pool. The fraction POCpetro contribution was highest in the heavily glacierized watershed (age‐weight percent: 0.39 ± 0.05; dual isotope: 0.42 (0.37–0.47)), demonstrating a glacial source of POCpetro to fjords. POCpetro was mobilized via glacier melt and subglacial flow, while POCbio was largely flushed from the non‐glacierized landscape by rain. Flow normalized POCbio concentrations exceeded POCpetro concentrations for all streams, but surprisingly were highest in the heavily glacierized watershed (mean: 0.70 mgL⁻¹; range 0.16–1.41 mgL⁻¹), suggesting that glacier rivers can contribute substantial POCbio to coastal waters. Further, the most heavily glacierized watershed had the highest sediment concentration (207 mgL⁻¹; 7–708 mgL⁻¹), and thus may facilitate long‐term POCbio protection via sediment burial in glacier‐dominated fjords. Our results suggest that continuing glacial retreat will decrease POC concentrations and increase POCbio:POCpetro exported from currently glacierized watersheds. Glacier retreat may thus decrease carbon storage in marine sediments and provide a positive feedback mechanism to climate change that is sensitive to future changes in POCpetro oxidation.
... Therefore, it is necessary to discuss the genesis of pyrite. In Fig. 8, we identified a significant positive correlation between the TS, TOC, and CRS, indicating that pyrite in the turbidity current environment is primarily related to the organoclastic sulfate reduction (Berner, 1982(Berner, , 1984Wei and Algeo, 2020;Di et al., 2021;Miao et al., 2021b), rather than methane seepage. This is because pyrite precipitation in methane seepages is associated with SD-AOM, which leads to a lack of correlation between TS and TOC Wei and Algeo, 2020;Miao et al., 2021b). ...
... We concluded that this phenomenon could be related to the content of available sulfate, TOC, and active iron in the enclosed environment. In the environments dominated by OSR, reactive iron, organic matter, and dissolved sulfate are the primary factors that control the content of authigenic pyrite (Berner, 1982(Berner, , 1984Jørgensen, 1982;Liu et al., 2019). Moreover, in the closed environment of turbidite, the raw materials needed for pyrite precipitation almost completely depend on the components carried by the turbidite and are less affected by the external environment (Volvoikar et al., 2020). ...
... Once they are reductively dissolved, more iron ions can be released to supply the precipitation of pyrite. The results show that with the development of OSR, the sedimentary environment will obviously be biased towards the reducing environment (Berner, 1982(Berner, , 1984Jørgensen, 1982;Volvoikar et al., 2020), which facilitates the dissolution of Fe ox and Fe mag . Therefore, the iron-excess sedimentary environment in the turbidity layers (322-328 cm and 335-346 cm) are the primary reasons for the final high content of pyrite. ...
carbon (C), sulfur (S), and iron (Fe) marine sedimentary cycles. However, sulfate reduction in unstable environment (turbidite deposition) is easily ignored, which results in a lack of understanding of the C, S, and Fe biogeochemical cycle. Therefore, to elucidate the role of turbidite sedimentation in the global C, S, and Fe biogeochemical cycle, total organic carbon (TOC), total sulfur (TS), iron speciation, pyrite contents, and sulfur isotopic composition in sediments (CL94) on the South China Sea continental slope were analyzed, along with sediment grain sizes, calcium carbonate (CaCO3) content, and K/Al and Ti/Al ratios. Based on petrographic characteristics, grain size parameters, and element geochemistry (K/Al and Ti/Al ratio), it was concluded that the mid-section (322–350 cm) of Site CL94 is a turbidite layer. Compared with normal sedimentary environment, δ34SCRS ( 39.7 ‰ on average) exhibits a high value in turbidite layer, which could be related to the high deposition rate and relatively closed environment caused by the turbidity current deposition. Furthermore, in situ deposition is virtually entirely unaffected by external influences, and this is the primary source of sulfide and reactive iron in the relatively closed environment. Thus, pyrite concentration in the turbidity layer fluctuates in conjunction with variations in sulfide and active iron. Moreover, the identification and data extraction of methane seeps were further complicated by the fact that the TS/TOC ratio and δ34SCRS features induced by the turbidity current were extremely similar to those of sediments around methane seeps. The examination of pyrite sulfur isotopic composition and TS/TOC ratios for detecting methane seepage requires further investigation.
... The organic carbon contained in seafloor sediments has a major influence on the global carbon cycle and Earth's climate (Hülse et al., 2017;Bauer et al., 2013). Seabed sediments have been estimated to accumulate approximately 126-350 Mt of organic carbon per year (Keil, 2017;Berner, 1982) and contain 87 Gt of organic carbon in their top 5 cm (Lee et al., 2019), 168 Gt in the top 10 cm (LaRowe et al., 2020a) and up to ∼ 2300 Gt in the top 1 m (Atwood et al., 2020), with the latter being equivalent to nearly twice that of soils on land. Continental shelves have the highest densities of sediment carbon across the global ocean, covering only 5 %-8 % of the marine area but an estimated 15 %-19 % of surficial organic carbon stocks (LaRowe et al., 2020a;Atwood et al., 2020) and 80 % of annual carbon burial (Bauer et al., 2013;Burdige, 2007). ...
... Although this standard approximation of grain density is not ideal, the variation under different environmental settings is generally found to be small when compared with differences in %OC and porosity. Therefore, the values of grain density are not expected to strongly drive variation in organic carbon density (Atwood et al., 2020;Lee et al., 2019;Middelburg, 2019;Martin et al., 2015;Berner, 1982). To incorporate uncertainty from our mud content predictions, estimates of dry bulk density were also calculated from the cell-specific predictions of the lower and upper bounds of the 95 % CI of mud content. ...
Quantification and mapping of surficial seabed sediment organic carbon have wide-scale relevance for marine ecology, geology and environmental resource management, with carbon densities and accumulation rates being a major indicator of geological history, ecological function and ecosystem service provisioning, including the potential to contribute to nature-based climate change mitigation. While global analyses can appear to provide a definitive understanding of the spatial distribution of sediment carbon, regional maps may be constructed at finer resolutions and can utilise targeted data syntheses and refined spatial data products and therefore have the potential to improve these estimates. Here, we report a national systematic review of data on organic carbon content in seabed sediments across Canada and combine this with a synthesis and unification of the best available data on sediment composition, seafloor morphology, hydrology, chemistry and geographic settings within a machine learning mapping framework. Predictive quantitative maps of mud content, dry bulk density, organic carbon content and organic carbon density were produced along with cell-specific estimates of their uncertainty at 200 m resolution across 4 489 235 km2 of the Canadian continental margin (92.6 % of the seafloor area above 2500 m) (https://doi.org/10.5683/SP3/ICHVVA, Epstein et al., 2024). Fine-scale variation in carbon stocks was identified across the Canadian continental margin, particularly in the Pacific Ocean and Atlantic Ocean regions. Overall, we estimate the standing stock of organic carbon in the top 30 cm of surficial seabed sediments across the Canadian shelf and slope to be 10.9 Gt (7.0–16.0 Gt). Increased empirical sediment data collection and higher precision in spatial environmental data layers could significantly reduce uncertainty and increase accuracy in these products over time.
... The reason for this difference is apparently that field studies using gravity coring are generally interested in sites with relatively high sedimentation rate and sea-surface productivity. Such sites are focused towards the shallow ocean Reduced sulfur burial ~2 ** Berner (1982) * This number reflects the total organic matter mineralized during the production of methane, assuming a stoichiometry of 1.7 C org :CH 4 , similar to the estimated stoichiometry for sulfate reduction (Jørgensen, 2021). ** Calculated from a pyrite burial rate of 1.2 Tmol S yr − 1 (Berner, 1982) and ...
... Such sites are focused towards the shallow ocean Reduced sulfur burial ~2 ** Berner (1982) * This number reflects the total organic matter mineralized during the production of methane, assuming a stoichiometry of 1.7 C org :CH 4 , similar to the estimated stoichiometry for sulfate reduction (Jørgensen, 2021). ** Calculated from a pyrite burial rate of 1.2 Tmol S yr − 1 (Berner, 1982) and ...
... Authigenic secondary minerals precipitation and their alteration to foraminifera shells in seep-associated sediments. (A) Typical authigenic secondary minerals precipitation, and the equations utilized to depict this process are derived from the works ofBerner (1982);Borowski et al. (2013);Liu et al. (2018), andMiao et al. (2021). (B) Altered foraminifera coated with high-Mg carbonate interlayers. ...
Cold seep foraminifera have attracted considerable attention as they provide valuable insights into the study of cold seeps. This study provides a comprehensive overview of the manifestations of foraminifera in cold seep environments and methane seepage activities. Certain taxa of benthic foraminifera, such as Uvigerina, Bolivina, Bulimina, Chilostomella, Globobulimina, Nonionella, Melonis, Epistominella, Cibicidoides, and Globocassidulina, are known to inhabit geochemical conditions induced by methane-rich environments and may feed on associated methanotrophic microbial communities. Secondary mineralization on foraminifera shells is a widespread manifestation in seep sediments, and alters the microstructure, elementary composition, and isotopic signatures of foraminifera. On one hand, the precipitation of secondary authigenic Mg-rich, Mn-rich, Sr-rich, and Ba-rich calcite coatings have been observed on microfossils. On the other hand, micron-sized crystal pyrite and gypsum aggregates can also grow on the foraminifera walls. The negative δ¹³C and positive δ¹⁸O anomalies in both planktonic and benthic foraminifera from seep-associated sediments can serve as proxies for tracing past seepage activities, either in their live form or being adulterated by methane-derived authigenic carbonate after deposition. Seeping activities are recognized with a significant impact on benthic foraminifera, and the presence of cold seep-related species and significant isotopic anomalies in shells can be used to reconstruct past methane seepage events. Intensive methane seepage tends to suppress benthic foraminifera populations, while moderate intensity seepage may lead to a thriving benthic foraminiferal community, with hypoxia-enduring taxa such as Uvigerina, Melonis, and Bulimina being predominant. In contrast, oxygen-loving epibenthic taxa such as Cibicidoides often occur in areas of low methane flux. Compared to planktonic foraminifera, the single species of benthic foraminifera can provide a more comprehensive record of seepage evolution. Live benthic specimens are preferred for in-situ seep studies, while the superimposition of secondary minerals on the original shells should not be ignored when observing dead individuals. The significance of the evolution of methane seepage, changes in environmental parameters of the living habitat, and species sensitivity in cold seeps are emphasized in explaining the variation in foraminiferal assemblages and fluctuations in stable isotopes.
... A first estimate, based on multiplying average organic carbon content of Holocene sediments by area and thickness, yielded 223 Tg C yr −1 , of which 10% and 88% are deposited on the continental shelf and slope, respectively 3 . Berner 4 argued that organic carbon is preferentially buried in deltaic shelf sediments (83% of a total burial rate of 126 Tg C yr −1 ). His estimates were subsequently revised by Hedges and Keil 5 to account for organic carbon burial in sediments of the continental shelves and upper slopes, respectively, and estimated that roughly 90% of organic carbon is buried in coastal and continental margin settings. ...
The role of continental margin sediments in the carbon cycle and the associated management potential for climate mitigation are currently poorly understood. Previous work has indicated that margin sediments store significant amounts of organic carbon, but few studies have quantified the rates at which organic carbon is accumulated. Here, we use machine learning to make spatial predictions of the organic carbon stocks and accumulation rates of sediments on the Norwegian continental margin. We show that surface sediments (upper 10 cm) store 814 Tg and accumulate 6 Tg yr⁻¹ of organic carbon. Shelf-incised glacial troughs account for 39% of the stocks and 48% of the accumulation, with the main accumulation hotspot located in the Skagerrak. Continental margin sediments accumulate organic carbon at scales much larger than vegetated coastal ecosystems in Norway because of their larger extent. Future studies should explore to what extent management interventions could increase accumulation rates, e.g., by minimising anthropogenic disturbance of seafloor sediments.
... It is important to monitor the temporal and spatial changes in total organic (TOC) and inorganic carbon (TIC) amounts in seafloor sediments to monitor the time-dependent changes of environmental factors. In Berner (1982), it is emphasized that to model the global carbon cycle, it is necessary to first understand the dynamics of the carbon cycle in productive environments. It has been emphasized that approximately 90% of TOC in marine environments is deposited (accumulated or conserved) along continental shelf sediments, while the remaining 10% is stored (accumulated or preserved) on the deep ocean floor. ...
... The KCF in places has abundant pyrite (Matthews et al., 2004;Morgans-Bell et al., 2001) and is notable for sulfurization of OM (van Kaam-Peters et al., 1998); when considering OM-bound Hg release, we therefore also consider that a portion of this Hg may in fact be associated with organic sulfur or present as inclusions in (framboidal) pyrite or metacinnabar (black HgS). These Hg species can (appear to) be coupled and correlated with TOC in sediments as they are either directly associated with OM and OM-breakdown processes (Berner, 1982(Berner, , 1984Raven et al., 2023;Werne Geochemistry, Geophysics, Geosystems 10.102910. /2024GC011502 et al., 2003 or preferentially form in the presence of OM (such as HgS, e.g., Pham et al., 2014). ...
Sedimentary mercury (Hg) has become a widely used proxy for paleo‐volcanic activity. However, scavenging and drawdown of Hg by organic‐matter (OM) and sulfides are important non‐volcanic factors determining variability in such records. Most studies, therefore, normalize total Hg (HgT) to a Hg “host‐phase” proxy (e.g., HgT/TOC for OM, HgT/TS for sulfides), with the dominant host‐phase determined based on the strongest observed (linear) correlations. This approach suffers from various non‐linearities in Hg‐host‐phase behavior and does not account for succession‐level, let alone sample‐level, Hg speciation changes. Thermal desorption characteristics or “profiles” (TDPs) for many Hg species during pyrolysis analysis are well‐established with applications including distinguishing between OM‐bound Hg and different Hg sulfides and oxides in (sub‐)recent sediments. We explore the use of TDPs for geological sediment (rock) samples and illustrate the presence of multiple release phases (Hg species)—correlated to geochemical host‐phase—in (almost) all the 65 analyzed Tithonian (146–145 Ma) silt and mudrock samples. By quantifying the Hg in each release phase for every sample, we find TOC concentration may determine ∼60% of the variability in the first (lower temperature) Hg TDP release phase: a stark difference with the total Hg released from these samples, where ∼20% of variation is explained by TOC variability. TDPs provide insight on sample‐level Hg speciation and demonstrate that, while the common assumption of single‐phase Hg speciation in sedimentary rocks is problematic, differences in Hg speciation can be detected, quantified, and accounted for using commonly applied techniques—opening potential for routine assessment.
... Jørgensen 1982;Postgate 1984;Widdel 1988;Shen and Buick 2004;Newton and Bottrell 2007;Leavitt et al. 2013;Fike et al. 2015). Ultimately, in the presence of iron, the terminal product of sulfate reduction is pyrite and the subsequent long-term burial of this reduced mineral represents a major net source of oxygen to the atmosphere, whereas pyrite weathering represents a major sink (Garrels and Perry 1974;Berner 1982). Reduced sulfur compounds can also act as electron donors for photosynthesis by some prokaryotes (Bryant and Frigaard 2006). ...
Understanding the long-term variance of seawater sulfate concentrations ([SO 4 ²⁻ ] sw ) is critical to understanding the dynamic relationship between the sulfur, carbon, calcium, and oxygen cycles, and their influence on Earth's habitability. Here, we explore how [SO 4 ²⁻ ] sw has changed throughout the Phanerozoic, and its impact on other elemental cycles. We do this by utilising the biogeochemical box model GEOCARBSULFOR. The model suggests that [SO 4 ²⁻ ] sw rose throughout the Paleozoic, declined during the Mesozoic, and then rose once more in the Cenozoic, generally matching geochemical proxies. Atmospheric oxygen mirrors [SO 4 ²⁻ ] sw changes during the Paleozoic and Mesozoic, but intriguingly, decouples during the Cenozoic. We further explored controls on [SO 4 ²⁻ ] sw by modifying the modelled gypsum fluxes via the incorporation of evaporite data from the geological record. We find that forcing gypsum burial with the observed evaporite deposition data causes the model to better match proxy records at some times, but worsens predictions at others. Finally, we investigate model reliance on a prescribed record of marine calcium concentrations, finding that it is a dominant control on modelled Phanerozoic [SO 4 ²⁻ ] sw , and that removing this control seriously degrades model predictions. We conclude that no model can yet simulate a reasonable evolution of both the calcium and sulfur cycles.
Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/topic/collections/sulfur-in-the-earth-system
Supplementary material: https://doi.org/10.6084/m9.figshare.c.7164928
... Organic carbon (OC) burial in marine sediments leads to CO 2 removal from the atmosphere and it is hence crucial to examine the controls on OC preservation in sediments (Berner, 1982). The heterogenous composition of bulk OC in marine sediments is composed of autochthonous marine organic materials produced in overlying waters and allochthonous terrestrial biospheric plant, soil, and sedimentary rock-derived petrogenic OC supplied via fluvial and eolian transport processes (Blattmann et al., 2018;Griffith et al., 2010;Tao et al., 2016). ...
The burial of organic carbon (OC) in marine sediments regulates CO2 content in the atmosphere. However, the OC sources and their effect on the OC preservation in sediments of the continental marginal sea remain elusive. Here, we survey the abundance, stable carbon and radiocarbon isotopes of OC, as well as mineral surface area and grain size in surface sediments from the shelf to the abyssal plain of the South China Sea. We found that the marine OC comprises the 63 ± 9% and 78 ± 14% of sedimentary OC off South China and Luzon, respectively. The petrogenic OC contributing to sedimentary OC in these sites is generally higher than that of soil OC (22 ± 10% vs. 12 ± 6%). The sedimentary OC off Taiwan is predominantly derived from petrogenic OC, accounting for 57 ± 10%, with remaining consisting of marine OC (36 ± 10%) and soil OC (6 ± 1%). High soil OC contents are found in fine sediments on the inner shelf off South China, and high petrogenic OC contents occur in fine sediments off Taiwan. Marine OC contents are high in fine sediments on the middle shelf and upper slope off South China, but low in coarse sediments on the outer shelf and upper slope, and fine sediments on the lower slope and abyssal plain. The OC sources, mineral surface area, and oxygen exposure time of OC together control the preservation of OC in sediments with their relative importance differing on varying depositional settings of this sea.
... The continental margin is the active terrestrial-ocean interface that serves as a primary location for the biochemical and sedimentary cycling of organic carbon (OC), nitrogen (N), and sulfur (S) (Berner, 1982;Jørgensen and Kasten, 2006;Hu et al., 2011;DeLaune and White, 2012;Hu et al., 2014;Jørgensen et al., 2019;Chen et al., 2021). Dynamic physicochemical reactions along continental margins create complex OC-N-S cycles that can be affected by local climate; however, the mechanistic link of climate change to the OC-N-S cycles is not well understood (Mcleod et al., 2011;Liu Q. et al., 2018;Liu X. T., et al., 2018;Sun et al., 2020;Liu X. T., et al., 2021;Wang et al., 2021;Zhao et al., 2021;Liu et al., 2023). ...
The correlation between the amount of organic carbon (OC) and sulfur (S) in sediments has been widely used as a paleosalinity indicator to distinguish between marine and freshwater environments. However, whether the ratio of total OC to total S (TOC/TS) can be used to identify unsteady or dynamic marine environments across sedimentary strata is still contended. An HZW1907 sediment core of 80 m in length was successfully collected in the middle of Hangzhou Bay (HZB), serving as one of the few boreholes that are crucial for the study of geologic and geo-environment changes in the coastal regions of eastern China since the Last Glacial Maximum (LGM). Total OC (TOC), stable carbon isotope, and TS of 82 subsamples from the HZW1907 core were analyzed to reconstruct the history of the shallow water biological pump and sulfur preservation record in the bay since the Late Pleistocene. Our results indicate that the samples had low concentrations of TOC (0.21%) and total nitrogen (TN) (0.02%), high mass ratio of TOC/TN (10.8), low δ¹³C (−24.9‰), low TS content (0.06%), and a high ratio of TOC/TS (9.1) from 33.6 ka BP to 12.3 ka BP, implying that freshwater organic matter (OM), algae, and C3 plant fragments were the main sources of OM in a relatively cold environment. The abundances of TOC, TN, and TS increased to 0.56%, 0.07%, and 0.4%, respectively, while δ¹³C (−23.9‰) increased and TOC/TS (2.7) decreased in the Holocene sediments, suggesting that seawater began to influence the composition of the sediments of HZB. Climate warming, which is likely to have impacted the results, was experienced from 12.3 ka BP. An OC isotope mixing model indicated that since the Mid-late Holocene, more than 70% of riverine OM accounted for the total OM. The TOC/TS ratio was identified as an effective indicator of seawater intrusion, with C/S ratios of 1–6 being considered to indicate a “sea–land transitional zone” sedimentary environment, a C/S >6 indicating freshwater, and a C/S<1 indicating normal marine facies. These findings provide crucial evidence for using TOC/TS to distinguish freshwater from marine environments and enhance our understanding of past climate changes. Therefore, these geochemical indicators can be used in conjunction with other sedimentary records to obtain accurate results about sedimentary evolution.
... This suggests more 503 closely coupled HgT-TOC behavior, as was found for the more organic-rich KCF interval analyzed by considering OM-bound Hg release, we therefore also consider that a portion of this Hg may in fact be 512 associated with organic sulfur or present as inclusions in (framboidal) pyrite or metacinnabar (black HgS). 513 These Hg species can (appear to) be coupled and correlate with TOC in sediments as they are either directly 514 associated with OM and OM-breakdown processes (Berner, 1982(Berner, , 1984 implies that the controlling factor for the sedimentary abundance of these phases during deposition might 517 have been organic-matter flux, so that even if other chemical species (e.g., sulfides) now bind Hg, the 518 abundance of these phases may still link to OM-drawdown. We hereafter refer to the first release phase as 519 organic-matter and organic-matter associated sulfur Hg (HgOMS) and the secondary release as 'other' Hg 520 species (HgOTH). ...
Sedimentary mercury (Hg) has become a widely used proxy for paleo-volcanic activity. However, scavenging and drawdown of Hg by organic-matter (OM) and sulfides are important non-volcanic factors determining variability in such records. Most studies, therefore, normalize total Hg (HgT) to a Hg “host-phase” proxy (e.g., HgT/TOC for OM, HgT/TS for sulfides), with the dominant host-phase determined based on the strongest observed (linear) correlations. This approach suffers from various non-linearities in Hg-host-phase behavior and does not account for succession-level, let alone sample-level, Hg speciation changes. Thermal desorption characteristics or ‘profiles’ (TDPs) for many Hg species during pyrolysis analysis are well-established with applications including distinguishing between OM-bound Hg and different Hg sulfides and oxides in (sub-)recent sediments. We explore the use of TDPs for geological sediment (rock) samples and illustrate the presence of multiple release phases (Hg species) – correlated to geochemical host-phase – in (almost) all the 65 analyzed Tithonian (146 – 145 Ma) silt and mudrock samples. By quantifying the Hg in each release phase for every sample, we find TOC concentration may determine ~60% of the variability in the first (lower temperature) Hg TDP release phase: a stark difference with the total Hg released from these samples, where ~20% of variation is explained by TOC variability. TDPs provide insight on sample-level Hg speciation and demonstrate that, while the common assumption of single-phase Hg speciation in sedimentary rocks is problematic, differences in Hg speciation can be detected, quantified, and accounted for using commonly applied techniques - opening potential for routine implementation.
... However, in Norway, only parts of the North Sea and Skagerrak have been mapped . Estimates of OC remineralization, accumulation and burial rates are even more limited (Berner, 1982;Burdige, 2007;Wilkinson et al., 2018;Luisetti et al., 2019; and natural rates of OC remineralization and storage also show large spatial and temporal variability. However, OC storage is usually higher in finer sediments in areas of low hydrodynamic activity. ...
... Globally, it is estimated that within surficial sediments 87,000 ± 43,000 Mt is held within the top 5 cm (Lee et al., 2019), with potentially up to 3,117,000 Mt OC held within the top 1 m (Atwood et al., 2020). Each year these stores grow by an estimated 156 Mt OC through the accumulation and burial of OC at the seabed (Berner, 1982;Hedges and Keil, 1995;Smith et al., 2015). However, anthropogenic pressures which increasingly disturb the seabed have the potential to not only disrupt benthic ecosystems but may also affect the OC stored within these sediments and could release carbon dioxide (CO2) (Duplisea et al., 2001), further contributing to global anthropogenic GHG emissions. ...
This briefing is the product of a research agreement between Danmarks Naturfredningsforening (DN) and the University of St Andrews (UStA), Department of Geography and Sustainable Development, with the aim to provide an estimate of the potential effects of bottom trawling on the OC stored within Denmark's surficial marine sediments.The focus of this briefing are the sub-tidal marine sediments within Denmark's Exclusive Economic Zones (EEZ). Additionally, the effect of bottom trawling on the sedimentary OC stocks within the MPAs that are composed of the Natura 2000 areas (N2000) and areas protected according to the Marine Strategy Framework Directive (MSFD) and within the 3, 6 and 12-nautical mile boundaries will be assessed to potentially allow new recommendations to be made for the development of appropriate management and policy interventions.
... 931The surface sediments at these sites are composed of silty 932 clay, clayey silt, and sandy silt( Figure 1). Sediment com-933 position was different between the sites, but the TOC/TS 934 contents remained below the predicted Holocene satura-935 tion line( Figure 5 F), indicating sulfate mineralization pro-936 cesses( Berner, 1982 ;Jørgensen and Kasten, 2006 ). Most 937 sites showed Hg profiles with enhanced contents at 10 and 938 20 cmbsf, and thus a relatively continuous sedimentation 939 with little disturbance. ...
The present study aims to understand the impact of submarine groundwater discharge (SGD) on a coastal area with different lithology and degrees of SGD. Sampling cam- paigns took place in Puck Bay and the Gulf of Gdansk, southern Baltic Sea encompassing years between 2009 and 2021. The methodological approach combined geophysical characterization of the surface sediments with detailed spatial and temporal (isotope) biogeochemical investigations of pore and surface waters, and was supported by nearshore groundwater and river surveys. Acoustic investigations identified areas of disturbance that may indicate zones of preferential SGD release. The composition of porewater and the differences in the bay’s surface
waters disclosed SGD as common phenomenon in the study area. Regional SGD was estimated through a radium mass balance. Local estimation of SGD, based on porewater profiles, revealed
highest SGD fluxes at the sandy shoreline, but relatively low elemental fluxes. Though SGD was low at the muddy sites corresponding elemental fluxes of nutrients and dissolved carbon exceeded those determined at the sandy sites due to intense diagenesis in the top sediments. SGD appears to be sourced from different freshwater endmembers; however, diagenesis in surface
sediments substantially modified the composition of the mixed solutions that are finally discharged to coastal waters. Overall, this study provides a better understanding of the SGD dynamics
in the region by a multi-approach and emphasizes the need to understand the processes occurring at the sediment-water interface when estimating SGD.
... The IPCC has suggested that carbon buried in marine sediments is an effective way to remove CO 2 from the atmosphere (Nellemann et al., 2009). About 90% of organic carbon in global ocean sediments is concentrated in marginal seas, while for inorganic carbon the percentage is over 50% (Berner, 1982;Hedges and Keil, 1995;Falkowski et al., 2000;Tesi et al., 2007;Song, 2011). Such a large quantity of buried carbon suggests that marginal sea sediments play a crucial role in the carbon cycle of marine ecosystems. ...
Marine primary production and terrestrial input are the main sources of buried carbon in sediments of marginal seas. Only marine-source carbon buried in sediments, fixed and stored by marine ecosystems, belongs to “blue carbon” and reflects marine ecosystems’ carbon sink function. The pattern of buried blue carbon in sediments, its flux, and its relationship with environmental changes remain unclear. The study aimed to investigate the composition of blue carbon in the sediments of Sanggou Bay, a special type of marginal sea. The analysis of sediment carbon sources was conducted through the C/N ratio and microscopic examination. The study also examined the long-term changes in the blue carbon burial fluxes. Results showed Blue carbon, which is sea-sourced carbon, accounted for about 23% of the total carbon content and its concentration ranged from 0.17% to 0.51%, with an average of about 0.25% ± 0.10%. The content of organic blue carbon in this sea area ranges from 0.09% to 0.26%, with an average of around 0.18% ± 0.04%. It constitutes approximately 72% of the buried blue carbon in the sediment, making it the primary component of buried blue carbon. Meanwhile, the content of inorganic blue carbon ranges from 0.01% to 0.32%. Over the past 70 years, the burial fluxes of sedimentary blue carbon, organic blue carbon and inorganic blue carbon in the Sanggou Bay are about 0.54 ± 0.22 mmol/(cm²a), 0.38 ± 0.07 mmol/(cm²a) and 0.17 ± 0.22 mmol/(cm²a), respectively; their long-term changes have been significantly affected by human aquaculture activities. Large-scale raft-rack aquaculture activities have caused a reduction in water flow velocity and an increase in the deposition of particulate organic matter, which in turn has led to the burial of organic blue carbon in the sediment. Additionally, the competition between aquaculture products and small calcareous organisms, such as mussels, foraminifera, may have inhibited the growth of small calcareous organisms. We suggest this has resulted in reduced burial fluxes of inorganic blue carbon and a decrease in its proportion among total blue carbon in the sea area. Our findings imply that aquaculture activities in Sanggou Bay had a negative impact on the burial of blue carbon in the sediments.
... Although marginal seas cover <20% of the total surface area of the ocean, nearly 90% of sedimentary OM is preserved on continental shelves and slopes (Ausín et al., 2021;Hedges and Keil, 1995). Thus, continental margins play an important role in the global carbon cycle in terms of OM preservation, and serve as transition zones for terrigenous OM entering the deep oceans (Berner, 1982;Mollenhauer et al., 2007). OM depocenters located on slopes caused by lateral transport have been found on some continental margins (Celtic slope at Goban Spur, Namibian slope) (de Haas et al., 2002;Inthorn et al., 2006). ...
https://authors.elsevier.com/a/1iMuA26gajkXI
... TS in sediments mainly consist of chrome reducible and organic sulfur. In oxic or suboxic conditions marine sediments demonstrate a positive correlation between TS and TOC contents with an average value of S/C ratio of 0.36 (Berner, 1982). In the investigated "seep-free" sediments, the average S/C value is 0.14 and consistent with oxic seawater (Goldhaber, 2005). ...
The East Siberian Arctic shelf is renowned for its active methane-rich fluid seeps, confirmed by numerous gas flares in the water column and direct observations of methane release from the seafloor. These cold-seep sites serve as natural laboratories for studying the impact of methane seepage on early diagenesis, authigenic mineral formation, and the geochemical cycles of carbon, sulfur, and other elements. This study examines the grain size and chemical composition of two sediment types from the Laptev Sea shelf: cold-seep sediments influenced by sulfate-driven anaerobic methane oxidation, and unaffected “seep-free” sediments (i.e., control site). High methane concentrations (up to 649 μM/L) in the surface layer of sediments indicate that the sulfate–methane transition zone is found close to the sediment–water interface approximately 5–6 cm below the seabed. At the
cold-seep site, thin layers containing up to 40% sand fraction were discovered among the fine-grained sediments.
We infer that upward-migrating fluids may contribute to the remobilization of the fine fraction, resulting in concentration of coarse particles. Cold-seep sediments are characterized by molybdenum (Mo) enrichment compared to the lithological background, although one “seep-free” core exhibits evidence of authigenic Mo deposition. The Mo concentration (up to 16.8 ppm) indicates that enrichment occurs under sulfidic conditions restricted to pore water, which are caused by anaerobic methane oxidation. The high Mo concentration in one “seep-free” core likely implies past cold-seep activity. A general Mo–U covariation indicates that the molybdenum enrichment in cold-seep sediments from the Laptev Sea outer shelf is controlled by a weak particulate shuttle process.
... Atmospheric pO 2 buildup through geologic time on Earth is directly related to increased burial of organic carbon (Berner 1982), a process influenced by continental flooding shifting deposition from short-lived oceanic crust to long-lived continental reservoirs. Similarly, flooding of Laurentia during a time in which its surface geology may have largely consisted of exposed crystalline basement following Cryogenian glaciation has been cited as a potential source of increased biolimiting nutrients and Ca 2+ concentrations in shallow-marine settings during the Cambrian. ...
Strata of the Ediacaran Period (635–538.8 Ma) yield the oldest known fossils of complex, macroscopic organisms in the geologic record. These “Ediacaran-type” macrofossils (known as the Ediacaran biota) first appear in mid-Ediacaran strata, experience an apparent decline through the terminal Ediacaran, and directly precede the Cambrian (538.8–485.4 Ma) radiation of animals. Existing hypotheses for the origin and demise of the Ediacaran biota include: changing oceanic redox states, biotic replacement by succeeding Cambrian-type fauna, and mass extinction driven by environmental change. Few studies frame trends in Ediacaran and Cambrian macroevolution from the perspective of the sedimentary rock record, despite well-documented Phanerozoic covariation of macroevolutionary patterns and sedimentary rock quantity. Here we present a quantitative analysis of North American Ediacaran–Cambrian rock and fossil records from Macrostrat and the Paleobiology Database. Marine sedimentary rock quantity increases nearly monotonically and by more than a factor of five from the latest Ediacaran to the late Cambrian. Ediacaran–Cambrian fossil quantities exhibit a comparable trajectory and have strong ( r s > 0.8) positive correlations with marine sedimentary area and volume flux at multiple temporal resolutions. Even so, Ediacaran fossil quantities are dramatically reduced in comparison to the Cambrian when normalized by the quantity of preserved marine rock. Although aspects of these results are consistent with the expectations of a simple fossil preservation–induced sampling bias, together they suggest that transgression–regression and a large expansion of marine shelf environments coincided with the diversification of animals during a dramatic transition that is starkly evident in both the sedimentary rock and fossil records.
... Oceans are an important carbon sink, with the long-term storage of organic matter (OM) in marine sediments playing a key role in the carbon cycle of earth (Berner, 1990;Burdige, 2005). Particularly, ocean margins bury >80% of the global sedimentary OM (SOM), despite occupying <8% of the global ocean area (Berner, 1982;Hedges and Keil, 1995). As the transition zone connecting the continent to the ocean, the high flux and efficiency of SOM burial in ocean margins can be attributed to high terrestrial OM (TOM) inputs, phytoplankton productivity, and sedimentation rates (McKee et al., 2004;Burdige, 2005). ...
Long-term organic matter (OM) burial in the ocean is essential to the global carbon cycle. Mud deposits, such as South Yellow Sea mud deposit (SYSMD) located in the central South Yellow Sea (SYS), are ideal for the study of long-term OM burial. A sediment core YS-A from the SYSMD was analyzed for lignin phenols and bulk OM properties to reveal the driving forces of sedimentary OM (SOM) fate during the Holocene. SOM burial was found to be dominantly influenced by sea level rise and increased East Asian summer monsoon during 11.0–7.0 ka BP. During 7.0–1.0 ka BP, the fate of SOM was controlled by El Ni˜no Southern Oscillation on the millennial time scale, and correlated with East Asian winter monsoon variability on the centennial time scale. Remarkably, anthropogenic perturbation has gradually overwhelmed long-term climate control on the fate of SOM since 1.0 ka BP, and this phenomenon became more evident after 0.4 ka BP.
... S3) (Hemingway et al., 2020;Turchyn et al., 2013), which lead to an overestimation of the evaporite contribution when using δ 34 S SO 4 and δ 18 O SO 4 to trace riverine SO 4 2sources. The typical pathway for microbial sulfate reduction is anaerobic respiration of organic carbon (Balci et al., 2007;Berner, 1982;Turchyn et al., 2013). It only affects the concentration and isotopic compositions of SO 4 2if the reduced phases are not re-oxidized. ...
The balance between alkalinity generation by carbonate and silicate weathering and sulfuric acid generation by sulfide weathering controls the effect of weathering on atmospheric pCO2 over geologic timescales. How this balance varies across environmental gradients remains poorly constrained. Here, we analyze this balance across an erosional gradient of two orders of magnitude in the Three Rivers (Yangtze River, Mekong River, and Salween River) Headwater Region (TRHR), eastern Qinghai-Tibet Plateau (QTP). By employing major element chemistry and multiple isotopes (δ34SSO4, δ18OSO4, and δ18OH2O) coupled with forward and inverse approaches, we unmix contributions of silicates, carbonates, evaporites, and sulfides to the total weathering budget. Across the TRHR, riverine SO42– is derived mainly from a mixture of an evaporite source with uniform values of δ34SSO4 and δ18OSO4, and a sulfide source that contributes highly variable values of δ34S (-12.2‰ to 4.1‰) and δ18O (-17.7‰ to -1.6‰). Contributions of sulfide oxidation to riverine SO42– vary from 16% to 94%, and sulfuric acid consumes 6% to 63% of the alkalinity produced by weathering. The fractions of weathering alkalinity derived from carbonate weathering range from 36% to 98% relative to silicate weathering. The combination of silicate, carbonate, and sulfide weathering suggests that the instantaneous weathering fluxes of most sampled catchments in the TRHR act as a sink of atmospheric CO2 over timescales shorter than marine carbonate burial (∼104 years), but as a carbon source over timescales longer than carbonate burial and shorter than sulfide burial (∼107 years). The spatial variability of the balance between alkalinity and acid generation, and, thus, the relationship between chemical weathering and atmospheric pCO2, are largely dependent on lithology. However, within comparable lithologic settings, sulfide and carbonate weathering rates rise with increasing erosion, whereas silicate weathering rates remain constant. Consequently, plateau weathering shifts from a sink to a source of atmospheric CO2 with increasing erosion. These findings suggest that sulfide weathering is more sensitive to erosion than carbonate and silicate weathering, and that it could play an important role in the long-term carbon cycle during mountain building.
... The burial of organic carbon (OC) in soils and sedimentary depocenters can remove carbon from the atmosphere over timescales of centuries to millennia (Hilton and West, 2020;Galy et al., 2015;Blair and Aller, 2012;Battin et al., 2009;Hayes 40 et al., 1999;Stallard, 1998;France-Lanord and Derry, 1997;Berner, 1982). OC buried in sedimentary basins is mainly sourced from tectonically active environments, like mountainous areas where physical erosion mobilizes hillslope bedrock and soil, generating sediment (e.g., Galy et al., 2015;Blair and Aller, 2012;Stallard, 1998). ...
Fluvial transport of organic carbon from the terrestrial biosphere to the oceans is an important term in the global carbon cycle. Traditionally, the long-term burial flux of fluvial particulate organic carbon (POC) is estimated using river suspended sediment flux; however, organic carbon can also travel in river bedload as coarse particulate organic matter (POMBed). Estimates of fluvial POC export to the ocean are highly uncertain because few studies document POMbed sources, flux and evolution during long-range fluvial transport from uplands to ocean basins. This knowledge gap limits our ability to determine the global terrestrial organic carbon burial flux. In this study we investigate the flux, sources and transformations of POMBed during fluvial transport over a ~1300 km long reach of the Rio Bermejo, Argentina, which has no tributary inputs. To constrain sourcing of POMBed, we analysed the composition and stable hydrogen and carbon isotope ratios (δ2H, δ13C) of plant wax biomarkers from POMBed at six locations along the Rio Bermejo, and compared this to samples of suspended sediment, soil, leaf litter and floating organic debris (POMfloat) from both the lowland and headwater river system. Across all samples, we found no discernible differences in n-alkane average chain length or nC29 δ13C values, indicating a common origin for all sampled POMBed. Leaf litter and POMfloat nC29 δ2H values decrease with elevation, making it a useful proxy for POMBed source elevation. Biomarker δ2H values suggest that POMBed is a mix of distally-derived headwater and locally-recruited floodplain sources at all sampling locations. These results indicate that POMBed can be preserved during transport through lowland rivers for hundreds of kilometres. However, the POMBed flux decreases with increasing transport distance, suggesting mechanical comminution of these coarse organic particles, and progressive transfer into the suspended load. Our provisional estimates suggest that the carbon flux from POMBed comprises less than 1 percent of the suspended load POC flux in the Rio Bermejo. While this represents a small portion of the river POC flux, this coarse and high density material likely has a higher probability of deposition and burial in sedimentary basins, potentially allowing it to be more effective in long-term CO2 drawdown relative to fine suspended particles. Because the rate and ratio of POMBed transport versus comminution likely varies across tectonic and climatic settings, additional research is needed to determine the importance of POMBed in the global carbon cycle.
... Recent estimates show that the coastal seas contribute 30-50% to the new primary production of global oceans (Pearl 1995). Moreover, deltaic and shelf sediments incorporate approximately 80% of the organic carbon sequestered in modern marine sediments (Berner 1982). Thus, alterations in river inputs and the accompanying potential changes in species composition of diatoms could have a significant impact on marine biogeochemical cycles. ...
... It was estimated that global oceans bury 180 × 10 12 g organic carbon (OC) per year (Burdige, 2005;Smith et al., 2015). Of the geological units in the ocean, the estuarine, coastal, and shelf regions are possibly the most important ones in terms of carbon burial (Bauer et al., 2013;Berner, 1982;Bianchi et al., 2018). With nearly 90% annual deposition of total OC in the global ocean, continental shelves are regarded as "hot spots" of carbon burial and decomposition, making them key locations of carbon cycle in the ocean (Berner, 1989;Bianchi et al., 2018;Burdige, 2005). ...
Continental shelves host 90% of annual organic carbon (OC) deposition in the global ocean and are regarded as "hot spots" of carbon burial and decomposition. Numerous studies have thus investigated OC sources, recent accumulation, long term preservation and key processes involved. Nonetheless, OC reactivity or lability, as a key property governing the fate of OC in the long term, received less attention, primarily due to a lack of proper technique of investigation. In this study, we conducted thermochemical decomposition analysis of OC using ramped-temperature pyrolysis/oxidation technique to investigate the reactivity of sedimentary OC along the Yangtze River estuary-shelf continuum. Our results reveal that sedimentary OC in the Yangtze River estuary-shelf region is relatively more stable than global average level, which is attributed to the winnowing of sediments due to frequent sedimentation-resuspension cycles. In general, OC reactivity increases gradually from the estuary to the inner shelf, which is governed by organo-mineral interactions and the progressive absorption of marine OC. Based on our results, we propose that OC reactivity is a key OC property to be considered in future organic carbon cycle frameworks.
... lacustris area and L3-open water). The solid black lines represent the typical relationship for modern marine sediments (C:S = 2.8 ± 1.5, Berner 1982;Berner and Raiswell 1984), while the dotted line represents the same relationship for euxinic environments and the dot-dashed line represents the typical relationship in freshwater environments with low sulphate concentrations (Leventhal, 1995) with 25 nmol g −1 in lower levels; F2: 108-352 nmol g −1 (spring)/163-3459 nmol g −1 (summer-autumn) (< 22.5 cm); F3: 185-569 nmol g −1 (< 27.5 cm)/200-3758 nmol g −1 (summer-autumn); F4: < 0.1 nmol g −1 throughout the profile. The lower levels with a higher proportion of sand had manganese values < 1 (5) nmol g −1 , with the exception of F4, with a peak up to 48 nmol g −1 at a depth of 88.5 cm in summer and 100 nmol g −1 at a depth of 47 cm in autumn (Fig. 9). ...
The shallow lakes are important freshwater ecosystems, since they support much of biodiversity and ecosystem services of life on land. Shallow lakes are highly dynamic ecological entities that can exist in several alternative stable states through regime shift caused by a natural or human disturbance that exceeds ecological thresholds for biological communities composition and structure equilibria. The sediment as a reservoir has a key role in the limnological regulation of wetlands linked to the fluxes of nutrients and elements in the biogeochemical interplay with the water and macrophytes. For this reason, the role of sediment in the limnology of the shallow coastal lake of Xuño (NW Iberian Peninsula) was explored by seasonally monitoring the chemical composition of water and sediments, also according to macrophyte species. The shallow depth determines the high availability of light in the bottom and a well-mixed water column maintain the surface of the water–sediment interface oxygenated. The oxic conditions of the bottom implies a top-down regulation of the water column in the Xuño shallow lake that limits the diffusion of phosphorus and trace metals (Fe, Mn, Cu, and Co) to the water, buffering eutrophication or contamination levels by immobilization in the sediments. In fact, the concentration of Hg in the lake water in spring, and also its bioavailability, are high due to its release from the sediment in suboxic conditions. The cover of helophyte species Phragmites Australis and Schoenoplectus Lacustris showed differences in the assimilation of organic monoester and diester phosphorus forms in the sediment. However, the water of the Xuño Lake shows an eutrophic status by the nutrient input associated with the birds populations as indicated by microbiological data.
... lacustris area and L3-open water). The solid black lines represent the typical relationship for modern marine sediments (C:S = 2.8 ± 1.5, Berner 1982;Berner and Raiswell 1984), while the dotted line represents the same relationship for euxinic environments and the dot-dashed line represents the typical relationship in freshwater environments with low sulphate concentrations (Leventhal, 1995) with 25 nmol g −1 in lower levels; F2: 108-352 nmol g −1 (spring)/163-3459 nmol g −1 (summer-autumn) (< 22.5 cm); F3: 185-569 nmol g −1 (< 27.5 cm)/200-3758 nmol g −1 (summer-autumn); F4: < 0.1 nmol g −1 throughout the profile. The lower levels with a higher proportion of sand had manganese values < 1 (5) nmol g −1 , with the exception of F4, with a peak up to 48 nmol g −1 at a depth of 88.5 cm in summer and 100 nmol g −1 at a depth of 47 cm in autumn (Fig. 9). ...
The shallow lakes are important freshwater ecosystems, since they support much of biodiversity and ecosystem services of life on land. Shallow lakes are highly dynamic ecological entities that can exist in several alternative stable states through regime shift caused by a natural or human disturbance that exceeds ecological thresholds for biological communities composition and structure equilibria. The sediment as a reservoir has a key role in the limnological regulation of wetlands linked to the fluxes of nutrients and elements in the biogeochemical interplay with the water and macrophytes. For this reason, the role of sediment in the limnology of the shallow coastal lake of Xuño (NW Iberian Peninsula) was explored by seasonally monitoring the chemical composition of water and sediments, also according to macrophyte species. The shallow depth determines the high availability of light in the bottom and a well-mixed water column maintain the surface of the water–sediment interface oxygenated. The oxic conditions of the bottom implies a top-down regulation of the water column in the Xuño shallow lake that limits the diffusion of phosphorus and trace metals (Fe, Mn, Cu, and Co) to the water, buffering eutrophication or contamination levels by immobilization in the sediments. In fact, the concentration of Hg in the lake water in spring, and also its bioavailability, are high due to its release from the sediment in suboxic conditions. The cover of helophyte species Phragmites Australis and Schoenoplectus Lacustris showed differences in the assimilation of organic monoester and diester phosphorus forms in the sediment. However, the water of the Xuño Lake shows an eutrophic status by the nutrient input associated with the birds populations as indicated by microbiological data.
... Coastal sediments play a critical role in global biogeochemical cycles by processing high loads of organic matter (OM) and removing and recycling nutrients in ecosystems. About 70-90 % of the global ocean OM burial and more than half of sedimentary OM mineralization has been estimated to take place in continental shelf sediments that only account for 7 % of the total seafloor (Berner, 1982;Middelburg et al., 1997;Thullner et al., 2009). The shelves have increasingly become exposed to bottom-trawling, affecting currently 14 % of the global and >50 % of the European shelf and continental slope sediments at <1000 m water depth, respectively (Amoroso et al., 2018). ...
Trawl-fishing is broadly considered to be one of the most destructive anthropogenic activities toward benthic
ecosystems. In this study, we examine the effects of bottom-contact fishing by otter trawls on the geochemistry
and macrofauna in sandy silt sediment in an area of the Baltic Sea where clear spatial patterns in trawling activity
were previously identified by acoustic mapping. We calibrated an early diagenetic model to biogeochemical data
from various coring locations. Fitting measured mercury profiles allowed for the determination of the sediment
mixing and burial velocity. For all sites, independent of the trawl mark density, good fits were obtained by
applying the model with the same organic matter loading and parameter values, while iron fluxes scaled linearly with the burial velocity. A sensitivity analysis revealed that the fitted sulfate reduction rate, solid sulfur contents,
ammonium concentration, and both the isotopic composition and concentration of dissolved inorganic carbon
provided reliable constraints for the total mineralization rate, which exhibited a narrow range of variability
(around ±20 % from the mean) across the sites. Also, the trawling intensity did not significantly correlate with
total organic carbon contents in surficial sediment, indicating limited loss of organic matter due to trawling. The
fits to the reactive iron, acid volatile sulfur, chromium(II) reducible sulfur contents, and porewater composition
demonstrate that sediment burial and mixing primarily determine the redox stratification. The mixing depth did
not correlate with trawling intensity and is more likely the result of bioturbation, as the analyzed macrofaunal
taxonomy and density showed a high potential for sediment reworking. The extraordinarily long-lived Arctica
islandica bivalve dominated the infaunal biomass, despite the expectation that trawling leads to the succession
from longer-lived to shorter-lived and bigger to smaller macrofauna. Our results further suggest that a clear
geochemical footprint of bottom-trawling may not develop in sediments actively reworked by tenacious
macrofauna.
Radiocarbon (Δ¹⁴C) serves as an effective tracer for identifying the origin and cycling of carbon in aquatic ecosystems. Global patterns of organic carbon (OC) Δ¹⁴C values in riverine particles and coastal sediments are essential for understanding the contemporary carbon cycle, but are poorly constrained due to under-sampling. This hinders our understanding of OC transfer and accumulation across the land–ocean continuum worldwide. Here, using machine learning approaches and >3,800 observations, we construct a high-spatial resolution global atlas of Δ¹⁴C values in river–ocean continuums and show that Δ¹⁴C values of river particles and corresponding coastal sediments can be similar or different. Specifically, four characteristic OC transfer and accumulation modes are recognized: the old–young mode for systems with low river and high coastal sediment Δ¹⁴C values; the young–old and old–old modes for coastal systems with old OC accumulation receiving riverine particles with high and low Δ¹⁴C values, respectively; and the young–young mode with young OC for both riverine and coastal deposited particles. Distinguishing these modes and their spatial patterns is critical to furthering our understanding of the global carbon system. Specifically, among coastal areas with high OC contents worldwide, old–old systems are largely neutral to slightly negative to contemporary atmospheric carbon dioxide (CO2) removal, whereas young–old and old–young systems represent CO2 sources and sinks, respectively. These spatial patterns of OC content and isotope composition constrain the local potential for blue carbon solutions.
LI Song 1， 2 ， YU Juhua 1， 2， 3， * ， WANG Li 1 ， WANG Huangping 2， 3 ， ZHENG Xiangzhou 2， 3 ， WANG Limin 2， 3 ， DING Hong 2， 3 ， ZHANG Yushu 2， 3 1. School of River and Ocean Engineering， Chongqing Jiaotong University， Chongqing 400074 2. Institute of Soil and Fertilizer， Fujian Academy of Agricultural Sciences， Fuzhou 350013 3. Fujian Key Laboratory of Plant Nutrition and Fertilizer， Fuzhou 350013 Abstract： Reduced inorganic sulfur (RIS) is the most active sulfur component in sediment， which controls the geochemical cycling of Fe， P， and heavy metals in aquatic ecosystems. However， the understanding on the distribution pattern of sediment sulfur and its mechanism in dammed rivers， where with redox environmental gradients undergo significant changes， remains limited. Combing field in situ sampling and sequential extraction procedure in the laboratory， we investigated the forms， concentrations， and spatial distribution pattern of RIS in surface sediments under the influences of cascade reservoirs in Jiulong River Watershed. The results showed that the concentrations of RIS in surface sediments of Jiulong River followed a descending order of： Pyrite-S> acid volatile sulfide (AVS)> essential sulfur (ES)， among which Pyrite-S was the dominant form， accounting for 83% to 90% of RIS. The sediment RIS concentrations of different types of water bodies in the Jiulong River watershed were in the order of reservoirs > tributaries > main streams. The distribution of RIS in surface sediments， such as Beixi River and Xixi River， was closely associated with the spatial location of reservoirs， showing a hotspot patches distribution. While the sediment RIS concentrations in the Nanxi River showed a gradually increasing trend from upstream to downstream along the flow direction. The construction and operation of cascade reservoirs played a role in intensifying the DOI： 10.13671/j.hjkxxb.2023.0174 李松， 余居华， 王丽， 等 .2023. 九龙江流域丰水期表层沉积物还原性无机硫分布特征及其水库驱动机制 ［J］. 环境科学学报， 43 (11) ： 125-133 LI Song， YU Juhua， WANG Li， et al. 2023. Distribution patterns of reduced inorganic sulfur in surface sediments and its reservoir driving mechanism during the flooding season in Jiulong River， China ［J］ .Acta Scientiae Circumstantiae， 43 (11) ： 125-133
For much of the pelagic sedimentary record, time control is limited to the resolution of precession cycles ( ca 20 kyr): the Milankovitch parameter that forms the most detailed metronome for the Cenozoic and Mesozoic Eras. The influence of precession is often detected in lithological alternations, where the duration represented by individual lithologies is not well constrained. Here the novel technique of extraterrestrial helium abundance ( ³ He ET ) is used to investigate the sedimentation dynamics and palaeoceanography within individual precessional cycles. High‐resolution ³ He ET timescales were produced for four precession cycles from the rhythmically bedded Scaglia Bianca Formation, a sequence of Upper Cretaceous (Cenomanian) deep‐marine pelagic limestones from central Italy that are well characterized by cyclostratigraphy. Using ³ He ET concentrations as a proxy for sedimentation rate allows instantaneous sedimentation rates and organic‐carbon mass accumulation rates to be calculated for each bed within a precession cycle. Eccentricity is known to modulate the amplitude of precession forcing, and precession cycles deposited under eccentricity maxima and minima were selected for comparison. Lithological changes through these chert–(black shale)–limestone cycles are explained using the concept of ‘palaeoenvironmental thresholds’; these timescale calculations indicate that when the amplitude of precessional insolation forcing was greatest (at eccentricity maxima) the palaeoenvironmental system spent longer in the more nutrient‐rich environment under which siliceous and organic‐rich sediments were deposited, reflecting increased time spent above a ‘threshold’ insolation level. Estimates of primary productivity are relatively elevated for organic‐rich beds. An increase in the flux of terrestrial helium ( ⁴ He terr ) during the deposition of cherts may have been coincident with an increase in terrestrially derived nutrients. The presented results indicate great potential for the use of ³ He ET to understand past oceanographic, climatic and sedimentological processes at high temporal resolution.
Studying monsoon dynamics during past warm time periods such as the Miocene Climatic Optimum (MCO; ∼16.9–14.5 Ma) could greatly aid in better projecting monsoon intensity, in the context of future greenhouse warming. However, studies on regional MCO temperature change and its effect on the monsoons during this time period are lacking. Here, we present the first high‐resolution, low‐latitude record of sea surface temperature (SST) and paleoceanographic change covering the Miocene Climatic Optimum, in the eastern equatorial Atlantic, at Ocean Drilling Program Site 959, based on TEX86 paleothermometry. SSTs were ∼1.5°C warmer at the onset of the MCO (16.9 Ma) relative to the pre‐MCO (∼18.3–17.7 Ma). This warming was accompanied by a transient increase in %total organic carbon. Prior to the MCO, sediment composition, geochemical proxy data as well as dinoflagellate cyst assemblages imply a productive surface ocean at Site 959. Immediately following the MCO onset (∼16.9–16.5 Ma), we record an intensification of the West African Monsoon (WAM) characterized by higher amplitude variability in all proxy records on precession to obliquity timescales. We interpret increased orbital‐scale SST, biogenic Ba and dinocyst assemblage variability to represent intensification of equatorial upwelling, forced by the WAM strength. Furthermore, higher SSTs during eccentricity maxima correlate to increased relative abundances of the warm and stratification‐favoring dinocyst Polysphaeridium zoharyi, during periods of low WAM intensity. Finally, while long‐term SSTs decline toward the middle Miocene, maximum SSTs and Polysphaeridium zoharyi abundances occur during MCO peak warming at ∼15.6 Ma.
In order to assess observational evidence for potential atmospheric biosignatures on exoplanets, it will be essential to test whether spectral fingerprints from multiple gases can be explained by abiotic or biotic-only processes. Here, we develop and apply a coupled 1D atmosphere-ocean-ecosystem model to understand how primitive biospheres, which exploit abiotic sources of H2, CO and O2, could influence the atmospheric composition of rocky terrestrial exoplanets. We apply this to the Earth at 3.8 Ga and to TRAPPIST-1e. We focus on metabolisms that evolved before the evolution of oxygenic photosynthesis, which consume H2 and CO and produce potentially detectable levels of CH4. O2-consuming metabolisms are also considered for TRAPPIST-1e, as abiotic O2 production is predicted on M-dwarf orbiting planets. We show that these biospheres can lead to high levels of surface O2 (approximately 1–5 %) as a result of CO consumption, which could allow high O2 scenarios, by removing the main loss mechanisms of atomic oxygen. Increasing stratospheric temperatures, which increases atmospheric OH can reduce the likelihood of such a state forming. O2-consuming metabolisms could also lower O2 levels to around 10 ppm and support a productive biosphere at low reductant inputs. Using predicted transmission spectral features from CH4, CO, O2/O3 and CO2 across the hypothesis space for tectonic reductant input, we show that biotically-produced CH4 may only be detectable at high reductant inputs. CO is also likely to be a dominant feature in transmission spectra for planets orbiting M-dwarfs, which could reduce the confidence in any potential biosignature observations linked to these biospheres.
The transfer of carbon from land to the near-coastal ocean is increasingly being recognized in global carbon budgets. However, a more direct transfer of terrestrial carbon to the deep-sea is comparatively overlooked. Among systems that connect coastal to deep-sea environments, the Congo Submarine Canyon is of particular interest since the canyon head starts 30 km into the Congo River estuary, which delivers ~7 % of the total organic carbon from the world’s rivers. However, carbon and sediment transport mechanisms that operate in the Congo Canyon, and submarine canyons more globally, are poorly constrained compared to rivers because monitoring of deep-sea canyons remains challenging. Using a novel array of acoustic instruments, sediment traps and cores, this study seeks to understand the hydrodynamic processes that control delivery of particulate organic carbon via the Congo Submarine Canyon to the deep-sea. We show that particulate organic carbon transport in the canyon-axis is modulated by two processes. First, we observe periods where the canyon dynamics are dominated by tides, which induce a background oscillatory flow (speeds of up to 0.15 m/s) through the water column, keeping muds in suspension, with a net upslope transport direction. Second, fast-moving (up to 8 m/s) turbidity currents occur for 35 % of the time during monitoring periods and transport both muddy and sandy particulate organic carbon at an estimated transit flux that is more than ten times the flux induced by tides. Remarkably, organic carbon transported and deposited in the submarine canyon has a similar isotopic composition to organic carbon in the Congo River, and in the deep-sea fan at 5 km of water depth. Episodic turbidity currents, together with background tidal currents thus promote efficient transfer of river-derived particulate organic carbon in the Congo Submarine Fan, leading to some of the highest terrestrial carbon preservation rates observed in marine sediments globally.
Mudstone properties vary widely, but systematically, both vertically and laterally at millimeter-to-kilometer scales. This variability can be detected by applying a range of physical, petrophysical, chemical, and paleontological methods to characterize the rocks at different scales and interpreting the resulting data using the sequence-stratigraphic approach.
This chapter concentrates on introducing the tools and techniques that provide data about texture, bedding, composition, and grain origin, which enable the characterization of mudstone strata at millimeter-to-kilometer scales. Specifically, it addresses the application of such tools and techniques to decipher depositional conditions and construct sequence-stratigraphic frameworks. This chapter provides key references for the tools and techniques commonly used to generate the texture, bedding, composition, and grain-origin data for further consideration. It then outlines our approach toward making detailed and systematic observations of the key attributes of mudstones in outcrops, cores, and thin sections. It concludes with an overview of the key sequence-stratigraphic concepts that we find useful for studying mudstones and a summary of the methods we use to construct and test a sequence-stratigraphic framework for mudstones. This approach is elaborated and illustrated in the following chapters.
The organic-rich rocks of the Duwi Formation have gained much attention in recent years because of the growing demand for their utilization as energy and metal sources. A depositional model for these important rocks is delineated in the present study based on multiple analytical approaches. Samples from these organic-rich rocks were collected from eight mines in the Qusseir-Safaga region along the Red Sea coast in the Eastern Desert of Egypt. These mines are located at El Nakheil, Younis, El Beida, Atshan, Hamadat, Tundub Bahri, Tundub Qubli, and Zog EL Bahr. The depositional model is based firstly on organic geochemical and petrographical analyses of the organic matter to identify its enrichment, composition, hydrocarbon potential, types and origin, and their relationship to rock minerals. Secondly, the inorganic geochemical analysis, including mineralogy and trace elements, is integrated to explore the lithological characteristics and to confirm the results obtained from other analyses. Only the El Nakheil, Atshan, Tundub Bahri, and Tundub Qubli mines are found to have total organic carbon content above 10 wt%. These mines contain hydrogen-rich organic matter that reached a maximum in the El Nakheil Mine as reflected in the Rock-Eval parameters of S2 (137.95 mg HC/g rock) and hydrogen index (HI of 707 mg HC/g TOC). The organic matter is composed mainly of large sheet-like alginite particles and prasinophytes that are finely laminated with minerals, planktonic debris of fish bones, and foraminifera without any sign of the presence of benthic organisms or bioturbation. This lamination is attributed to the occurrence of condensed sections in the studied mines. In addition, the high organic enrichment in terms of quantity and quality is accompanied by enriched metal composition including trace elements that signify anoxic conditions and low sedimentation rates. This composition points to the occurrence of prominent anoxic conditions that are stabilized by a slow sea level rise, which inhibits water circulation and water column stagnation in a restricted basin. The depositional model emphasizes the optimal balance between anoxia, sedimentation rate, and paleoproductivity that resulted in enhanced organic matter preservation in a condensed section. The deposition of the organic-rich rocks is situated in the deep parts of the basin or depocenters that reached their present-day distribution by topographic inversion. The organic and metalliferous reserves in these organic-rich sediments are calculated in the studied mines. The estimation of these reserves is found to be economic for many trace metals in an ore reserve that reached 151742 tons in one bed alone within the Duwi Formation.
Global climatic and palaeogeographical changes generated a siliciclastic–carbonate system with high organic matter accumulations in a shallow sea during
the lower Permian in Western Gondwana. The 60 m thick mixed siliciclastic–
carbonate succession (Irati Formation and the base of the Serra Alta Formation)
from the Paran a Basin represents a singular record of the interplay between carbonate production and siliciclastic input, providing a window of opportunity to
integrate large-scale depositional architecture with facies and geochemical analyses. The detailed study of cores supported by outcrop columnar sections
revealed a siliciclastic-dominated, retrogradational to aggradational facies, and
a carbonate-dominated, mixed aggradational to progradational facies composing
three depositional sequences that record an outer-ramp and mid to upper-ramp.
An integrated approach based on the description of facies and microfacies,
organic geochemistry and mineralogical composition, indicated high-frequency
palaeoenvironmental changes during the evolution of this restricted basin. Climate changes, resulting in humid and dry phases, produced ideal conditions for
high organic matter production and dolomite formation. The high organic matter production (humid phases) in addition to the restricted condition was
responsible for the anoxic bottom waters that were widespread due to the low
angle and homoclinal platform. Nutrient-rich freshwater inflows in the anoxic
and hypersaline restricted basin created a density-stratified water column causing low-salinity surface and anoxic bottom water, which allowed planktonic
life, typical of lakes, such Botryococcus braunii, to flourish in the photic zone
and sulphur bacteria to populate below the chemocline. Microbial activity
induced primary dolomite precipitation (dry phases) and widespread formation
of synsedimentary dolostone. Freshwater inflow and marine incursions are
reflected in the organic matter accumulation (kerogen types I and II, respectively), generating bituminous shale with high total organic carbon (5 to
27 wt.%).
Upward diffusion of dissolved methane and associated anaerobic oxidation of methane (AOM) coupled with microbial sulfate reduction (MSR) are widespread in normal hemipelagic sediments of continental margins. The occurrence of authigenic sulfur enrichment in such sediments is usually regarded as an indicator of AOM; however, extensive MSR and authigenic iron sulfide generation also occur in turbidites. Therefore, research attention should be directed toward determining the geochemical features of authigenic sulfur mineralization in methane-rich background sediments and turbidites. Here we report the sedimentology and geochemical composition of sediments from four piston cores (CL30, CL44, CL47, and CL3A) containing turbidite layers from methane-rich areas of the South China Sea. The turbidite layers were deposited at 17-15 kyr BP or earlier during the last glacial period and were located above the present sulfate-methane transition zone (SMTZ). The median grain size, proportion of sand-sized grains, and Si, Ti, K, and Zr contents show marked elevation in the turbidite layers compared with the background sediments, indicating the input of large amounts of terrigenous detrital matter with coarser grains. High total sulfur (TS) contents and low δ 34 S AIS values (AIS: acid-insoluble sulfur) (− 35.2‰ to − 26.1‰) are observed within turbidite layers relative to the background hemipelagic sediments in core CL44. These results suggest that intensive sulfidization occurred as a result of enhanced organoclastic sulfate reduction rates in turbidite horizons, which were probably caused by the resultant decrease in downward oxygen flux and waning bioturbation after rapid deposition of turbidites. In comparison, TS contents are higher and δ 34 S AIS values are positive (0.2‰-46.8‰) within the SMTZ on account of the rapid consumption of sulfate and build-up of isotopically heavier hydrogen sulfide pools via intensive AOM. Moreover, authigenic barium (Ba) enrichments commonly occur in the depth interval immediately above the SMTZ rather than within turbidite layers; therefore, they serve as a useful indicator of the position of the SMTZ. This study presents distinct differences in the geochemical compositions of turbidity deposits and methane-rich background sediments and highlights that a multi-proxy approach including sedimentological and geochemical analyses should be used to constrain the types of MSR in deep-sea sediments, given the common occurrence of turbidites and subsurface methane release in marginal deep-sea areas. It is also suggested that if applied with caution, S-C-Ba geochemical patterns can be used to identify palaeo-SMTZs and palaeo methane-rich zones in turbidite-containing strata.
Deltas, being areas where river sediments accumulate, are sensitive to changes in climate and anthropogenic processes that affect sediment generation. The Omo Delta, on the Ethiopia–Kenya border, is constantly changing due to fluctuating lake levels, a variable climate, and rapidly changing land use. Due to field data scarcity and the region's limited accessibility, we relied on remote sensing (RS) data to investigate delta extent between 1990 and 2018 and attempted to disentangle the effect of climatic from anthropogenic variables. We obtained a time series of delta extent from Landsat imagery using Random Forest (RF) classification. Using parametric and non‐parametric regression techniques, we regressed the delta extent on Lake Turkana levels, Omo River discharges, Omo‐Gibe Basin rainfall, tree cover loss, and irrigation extent. The RF algorithm distinguished water from land with high (>90%) accuracies and revealed Omo Delta extent fluctuations ranging from 949 km2 in 1993 to 651 km2 in 2000. Lake water level, which depends on the rainfall over the Omo‐Turkana Basin, emerged as the best predictor of delta extent. However, the annual rainfall over the Omo‐Gibe Basin showed no correlation with delta extent. The regression models further show a connection between delta extent, irrigation extent, and tree cover loss. We conclude that rainfall indirectly influences delta extent across the Omo‐Turkana Basin. Regression models indicate additional cumulative effects of human activity in the Omo‐Gibe Basin but fall short in explaining delta dynamics.
The quantification and mapping of surficial seabed sediment organic carbon has wide-scale relevance across marine ecology, geology and environmental resource management, with carbon densities and accumulation rates being a major indicator of geological history, ecological function, and ecosystem service provisioning, including the potential to contribute to nature-based climate change mitigation. While global mapping products can appear to provide a definitive understanding of the spatial distribution of sediment carbon, there is inherently high uncertainty when making estimates at this scale. Finer resolution national maps which utilise targeted data syntheses and refined spatial data products are therefore vital to improve these estimates. Here, we report a national systematic review of data on organic carbon content in seabed sediments across Canada and combine this with a synthesis and unification of best available data on sediment composition, seafloor morphology, hydrology, chemistry, geographic setting and sediment mass accumulation rates within a machine learning mapping framework. Predictive quantitative maps of mud content, sediment dry bulk density, and organic carbon content, density and accumulation, were each produced along with cell specific estimates of their 95 % confidence interval (CI) bounds at 200 m resolution across 4,489,235 km2 of the Canadian continental margin (92.6 % of the seafloor area above 2,500 m). Fine-scale variation in carbon stocks was identified across the Canadian continental margin, particularly in the Pacific and Atlantic Ocean regions. Carbon accumulation was predicted to be concentrated in coastal areas, with the highest rates in the Gulf of St Lawrence and Bay of Fundy. Overall, we estimate the standing stock of organic carbon in the top 30 cm of surficial seabed sediments across the Canadian shelf and slope to be 10.7 Gt (95 % CI 6.6 – 16.0 Gt), and accumulation at 4.9 Mt per year (95 % CI 2.6 – 9.3 Mt y-1). Increased in-situ sediment data collection and higher precision in spatial environmental data-layers could significantly reduce uncertainty and increase accuracy in these products over time.
In polar regions, glaciers are retreating onto land, gradually widening ice-free coastal waters which are known to act as new sinks of atmospheric carbon. However, the increasing delivery of inorganic suspended particulate matter (iSPM) with meltwater might significantly impact their capacity to contribute to carbon sequestration. Here, we present an analysis of satellite, meteorological, and SPM data as well as results of the coupled physical-biogeochemical model (1D GOTM-ECOSMO-E2E-Polar) with the newly implemented iSPM group, to show its impact on the ecosystem dynamics in the warming polar fjord (Hornsund, European Arctic). Our results indicate that with a longer melt season (9 days per decade, 1979–2022), loss of sea ice cover (44 days per decade, 1982–2021) and formation of new marine habitat after the retreat of marine-terminating glaciers (around 100 km2 in 1976–2022, 38 % increase in the total area), glacial meltwater has transported increasing loads of iSPM from land (3.7 g·m−3 per decade, reconstructed for 1979–2022). The simulated light limitation induced by iSPM input delayed and decreased phytoplankton, zooplankton, and macrobenthos peak occurrence. The newly ice-free areas markedly contributed to the plankton primary and secondary production, and carbon burial in sediments (5.1, 2.0, and 0.9 GgC per year, respectively, average for 2005–2009 in the iSPM scenario). However, these values would have been higher by 5.0, 2.1 and 0.1 GgC per year, respectively, without iSPM input. Carbon burial was the least affected by iSPM (around 16 % decrease in comparison to 50 % for plankton primary and secondary production) and thus the impact of marine ice loss and enhanced land-ocean connectivity should be investigated further in the context of carbon fluxes in expanding polar fjords.
Ediacaran to Early Cambrian sequences are well preserved in several synclines within the Lesser Himalaya. We have conducted multi-proxy geochemical and stable isotopic studies on carbonaceous sediments of the basal Tal Group to decipher redox conditions of Earliest Cambrian Ocean. Organic matter is immature, predominantly aliphatic and likely derived from marine phytoplankton. The S/C(organic) ratios above 0.4; strong enrichment of redox sensitive trace elements V, Mo, U and Cd; higher DOPT, U/Th, V/Sc, Mo/Sc and V/(V+Ni) ratios; V/Al-U/Al-Mo/Al systematics and U-Mo enrichment factors indicate anoxic to euxinic conditions of deposition. Large variations (5-7 ‰) in 13C likely reflect spatial heterogeneity or vertical gradient in DIC compositions of the Early Cambrian Ocean, and possibly captures the part of Basal Cambrian negative Carbon isotope Excursion (BACE). Finely disseminated texture of pyrite framboids with sizes mostly below 10 µm suggest sulfide reduction within the water column in an open system. Isotopically heavy 34S values (+4.5 – +22.8 ‰) overlap with the 34Ssulfate of contemporary Fortunian ocean (+10–+40‰) suggesting sulfidic conditions and small size of the sulfate reservoir. Whereas, the REE+Y proxies of the same set of samples show oxidised seawater like patterns, with strong HREE enrichment, positive Y and La anomalies and negative Ce anomaly (avg. Ce/Ce* = 0.78), indicating REE uptake by phytoplankton from an oxidised euphotic surface zone. The combined geochemical and isotopic data suggest strongly stratified ocean with sulfidic bottom water and oxidised surface water. Episodic shoaling of anoxic deep water onto the surface possibly caused the extinction of benthic Ediacaran fauna, and the surface oxidised zone likely provided the niche for further metazoan radiation.
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