Burial Efficiency Research Articles

Organic carbon burial dynamics at the Chukchi Shelf margin: Implications for the Arctic Ocean carbon sink

Organic carbon (OC) burial plays a crucial role in regulating the Arctic Ocean's capacity to uptake atmospheric CO₂. In this study, we demonstrate the transport, deposition, and degradation patterns of different sources of OC to reveal burial dynamics at the Chukchi Shelf margin, a region with the highest primary production in the Arctic Ocean currently affected by dramatic sea ice retreat. Observations of suspended particulate material show a pronounced separation of terrestrial and marine OC in the water column, which subsequently influences OC lateral transport and differential deposition. Easily suspendable terrestrial OC is concentrated in the upper 10 m of water or sea ice and transported to the Canada Basin, where it undergoes severe degradation of fresh carbon in the water column and uppermost sediments. In contrast, faster-settling marine OC is more likely to be buried in the canyons and at the Chukchi Shelf margin, with ice algae contributing about 14 % and 55 % of OC burial in areas south and north of 73°N, respectively, leading to higher initial burial efficiency. Increasing Arctic marine primary production could thus enhance the region's role as a carbon sink over millennial timescales, although the burial efficiency of terrestrial OC will eventually exceed that of marine OC with prolonged burial time. Our findings highlight the importance of lateral transport, differential deposition, and selective degradation in Arctic carbon burial, providing a basis for objectively assessing the future capacity of the Arctic carbon sink and its feedback to climate change.

Foraminiferal denitrification and deep bioirrigation influence benthic biogeochemical cycling in a seasonally hypoxic fjord

Benthic macro- and micro-biota often play significant roles in controlling the biogeochemical dynamics in sediments. Their activity can be influenced by oxygen availability and impacted by the rise in global hypoxia in coastal regions over the last decades. To understand how these organisms interact with coastal hypoxia and influence sediment biogeochemistry, we undertook a study of early diagenesis in Bedford Basin, a seasonally hypoxic fjord on the West Atlantic coast in Nova Scotia, Canada, using a combination of observations and reaction-transport modeling. We observed that the seafloor was a source of ammonium and sink of nitrate with average fluxes of 2.2 ± 1.8 and −0.9 ± 0.7 mmol m−2 d−1 respectively. The diffusive oxygen uptake was 14 ± 4.6 mmol m−2 d−1 and the total organic carbon content in collected sediment cores was 5–7 % with a C/N ratio of ∼10. The pyrite content increased steadily from 0.5 wt% Fe at surface to ∼2 wt% Fe at 20 cm depth. Hydrogen sulfide was negligible down to 25 cm depth most of the time. The sediment was inhabited by tube-forming polychaete Spiochaetopterus sp. that formed tubes up to ∼30 cm in length. The living foraminiferal assemblage in the top 5 cm sediment was found to be dominated (>85 %) by nitrate-storing and denitrifying benthic foraminifera Stainforthia fusiformis. These observations were used to develop and constrain a biogeochemical reaction-transport model. The model results suggest that the observed decrease in porewater concentrations of ammonium and dissolved inorganic carbon below 5 cm depth, was due to deep bioirrigation by tubeworms, accounting for almost 50 % of the benthic efflux. The model further revealed that the deep bioirrigation along with bioturbation and iron cycling prevented accumulation of free sulfide in the top 25 cm sediment despite oxygen penetration depths of ∼1 mm. Modelled organic carbon and nitrogen deposition was 25.2 and 2.9 mmol m−2 d−1 with burial efficiencies of 23 % and 17 %, respectively. The model indicated a total denitrification rate of 1.3 mmol N m−2 d−1 that was largely (∼70 %) driven by benthic foraminifera. This study reports the first evidence of foraminiferal denitrification in western Atlantic coastal sediments, and suggests that eukaryote mediated denitrification is an important driver of sediment N-loss in seasonally hypoxic environments, a process that has been traditionally assumed to be carried out by prokaryotic microbes.

Thermal stability of sedimentary organic carbon in a large river dominated marginal sea

The thermal stability of organic carbon (OC) in marine sediments is one of the critical factors that influences its burial efficiency in marine environments. However, the distribution patterns and influencing factors of the thermal stability of OC in marginal seas remain poorly understood. In this study, we conducted the thermal gravimetric analysis (TGA) of OC in surface sediments of the Changjiang Estuary (CE) and its adjacent East China Sea (ECS) shelf. Both labile and refractory organic matter (OML and OMR) contents derived from the TGA were higher in the CE and Zhe-Min Coast (ZMC) mobile muds relative to those in the sandy areas. The average Carbon Reactivity Index (CRI) is 69.3 ± 4.2 %, ranging from 62.8 % to 85.1 %. Most of the stations in the CE and ZMC mobile muds were characterized by relatively low CRI values, while only some stations in the inner estuary and outer shelf had higher CRI values. As a result, the CRI values correlated reversely with the OC contents and positively with the median grain size, especially in sandy sediments. Despite being sandy sediments, there were significant differences in the thermal stability of OC among the three different sandy sediment areas, with the highest CRI value in the inner estuary, lower CRI values in the outer estuary and outer shelf sediments, possibly related to the sources and composition of OC in different regions as shown by the negative correlation between CRI and δ13C for sandy sediments. Compared with certain European marginal seas, the sedimentary OC (SOC) in the CE and ECS shelf exhibits greater thermal stability, which is probably linked to the reduced preservation efficiency of OC caused by the extensive sediment dynamics in this area. This study supports the notion that organo-mineral interactions and the sources are two major factors controlling the reactivity of OC.

Silicon balance in an integrated multi-tropical aquaculture ecosystem, Sanggou Bay, China

Farmed aquaculture species play an important role in regulating nutrient cycles in farming systems. Compared with nitrogen and phosphorus, the role of farmed species in the silicon (Si) cycle remains poorly understood. To help reduce this uncertainty, we clarified the sources and sinks of silicate and quantified the Si pools in an aquaculture system in Sanggou Bay (SGB). The results showed that dissolved inorganic nutrient levels were significantly lower during the dry season than during the wet. Dissolved silicate (DSi) is a potential limiting factor for phytoplankton growth during spring, and phosphorus limitation occurs during summer. The budget results indicated that large amounts of nitrogen, phosphate (DIP), and DSi were buried in the sediment or transformed into other forms during both the wet and dry seasons. The nitrogen and DIP cycles were strongly influenced by bivalve excretion and farmed species harvesting; however, these processes had little impact on the Si cycle. Si availability depends on both external inputs and internal recycling. DSi was primarily supplied from the Yellow Sea, with a minor contribution from the river due to river discharge during spring. However, during summer, riverine inflow (accounting for 83% of the total influx) was the major DSi source followed by benthic flux (12%). Biogenic silica (BSi) burial efficiency in the sediment was estimated to be 78% during spring and 23% during summer. The BSi preservation efficiency in bivalves during spring was high (53%), leading to a higher Si retention than in river discharge. Bivalves biodeposition plays an important role in the Si burial process. We suggest that this high retention is essentially controlled by the biodeposition mechanism, which is directly controlled by the exotic suspension feeders. Bivalves have the potential to alter Si retention in the bay by producing large amounts of biodeposits and accelerating the silica cycle, which may lead to more carbon dioxide being absorbed by diatoms.

Characterization of sediment organic matter in the outer Yangtze River Estuary using stable isotopes, optical techniques, and FT-ICR-MS: Implications for the carbon burial mechanism

The burial of sediment organic matter (SOM) in the estuary and shelf plays an important role in the global carbon cycle. However, it is challenging to determine the source, composition, and burial of SOM in the coastal sea, especially at the molecular level. This was explored in the coastal area outside the largest Yangtze River of China with multiple techniques including elemental and stable isotopic analysis, absorption spectroscopy, fluorescence excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC), and ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The end-member mixing analysis based on δ13C and δ15N showed a dominance of marine contribution (up to 70%) at most stations while the terrestrial contribution increased to >55% nearshore in summer at a high fluvial sediment flux. This was consistent with the offshore decreasing humic-like C1 and C2, humification index (HIX), %lignin-like compounds, and %CHO but increasing tryptophan-like C3, biological index (BIX), %protein-like compounds, and %CHOS from EEMs-PARAFAC and FT-ICR-MS analysis. The %clay correlated positively with SOM content, HIX, %lignin-like compounds, O/C, and modified aromaticity index (AImod) but correlated negatively with %C3, H/C, and the relative abundance of labile formulas (MLBL), while %silt showed contrasting correlations. These results indicated the fine clay sediments adsorbed more humified, aromatic, oxygenated, and terrestrial compounds that were probably more resistant to biodegradation and thus had a higher burial efficiency than those on the silty sediments. Principal component analysis based on SOM indices further revealed different characteristics of SOM in the nearshore, northern offshore, and southern offshore regions, which were probably dependent on the delivery by local current systems. Overall, these findings contributed to unraveling the source and molecular composition of SOM associated with different grain size sediments and local current delivery, which are fundamental for understanding the factors underlying carbon burial in the complex coastal environment.

Chemical speciation, reactivity, and long-term burial of sedimentary phosphorus in Green Bay, a seasonally hypoxia-influenced freshwater estuary

Sediment cores were collected along a trophic gradient in Green Bay, a seasonally hypoxia-influenced freshwater estuary in Lake Michigan, to measure various phosphorus (P) species, including exchangeable-P (Ex-P), iron-bound-P (Fe-P), biogenic-apatite and/or CaCO3-associated-P (CFA-P), organic-P (Org-P) and detrital-apatite-P (Detr-P). Although total phosphorus (TP) decreased with increasing depth, different P species exhibited distinct vertical distribution patterns with different post-depositional behaviors. The Ex-P, Fe-P and CFA-P species were identified as potentially bioavailable-P (BAP). Little variation was observed for Org-P and Detr-P species, especially below the upper-active-layer, both serving as the primary sink for P in sediment. Detr-P% decreased consistently from the near river plume station to the open bay in the north. P accumulation rates were estimated at 25.1 mmol-P/m2/yr (779 mg-P/m2/yr) in the south, 10.9 mmol-P/m2/yr (338 mg-P/m2/yr) in the central region, and 8.1 mmol-P/m2/yr (252 mg-P/m2/yr) in the north of Green Bay, showing a decrease in the depth of the upper active layer for P regeneration along the south-north transect. The overall potential P regeneration back into the water column increased from 2.8 mmol-P/m2/yr (87 mg-P/m2/yr) in the south, and 3.3 mmol-P/m2/yr (101 mg-P/m2/yr) in the central region to 5.6 mmol-P/m2/yr (173 mg-P/m2/yr) in the north of the bay, corresponding to P burial efficiencies of ∼89 %, 70 % and 31 % along the trophic gradient. The recent decrease in Detr-P and thus the increase in BAP over the last 2–3 decades could be related to anthropogenic activities, such as damming and implementation of agricultural conservation practices. Conversely, a recent increase in TOC/TOP ratios may reflect the increased extent of trophic status and seasonal hypoxia in bottom waters and enhanced regeneration and recycling of particulate P in Green Bay since the 1960s. New results from this study provide an improved understanding of the linkage between sources, internal cycling, and long-term burial of P in the basin.

Influence of changing water mass circulation on detrital component and carbon burial of late Pleistocene and Holocene sediments in the eastern-central Mid-Adriatic deep

A sediment core was retrieved in the eastern-central Mid-Adriatic Deep (MAD) to study the changes in the water mass circulation and their effect on carbon burial efficiency and the provenance of a detrital sediment component. An age-depth model of the sediment core POS-514-40-11 is based on radiocarbon dating and tephrochronology. Two tephra were correlated to the Neapolitan Yellow Tuff and Pomici di Mercato eruptions, extending the previously known distribution of Pomici di Mercato tephra. Based on the analysis of heavy mineral (HM) assemblages throughout the core, for the first time the occurrence of Eastern Adriatic current (EAC) was estimated at ca. 15 ka BP, i.e., at the beginning of the post last glacial maximum (LGM) transgression. During the late Pleistocene, the detrital component was dominated by Paleo-Po river sediments, which gradually shifted toward the Albanian province as a basin-wide counterclockwise circulation was established. Mass accumulation rates of organic carbon (OC), stable isotopes of carbon (δ 13C) and nitrogen (δ 15N) as well as C/N ratios, showed that carbon burial was affected by sea level rise and climatic changes. Climatic effects are observed during cold periods i.e., the Younger Dryas and the 8.4–7.9 ka cold period when terrestrial OC was dominant. In the latter case dominance of terrestrial carbon was due to the North Adriatic dense water (NAddW) influence. On the other hand, sea level rise increased MAD distance from the main river mouths/deltas, resulting in decreased influx of terrestrial organic carbon and lower accumulation rates of organic carbon in general. This reconstruction of the oceanographic setting is valuable considering that the Adriatic Sea is one of the key locations for the formation of DW and thus affects the overall Mediterranean circulation.

Nickel's behaviour in marine sediments under aerobic to anaerobic diagenetic conditions

In the marine environment, nickel distributions are linked to the biogeochemical cycling of both organic matter and manganese. Thus, Ni and its isotopes have the potential to be used to reconstruct changes of bioproductivity and oxygenation in paleoenvironments. However, their utility relies on an understanding of the behaviour of Ni in modern marine environments. Here we investigate the distribution of Ni under a range of oxidation-reduction conditions, with organic carbon (Corg) burial rates that range from approximately 0.08 to 8.4 mmol m−2 d−1, none of the sites show deep (> 5 cm) penetration of dissolved oxygen into the sediment. We present Ni concentrations for sediments and pore fluids, as well as Ni isotope compositions from pore fluids, from the California and Mexico continental margins. The sites are sufficiently reducing that solid-phase Mn concentrations are typically <1000 ppm, but two of the stations, where oxygenated bottom water bathes the underlying sediment, have near-surface sediment Mn concentrations that reach up to 2.3%.Dissolved Ni is lower in pore fluids for stations with high solid phase Corg compared to those stations with oxygenated bottom water and high solid phase Mn concentrations. The calculated benthic fluxes of Ni at all stations are small relative to their burial rates, which implies a high Ni burial efficiency (> 85%). Pore fluid δ60Ni values range from approximately −0.39 to +2.36 ‰, with the higher δ60Ni values occurring at the Corg-rich station, and the lower values at the Mn-rich stations. At the station with the highest Corg content, the distribution of solid-phase Ni as a function of Corg content is consistent with the strong association of Ni with Corg seen at open-ocean upwelling margins globally. In contrast, the other stations investigated here clearly do not show such an association. Our data offer support for the notion that Ni accumulation within sediments is linked to organic matter accumulation in regions of high photic zone productivity and where the sediments are reducing. However, at the sites in our study where Mn oxidation-reduction reactions occur near the sediment-water boundary, any simple relationship between Ni and Corg burial is obfuscated. With a sufficiently deep oxygen penetration depth and the formation of a solid-phase Mn oxide layer, Ni burial within the sediment can be highly efficient. Importantly, Ni is well preserved in sediments deposited under the full range of conditions studied here. This observation of high Ni preservation is an important constraint if Ni is to be used as a proxy to reconstruct paleoenvironmental conditions.

Zinc isotopic evidence for enhanced continental weathering and organic carbon burial in the Early Silurian

The Late Ordovician and Early Silurian periods experienced glaciation and mass extinctions. However, debates exist regarding the factors that initiated the glaciation and the subsequent delay in biotic recovery. To uncover the relationships between paleoclimate, marine redox states, and biotic recovery in the Early Silurian, temporal variations in Zinc (Zn) isotopic compositions along with other multi-geochemical proxies were analyzed for a carbonate-dominated section in South China. A stratigraphic δ66Zn trend was found in studied section, indicating a widespread disturbance to the marine Zn cycle. A significant negative shift in δ66Zn by up to ∼0.7 ‰ was observed immediately following the Hirnantian Glaciation and HICE, which can be attributed to a combination of reduced burial efficiency of organic carbon, fast weathering of large igneous provinces and increased riverine Zn input. This was followed by a ∼ 0.4 ‰ rise in δ66Zn values, alongside a sharp decrease in δ13C values, indicating an increase in sulfide precipitation (e.g., ZnS, FeS) due to expansions of euxinia. Subsequently, a notable rise in δ66Zn values by up to ∼1.1 ‰ is interpreted as an increase in organic carbon burial, given the concurrent variation of δ66Zn and δ13C during this period. The findings suggest that the increase in organic carbon burial, a reduction in reverse weathering, or a combination of them contributed to the glaciation in Silurian. Furthermore, the weathering-induced high primary productivity led to anoxic water conditions in the latest Hirnantian and Rhuddanian. This prolonged marine anoxia in seawater thus caused the deposition of organic-rich sediments and hindered biotic recovery in the Rhuddanian.

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.

Lithium isotopic constraints on the evolution of continental clay mineral factory and marine oxygenation in the earliest Paleozoic Era.

The evolution of oxygen cycles on Earth's surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic-Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organic carbon production and burial respond to global environmental changes and whether these feedbacks trigger global oxygenation during this interval. Here, we report a large lithium isotopic and elemental dataset from marine mudstones spanning the upper Neoproterozoic to middle Cambrian [~660 million years ago (Ma) to 500 Ma]. These data indicate a dramatic increase in continental clay formation after ~525 Ma, likely linked to secular changes in global climate and compositions of the continental crust. Using a global biogeochemical model, we suggest that intensified continental weathering and clay delivery to the oceans could have notably increased the burial efficiency of organic carbon and facilitated greater oxygen accumulation in the earliest Paleozoic oceans.

Early Diagenetic Controls on Sedimentary Iodine Release and Iodine‐To‐Organic Carbon Ratios in the Paleo‐Record

AbstractIodine cycling in the ocean is closely linked to productivity, organic carbon export, and oxygenation. However, iodine sources and sinks at the seafloor are poorly constrained, which limits the applicability of iodine as a biogeochemical tracer. We present pore water and solid phase iodine data for sediment cores from the Peruvian continental margin, which cover a range of bottom water oxygen concentrations, organic carbon rain rates and sedimentation rates. By applying a numerical reaction‐transport model, we evaluate how these parameters determine benthic iodine fluxes and sedimentary iodine‐to‐organic carbon ratios (I:Corg) in the paleo‐record. Iodine is delivered to the sediment with organic material and released into the pore water as iodide (I−) during early diagenesis. Under anoxic conditions in the bottom water, most of the iodine delivered is recycled, which can explain the presence of excess dissolved iodine in near‐shore anoxic seawater. According to our model, the benthic I− efflux in anoxic areas is mainly determined by the organic carbon rain rate. Under oxic conditions, pore water dissolved I− is oxidized and precipitated at the sediment surface. Much of the precipitated iodine re‐dissolves during early diagenesis and only a fraction is buried. Particulate iodine burial efficiency and I:Corg burial ratios do increase with bottom water oxygen. However, multiple combinations of bottom water oxygen, organic carbon rain rate and sedimentation rate can lead to identical I:Corg, which limits the utility of I:Corg as a quantitative oxygenation proxy. Our findings may help to better constrain the ocean's iodine mass balance, both today and in the geological past.

Sources and high burial efficiency of fossil organic carbon in small bays and implication for coastal carbon cycle

Coastal seas receive and store large amounts of organic carbon (OC) from land and ocean, thereby playing a crucial role in the global carbon cycle. Understanding factors that influencing OC sources and burial efficiencies in coastal areas have been challenging. We selected the Jiaozhou Bay (JZB) and its surrounding rivers heavily affected by human activities as a case study small bay. We presented bulk parameters of grain size, sediment surface area (SSA), TOC content and carbon isotopes (δ13Corg and Δ14Corg), terrestrial biomarkers (∑C27 + C29 + C31n-alkanes) and marine biomarkers (brassicasterol and dinosterol) in surface sediments and suspended particulates. Our results showed low TOC and biomarker contents in the Dagu River Estuary from the west of the JZB associated with coarse sediments and lower SSA. To estimate the OC proportions, we applied a three-end member mixing model based on TOC δ13Corg and biomarker ratios and obtained the OC contribution from phytoplankton (average 52 %), soil (average 34 %) and wetlands (average 14 %). A transect from east to west of the JZB was selected to further assess the OC age composition based on radiocarbon isotopic (14C) measurements for a new perspective. The lower Δ14Corg values in the east revealed fossil OC contributions from human activities, such as petroleum pollutant inputs from sewage outlets. Based on a dual‑carbon isotope (δ13Corg and Δ14Corg) mass balance mixing model, the OC contributions were 40 %, 34 %, 14 %, 12 % from fossil carbon, phytoplankton, wetlands and soil, respectively. The very high burial efficiency of fossil OC in JZB (111 ± 19 %) indicated that small bays such as the JZB could be an important sedimentary carbon sink.

Degradation and accumulation of organic matter in euxinic surface sediments

The impact of oxygen on the preservation of organic matter in marine surface sediments is still controversial. We revisited this long-standing debate by determining the burial efficiency of sedimentary organic matter in the Black Sea, the largest anoxic and euxinic basin in the modern ocean. Surface sediments were sampled in the Danube paleodelta on the northwestern margin of the Black Sea at 420–1550 m water depth. Steady-state modeling of solid species (particulate organic carbon and nitrogen) and solutes (ammonium, sulfate, and total alkalinity) in sediments was performed to quantify rates of mass accumulation, particulate organic matter (POM) degradation, and POM burial. We develop a novel analytical model to quantify these rates applying an inverse modelling approach to down core data accounting for molecular diffusion, sediment burial and compaction. Our model results indicate that 56.7 ± 6.6 % of the particulate organic matter deposited in the study area is not degraded in surface sediments but accumulates below 10 cm sediment depth. This burial efficiency is substantially higher than those previously derived for seafloor areas underlying oxygenated bottom waters. Hence, our study confirms previous studies showing that euxinic bottom water conditions promote the preservation of particulate organic matter in marine sediments.

Phosphorus cycling during the Hirnantian glaciation

Unlike other mass extinctions of the Phanerozoic, the Late Ordovician mass extinction took place during an icehouse interval, accompanied by the glaciation of Gondwana. Ice sheets reached their maximum during the Hirnantian and global sea-level dropped substantially. Consequently, the shallow tropical shelf environments of Laurentia and Baltica became subaerially exposed or remaining submerged shelves were characterized by very shallow water-depths. Redox proxies suggest that most shallow shelf settings were well oxygenated to that time, while the global extent of anoxic environments increased, implying that deoxygenation was confined to the open ocean. We speculate that the burial rate of the nutrient phosphorus (P) on shelves was minimal during the Hirnantian glacial maximum (HGM) due to bypass of the shelves in respect to the incoming riverine dissolved load. Hence, a large excess of bioavailable P entering the open ocean would have stimulated phytoplankton production which lowered oxygen concentrations by aerobic respiration.In order to test this hypothesis, we determined reactive P (Preact) contents in two low-latitude carbonate successions (Anticosti Island and Estonia) spanning the HGM. Moreover, we measured total organic carbon (C) concentrations and calculated C/P ratios to evaluate the burial efficiency of P. Samples from both sites are characterized by overall low Preact contents. We observe a decreasing trend in Preact towards the HGM, reaching a minimum during the initial transgression thereafter. C/P ratios suggest efficient P-burial throughout the study interval and, hence, Preact contents are assumed to be a direct measure of primary productivity, P-availability, and P-burial. Using the Preact concentrations, we modeled shelf P-burial fluxes with estimates for global shelf area and sedimentation rates. The model suggests that shelf P-burial fluxes around the HGM were approximately halved due to a reduced shelf area and minimum Preact contents. With the assumption of a constant P-input to the ocean, the proposed scenario serves as a plausible explanation for the observed redox gradients.

Large contributions of petrogenic and aged soil-derived organic carbon to Arctic fjord sediments in Svalbard

Svalbard fjords are recognized as hotspots for organic carbon (OC) burial and storage due to their high sedimentation rates, which effectively trap terrestrial sediments and inhibit extensive OC remineralization. In this study, we investigated surface sediments (n = 48) from eight Svalbard fjords, along with bedrock (n = 17), soil (n = 28), and plant (n = 12) samples, to identify the sources of sedimentary OC in these fjords using geochemical parameters. All examined surface sediments from the fjords showed a depletion in 14Corg (− 666.9 ± 240.3‰), indicating that recently fixed terrestrial and marine biomass alone cannot account for the entire sedimentary OC pool. Conventional bulk indicators such as Norg/TOC ratio and δ13Corg were insufficient for fully determining the sources of sedimentary OC. Therefore, we employed a four-end-member approach, using Δ14Corg, δ13Corg, and lignin phenols to assess the relative contributions of petrogenic, soil-derived, plant-derived, and marine OC to the sedimentary OC pool. The analyzed fjord sediments consisted, on average, of 59.0 ± 28.1% petrogenic OC, 16.8 ± 12.1% soil-derived OC, 2.5 ± 2.2% plant-derived OC, and 21.8 ± 18.5% marine OC. This approach highlights the substantial contributions of petrogenic and aged soil-derived OC to present-day sedimentary OC in Svalbard fjords. Considering predicted global warming, accelerated inputs of petrogenic and soil-derived OC into fjords due to rapid glacier retreat may significantly impact the active carbon cycle and potentially contribute to CO2 emissions to the atmosphere, depending on burial efficiency.

The ecological functions of dung beetles are shaped by multiple dimensions of diversity

Abstract A mechanistic understanding of the relationship between multiple dimensions of species diversity and ecosystem functioning is needed to safeguard ecological processes critical to human well‐being. We evaluated how taxonomic, functional and phylogenetic diversities, as well as the assembly mechanisms of dung beetle communities, percent forest cover and landscape fragmentation, affect dung burial, soil excavation efficiency and dung fly larvae abundance in Los Tuxtlas Biosphere Reserve, a complex tropical landscape. Dung beetle functions were measured in 15 landscapes representing a gradient of forest cover loss (0%–100%). Phylogenetically clustered assemblages of large tunneler dung beetles showed the highest dung burial efficiency across the landscape. Fly larvae abundance was negatively correlated with the taxonomic diversity and functional evenness of dung beetles. Forest cover and landscape fragmentation did not significantly affect dung burial effectiveness, suggesting a high degree of functional redundancy. Dung burial efficacy is mainly driven by selection mechanisms, in which a single or a few phylogenetically close species disproportionately affect a given function. Fly larvae abundance was controlled by a complementary functional effect where each dung beetle species additively affected fly larvae survival. Hence, multiple functions are maintained by contrasting mechanisms and different diversity dimensions. High dung beetle species richness may foster pest fly control in tropical landscapes such as Los Tuxtlas Biosphere Reserve. Our findings highlight the need to assess multiple dimensions of diversity since each can operate concurrently and contrastingly on the different ecological functions of species assemblages.

The Lower Cambrian Xiaoerbulake Formation in the Tarim Basin as a potential carbonate source rock

The oil and gas exploration of the Middle and Lower Cambrian in the Tarim Basin reveals widely distributed source rocks with the Yuertusi Formation being recognized as high-quality source rocks that are distributed in a rather small range. The Xiaoerbulake Formation that is right under the Yuertusi Formation has also been eyed as potential high-quality source rocks and is studied through analyses focusing on the stratigraphic development, the abundance, type, and maturity of organic matter, and the paleoproductivity of a dark-colored algae dolomite within the formation. The results show that the dolomite is rich in organic matter of mainly types I and II kerogens. Although reached the high mature to over-mature stage, the dolomite was deposited in an anoxic sedimentary environment featuring a high paleoproductivity level and a high organic carbon burial efficiency, quite favorable for the development of high-quality source rocks. The study provides material evidence to the Middle-Lower Cambrian subsalt source rock-reservoir-caprock combination model for the Tarim Basin.

Contrasting sources and fates of sedimentary organic carbon in subtropical estuary-marginal sea systems

Sediments deposited in subtropical deltas and continental shelves are the “recorders” of sources, transport processes, and accumulation of organic carbon (OC) at the land-ocean interface, but their role in the global carbon cycle remains poorly constrained. In this study, we determined the abundance and carbon isotopic composition (δ13C and Δ14C) of bulk OC, as well as characteristics of specific biomarker compounds (plant wax n-alkanes, n-fatty acids, and phytoplankton sterols) in surface sediments from the Pearl River estuary (PRE) and adjacent continental shelf of the northern South China Sea (SCS) in order to examine the sources and fates of OC delivered to a large subtropical river-marginal sea system. We observed marked spatial variability in the sources, hydrodynamic processes and accumulation of sedimentary OC in PRE and northern SCS shelf, with the emergence of two distinct regimes reflected in the bulk OC isotopic characteristics of surface sediments. In Pearl River impacted regions, relatively fresh terrestrial OC (OCterr) was subject to substantial degradation and aging during transport within the estuary and from the estuary to the shelf. In contrast, sedimentary OC in the Taiwanese river impacted region comprised a mixture of fluvially-derived refractory OCterr from the Choshui River and modern marine OC. Burial efficiencies of OCterr are also spatially heterogeneous as a result of these different OC sources and hydrodynamic processes. The overall OCterr burial efficiencies are relatively low in the Pearl River influenced region, with an average value of 27 ± 10% in the PRE and an average value of 17 ± 6% in the western shelf, in contrast to the higher values in the region impacted by Taiwanese rivers (55% ± 39%).These findings suggest both sources and hydrodynamic processes during transport exert strong influence on the fate of OC, with important implications for the role of river-dominated marginal seas in the global carbon cycle.

Distinct variations and mechanisms for terrestrial OC 14C-ages in the Eastern China marginal sea sediments since the last deglaciation

Marginal seas serve as the depocenter and reactor for terrestrial organic carbon (OC) transported by fluvial systems, however, mechanisms controlling the preservations and radiocarbon ages of down-core sedimentary terrestrial OC still remain poorly understood. Here, we employ radiocarbon analyses of both bulk OC and compound-specific terrestrial biomarker (long chain fatty acids) on sediment cores collected from the Eastern China marginal seas with depositional ages spanning the last 14 kyr. In the southern Yellow Sea (core C04), we find persistent high burial efficiency (94 ± 27% on average) of aged terrestrial OC with apparent initial radiocarbon ages (AIRs, i.e., radiocarbon age corrected for natural decay since deposition) of 1521–6115 yr, which showed an increasing trend from the marine transgression stage to the mid-late Holocene. This trend reflected changes of terrestrial OC age transported by the Huanghe (Yellow River), which in turn was caused by deeper soil erosion of older OC from the Chinese Loess Plateau when rainfall was higher during the mid-late Holocene. In contrast, terrestrial OC AIRs in the East China Sea (core F10B) were significantly older than those in the southern Yellow Sea, with an opposite trend of higher values during marine transgression stage compared with the mid-late Holocene. This spatial difference may arise from significant hydrodynamic process aging in the East China Sea, which further elevated terrestrial OC ages during lateral transports. Our results revealed contrasting scenarios of terrestrial OC ages and preservations in the southern Yellow Sea and the East China Sea, underscoring the important roles of hydroclimate and regional hydrodynamic processes in regulating the burial of terrestrial OC in marginal seas.