Carbon Burial Research Articles

Microbial mutualism in boring clams (Tridacna crocea):Ally shoring of oceans

Ocean ecosystems are highly effective in the recycling of energy and matter. Carbon fixation is almost recycled because net carbon burial in terrestrial systems and export to the ocean via rivers. Heterotrophs efficiently reprocess organic matter because they depend on the energy in organic matter. Withal, heterotrophs cannot use total organic energy because some is shunted into metabolites like ammonium, and under anoxic conditions into reduced substances such as sulphide. These reduced inorganic compounds are used by chemo (litho) autotrophs to obtain energy for inorganic carbon fixation. Host - associated microbial symbionts are critical to the conversion of inorganic carbon into organic biomass (Beinart, R.A., 2019). In the world’s oceans, Boring clams belongs to family Teredinidae, (Shipworms) with habitat of eating wood, assisted by cellulases from the intracellular symbiotic gammaproteobacteria that inhabit their gills. Other shipworms (Kuphus polythalamius) also relying on gill-dwelling gammaproteobacteria for sulphur oxidation (Altamia et al., 2020) and Methane Oxidation. The Symbionts of the gills Teredinibacter turnerae T7901 and similar strains are among the greatest sources of Biosynthetic Gene Clusters (BGCs), with content equivalent to well-known commercial manufacturers such as Streptomyces spp. This implies that shipworms might be a good source of new compounds for drug discovery (Altamia et al., 2020).

Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM) is a hyperthermal event at ∼56 Ma ago, caused by rapid and massive carbon releases into the ocean-atmosphere system. Currently, the PETM ocean acidification is mainly quantified in the surface ocean. By contrast, PETM carbonate chemistry changes of the deep ocean, a larger carbon reservoir, are largely qualitatively constrained by sedimentary calcium carbonate contents (%CaCO3). Here, we revisit a previously proposed method for quantifying Early Cenozoic deep-water carbonate chemistry, using boron to calcium ratios (B/Ca) in extinct benthic foraminifera Nuttallides truempyi (Brown et al., 2011). We show that calibrating core-top B/Ca in the extant relative of N. truempyi against deep-water calcite saturation degree (Ω, Ω = [CO32−] /[CO32−]saturated), rather than calcite saturation state (Δ[CO32−], Δ[CO32−] = [CO32−] - [CO32−]saturated) as originally proposed better reflects Early Cenozoic carbonate chemistry changes. Furthermore, we provide multiple deep-water Ω reconstructions paired with benthic foraminiferal carbon isotopes during the PETM. At two sites, deep-water Ω recovered synchronously with carbon isotopes but lagged the sedimentary %CaCO3 rebound, indicating a slower post-PETM deep-water Ω recovery than previously thought. This may imply that during the PETM recovery phase, carbon could have been injected into the ocean-atmosphere system, despite net carbon loss, over a prolonged period after the initial release. If so, during this period, carbon removal from the ocean via calcite burial on the seafloor in response to enhanced silicate weathering may be weakened, suggesting that more carbon was sequestered via other processes such as those related to organic carbon burial.

Timing and tempo of organic carbon burial in the Monterey Formation of the Santa Barbara Basin and relationships with Miocene climate

Understanding the transfer of carbon between Earth's surface reservoirs is necessary for interpreting climate transitions in Earth history and predicting future climate change. Warming associated with the 16.9–14.7 Ma Miocene Climate Optimum and subsequent cooling during the 14.7–13.8 Ma Middle Miocene Climate Transition provide opportunities to study carbon cycle dynamics in the geologically recent past. The Monterey Hypothesis interprets the Middle Miocene Climate Transition cooling as part of a positive feedback in which enhanced organic carbon burial on the eastern Pacific margin drew down atmospheric CO2. This idea has been supported by the correlation of organic-rich deposits in the Monterey Formation in coastal California with the mid-Miocene Monterey Event, a globally-observed positive shift in the δ13C of marine carbonates that may be indicative of elevated burial of δ13C-depleted organic carbon. Here, we use 31 new U-Pb zircon laser ablation inductively coupled plasma mass spectrometry ages and 14 new isotope dilution thermal ionization mass spectrometry ages from volcanic ash beds in the Monterey Formation along the Santa Barbara coast to constrain the timing and tempo of organic carbon mass accumulation in some of the most organic-rich rocks in California. The new age model demonstrates that peaks in organic carbon mass accumulation rate in the Monterey Formation do not coincide with the Monterey Event, and that total organic carbon content in the Miocene Santa Barbara Basin is inversely correlated with sedimentation rate. We propose that changes in organic carbon burial rates in the Monterey Formation were driven by a combination of sea-level change and local tectonically-mediated basin formation, which provided first-order controls on sedimentation rate, and that organic carbon burial in the Monterey Formation is better described as a response to, rather than a driver of, global climate.

Wildfire activity and impacts on palaeoenvironments during the late Paleozoic Ice Age - New data from the North China Basin

The Late Paleozoic is widely recognized as a ‘high-fire’ world. However, the impact of wildfires on the vegetational change as well as the relationship between fire and low atmospheric pCO2 and high pO2 in the Late Paleozoic remains a matter of debate. New data on fossil charcoal and pyrogenic PAHs in coal deposits from the Yuzhou Coalfield, the southern part of the North China Basin, are integrated into previous studies to increase our current understanding of the role of wildfires on land and in marine environments during the late Carboniferous and early Permian. Analyses of bulk petrographic and organic geochemical data indicate that during deposition of the Taiyuan Formation (late Gzhelian and early Asselian Stage) wildfires were more prevalent and were characterized by a large proportion of crown fire. A previous plant macrofossil assemblage study of the Taiyuan and Shanxi formations, together with fire traits of ancient plant lineages, indicates that wildfire may likely be one of the major drivers of the thriving of the Cathaysian Flora during this period. Wildfire and post-wildfire processes might have acted as important controlling factors for organic carbon burial. Persistent organic carbon sequestration (as coals or charcoal) on land and increasing organic carbon burial in the ocean are coincident with the peak in pO2 during the apex of the Late Paleozoic Ice Age.

The impact of volcanic ash deposition and the Storegga Slide on organic carbon preservation processes in marine sediments near Iceland

The burial of organic carbon (OC) in marine sediments is a considerable sink for carbon, removing OC from the active ocean-atmosphere system. Both the total OC buried, and the proportion of OC retained in sediments after burial, varies by location, with some areas of the ocean floor known to be ‘hotspots’ of OC sequestration. Two potential such hotspots may be sediments containing high proportions of tephra (the unconsolidated products of explosive volcanism), and locations of turbidite deposition, but knowledge of specific burial regimes in such locations remains poorly constrained. To fully investigate these processes, we performed a holistic (organic and inorganic) geochemical analysis of samples from the Aegir Ridge, which contain both tephra layers and material from the Storegga Slide, a large turbidite. We show sediments found between the Storegga Slide and the tephra are a location of high OC preservation, linked to reducing conditions caused by the rapidly deposited slide layer sealing the sediments from overlying water column O2. We see little evidence for tephra positively affecting OC preservation at our site, but this is likely a feature of specific burial conditions, with the responsible mechanisms depending highly on the nature of the tephra. Our findings demonstrate how even in locations proposed as OC burial hotpots, the processes controlling this burial are highly complex, and that levels of sedimentary OC burial must be assessed on a case-by-case basis.

Carbohydrate compositional trends throughout Holocene sediments of an alpine lake (Lake Cadagno)

Carbohydrates are a ubiquitous constituent of organisms and contribute significantly to sedimentary organic carbon pools. Yet, the factors that control the degradation and long-term preservation of sedimentary carbohydrates are not well understood. Here, we investigate carbohydrate pool sizes and chemical compositions in high-altitude, meromictic Lake Cadagno (Switzerland) over a 13,500-year-old sedimentary succession that has recorded past changes from oxic to anoxic conditions and consists mostly of intercalations of lacustrine sediments and terrestrial-derived sediments. Analyses of the organic matter chemical composition by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) show that carbohydrates are selectively preserved over other organic matter constituents over time. The carbohydrate pyrolysis products levosugars (potentially cellulose-derived) and (alkyl)furans and furanones (potentially pectin-derived) dominate both lacustrine and terrestrially derived sediment layers, suggesting aquatic and terrestrial-derived sources of these compounds. Carbohydrate monomer analyses indicate galactose and glucose as dominant monomers and show no clear differences between aquatic and terrestrial organic matter. No clear impacts of past changes in redox conditions on carbohydrate compositions were observed. Our study shows that carbohydrates are a major contributor to sedimentary organic carbon burial in Lake Cadagno and indicates the effective preservation of both aquatic and terrestrial derived carbohydrates over millennia in lake sediments.

Did sea level change drive carbon isotopic trends in the Madison Shelf? Sequence stratigraphy and carbon isotopes in the Mississippian Lodgepole Formation of southwest Montana

The Lower Mississippian Lodgepole Formation of Montana and Wyoming records one of the largest positive carbon isotopic excursions of the Phanerozoic. This globally recognized up to 7‰ increase in δ13Ccarb values occurs across the North American Kinderhookian-Osagean boundary (referred to as the KO excursion). It has been argued to reflect significant organic carbon burial, possibly linked to the onset of the Late Paleozoic Ice Age. Previously proposed correlations between carbon isotopic patterns and the sequence stratigraphic framework within these strata suggests that changes in sea level could have played a significant role in the expression and/or magnitude of the KO excursion in the Madison Shelf. This study explores the relationship between carbon isotopic values and sea level change at multiple scales. To accomplish this, we provide a comprehensive overview of the sedimentological and stratigraphic framework and address uncertainty about the number of sequences in the Lodgepole Formation. Our results support a three-sequence model for the Lodgepole Formation. Based on the number of sequences and the placement of sequence stratigraphic surfaces, we see little evidence of statistically significant correlation between carbon isotopic trends and the sequence stratigraphic framework. We argue that sea level change was not the primary driving mechanism for carbon isotopic trends in the Madison Shelf, nor the KO excursion. Instead, we support models that invoke global ocean anoxia and/or destabilization of the global carbon cycle due to land plants.

Carbonate uranium isotopes across Cretaceous OAE 2 in southern Mexico: New constraints on the global spread of marine anoxia and organic carbon burial

Oceanic anoxic events (OAEs) represent discrete intervals of decreased marine oxygen concentrations often associated with volcanism, enhanced organic carbon burial coupled with positive δ13C excursions, and significant biotic turnover. Cretaceous OAE 2 (ca. 94 Mya) is especially notable for globally-distributed changes in calcareous invertebrate and plankton populations. While the presence of organic-rich facies is consistent with locally anoxic environments in many cases, determining the global extent of anoxia is more problematic. To address this issue, we investigate uranium isotope (δ238U) compositions of upper Cretaceous (Cenomanian-Turonian) open marine platform carbonates from southern Mexico as a proxy for global seawater redox conditions. These data are complementary to previous δ238U studies across OAE 2 in both black shales and pelagic carbonates, which have yielded variable results that reflect both global redox and local depositional processes. In Morelos Formation carbonates, a significant and well-defined negative δ238U excursion down to a nadir of −0.6‰ is recorded over an ∼40 m interval. This is consistent with the expansion of marine anoxia, pointing to an areal extent of anoxic seawater of about 1–10% of the global seafloor (or ∼5 to 50 times the modern value). Importantly, based on biostratigraphically-controlled estimates of sediment accumulation rates, the δ238U anomaly precedes the δ13C excursion by a median of ∼45 to 51 kyr (95th percentile confidence interval, CI) or ∼105 to 120 kyr (95th percentile CI) depending on how the onset of the δ238U anomaly is estimated. These results, along with previously reported thallium isotope and trace metal data, suggest that anoxic expansion preceded carbon cycle perturbation. This observation further increases estimates of the duration of OAE 2, implying that widespread ocean anoxia may have lasted >900 kyr.

Mangrove carbon budgets suggest the estimation of net production and carbon burial by quantifying litterfall

Soil carbon burial is the major process enabling mangroves to function as carbon sinks. However, the amount of deposited materials derived from allochthonous or autochthonous inputs in the soil carbon pool of mangroves remains uncertain. Mangrove-derived carbon burial is often laboriously estimated by monitoring the production and decomposition. In this study, ten carbon budgets covering different habitat features were constructed in situ for two mangrove species (Kandelia obovata and Avicennia marina) with distinct root structures. The mangrove-derived carbon burial rate was 0.25–1.55 Mg C ha−1 yr−1 for K. obovata and 0.36–1.00 Mg C ha−1 yr−1 for A. marina. Combined with other studies, there were positive and linear correlations between the carbon burial rate and litterfall production for the two mangroves, which suggests that the carbon burial rate for K. obovata and A. marina can be estimated using 14.8 % and 10.9 % of the litterfall production rate, respectively. The results of dbRDA with DistLM models further showed that wind speed and precipitation were the main factors affecting carbon burial in K. obovata and A. marina mangroves.

Heterogeneous sulfide reoxidation buffered oxygen release in the Ediacaran Shuram ocean

Ediacaran (∼635–539 Ma) carbonate rocks record the largest negative carbonate-carbon isotope excursion in Earth history, termed the Shuram Excursion (SE). This event has been attributed to anaerobic oxidation of dissolved organic carbon as a result of enhanced weathering inputs of sulfate to the ocean during the amalgamation of Gondwana. However, the effect of carbon–sulfur cycle interplay on the net redox state of the ocean–atmosphere system remains unclear, impeding our understanding of the co-evolution of life and the environment during the Ediacaran. Here, we generate high-resolution records of paired sulfate sulfur and oxygen isotopes, in addition to phosphorus concentrations, for the SE interval in South Australia (Parachilna Gorge) and South China (Jiulongwan and Xiang’erwan sections, Three Gorges), and we evaluate these data in the context of COPSE biogeochemical model simulations to assess net long-term redox changes. Our results support widespread H2S reoxidation in shelf areas during the SE, which would have buffered the net release of oxygen sourced from the burial of organic carbon and pyrite. Varying degrees of H2S reoxidation on different cratons likely contributed significantly to high spatial heterogeneity in both local oceanic redox state and nutrient availability, which characterized local oxygen-deficient conditions in an overall oxygenated SE shelf ocean, and likely affected the distribution of the Ediacaran Biota. Our study highlights the important role of H2S reoxidation in the coevolution of marine redox conditions and complex life during the critical Ediacaran period.

The Global Turbidity Current Pump and Its Implications for Organic Carbon Cycling.

Submarine turbidity currents form the largest sediment accumulations on Earth, raising the question of their role in global carbon cycles. It was previously inferred that terrestrial organic carbon was primarily incinerated on shelves and that most turbidity current systems are presently inactive. Turbidity currents were thus not considered in global carbon cycles, and the burial efficiency of global terrestrial organic carbon was considered low to moderate (∼10-44%). However, recent work has shown that burial of terrestrial organic carbon by turbidity currents is highly efficient (>60-100%) in a range of settings and that flows occur more frequently than once thought, although they were far more active at sea-level lowstands. This leads to revised global estimates for mass flux (∼62-90 Mt C/year) and burial efficiency (∼31-45%) of terrestrial organic carbon in marine sediments. Greatly increased burial fluxes during sea-level lowstands are also likely underestimated; thus, organic carbon cycling by turbidity currents could play a role in long-term changes in atmospheric CO2 and climate.

Tethyan ocean acidification triggered the end-Triassic mass extinction: New Ca isotopic constraints from the Qiangtang Basin

Oceanic acidification has long been suggested as a potential environmental trigger of marine ecosystem collapse in the Earth’s history. However, evidence for oceanic acidification as an important controlling mechanism of the end-Triassic mass extinction is still limited. Here, the first coupled carbon- and calcium-isotope records across the Triassic-Jurassic transition are provided. The calcium isotope (δ44∕40Ca) profile from the Qiangtang Basin, eastern Tethys exhibits a prominent negative excursion of ∼0.3‰ at the Triassic-Jurassic (T-J) boundary, which is consistent with the onset of negative δ13C excursion, suggesting a possible relationship between large-scale volcanic eruption and calcium isotopic composition. The Ca isotope perturbation during the T-J boundary is interpreted to be triggered by a significant decrease in CaCO3 burial related to CO2-induced ocean acidification. The coupled δ13C and δ44/40Ca records reveal that the carbon cycle perturbations controlled oceanic acidification and decreased carbonate burial. This provides robust evidence for the causal link between oceanic acidification, carbon cycle perturbation in response to Central Atlantic Magmatic Provence (CAMP), and the T-J boundary mass extinction.

The Intensification of Prolonged Cooling Climate-Exacerbated Late Ordovician–Early Silurian Mass Extinction: A Case Study from the Wufeng Formation–Longmaxi Formation in the Sichuan Basin

The Late Ordovician–Early Silurian period was a significant transitional phase in geological history and has garnered global interest. This study focuses on the black shale series of the Wufeng Formation–Longmaxi Formation of the Upper Ordovician–Lower Silurian period in the Sichuan Basin. Based on the logging curves and lithological characteristics of the Yucan-1 Well, 46 black shale samples were collected from the target layer section for clay mineral XRD (46 samples) analysis and whole-rock XRF (14 samples) analysis. The results indicate that three third-order sequences (SQ1, SQ2, and SQ3) are present in the Wufeng Formation–Longmaxi Formation of the Yucan-1 Well, and two subfacies and three microfacies were identified. In conjunction with the characteristics as well as the characteristic parameters of whole-rock oxide and clay mineral content ((I/C), (S + I/S)/(I + C), CIA, CIA-error, CIW, PIA, MAP, and LST), the Wufeng Formation–Longmaxi Formation of the Yucan-1 Well is divided into three intervals. Interval I is the Wufeng Formation. During this interval, weathering intensity, surface temperature, and precipitation gradually decreased, while the climate shifted from warm and humid to cold and dry. This corresponds to two pulse-type biological extinction events and represents an interval of increasing organic carbon burial. Interval II encompasses the bottom-middle part of the Longmaxi Formation. Weathering intensity, surface temperature, and precipitation were characterized by smooth, low values. Subsequently, the climate was predominantly cold and dry. This was the primary interval of organic carbon enrichment. Interval III extends from the upper part to the top of the Longmaxi Formation. Weathering intensity, surface temperature, and precipitation gradually increased. The climate transitioned from cold and dry to warm and humid. Organic carbon burial gradually decreased, while sea levels dropped. This indicates that climate cooling was the primary controlling factor for this biological extinction event. In combination with previous divisions of graptolite zones in the Yucan-1 Well, it is postulated that this biological extinction event may primarily have been pulse extinction. The continuous cooling of the climate in the later period led to the continuous extinction of organisms that survived the disaster. Until approximately 438.76 Ma at the top of the Longmaxi Formation, the climate environment recovered to pre-extinction conditions, with a transition to a warm and humid climate again.

Changing sources and burial of organic carbon in the Chukchi Sea sediments with retreating sea ice over recent centuries

Abstract. Decreasing sea ice extent caused by climate change is affecting the carbon cycle of the Arctic Ocean. In this study, surface sediments across the western Arctic Ocean are investigated to characterize sources of sedimentary organic carbon (OC). Bulk organic parameters (total organic carbon, total nitrogen, δ13Corg, and δ15N) and molecular organic biomarkers (e.g., sterols and highly branched isoprenoids – HBIs) are combined to distinguish between sympagic, pelagic, and terrestrial OC sources. Their downcore profiles generated at the Chukchi Sea R1 core site (74∘ N) are then used to evaluate changes in the relative contribution of these components of sedimentary OC over the last 200 years with decreasing sea ice. Our data evidence that, from the 1820s to the 1930s, prevailing high sea ice cover inhibited in situ primary production, resulting in prominent land-derived material in sediments. Then, from the 1930s to the 1980s, primary production started increasing with the gradual decline of summer sea ice. The ratio of sympagic and pelagic OC began to rise to account for the larger portion of sedimentary OC. Since the 1980s, accelerated sea ice loss led to enhanced primary production, stabilizing over the last decades due to freshwater-induced surface ocean stratification in summer.

Carbon and nutrient sequestration in small impoundments: a regional study with global implications

ABSTRACT The rate of sequestration of carbon, nitrogen, and phosphorus by lentic ecosystems informs both the global carbon budget and the remediation of eutrophication. Here we estimate carbon, nitrogen, and phosphorus burial in sediments of 34 lakes in Missouri, USA, and compare them to those found in other agricultural areas as well as to global estimates. Mean sediment accumulation rates varied by orders of magnitude among study regions, with the largest values (average 6 cm yr−1) in impounded systems surrounded by intensive agriculture. Rates increased with the drainage ratio and decreased with the abundance of other surface water in the catchment (e.g., farm ponds). Average organic carbon burial differed by an order of magnitude among study regions (average 150–2100 g m−2 yr−1) with differences related to the drainage ratio and eutrophication. Organic carbon burial was strongly correlated with burial rates of nitrogen and phosphorus. Comparisons with a diversity of global data show that extremely high rates of biogeochemical burial in many Midwestern USA impoundments are likely due to the details of agricultural cropping systems, landscape configuration, and soil characteristics.

Holocene organic carbon burial in southwest China and potential response to climate variations

The deposition of organic carbon (OC) in terrestrial water bodies serves as an important carbon sink in global carbon cycle, while the responding mechanism of organic carbon accumulation rate (OCAR) to various climate processes is still unclear. Here, we provide a continuous sediment record covering the past 11.1 kyrs retrieved from Beihai Wetland, which is predominantly influenced by the Indian Summer Monsoon (ISM) in southwest China. The temporal variation of OCAR was established and classified into five evolution stages. Subsequently, potential responses of OCAR to climatic and environmental processes were evaluated based on the Spearman’s rank correlation analysis between OCAR and individual sedimentary proxies. During the early Holocene, relatively stable and low OCAR was determined owing to the predominant contributions of detrital influx and low terrestrial organic matters. Following the intensification of summer monsoon and corresponding increase in regional precipitation, extremely low OCAR were yielded in the mid-Holocene, resulted from low values of both sedimentary accumulation rate (SAR) and Loss on Ignition (LOI). The abrupt retreat of ISM led to the development of current wetland from a lake-like system, while the extremely low SAR contributed significantly to the identified low OCAR values between 5.2 and 3.0 cal. kyr BP. Afterwards, the wetland developed progressively following further retreat of ISM, that the preservation of a great amount of organic matters contributed significantly to both SAR and LOI, resulting in the highest OCAR levels during the Holocene. In addition, the rapid decline of OCAR during the last 700 years was interpreted in terms of intensified regional human activities. Such increase in OCAR during the late Holocene was broadly reported from the southwest China, proposing potential responses to the large-scale climate changes, namely the variation of ISM.

Productivity-induced redox transition within the Niobrara formation, western Interior seaway, Colorado

Deposition of organic rich shale/marl within the Niobrara Formation during the Coniacian to Santonian Ocean anoxic event (OAE 3) within the Western Interior Seaway presents a unique record of variable organic carbon burial under a greenhouse climate. In order to understand the mechanisms behind the changes from low to high organic carbon burial, and how this high burial rate was sustained for over 3 Ma, productivity within the surface waters and subsequent preservation of organic matter within the sediments were investigated in this study. Based on the multiproxy approach adopted herein, the sedimentary record of the Niobrara Formation in northern Colorado can be separated into two distinct intervals: Interval 1 and Interval 2. Interval 1 is bioturbated, organic lean and oxic, with low to moderate trace metal enrichment except for Mn. Interval 2 is laminated, organic-rich, more enriched in trace metals U, V and Mo, and less enriched in Mn, typical of anoxia during deposition. The transition from oxic to anoxic conditions coincides with greater enrichments in TOC, Cu and Ni, suggesting enhanced productivity is associated with redox transitions within the Niobrara Formation. These local changes in productivity and redox conditions are sudden and coincide with recurring iron (Fe) and phosphorus (P)-rich bentonites, evidence of ash deposition that could have enhanced nutrient supply, productivity and accumulation of organic carbon. Consequently, perturbations of the global carbon cycle associated with OAE 3 were inferred to have occurred in Interval 2.High total Fe, total sulfur, Fe/Al, and trace metal enrichments in Interval 2 are intrinsically linked to prevalence of anoxic bottom-water conditions which enhanced burial of pyrite and organic matter. Results from productivity proxies and Fe–S–C ternary plots show that Fe limitation on pyrite formation under anoxic porewater enhanced organic carbon burial and preservation. This implies Fe enrichment within the sediments favored pyrite formation instead of organic matter sulfidization, leading to a complex relationship between S and organic carbon in the marine sediments during Niobrara deposition.

Anthropogenically driven changes to organic matter input in sediments of Lake Chaohu, Eastern China, over the past 166 years

Characterizing how and to what extent human activities have influenced organic matter (OM) input in lake sediments is essential for a thorough study of the carbon cycle and carbon burial in lake systems, but this issue has not yet been addressed. Here, the source and composition of OM in sediments of Lake Chaohu, Eastern China, over the past 166 years, were determined by analyzing stratigraphic variations in aliphatic hydrocarbons and OM pyrolysis parameters in a dated sediment core. These data, coupled with documental records, were further used to elucidate the pattern and controlling factors of OM input in the sediments. The lowest hydrogen index (HI), lowest long-chain n-alkane concentrations, and highest Paq (proxy of aquatic macrophyte input) in sediments prior to ca. 1956 indicate a minimal input of OM from phytoplankton and terrestrial plants and a larger input from submerged macrophytes. This may represent the features of OM input in primitive conditions given the mild human activities around the lake before the 1950s. In sediments from ca. 1962 to 1985, elevated HI and C17/C16n-alkane ratios indicate a greater input from phytoplankton, while the high abundances of long-chain n-alkanes and αβ-hopanes reflect an anomalously high input from terrestrial plant and fossil OM. These variations might have been caused by the rapid development of agriculture during this period, which accelerated catchment erosion and petroleum contamination and promoted the transport of allochthonous OM and nutrients to the lake. The lowest Paq in sediments during this period indicates reduced input from submerged macrophytes, probably resulting from a dam installation that modified the water to an unfavorable plant depth. In sediments after ca. 1989, the highest values of HI, short-chain n-alkane abundances, and C17/C16n-alkane ratios indicate a further increase in OM input from phytoplankton, a response to domestic and industrial discharge and subsequent lake eutrophication.

Carbon Accumulation Associated with Its Influencing Factors in Sediments from the Poyang Basin

Carbon burial in lake sediments has a profound impact on the global carbon cycle. In this study, the burial characteristics of organic carbon (OC) in typical sediments from the Poyang basin over the past hundred years were investigated and the influencing factors and driving mechanism were determined. The results showed that carbon burial in the Poyang basin sediments was mainly driven by human activities, whereas the change in the OC accumulation rate was related to precipitation, forest land area, water area, construction land area, urbanization rate, application of agricultural fertilizers, per capita GDP and population.

Organic matter enrichment in Asia's palaeolake controlled by the early and middle Eocene global warming and astronomically driven precessional climate

The sediments deposited in continental lake systems record sensitive palaeoclimate signals and provide better perspectives for understanding rapid palaeoclimate changes and their implications. To better understand the terrestrial record and climate-driven organic matter enrichment mechanism in a low-latitude region, which have rarely been investigated, we studied the Eocene terrestrial records from the Beibuwan Basin, South China Sea (SCS). Cyclostratigraphic analysis was conducted to assess the orbital forcing. Milankovitch-scale astronomical signals were determined by spectral analyses, evolutionary Fast Fourier transform, and sedimentation rates estimation of the natural gamma ray logging data in the depth domain. A floating astronomical time scale (ATS) was constructed based on astronomical tuning that converts the depth domain to the time domain by sedimentation rates. The ATS was calibrated using published dating result of 35.2 Ma from the Eocene to the Oligocene. This ATS constrains the ages of two organic-rich lacustrine petroleum source intervals of the Eocene Liushagang Formation in the Beibuwan Basin at ∼49-47 Ma and ∼40.9–40.2 Ma, respectively. A comparison of the timing of these two source rocks with a published global benthic carbon and oxygen isotope series shows that they correspond to Eocene positive carbon isotope excursions. This finding suggests that organic carbon burial in Eocene lacustrine basins responded to early and middle Eocene Climatic Optimum (i.e., EECO and MECO). We used geochemical data based on X-ray fluorescence core scans for further investigation of the effect of orbital forcing on organic matter enrichment. The high Rb/Sr, K + Ti + Rb and Sr/Ca geochemical ratios and stable Mo and U/Th values all correspond to the precessional minimum, suggesting that the orbital precessional minimum is responsible for a warm and humid climate, and brackish and hypoxic water conditions. Thus, four schematic hypotheses were proposed to explain the effect of the precessional monsoonal climate on organic matter enrichment. This study provides a terrestrial record that documents the mid-Eocene global warming event well and provides evidence that the orbital precessional climate controlled organic matter enrichment in Asia's palaeolake.