Search

Lakes act as natural reservoirs for storing organic material, and comprehending how organic carbon (OC) and black carbon (BC) are deposited in lake sediments is crucial for understanding the global carbon cycle and its impact on climate and ecosystems. In this study, we examined changes in the deposition patterns of OC and BC in Yinjia Lake (YJL) over the past 110 years, using a 60 cm sediment core dated with 210Pb. Our aim was to discern how these changes relate to human activities and other influencing factors in the region of southeast Hubei, central China. Our findings revealed a consistent rise in total organic carbon (TOC) and total nitrogen (TN) concentrations, indicating a gradual increase from the bottom upwards. Analysis of C/N ratios and δ13C values showed that the OC in the sediment mainly originated from phytoplankton and terrestrial C3 plants. Over the past century, OC burial rates (OCBR) in the YJL core increased from 61.35 to 86.69 g m−2 yr−1, primarily due to increased primary production resulting from intensified local agriculture and urban growth. Temperature was found to influence OCBR, while precipitation had little impact on OCBR dynamics in sedimentary environments. BC burial rates in YJL ranged from 3.67 to 11.51 g m–2 yr–1, significantly exceeding those observed in other lakes worldwide. The fluctuations in BC burial rates correlated with shifts in local industrial practices and energy consumption. In recent years (post-2005), BC burial rates have declined, likely due to reduced pollutant emissions resulting from the implementation of emission-control policies in China. These results provide valuable insights into the interactions between human activities, climate variability, and carbon cycling in lacustrine environments, with implications for regional carbon budgets, ecosystem management, and climate-change mitigation strategies. [ABSTRACT FROM AUTHOR]

Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we show that Holocene fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the contourite drifts are due to high rates of sedimentation. Over the past 50 million years, sedimentation rates at the studied contourite drift sites have overall increased, coincident with decreasing atmospheric CO2 and a cooling global climate. Our work suggests that a ramp‐up of the bottom‐current carbon pump has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the overall global cooling after the Eocene Thermal Maximum. Plain Language Summary: Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we examine data from modern contourite drifts (large‐scale, alongslope‐trending bottom‐current deposits) across the globe and show modern fluxes of organic carbon into the drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1 to 2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the drifts are due to high rates of sedimentation in these deepwater environments, which are driven primarily by vigorous bottom currents—in other words, by a bottom‐current pump that is highly efficient at burying organic carbon. Our work suggests that a ramp‐up of the bottom‐current carbon pump, attributable to progressive intensification of global ocean circulation over the past 50 million years, has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the global cooling after the Eocene Thermal Maximum. Sedimentary records of past organic carbon fluxes in contourite drifts over geologic time could well prove useful in informing predictions of future climate. Key Points: Modern fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1The fluxes into the drifts are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zonesOver the past 50 million years, the bottom‐current pump has accelerated removal of carbon from the oceanic water [ABSTRACT FROM AUTHOR]

According to Milankovitch's theory, periodic climate change in Earth's history is controlled by the periodic changes in the Earth's orbit and axis of rotation. Milankovitch cycle include eccentricity, obliquity, and precession cycles. In addition to them, there are also some amplitude modulation (AM) cycles that affect the climate system through a series of "nonlinear" feedback processes, such as the 173 kyr obliquity AM cycle. Previous studies have demonstrated that the -170 kyr cycle modulate the paleoclimate and carbon cycle at mid- high latitude regions in the Meso-Cenozoic. However, due to the limitation of astronomical solutions and the lack of high-resolution geological records, the -170 kyr cycle has been less reported in the Paleozoic Era. In this study, cyclostratigraphic analysis of natural gamma ray (GR) logging data from four wells (Ji30, Ji31, Ji32, and Ji174) and total organic carbon (TOC) data from well Ji174 penetrating the Early Permian Lucaogou Formation in Jimusar Sag, Junggar Basin suggests preservation of eccentricity, obliquity, and precession cycles, and the -170 kyr AM cycle. Through the astronomical tuning of GR logging data obtained from four wells to eccentricity target cycles, we established the floating astronomical time scale (ATS). The results indicate an average sedimentation rate ranging from 7.4 to 9.5 cm/kyr and a duration from 2.8 to 3.2 million years (Myr) for the Lucaogou Formation. The differences in sedimentation rate and duration among these four wells may result from different well locations. Moreover, the -170 kyr cycle signal has been identified in the detrended GR logging and TOC data series, and its obliquity AM series. This signal might be attributed to the obliquity AM cycles originated from the interaction between s3 and s6 (s3 and s6 represent the precession of nodes of Earth and Saturn), which was recorded in the GR logging and TOC data time series due to nonlinear responses within the depositional system. [ABSTRACT FROM AUTHOR]

The long-term burial of organic carbon in marginal seas plays a critical role in Earth's carbon cycle and climate change. However, the mechanism of organic carbon (OC) burial in the Okinawa Trough (OT) during glacial-interglacial timescales remains unclear. In this study, we analyzed the foraminiferal carbon isotopes, total organic carbon (TOC), and d13C-TOC over the past 200 ka in core Z1 collected in the central OT. We aimed to reveal the history of OC burial in the middle Okinawa Trough during the past 200 ka, and we combined our findings with relevant paleoenvironmental indices to reveal underlying mechanisms. We found reduced surface primary productivity during MIS 6, which may indicate changes in the pathways of the Kuroshio Current (KC). Furthermore, we observed decoupling between high TOC flux and low OC burial during glacial periods. We proposed that the dilution effect caused by the high sedimentation rate and poor OC preservation during the glacial period resulted in the low TOC content. Ventilation of the North Pacific Intermediate Water (NPIW) regulated the redox conditions of the intermediate water in the Okinawa Trough. Additionally, the intensified Kuroshio Current during interglacial phases led to water column stratification, creating reducing conditions in the bottom water and facilitating improved OC preservation. Subsequently, the enhanced water column oxygenation resulting from the oxygen carried by the intensified glacial NPIW weakened the burial of OC. This study sheds new light on our understanding of the carbon cycle in marginal seas on a glacial-interglacial timescale. [ABSTRACT FROM AUTHOR]

Abstract Bottom currents play a major role in deep‐sea sedimentation, but their significance in the burial of organic carbon is poorly quantified at a global scale. Here we show that Holocene fluxes of organic carbon into the contourite drifts are high, with a global average of 0.09 g cm−2 Kyr−1. At individual drift sites, fluxes are commonly 1–2 orders of magnitude greater than rates in surrounding areas and in global depth‐similar zones. These high fluxes of organic carbon into the contourite drifts are due to high rates of sedimentation. Over the past 50 million years, sedimentation rates at the studied contourite drift sites have overall increased, coincident with decreasing atmospheric CO2 and a cooling global climate. Our work suggests that a ramp‐up of the bottom‐current carbon pump has accelerated removal of CO2 from the atmosphere and oceanic water, thus contributing to the overall global cooling after the Eocene Thermal Maximum.

According to Milankovitch’s theory, periodic climate change in Earth’s history is controlled by the periodic changes in the Earth’s orbit and axis of rotation. Milankovitch cycle include eccentricity, obliquity, and precession cycles. In addition to them, there are also some amplitude modulation (AM) cycles that affect the climate system through a series of “nonlinear” feedback processes, such as the 173 kyr obliquity AM cycle. Previous studies have demonstrated that the ∼170 kyr cycle modulate the paleoclimate and carbon cycle at mid-high latitude regions in the Meso-Cenozoic. However, due to the limitation of astronomical solutions and the lack of high-resolution geological records, the ∼170 kyr cycle has been less reported in the Paleozoic Era. In this study, cyclostratigraphic analysis of natural gamma ray (GR) logging data from four wells (Ji30, Ji31, Ji32, and Ji174) and total organic carbon (TOC) data from well Ji174 penetrating the Early Permian Lucaogou Formation in Jimusar Sag, Junggar Basin suggests preservation of eccentricity, obliquity, and precession cycles, and the ∼170 kyr AM cycle. Through the astronomical tuning of GR logging data obtained from four wells to eccentricity target cycles, we established the floating astronomical time scale (ATS). The results indicate an average sedimentation rate ranging from 7.4 to 9.5 cm/kyr and a duration from 2.8 to 3.2 million years (Myr) for the Lucaogou Formation. The differences in sedimentation rate and duration among these four wells may result from different well locations. Moreover, the ∼170 kyr cycle signal has been identified in the detrended GR logging and TOC data series, and its obliquity AM series. This signal might be attributed to the obliquity AM cycles originated from the interaction between s3 and s6 (s3 and s6 represent the precession of nodes of Earth and Saturn), which was recorded in the GR logging and TOC data time series due to nonlinear responses within the depositional system.

Temperate lake sediments store a substantial amount of organic carbon (OC) over millennia. Despite the importance of quantifying terrestrial carbon budgets for Nature-based Solutions, the long-term accumulation of OC in European temperate lakes is poorly constrained. In this study, we analyzed 30 lake sediment records to generate a preliminary first-order estimate of Holocene OC accumulation rate (OCAR) and OC storage in UK lakes. We also examined the environmental variables that influence OCAR and produced synthesized Holocene records of %OC and z -scores of log-transformed OCAR and sediment accumulation rate (SAR) at 500-year resolution. Based on our estimation, we report an average Holocene OCAR of 7.4 ± 5.5 g C m−2 yr−1 and a Holocene total OC storage of 0.24 ± 0.18 Pg C in UK lakes. Apart from latitude, no relationship was found between the average Holocene OCAR and the various environmental variables (i.e. temperature, precipitation, surface area, catchment area, depth, altitude, and geology type). During the Holocene, OCAR closely resembles variations in SAR, whereas the increase in %OC is likely explained by the warming climate. Early Holocene variations in OCAR were primarily climate-driven. In contrast, the anthropogenic impact on the landscape exerted a predominant influence on OC burial during the middle-late Holocene. Our results improve the current understanding of terrestrial carbon budgets in the UK and demonstrate the under-appreciated importance of lakes as long-term OC stores. [ABSTRACT FROM AUTHOR]

Long‐term organic carbon (OC) burial on continental shelves has been widely recognized for regulating atmospheric CO2 (pCO2) and the global climate. However, quantitatively assessing shelf OC burial's role and process in prominent climate transitions is challenging. Using 367 drilling sites, we evaluated the impact of OC burial on the Sunda Shelf, the world's largest tropical shelf, on the middle Miocene carbon perturbation and climate change. Comparing the Miocene Climatic Optimum (MCO) and the Middle Miocene Climate Transition (MMCT) results demonstrated that OC was buried faster during the MMCT with an increment of 0.07–0.14 × 103 GtC/Myr. This would cause an additional 34.77–69.16 ppm pCO2 sequestration, contributing at least one‐sixth of the global pCO2 reduction. We found OC burial regulated the long‐standing Monterey carbon isotope excursion via negative and positive feedbacks during the MCO and MMCT, respectively. Expanded terrestrial carbon reservoirs and enhanced burial efficiency were key steps in the latter positive feedback. Plain Language Summary: The organic carbon (OC) formed by the photosynthesis of marine and terrestrial organisms consumes atmospheric CO2 (pCO2). Its long‐term burial in marine environments, especially on continental shelves, could influence the global carbon cycle and induce climate change. However, precisely assessing how much OC has been buried on shelves and quantifying how it affected climate change in the geological past is challenging. This is mainly due to the difficulty of obtaining complete spatial‐temporal records buried deeply on shelves and the complexity of climate feedbacks involving OC burial. To fill this gap to a certain extent, we calculated the middle Miocene OC burial of the Sunda Shelf, the world's largest tropical shelf, using 367 drilling sites and evaluated its impact on the profound carbon perturbation and climate transition of this period. We found that more OC was buried during the greenhouse period, but a faster burial rate occurred after polar cooling. The accelerated OC burial on the Sunda Shelf would cause an additional 34.77–69.16 ppm pCO2 sequestration, accounting for at least one‐sixth of the global pCO2 reduction of the middle Miocene. Efficient OC burial on the shelf was promoted by drainage system progradation and vegetation expansion arose along with sea level drop. Key Points: Organic carbon (OC) burial on the Sunda Shelf is essential to the global carbon cycle during the middle MioceneThe OC burial rate of the Middle Miocene Climate Transition (MMCT) was faster than that of the Miocene Climatic OptimumExpanded terrestrial carbon reservoirs and enhanced organic matter burial efficiency promoted the MMCT [ABSTRACT FROM AUTHOR]

Marginal seas play a crucial role in the global carbon cycle, contributing approximately 20% of the net CO 2 uptake by the world's oceans. The North Yellow Sea (NYS), a semi-enclosed marginal sea in the western Pacific Ocean, serves as a significant carbon sink influenced by factors such as sea level changes, monsoon dynamics, ocean currents, and El Niño-Southern Oscillation (ENSO) activity. This study examines a 538 cm-long sediment core W03 from the NYS (10.3 kyr BP to present). We analyzed Organic Carbon (OC) proxies, including total organic carbon (TOC), the stable carbon isotope (δ13C) of TOC, total nitrogen (TN) and marine-produced lipid biomarkers. Our findings demonstrate a strong correlation between OC burial and sea-level fluctuations during the early Holocene, driven by the exposure of the continental shelf. During the mid-Holocene, the intrusion of the Yellow Sea Warm Current increased salinity and temperature conditions and nutrient levels of sea water, thereby enhancing marine OC burial. Over the last 3.3 kyr BP, ENSO variability and intensified East Asian Winter Monsoon (EAWM) strengthened the coastal currents, contributing to better OC preservation. Additionally, human activities on the surrounding mainland increased terrestrial input, altering the OC burial. The heightened activity of the Kuroshio Current also introduced more saline and warm water masses into the NYS, impacting phytoplankton productivity and community structure, as indicated by increased C 37 alkenones. This study highlights the complex interplay of geological factors in OC burial processes within the NYS, providing valuable insights into OC dynamics in marginal seas under the impact of global change. • Early Holocene sea level changes significantly impacted OC burial in North Yellow Sea • EAWM and precipitation dominate OC burial, with YSWC impacting marine OC via high salinity • Intensified ENSO and EAWM prompt robust coastal currents, reducing exposure time and OC degradation [ABSTRACT FROM AUTHOR]

The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) is characterized by a marked positive carbon isotope excursion (CIE) recorded in global marine basins. This CIE results from a global-scale increase in organic matter burial, facilitated by high productivity and seawater deoxygenation. To date, however, the precise pattern of changes in the burial rate of organic matter through the event has not been well constrained. In this work, we present a compilation of data from 42 globally distributed OAE 2 sites, as well as organic carbon isotope (δ 13C org), total organic carbon (TOC), and trace element concentration data from a new OAE 2 interval in southern Tibet, China. In southern Tibet, the absence of redox-sensitive trace element enrichment through OAE 2 indicates prevailing oxic conditions. Organic carbon (OC) mass accumulation rate (MAR) at this site decreased from the lower part of the CIE to the upper part, in contrast to an approximate doubling of organic carbon MAR in the upper part observed globally. This result, coupled with detailed analysis of the compilation, shows that redox was a key factor controlling organic burial rates during OAE 2, with OC MAR scaling positively with increasing deoxygenation. Leveraging a biogeochemical model to simulate these data suggets that 5–20% of the seafloor became anoxic during OAE 2, and that this deoxygenation was accompanied by 100% to 200% increase in global seawater P concentration. Our findings indicate that during OAE 2, elevated nutrient levels may have resulted from enhanced recycling from sediments under reducing conditions, sustaining intensified primary production and subsequent organic carbon export and burial. • Redox is a key factor controlling organic burial rates during OAE 2. • Biogeochemical modeling suggests 5–20% of seafloor anoxia during OAE 2. • Seawater P concentrations increased 1–2 times over background levels during OAE 2. [ABSTRACT FROM AUTHOR]

One of the key challenges in understanding the role of hadal trenches in the marine organic carbon (OC) cycle is the need to distinguish OC sources, assess accumulation rates, and identify controlling processes. To address this, sediment core samples from the southern Mariana Trench were analyzed for their contents and carbon isotopes (13C and 14C) of both total OC (TOC) and saturated long-chain fatty acid (n -LCFA). Our findings indicate that sedimentary OC in the southern Mariana Trench is primarily derived from marine sources, as indicated by TOC-δ13C values ranging from −19.9‰ to −17.0‰ and the ratios of TOC to total nitrogen (TOC/TN) of 5.5–8.4. The 14C ages of TOC and n -LCFA ranged from 7159 to 22,662 yr and 8713 to 22,819 yr, respectively, with both showing gradual down-core increasing trends. This allows for a conservative estimation of sedimentation rate of 17.5–18.7 cm kyr−1 in the southern Mariana Trench, leading to a sedimentary OC accumulation rate of 529–942 g C m−2 kyr−1, which is 1–2 orders of magnitude higher than that observed in the abyssal plain. We propose that the continuous lateral downslope transport played a significant role in focusing pre-aged OC into the southern Mariana Trench. Therefore, hadal trenches are likely to accumulate substantial amounts of sedimentary OC in the deep ocean. • A gravity sediment core MT03 was collected from the southern Mariana Trench. • Contents and carbon isotopes (13C and 14C) of both TOC and n -LCFA were analyzed. • The sediment OC in core MT03 was primarily derived from marine sources. • Sedimentation rate of 17.5–18.7 cm kyr−1 estimated based on 14C ages of organics. • Pre-aged OC accumulated in the trench with a burial flux of 529–942 g C m−2 kyr−1. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the past 20 years, the exploration of deep ocean trenches has led to spectacular new insights. Even in the deepest canyons, an unusual variety of life and unexpectedly high benthic oxygen consumption rates have been detected while microbial processes below the surface of the hadal seafloor remains largely unknown. The information that exist comes from geophysical measurements, especially related to seismic research, and specific component analyses to estimate the carbon export. In contrast, no information is available on metabolic activities in deeper buried sediments of hadal environment. Here we present the first pore water profiles from 15 up to 11 m long sediment cores recovered during three expeditions to two hadal zones, the Japan Trench and the Atacama Trench. Despite low levels of organic debris, our data reveal that rates of microbial carbon turnover along the trench axes can be similar to those encountered in much shallower and more productive oceanic regions. The extreme sedimentation dynamics, characterized by frequent mass wasting of slope sediments into the trenches, result in effective burial of reactive, microbially available, organic material. Our results document the fueling of the deep hadal biosphere with bioavailable material and thus provide important understanding on the function of deep‐sea trenches and the hadal carbon cycle. Plain Language Summary: For a long time, it was assumed that in water depths below 6,000 m, biological species diversity and microbial activity is very low. Recent studies could already provide clear evidence that significant degradation of organic material occurs even at the seafloor surface in deep‐sea trenches. No comparable information is available yet about the situation below the surface layer. Here, data are presented for the first time that help to close this knowledge gap. Based on geochemical parameters, it can be proven that very active degradation processes also take place in the deeper buried layers in deep‐sea trenches. Rates correspond in magnitude to sediments from shallower water depths with considerably higher contents of organic material. The authors attribute this finding primarily to sedimentation dynamics in deep‐sea trenches. The steep flanks of trenches, sometimes associated with seismic activity, repeatedly favor the sliding of large sediment packages into basins along trench axes. Rapid burial removes less degraded, and thus more microbially available material from oxic surface and preserves it for subsequent processes such as sulfate reduction. The unique results provide important new insights into the function of deep‐sea trenches and the hadal carbon cycle. Key Points: Hadal subseafloor pore water profiles from the Japan Trench and Atacama Trench document unexpectedly high microbial turnover ratesFrequent alternations between hemipelagic sedimentation and mass wasting lead to high burial efficiency of reactive organic carbonMicrobial activities in deep‐sea trenches may be similar to those at the edge of high‐production areas [ABSTRACT FROM AUTHOR]

Abstract In the past 20 years, the exploration of deep ocean trenches has led to spectacular new insights. Even in the deepest canyons, an unusual variety of life and unexpectedly high benthic oxygen consumption rates have been detected while microbial processes below the surface of the hadal seafloor remains largely unknown. The information that exist comes from geophysical measurements, especially related to seismic research, and specific component analyses to estimate the carbon export. In contrast, no information is available on metabolic activities in deeper buried sediments of hadal environment. Here we present the first pore water profiles from 15 up to 11 m long sediment cores recovered during three expeditions to two hadal zones, the Japan Trench and the Atacama Trench. Despite low levels of organic debris, our data reveal that rates of microbial carbon turnover along the trench axes can be similar to those encountered in much shallower and more productive oceanic regions. The extreme sedimentation dynamics, characterized by frequent mass wasting of slope sediments into the trenches, result in effective burial of reactive, microbially available, organic material. Our results document the fueling of the deep hadal biosphere with bioavailable material and thus provide important understanding on the function of deep‐sea trenches and the hadal carbon cycle.

The carbon cycle on the Earth’s surface is linked to long-term variations in atmospheric CO2 as well as carbon sequestration in various pools. The burial of particulate organic carbon (OC) in marine sediments is also highly sensitive to the global climate over geological time scales, but with little known about OC burial and its regulations over glacial-interglacial cycles. Here, we present a long-term OC record over the past ∼380 kyr, from the Northwest Pacific Ocean, an ideal region for studying OC burial and its environmental implications on glacial-interglacial timescales. We observed a distinct cyclicity of higher OC burial in glacial periods, which was coupled with input from Asian dust and the Kuroshio Current but seemingly decoupled from biogenic element contents, implying a limited effect of marine productivity on OC burial. Moreover, the sedimentary record of OC was synchronous with oceanic redox conditions, especially the redox sensitive elements at the sediment-water interface, indicating a relatively reducing conditions that enhanced OC preservation during glacial periods. The overall glacial-interglacial OC burial regime in the Northwest Pacific Ocean was conceptually constructed. It showed a higher efficiency of OC burial during glacial periods and significant degradation during interglacial periods. The findings of this study highlighted the important contribution of environmental redox conditions on OC burial in the deep Northwest Pacific, demonstrating the sensitivity of the carbon cycle to global climate on an orbital scale.

• Sediment resuspension drives refractory organic carbon (OC) transfer into seawater. • OC transfer results in the enhancement of dissolved OC bioavailability. • Refractory OC accumulates on particles during sediment resuspension. • The magnitudes of OC transfer are affected by sediment grain sizes. The transfer of particulate organic carbon (POC) to dissolved organic carbon (DOC; OC transfer P-D) is crucial for the marine carbon cycle. Sediment resuspension driven by hydrodynamic forcing can affect the burial of sedimentary POC and benthic biological processes in marginal sea. However, the role of sediment grain size fraction on OC transfer P-D and the subsequent impact on OC cycling remain unknown. Here, we conduct sediment resuspension simulations by resuspending grain-size fractionated sediments (< 20, 20–63, and > 63 μm) into filtered seawater, combined with analyses of OC content, optical characteristics, 13C and 14C isotope compositions, and molecular dynamics simulations to investigate OC transfer P-D and its regulations on OC bioavailability under sediment resuspension. Our results show that the relative intensities of terrestrial humic-like OC (refractory DOC) increase in resuspension experiments of < 20, 20–63, and > 63 μm sediments by 0.14, 0.01, and 0.03, respectively, likely suggesting that sediment resuspension drives refractory DOC transfer into seawater. The variations in the relative intensities of microbial protein-like DOC are linked to the change of terrestrial humic-like OC, accompanied by higher DOC content and reactivity in seawater, particularly in finer sediments resuspension experiments. This implies that transferred DOC likely fuels microbial growth, contributing to the subsequent enhancement of DOC bioavailability in seawater. Our results also show that the POC contents increase by 0.35 %, 0.66 %, and 0.93 % in < 20, 20–63, and > 63 μm resuspension experiments at the end of incubation, respectively. This suggests that the re-absorption of OC on particles may be a significant process, but previously unrecognized during sediment resuspension. Overall, our findings suggest that sediment resuspension promotes the OC transfer P-D , and the magnitudes of OC transfer P-D further influence the DOC and POC properties by inducing microbial production and respiration. These processes significantly affect the dynamics and recycling of biological carbon pump in shallow marginal seas. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Due to high productivity, periodic submersion, and rapid sedimentation rate, mangroves are important carbon sinks in tropical-subtropical coastal zones. Mangrove expansion can significantly enhance burial carbon storage in coastal zones and has been reported in many subtropical regions due to climate change in recent years. To better understand the response of carbon storage to climate change in subtropical-tropical coastal zones, it is necessary to estimate the change in burial organic carbon (OC) storage in mangroves undergoing expansion. In the Nanliu River estuary of South China, the total mangrove area has increased from 72 to 622 ha in recent decades. Based on a sedimentology study combined with historical satellite images analysis, the accumulation rate of burial OC in these mangroves is estimated to be 400–500 g‧m−2‧y−1, of which the part imported to the stratigraphy beneath the mangrove deposit layer is approximately 130 g‧m−2‧y−1. Globally, the reported OC accumulation rate is linearly correlated to the accretion rate in mangroves. The accumulation rate of mangrove burial OC estimated in this study is significantly higher than the corresponding value on this fitted curve, indicating that the OC accumulation rates may be underestimated in such mangroves because the OC imported to the lower root layer has been not been taken into account. Based on the estimated OC accumulation rate and the time-series data of the mangrove area, the increase in burial OC storage in the mangroves of the Nanliu River estuary from 1988 to 2018 is estimated at more than 35 Gg. This study provides an example of estimating soil OC storage increase in expanding mangroves, which can help us better understand the response of coastal carbon pool to climate change.

The burial of organic carbon in lake sediments plays an important role in the terrestrial carbon cycle. Clarifying the current status of carbon burial in the lakes of Central Asia is of great significance for the application of carbon balance assessments. With the analysis of the total organic carbon and nitrogen and the carbon isotope and organic carbon burial rate in the core sediment of the North Aral Sea, the status and influencing factors of organic carbon burial over the past 70 years can be revealed. The results showed that the main source of organic carbon was predominantly from lacustrine aquatic plants. However, the contribution of terrigenous organic carbon increased from the 1950s to the 1960s. The burial rate of organic carbon in North Aral Sea sediments was consistent with the overall change in the regional temperature. The burial rate of organic carbon showed an upward trend as a whole with an average of 28.78 g·m−2·a−1. Since 2010, the burial rate of organic carbon has stood at the highest level in nearly 70 years, with an average of 55.66 g·m−2·a−1. The protection of a lake by human beings can not only significantly improve the lake's aquatic ecosystem but also help to increase the burial rate of the lake's organic carbon. [ABSTRACT FROM AUTHOR]

Knowledge of sedimentary organic carbon (OC) in hadal trenches, the deepest ocean realm, is rudimentary. Here, we conducted a comprehensive analysis of total OC (TOC), stable and radio‐carbon isotopes (δ13C and Δ14C), and biomarkers (e.g., n‐alkanes, n‐alkanols and n‐fatty acids) in 12 sediment cores collected from hadal (trench axis) and non‐hadal (abyssal plains and slopes) settings of the Kermadec Trench (Southwestern Pacific) and Atacama Trench (Southeastern Pacific) regions. Our results show that the TOC in the Atacama Trench region (0.86% ± 0.69%) is significantly higher than that of the Kermadec Trench region (0.29% ± 0.08%), likely related to different surface primary productivity. In both trench regions, the hadal sites are generally characterized by more negative δ13C, higher TOC/TN ratio, and similar or higher abundance ratio of terrigenous/marine biomarkers as compared to the non‐hadal sites, suggesting the selective preservation of terrigenous biogenic/fossil OC at the hadal trench axis. The linear increase in 14C age with sediment depth in non‐hadal cores reflects steady depositional conditions, whereas seven out of eight hadal sediment cores show 14C age reversals presumably due to occasional mass‐transport deposits. Our results suggest (1) a strong heterogeneity in sedimentary OC characteristics between trenches and within each trench and (2) relatively high accumulation rates of terrigenous OC in both the Kermadec Trench (0.35 ± 0.04 g m−2 yr−1) and the Atacama Trench (1.4 ± 0.5 g m−2 yr−1). Thus, hadal trenches appear to represent an important environment for terrigenous carbon deposition in the deep ocean. Plain Language Summary: The hadal zone mainly composed of trenches is the deepest ocean realm with water depth over 6,000 m. Due to the challenge of observation and sampling at the extreme depth, the hadal zone is one of the least explored ecosystems on Earth. Limited studies have suggested that hadal trenches have higher benthic biomass and microbial activity compared to surrounding abyssal plains, which has overturned a traditional view that the hadal zone is a "biological desert." Here, we conducted comprehensive geochemical analysis of sedimentary organic carbon in Kermadec Trench (Southwestern Pacific) and Atacama Trench (Southeastern Pacific). Our goal is to understand source, distribution, and burial of organic carbon that is an important food and energy source for benthic organisms in hadal trenches. We have obtained three key findings. (1) While extensive heterogeneity in sedimentary organic carbon in trench interior and between two trenches, the trench bottoms generally have higher fractional abundance of terrigenous organic carbon compared to surrounding abyssal/bathyal sites. (2) Mass‐transport deposits induced by episodic events (like earthquakes) profoundly influence organic carbon content and compositions in hadal trenches. (3) The hadal zone is an important but previously overlooked sink for terrigenous organic carbon in the deep ocean. Key Points: Sedimentary organic carbon (OC) reflects extensive variations among inter‐ and intra‐trenchesMore terrigenous OC was buried at hadal axis sites compared to non‐hadal sitesThe hadal zone is an important and previously overlooked sink for terrigenous OC in deep ocean [ABSTRACT FROM AUTHOR]

[Display omitted] • Vegetation area of Poyang Lake expanded by over 50 % following TGD regulation. • OC burial within the lake sediments increased by 3.82–4.60 times following TGD regulation. • TGD-triggered lake level decline was responsible for the lake OC burial enhancement. Lakes play a dominant role in the global carbon cycle, serving as crucial long-term carbon (C) sinks. Carbon burial within lakes is influenced by changes in both inflowing and outflowing processes. While considerable attention has been given to studying the former, the latter has often been overlooked and remains insufficiently documented. In this study, we investigated the variations in organic carbon burial within Poyang Lake, the largest freshwater lake in China, which mainly discharges into the Changjiang River. This study focused on the response of organic carbon burial to the regulation of a mega dam, the Three Gorges Dam, along the lake's main channel. The mean organic carbon accumulation rate in Poyang Lake sediments increased substantially by 3.82–4.60 times after the year 2000, compared to the preceding period. Furthermore, the Three Gorges Dam induced an abnormal reduction in lake levels by 1.38 m during the dry season, leading to a translocation of approximately 0.42 billion m2 of water area toward vegetated systems. The pronounced expansion of vegetation across the shallow floodplain of Poyang Lake is identified as the primary driver behind the enhanced organic carbon burial within the lake sediments. These findings emphasize the imperative to further investigate and address the global issue of organic carbon accumulation in lake floodplain sediments, particularly in the context of riverine dams. These results shed light on the ecological implications of mega-dam regulation on organic carbon dynamics and underscore the significance of understanding and mitigating the associated environmental impacts. [ABSTRACT FROM AUTHOR]

• We propose a dynamic deposition and mineralization model of organic C in sediments. • The model can predict changes in organic C burial in different water systems. • The organic C burial capacity of sediments may be much lower than expected. • Our findings provide new insights into sediment organic C sinks. The burial amount of organic carbon (OC) in lake sediments is constantly changing owing to mineralization. Statically measured OC does not entirely reflect the dynamic OC processes in lake sediments. This study proposes a dynamic deposition and mineralization model for sedimentary OC (DMSOC) and applies it to eight sedimentary cores from two lakes to invert the history of OC in sediments. The results showed that the trophic level and temperature of the lake predominantly affected the amount of deposited OC (De-OC). The amount of mineralized OC in the sediments is adversely affected by the end sources, burial time, and trophic level of the lake. The OC end source mainly determined the mineralization rate in the following order: algae > aquatic > terrestrial sources. Burial time primarily affected the compositional characteristics of the remaining OC, owing to the asynchronous mineralization of OC from different sources. The De-OC of Dianchi Lake, a eutrophic lake, increased more than twice compared to that of the scenario 100 years ago. The De-OC content of Fuxian Lake, an oligotrophic lake, decreased by approximately 25 %. The greenhouse effect may further reduce the carbon sequestration capacity of lakes, particularly oligotrophic lakes. With a set burial age, the model results show that the increase in OC storage in lake sediments may be much lower than expected. Therefore, the roles of different types of lakes in the carbon cycle must be reassessed. [ABSTRACT FROM AUTHOR]

Oxygen minimum zones (OMZs) in the ocean are expanding. This expansion is attributed to global warming and may continue over the next 10 to 100 kyrs due to multiple climate CO2-driven factors. The expansion of oxygen-deficient waters has the potential to enhance organic carbon burial in marine sediments, thereby providing a negative feedback on global warming. Here, we study the response of dissolved oxygen in the ocean to increased phosphorus and iron inputs due to CO2-driven enhanced weathering and increased dust emissions, respectively. We use an ocean biogeochemical model coupled to a general ocean circulation model (the Hamburg Oceanic Carbon Cycle model, HAMOCC 2.0) to assess the impact of such regional deoxygenation on organic carbon burial in the modern ocean on time scales of up to 200 kyrs. We find that an increase in input of phosphorus and iron leads to an expansion of the area of the OMZ impinging on continental margin sediments and a significant decline in bottom water oxygen in the open ocean relative to pre-industrial conditions. The associated increase in organic carbon burial could contribute to the drawdown of ~1,600 Gt of carbon, which is equivalent to the total amount of CO2 in the atmosphere predicted for the year 2100 in a business as usual scenario, on time scales of up to 50 kyrs. The corresponding areal extent of sediments overlain by bottom waters with little or no oxygen as estimated by the model is not very different from the minimum area estimated for two major oceanic anoxic events in Earth's past. Such events were associated with major perturbations of the oceanic carbon cycle, including high rates of organic carbon burial. We conclude that organic carbon burial in low oxygen areas in the ocean could contribute to removal of anthropogenic CO2 from the atmosphere on long time scales.

• Primary dolomite is ubiquitous in terminal Ediacaran microbial mats. • Mg-rich carbonate aggregates and EPS-like microstructures are preserved. • Petrographic and geochemical data support an organogenic origin for the dolomite. • Organogenic dolomites likely contributed to the formation of ancient dolostones. The widespread occurrence of dolostones in Paleozoic and Precambrian sequences stands in stark contrast to the difficulty of precipitating dolomite in experiments at low temperature under abiotic conditions. The discoveries of dolomite within modern microbial mats and the successful synthesis of proto-dolomite under ambient conditions catalyzed by various microorganisms and organic molecules lend support to the development of organogenic dolomite models. Despite this, convincing evidence for ancient primary dolomite precipitation is rare, mainly due to post-depositional modifications of original textures and mineralogy. Here we present petrographic, mineralogical and C-isotopic data of carbonates preserving primary sedimentary textures in the late Ediacaran Shibantan Member of the Dengying Formation from the eastern Yangtze Gorges area, South China. These carbonates are characterized by calcite layers intercalated with millimeter-thick, organic-rich layers that contain up to 50 % dolomite. Petrographic observations and Raman imaging show that the dolomite occurs preferentially in microbial mats and is closely associated with organic matter. Scanning electron microscopy also revealed the presence of Mg-rich nanoscopic carbonate aggregates and ribbon-like microstructures akin to mineralized extracellular polymeric substances (EPS) in mat layers. These observations are inconsistent with replacive origins but instead support an organogenic origin for the Shibantan dolomite. The relatively high TOC (total organic carbon) contents and consistently positive δ13C carb values (up to +4.8 ‰) suggest enhanced burial of organic carbon produced in microbial mats during the Shibantan deposition. Subsequent organic degradation by microorganisms in anoxic, early diagenetic environments likely promoted the ubiquitous formation of organogenic dolomite in Shibantan microbial mats. Our study highlights the important roles of organogenic dolomites in interpreting the wide occurrence of Paleozoic and Precambrian dolostones. [ABSTRACT FROM AUTHOR]

The burial of organic carbon in lake sediments plays an important role in the terrestrial carbon cycle. Clarifying the current status of carbon burial in the lakes of Central Asia is of great significance for the application of carbon balance assessments. With the analysis of the total organic carbon and nitrogen and the carbon isotope and organic carbon burial rate in the core sediment of the North Aral Sea, the status and influencing factors of organic carbon burial over the past 70 years can be revealed. The results showed that the main source of organic carbon was predominantly from lacustrine aquatic plants. However, the contribution of terrigenous organic carbon increased from the 1950s to the 1960s. The burial rate of organic carbon in North Aral Sea sediments was consistent with the overall change in the regional temperature. The burial rate of organic carbon showed an upward trend as a whole with an average of 28.78 g·m−2·a−1. Since 2010, the burial rate of organic carbon has stood at the highest level in nearly 70 years, with an average of 55.66 g·m−2·a−1. The protection of a lake by human beings can not only significantly improve the lake’s aquatic ecosystem but also help to increase the burial rate of the lake’s organic carbon.

The Smithian/Spathian boundary (SSB) represents a major climatic-oceanic-biotic event within the ~5-Myr-long recovery interval of the Early Triassic following the end-Permian mass extinction. The SSB was associated with pronounced cooling following the middle Smithian hyper-greenhouse, a ~ +2 to +8‰ positive carbon isotope excursion, and a second-order mass extinction, yet its underlying cause(s) remain poorly understood. Here, we review oceanic environmental changes during the middle Smithian to early Spathian interval and their potential mechanisms. In addition, we undertook an analysis of the carbon‑sulfur‑iron (C-S-Fe) systematics of the South Majiashan section, which was located on the paleo-western margin of the South China Craton during the Early Triassic, to better understand the causation of these environmental changes. This analysis revealed low δ13C carb (i.e., the N3 minimum) in the middle Smithian but rapidly rising δ13C carb (i.e., to the P3 maximum) and δ34S CAS within the SSB interval (i.e., late Smithian-earliest Spathian). Both the middle Smithian and SSB intervals are marked by development of marine euxinia, which we hypothesize had fundamentally different causes. The middle Smithian was associated with hyperwarming (the "Smithian Thermal Maximum"), which was probably triggered by a peak in magmatic activity of the Siberian Traps LIP. In contrast, the SSB interval was associated with global climatic cooling, which may have stimulated oceanic overturning circulation and upwelling on continental margins, leading to transient local increases in marine productivity and expansion of oceanic oxygen-minimum zones (OMZs). The concurrent positive excursions in δ13C carb and δ34S CAS at South Majiashan and other sections worldwide are evidence of enhanced burial of organic carbon and pyrite on a regional or global scale, as well as of a concurrent decline in atmospheric p CO 2 that may have positively re-enforced the SSB cooling event. [ABSTRACT FROM AUTHOR]

Mangrove wetlands are some of the most important locations of organic carbon (OC) sequestration and storage in the world on a per area basis. The high stocks of soil OC are driven by generally high burial rates and efficient preservation of organic material over past millennia of relatively slow and consistent sea level rise. Although the global average rate of OC burial in mangrove wetlands is relatively high, the range in the literature varies by up to two orders of magnitude. The objective of this research was to measure burial rates of OC, CaCO3, and nutrients [total nitrogen (TN) and phosphorous (TP)] across a pronounced ecosystem gradient of productivity and salinity in the coastal Everglades of southwestern Florida, USA. Concentrations and burial rates of both CaCO3 (range 13–1233 g m−2 y−1) and TP (range 0.10–1.59 g m−2 y−1) decreased significantly with distance from the Gulf of Mexico. In contrast, there was less spatial variability in OC (134 ± 12 (1 SE) g m−2 y−1) and TN (6.2 ± 0.4 g m−2 y−1) burial rates. However, significant (P < 0.001) regional differences in OC burial rates were observed relative to mangrove primary productivity. Over a centennial timescale, downstream sites buried 14% of annual net primary production, midstream sites buried 22%, and upstream sites preserved less than 10%. [ABSTRACT FROM AUTHOR]

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 CO 2. 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 δ 13C of marine carbonates that may be indicative of elevated burial of δ 13C-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. • A new age model for the Monterey Fm incorporates 45 U-Pb zircon ages. • Organic C burial maxima in Monterey Fm: asynchronous with global δ 13C DIC excursions. • Organic carbon burial rates in Monterey Fm were controlled by sedimentation rate. • Organic C deposition in Monterey Fm: a response to basin formation, climate change. [ABSTRACT FROM AUTHOR]

Coastal depositional systems play a crucial role in the sequestration of terrigenous organic carbon (OC), especially deltas and coastal mud belts, which are two of the most efficient OC burial hotspots. Investigation into long-term coastal OC burial is challenging since the analysis of modern coastal environments only provides a snapshot of OC burial. Marine Isotope Stage 3 (MIS 3) refers to a unique interval in the last glacial period, characterized by a protracted falling sea level punctuated by millennial-scale climate oscillations. The study of OC burial during MIS 3 can help to estimate and predict changes in coastal OC burial driven by sea-level oscillations and extreme climate events. Here, we target late MIS 3 strata beneath the southern East China Sea. Based on the analysis of total organic carbon, total nitrogen content, stable organic carbon isotopic composition, and major and trace elements, this study demonstrates that relative sea-level changes control sediment provenance and sedimentary processes in coastal environments, which in turn regulate coastal OC burial during the late MIS 3. The burial of OC in the coastal ocean during MIS 3 deviates from the typical expectation that carbon burial is facilitated during transgression or high sea-level periods. Sediments deposited during high sea-level periods in late MIS 3 exhibit the lowest OC burial flux and contents due to long-distance transport from distant sources. The study highlights that the highest burial flux and contents of OC were found in deposits preserved during sea-level lowstands. This indicates that short-distance transport, local sources, and mountainous rivers affected by the monsoon and experience frequent floods, are associated with the highest OC burial and contents. Short and rapid climate warming events likely contribute to OC burial in late MIS 3 by intensifying precipitation and nutrient-rich supplies, thereby increasing the input of terrestrial and marine OC. This observation is noteworthy as it challenges the conventional understanding of the relationship between sea level and carbon burial. The study of OC burial in late MIS 3 is helpful in understanding how OC burial reacts to sea level oscillations and rapid climate warming events. • Relative sea-level changes control organic carbon burial of the coastal system through regulating shifts in depositional environments and changes in sediment provenance. • Warming periods promote organic carbon burial in Late MIS 3 through intense precipitation and rich supplies of nutrients that increase the terrestrial and marine OC input. • Low sea-level stages are potential organic carbon sequestration periods. [ABSTRACT FROM AUTHOR]

The Toarcian Oceanic Anoxic Event (T-OAE,~183 Myr) was a long-lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarcian and its influence on marine biogeochemical cycles are still not fully understood. Here we assess the spatial extent of anoxia in the NW Tethys Ocean during the T-OAE, the relationship with ocean circulation and the impact on organic carbon burial, using new and existing sedimentary records from the European Epicontinental Shelf in combination with general circulation model results. We demonstrate that bottom waters on the southwestern part of the shelf were mainly oxic during the T-OAE, while those in the northeastern basins were mostly anoxic or even sulfidic. Results for two ocean-atmosphere models (Fast Ocean-Atmosphere Model and Massachusetts Institute of Technology general circulation model) suggest the presence of a strong clockwise gyre over the European Epicontinental Shelf, which brought oxygenated equatorial waters from the Tethys Ocean to the southern shelf. The northward limb of the gyre was significantly weakened due to the rough bathymetry of the northern shelf, making this relative small region highly sensitive to local ocean stratification. These sluggish ocean dynamics promoted bottom water anoxia and enhanced burial of organic carbon in the northeastern basins, which accounted for 3-5% of the total carbon extracted from the ocean-atmosphere system as recorded by the positive carbon isotope shift. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) burial in nondeltaic continental shelves is an important part of the global carbon cycle. Of these, the Taiwan Strait (TWS) is a typical, nondeltaic shelf region that is influenced by a variety of factors including strong ocean currents, coastal upwelling, and small river inputs. To better understand how these factors influence OC burial in the TWS, we measured total organic carbon and total nitrogen contents as well as the stable carbon isotopes of sedimentary organic matter (δ13Corg) from the TWS. We also measured glycerol dialkyl glycerol tetraethers in surface sediments collected from the TWS. The concentrations of sedimentary total organic carbon and total nitrogen along the coast were high but decreased in areas more central to the TWS. This gradient was controlled by both hydrological conditions and coastal upwelling. The calculated accumulation rate of organic carbon ranged from 1.9 to 47.2 g C/m2/year and was comparable to other areas of the Chinese marginal seas. The source contribution calculated from the three‐end‐member model revealed that mostly marine OC was buried in the upwelling regions. In comparison, OC derived from terrestrial plant and soil was buried in the estuaries. Collectively, these results showed that the TWS may serve as a CO2 sink in the global carbon cycle. This is due to the preservation of the labile portions of the OC derived from plant and marine source, which formed the main component of the buried OC in the TWS. Plain Language Summary: Organic carbon (OC) burial in nondeltaic continental shelves is an important part of the global carbon cycle. Of these, the Taiwan Strait is a typical, nondeltaic shelf region that is influenced by a variety of factors including strong ocean currents, coastal upwelling, and small river inputs. This study addressed what control the distribution of OC and where different sources of OC (e.g., soil, plant, and marine) are buried. We demonstrated that the distribution of burial of OC was controlled by both hydrological conditions and coastal upwelling. Also, since the easily degradable marine OC formed the main component of the buried OC, we revealed that the Taiwan Strait may serve as a CO2 sink in the global carbon cycle. Key Points: A multiproxy analysis of sedimentary OC in the Taiwan Strait was discussedHydrological conditions controlled OC spatial distribution in the Taiwan StraitThe Taiwan Strait may serve as a CO2 sink in the global carbon cycle [ABSTRACT FROM AUTHOR]

Abstract: Lakes and reservoirs transform, emit, and bury carbon that is exported from land and are thus significant components of terrestrial carbon budgets. Their significance is often assessed by integrating these water bodies into terrestrial primary production. However, the transfer of inorganic carbon (IC) is likely a sticking point for these integrations because IC is not part of net ecosystem production. Here we integrated carbon evasion and organic carbon (OC) burial in a lake in the context of inorganic and OC cycling in a karst catchment from a system perspective. The lake emitted carbon dioxide (CO2) and buried OC at rates of 1.0 ± 0.2 and 0.9 ± 0.2 g C m−2 a−1, respectively, approximately equaling 13% and 11% of catchment net ecosystem production, respectively. These proportions represent significant influences on terrestrial carbon budgets, given an organic origin. However, catchment carbon export is dominated by IC that is derived from carbonates dissolved by soil CO2. Lake CO2 evasion accounts for less than 0.1% of soil CO2 efflux, suggesting little potential in significantly altering terrestrial carbon budgets. This comparison indicates the significance of aquatic CO2 evasion, requiring an adjustment of terrestrial carbon budgets to recognize their dependence on carbon origins. The significance may be overstated if inorganic origin is ignored. Our study suggests that a careful reassessment of the significance of CO2 evasion and OC burial in freshwater ecosystems to local and global carbon budgets, with full consideration of their sources, is necessary and pressing. [ABSTRACT FROM AUTHOR]

Anthropogenic inputs are increasing the CO2content of the atmosphere, and the CO2and total inorganic C in the surface ocean and, to a lesser degree, the deep ocean. The greenhouse effect of the increased CO2(and, to a lesser extent, other greenhouse gases) is very probably the major cause of present global warming. The warming increases temperature of the atmosphere and the surface ocean to a greater extent than the deep ocean, with shoaling of the thermocline, decreasing nutrient flux to the surface ocean where there is greater mean photosynthetic photon flux density. These global changes influence algae in nature. However, it is clear that algae are important, via the biological pump, in decreasing the steady state atmospheric and ocean surface CO2, and thus decreasing radiative forcing, a reduction enhanced by algal increases in albedo. As well as these natural processes there are possibilities that algae can, with human intervention, partly offset the increase in atmospheric CO2. One possibility is to grow algae as sources of fuel for transport, in principle providing an energy source that is close to CO2-neutral. The other possibility is to increase the role of algae in sequestering CO2as organic C over periods of hundreds or more years in the deep ocean and marine sediments and/or increasing albedo and decreasing radiative forcing of temperature. There are problems, currently unresolved, in the economically viable production of algal biofuels without carbon trading subsidies. Enhanced algal CO2sequestration also has costs, both in resource input (phosphorus (P) from high P content rocks, a limited resource with a competing use as an agricultural fertilizer) and adverse environmental effects. For example, ocean anoxic zones producing N2O and increased algal production of short-lived halocarbons by algae that both, through breakdown, destroy O3and increase UV flux to the Earth’s surface. [ABSTRACT FROM PUBLISHER]

Glaciers enhance terrestrial erosion and sediment export to the ocean. Glaciers can also impact mineral specific weathering rates relative to analogous non-glacial terrains. In tandem these processes affect continent sediment export to the oceans over glacial-interglacial cycles. This study summarizes field data from glacial and non-glacial Icelandic river catchments to quantify the impact of weathering regime on iron and aluminium (oxyhydr)oxide mineral formation and flux rates. Aluminium and iron (oxyhydr)oxides are strong indicators of organic carbon preservation in soils and marine sediments. Tracing changes in (oxyhydr)oxide formation and deposition therefore provides a means of evaluating potential changes in organic carbon sequestration rates over glacial-interglacial cycles. Overall, there are several measurable chemical differences between the studied glacial and non-glacial catchments which reflect the key role of soil formation on terrestrial weathering. One of the noted chemical differences is that weathering in non-glacial catchments is characterized by higher apparent rates of iron and aluminium (oxyhydr)oxide formation relative to glacial catchments. However, the offset in (oxyhydr)oxide formation does not appear to be transferred into river sediment compositions, and physical weathering appears to be the dominant control of river sediment composition and export. Glacial rivers export far more total sediment to nearshore marine environments than analogous non-glacial rivers suggesting glacial weathering enhances carbon burial by increasing nearshore marine (oxyhydr)oxide accumulation. [ABSTRACT FROM AUTHOR]

Mangroves are rapidly being lost to deforestation in many locations while expanding their areal extent in other subtropical and temperate regions. Currently, there is a paucity of information on how these changes may alter the carbon accumulation capacity of coastal areas. Here, sediment cores were collected from two areas and used to determine the influence of mangrove migration and deforestation on sediment carbon stocks and accumulation rates. The deforested area contained lower sedimentary organic carbon stocks (2767 ± 580 g m −2 ) compared to the preserved area (6949 ± 84 g m −2 ). Sediment accumulation rates, derived from excess 210 Pb and 239+240 Pu depositional signatures, ranged from 0.19 to 0.35 cm yr −1 . The total sedimentary organic carbon (TOC) accumulation rates for the period after mangrove deforestation (2005–2011) exhibited significant differences between preserved areas (Core C: 43.9 ± 6.9 g m −2 yr −1 ; Core D: 83.1 ± 5.9 g m −2 yr −1 ) and the deforested area (Core B: 25.8 ± 6.0 g m −2 yr −1 ), suggesting a decline after deforestation. For the preserved area, the TOC accumulation under mangrove dominance (65.5 ± 16.3 g m −2 yr −1 , after 1944) was higher than under saltmarsh dominance (23.5 ± 15.9 g m −2 yr −1 , before 1944), as revealed by carbon isotopic signatures (δ 13 C). The increase in the TOC accumulation due to mangrove expansion in this New Zealand estuary was conservatively estimated as three-fold higher, and two-fold higher in stocks in comparison to the period when this ecosystem was dominated by non-mangrove vegetation. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) accumulation and storage in lake sediments is considered to be an important component of global C cycling. However, the storage of OC in Chinese lakes is not well constrained, and its role in future global change processes has rarely been considered. Here, we analyzed the OC burial and its correlation with lake catchment properties in Chinese lakes that have experienced heavy anthropogenic influence over the last ∼150 years. We compiled OC data from sixty-four lakes from the literature. The results showed that organic carbon accumulation rates (OCARs) in Chinese lakes ranged between 1.4 and 259.5 g m −2 yr −1 , with a mean of 22 g m -2 yr −1 over the past ∼150 years, consistent with the global estimate of the carbon burial rate in lake sediments (11–26 g m −2 yr −1 ). Extrapolated to the whole country, a total of 269.5 Tg OC (ranging from 138.9 to 690.4 Tg C) was stored in Chinese lakes over the past 150 years. Spearman analysis revealed that OCARs strongly depended on lake and catchment size, precipitation, temperature, longitude, altitude and anthropogenic activities. Moreover, OCARs showed an increasing trend, especially after the 1950s, coinciding with land use changes and lake nutrient level shifts. [ABSTRACT FROM AUTHOR]

The beginning of the Late Cretaceous (Cenomanian) attested to a major marine transgression interrupted by sea level falls in north Africa, which led to significant environmental perturbation and widespread accumulation of organic matter-rich sediments. During this period, northern Egypt was located at the southern edge of the Tethys Ocean and deposition of thick siliciclastic alternations between shales, siltstones, and sandstones of the Bahariya Formation took place in the BED2 gas field of the Abu Gharadig Basin, north Western Desert. An integrated approach of palynofacies analysis and palynomorph composition, organic petrography, and geochemical analysis of total organic carbon (TOC)/Rock-Eval pyrolysis, carbonate content, XRD analysis, and clay mineralogy of thirty-nine cutting samples obtained from the lower-middle Cenomanian Bahariya Formation was conducted. This approach was used to characterize organic matter and possible occurrence of source rock intervals, paleoenvironmental and paleoclimatic conditions and their role in organic matter accumulation. Moderate to high proportions of pteridophyte and water fern spores and pollen grains of Araucariaceae (Araucariacites), Cheirolepidiaceae (mainly Classopollis), and Gnetalean (Elaterate pollen) and Afropollis versus the sparsely recorded xerophilous ephedroids (Ephedripites) indicate prevalent conditions of a warm and humid climate. This is consistent with clay mineral composition that is dominated mainly by kaolinite and smectite compared to low illite and the lack of chlorite, which indicated a predominantly warm-humid climate state. Palynofacies analysis showed two assemblages; the first one is dominated by phytoclasts and indicates gas-prone Type III kerogen and deposition in a fluvio-deltaic environment. The second palynofacies assemblage is characterized by moderate abundance of phytoclasts and AOM mostly of terrestrial origin, suggesting a mixed Type III/II kerogen and deposition in a marginal to shallow neritic shelf environment. The organic geochemical characterization showed relatively low average values of TOC, S 2 , and HI, indicating that the Bahariya Formation is characterized by Type III gas-prone kerogen. Thermal maturity of the Bahariya Formation ranges from immature to the early stage of the oil window. Additionally, organic matter characteristics of the Bahariya Formation are qualitatively and quantitatively similar to their equivalents from nearby basins. Low TOC contents are attributed to a high sedimentation rate and an increased terrestrial input of sand- and silt-sized fractions at shallow water column settings that controlled strong dilution and decomposition versus low burial efficiency of the organic matter. • Cenomanian Bahariya Formation was studied using palynology, geochemistry and organic petrography. • Spores and pollen confirmed a warm-humid climate during the Cenomanian in this part of the southern Tethys. • The Bahariya Formation has poor source rock potential, but the lower intervals show very good potential. • Organic matter assessment is characterized mainly by type III gas-prone kerogen. • T max and VRo indicate immature to early mature oil window consistent with spore color analysis. [ABSTRACT FROM AUTHOR]

The upper reaches of the Yangtze River have experienced increasing anthropogenic stress. Quantitative tracing of carbon (C) sources and ecological risks through biomarkers i.e., polycyclic aromatic hydrocarbons (PAHs) and n -alkanes is significant for C neutrality and sequestration. Here, source and sink patterns, and factors influencing C burial and biomarker components in a small catchment of Dianchi Lake were explored. The sediment core covered the period 1855–2019. Before 1945, the organic C accumulation rate (OCAR) ranged from 0.71 to 5.12 mg cm−2 yr−1, and the PAHs and n -alkanes fluxes were 106.99–616.09 ng cm−2 yr−1 and 5.56–31.37 μg cm−2 yr−1. During 1945–2005, the OCAR, PAH, and n -alkane burial rapidly increased from 3.19 to 16.17 mg cm−2 yr−1, 230.40 to 2538.81 ng cm−2 yr−1, and 11.63 to 61.90 μg cm−2 yr−1. During 1855–2019, deposition fluxes of PAHs and n -alkanes increased 13.01 and 9.14 times, resulting in increased C burial, driven by environmental changes. A PMF model and the diagnostic ratio indicated that PAHs from coal combustion and traffic emission increased from 22.32% to 65.20% during 1855–2019. The PAH concentrations reflected normal–moderate contamination and potential risks to the aquatic environment. The results facilitate a comprehensive understanding of anthropogenic-driven interactions between increasing OC burial and ecological risks. [Display omitted] • OC burial was 8.6–39.3 mg cm−2 yr−1 during 1855–2019, driving biomarker components. • Deposition fluxes of PAHs and n -alkanes increased by 13 and 9 times. • The coal combustion-derived pollutants enhanced from 22.3% (1855) to 65.2% (2019). • Surface rapid change driving organic pollutants and OC burial was highlighted. [ABSTRACT FROM AUTHOR]

Certain coastal ecosystems such as mangrove, saltmarsh and seagrass habitats have been identified as significant natural carbon sinks, through the sequestration and storage of carbon in their biomass and sediments, collectively known as ‘blue carbon’ ecosystems. These ecosystems can often thrive in extreme environments where terrestrial systems otherwise survive at the limit of their existence, such as in arid and desert regions of the globe. To further our understanding of the capability of blue carbon ecosystems to sequester and store carbon in such extreme climates, we measured carbon sediment stocks in 25 sites along the Western Arabian Gulf coast. While seagrass meadows and saltmarsh habitats were widely distributed along the coast, mangrove stands were much reduced as a result of anthropogenic pressures, with 90% of stands having been lost over the last century. Carbon stocks in 1 m deep surface sediments were similar across all three blue carbon habitats, with comparable stocks for saltmarsh (81 ± 22 Mg C _org ha ^−1 ), seagrass (76 ± 20 Mg C _org ha ^−1 ) and mangroves (76 ± 23 Mg C _org ha ^−1 ). We recorded a 38% decrease in carbon stocks between mature established mangrove stands (91 Mg C _org ha ^−1 ) and recently planted mangroves (56 Mg C _org ha ^−1 ). Mangroves also had the lowest carbon stock per total area owing to their very limited spatial coverage along the coast. The largest stock per total area belonged to seagrass beds as a result of their large spatial coverage within the Gulf. We employed ^210 Pb dating to determine the sediment accretion rates in each ecosystem and found mangrove habitats to be the most efficient carbon sequesters over the past century, with the highest carbon burial rate of the three ecosystems (19 g C _org m ^−2 yr ^−1 ), followed by seagrass (9 g C _org m ^−2 yr ^−1 ) and saltmarshes (8 g C _org m ^−2 yr ^−1 ). In this work, we describe a comprehensive comparison of sediment stocks in different blue carbon ecosystems within a single marine environment and across a large geographical area, and discuss our results in a global context for other blue carbon ecosystems in the dry tropics.

Total organic carbon (TOC) in lake sediments from upstream catchments is deposited and buried in substrate, recording historical environmental changes. However, the linkage among natural variability, anthropogenic activity, and TOC burial for has not yet been clarified. This study examined the lake sediments of five 200-cm-deep dated depositional cores in west Dongting lake, China to quantify the magnitude, allocation, and amplitude of TOC burial. 44.47–59.36% of TOC burial flux was buried at 100–200 cm, suggesting lake sediments at deep layers stored considerable carbon. TOC burial rate (BR TOC) decreased along the lake entrance to its body, which was explained by the geochemical differences. Since 1900, BR TOC presented an increasing with a 4–7 times uptrend, showing three sedimentary stages with the increased human disturbance, such as deforestation, hydroelectric facilities. Moreover, the coefficient of variation of BR TOC in the third stage was lower than that in the second stage for the implementation of watershed reforestation and reservoir construction. Our findings stressed that natural variations of lake sedimentation background induced the change of TOC burial among the depositional sites, and enhanced that anthropogenic perturbation drove its chronological increases. This research unveiled the linkage between TOC burial, natural variability, and human disturbance from the perspective of burial evolutions in a lacustrine sedimentary environment. [Display omitted] • BF TOC was 14.42–23.87 kg m−2 of which the deep layer accounted for 44.47–59.36%. • TOC burial revealed a decreasing gradient from the lake entrance to its body. • BR TOC increased 4–7 times Since 1900 with a marked stage-in trend. • TOC burial underwent evolutions of two typological sites and three stages. [ABSTRACT FROM AUTHOR]