Terrestrial Organic Matter Input Research Articles

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 ± 15 ng g−1) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km3 yr−1) and organic carbon accumulation rates (9.3 ~ 49.4 g m−2 yr−1) were elevated compared to other fjords. Furthermore, the δ13C (–27 ~ –24‰) and δ34S values (–10 ~ 15‰) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more OM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems.

Effects of climate warming and nitrogen deposition on subtropical montane ponds (central China) over the last two centuries: Evidence from subfossil chironomids

Many remote montane ecosystems are experiencing biogeochemical changes driven by warming climate and atmospheric pollution. Compared with circumpolar and temperate lakes, the responses of subtropical montane lakes to these external stressors have been less investigated. Here we present sedimentary multi-proxies records (i.e. chironomids, elements and stable isotope of carbon and nitrogen) in 210Pb-dated cores from two montane ponds (central China). Before the 1900s, low biomass and the dominance of opportunistic species (e.g. Chironomus anthracinus-type) in both ponds might be in response to cold and harsh condition. Thereafter, chironomid communities in both ponds experienced pronounced shifts. Nutrient-tolerant/warm-adapted species (e.g. Chironomus sp., Polypedilum nubeculosum-type and Endochironomus impar-type) proliferated and biomass increased synchronously after the 1900s, suggestive of favorable condition for chironomid growth. Redundancy analyses revealed that changes in chironomid communities in both ponds were significantly correlated with rising temperature and δ15N depletion. Prolonged growing season and nitrogen subsidy would increase primary productivity, and hence enhancing food availability for chironomids. Catchment-mediated indirect effects of warming and nitrogen deposition, such as hydrological changes and terrestrial organic matter inputs, would impose further influences on chironomid communities. Taken together, the combined effects of climate warming and nitrogen deposition have caused significant shifts in primary consumers of these montane ponds, and imposed cascading effects on structure and function of subtropical montane aquatic ecosystems.

Neritic ecosystem response to Oceanic Anoxic Event 2 in the Cretaceous Western Interior Seaway, USA

Cretaceous oceanic anoxic events (OAEs) were periods of geologically short (<1 million years) global change characterized by elevated temperatures, changes in ocean biogeochemistry, ecological turnover, and the global-scale deposition of black shales. After decades of OAE research, the intensity and spatiotemporal heterogeneity of ocean anoxia and its direct effects on marine ecology remain areas of active study. We present high-resolution organic geochemical and foraminiferal records from the western margin of the Western Interior Seaway (WIS) during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2, ~94 Ma) that indicate reorganization of a neritic ecosystem in response to sea-level rise, and dynamic changes in redox conditions that were likely driven by enhanced marine productivity. A significant transgression prior to OAE2 decreased terrestrial organic matter input and led to enhanced productivity, anoxic bottom waters and sediments, and episodic photic zone euxinia. During the middle of OAE2, further enhanced productivity led to the “Heterohelix shift” in planktic foraminifera, the “Gavelinella acme” in benthic foraminifera, and deoxygenation in sediments, bottom waters, and the upper water column. The combined use of high-temporal resolution algal, bacterial, and terrestrial biomarkers, in addition to foraminiferal records, demonstrates the sensitivity of marine autotrophic and heterotrophic communities to sea-level rise and variable water column oxygenation in marginal marine settings during hyperthermal events. Furthermore, our results reveal the temporal and spatial heterogeneity of anoxia during OAE2 in the WIS. This study highlights widespread shallow marine feedbacks during global change that may affect neritic ecosystems under future warming scenarios.

Depositional history of low-mature coals from the Puyang Basin, Yunnan Province, China

Late Miocene samples from the Xiaolongtan Formation in Puyang Basin were sampled systematically from bottom to top of the main coal seam. Organic petrological as well as geochemical methods have been applied, aiming at the reconstruction of the depositional environment. The studied samples contain abundant detrovitrinite and liptinite macerals with high ash but low to moderate sulfur contents. This data indicates that the samples were deposited in topogenic mires without marine influence, but with fluctuations of water table and/or water influx which are mirrored by ash and sulfur content. The low values of tissue preservation and vegetation index, but high values of gelification index and groundwater index (GWIAC) in the studied coal imply a peat accumulation in inundated marshes under slightly oxic to anoxic depositional conditions with input of herbaceous plants mainly. An extended data set on vitrinite reflectance, volatile matter, Rock-Eval Tmax and HI suggests a coalification ranging from subbituminous C to B coal.The high concentration of long chain n-alkanes in the studied samples is typical for kerogen derived predominately from higher terrestrial plants. The applied biomarker ratios together with the detected hopenes further confirm the low thermal maturity level, as well as high water table and terrestrial organic matter input during peat accumulation. The variable concentrations of terpenoids and sesquiterpenoids suggest a dominant angiosperm input, but with a relatively high proportion of gymnosperms during some periods of peat deposition.

Terrestrial organic matter input drives sedimentary trace metal sequestration in a human-impacted boreal estuary

Coastal sediments play a fundamental role in processing anthropogenic trace metal inputs. Previous studies have shown that terrestrial organic matter (OM) is a significant vector for trace metal transport across the land-to-sea continuum, but little is known about the fate of land-derived metal-OM complexes in coastal sediments. Here, we use a comprehensive set of sediment pore water and solid-phase analyses to investigate how variations in terrestrial OM delivery since the 1950s have influenced trace metal accumulation and diagenesis in a human-impacted boreal estuary in the northern Baltic Sea. A key feature of our dataset is a strong correlation between terrestrial OM deposition and accumulation of metal-OM complexes in the sediments. Based on this strong coupling, we infer that the riverine input of terrestrial metal-OM complexes from the hinterland, followed by flocculation-induced settling in the estuary, effectively modulates sedimentary trace metal sequestration. While part of the trace metal pool associated with these complexes is efficiently recycled in the surface sediments during diagenesis, a substantial fraction is permanently buried as refractory metal-OM complexes or through incorporation into insoluble sulfides, thereby escaping further biological processing. These findings suggest that terrestrial OM input could play a more pivotal role in trace metal processing in coastal environments than hitherto acknowledged.

Quantitative landscape reconstruction and erosion history during the past 1,100\xa0years in the Skogaryd Research Catchment, southern Sweden

A sediment sequence from a small forest lake in southwestern Sweden was investigated to explore the effects of forestry and land-use on catchment erosion and delivery of organic and minerogenic matter to the lake. Catchment-scale vegetation changes during the last 1,100 years were reconstructed quantitatively at 50-year resolution using pollen analysis and the Landscape reconstruction algorithm (LRA). Variations in terrestrial organic matter input to lake sediments were assessed by total organic carbon (TOC) content and carbon to nitrogen (C/N) ratios. Changes in minerogenic matter were analysed using X-ray fluorescence (XRF) scanning. The results show that Skogaryd was not intensively used for agriculture throughout the past 1,100 years, but its land-use changes were very sensitive to societal changes. Between ca. ad 950 and 1350, local land-use was characterized by small-scale agricultural activities associated with the Medieval expansion, and enhanced soil erosion was recorded by increased K, Ti and Rb deposition. Around ad 1350 much of the farmland was abandoned, most likely in response to outbreaks of plague. The abandonment of farmland caused increased coniferous woodland cover and lower soil erosion. From the 16th century land-use expanded and gradually intensified, concurrent with a population increase documented in the study area between ca. ad 1600 and 1850. Intensive exploitation of the forest led to soil erosion and increased terrestrial organic and minerogenic matter export to the lake. These processes peaked with the artificial drainage of a nearby wetland for agricultural purposes. During the 20th century, modern forestry management started with the plantation of conifers, and soil erosion declined.

Total organic carbon and pyrolysis analysis of the Lower Cretaceous in Compton Bay and Atherfield, Isle of Wight (England)

The Wessex Basin (United Kingdom) includes hundreds of meters of Lower Cretaceous clays, silts, and sands deposited in a wide range of depositional environments. Studies have investigated these depositional systems from the organic matter (OM) perspective. However, questions remain concerning the composition, source, and the overall depositional constraints on the distribution of sedimentary OM in this area. Elemental (carbonate % and total organic carbon - TOC) and pyrolysis analyses were conducted on representative lithofacies of the Lower Cretaceous from the Wessex Basin at the Compton Bay and Atherfield sections, Isle of Wight. The highest TOC contents were determined in the upper part of the Ferruginous Sands and Sandrock formations. These elevated TOC intervals are associated with predominantly estuarine deposition. Except for one sample from the Vectis Formation, Hydrogen Index (HI) in all studied units is low and indicates Type IV kerogen assemblages, interpreted to be linked with strongly variable climates (with pronounced dry periods) and significant water table fluctuations in the source area and during transport. The one sample with a Type II-III kerogen assemblage from the lagoonal Vectis Formation supports previous studies which suggested that OM in the Vectis Formation varied vertically as a function of fluvial sediment and terrestrial organic matter input to the lagoonal environment with changes in salinity, sediment resuspension, and turbulence as a result controlling the abundance of dinoflagellate cysts.

Climatic and human impact on the environment: Insight from the tetraether lipid temperature reconstruction in the Beibu Gulf, China

Organic proxies have been widely used to reconstruct temperature and terrestrial input variation at the interface between land and sea. However, the impact of human activities on these proxies has been little constrained, which might cause the misinterpretation of the sediment profile. In order to study the climatic and human impact on the environment, proxies in coastal regions, glycerol dialkyl glycerol tetraethers (GDGTs) in a sediment core spanning 115 years was analyzed from Beibu Gulf, China. The results indicate that isoprenoid GDGTs in the Beibu Gulf were mainly derived from Thaumarchaeota and the branched GDGTs originated mainly from terrestrial soil bacteria. The TEX86 index was applied to reconstruct the temporal SST variation. The results show that variation of TEX86-derived SST is controlled mainly by East Asian Monsoon system and partly by ENSO events. The methylation index of branched tetraethers or the cyclization index of branched tetraethers (MBT/CBT) derived mean annual air temperature (MAAT) agreed with MAAT record at the Qinzhou Station before 1982 AD. However, the population growth and economic development after 1982 AD caused the reduction of terrestrial organic matter input and increase of nutrient, leading to the thriving of Thaumarchaeota and increasing of in situ branched GDGTs proportion, which created the scatter of the MBT/CBT-reconstructed MAAT after 1982 AD. Therefore, human influence on GDGT proxies can be constrained in this way to avoid misinterpretation of paleoclimate and paleoenvironment records.

Lacustrine environmental evolution and implications on source rock deposition in the Upper Cretaceous-Paleocene of the South Yellow Sea Basin, offshore eastern China

Lacustrine source rocks are well developed within the Upper Cretaceous-Paleocene in the South Yellow Sea Basin (SYSB) in offshore eastern China. Understanding the deposition of these source rocks could provide critical information for hydrocarbon exploration in the SYSB, as well as reveal the paleoenvironment across the Cretaceous/Paleogene boundary in eastern China. This study investigates the lacustrine environmental evolution during the Upper Cretaceous Taizhou Formation (K2t) to Paleocene Funing Formation (E1f) within the SYSB and its implications on source rock deposition based on core observation combined with organic geochemical indicators. Multiple maturity parameters (vitrinite reflectance, Tmax and biomarker isomerization ratios) reveal that the organic matter (OM) has reached early oil window maturity. The OM of source rocks is dominated by kerogen Type II-III (liptinite and vitrinite). Anoxic, saline-brackish deep to semi-deep lacustrine environments prevailed during the deposition of K2t2 (second member of the K2t), E1f2 (second member of the E1f) and E1f4L (lower unit of fourth member of the E1f). The deposition of three intervals was influenced by marine incursion, as evidenced by geochemical and paleontological results. Low to moderate TOC contents (avg. 0.78 wt% to 1.91 wt%), which corresponds to low to moderate terrestrial OM input, are observed through three intervals. Abundant freshwater, together with high terrestrial OM flowed into the lacustrine environments during the deposition of E1f4U (upper unit of fourth member of the E1f), leading to dysoxic-oxic and freshwater conditions. High terrestrial OM input is probably the major controlling factor for relatively high TOC contents (avg. 2.49%) in the E1f4U. An evolution from balanced-fill to overfilled lake-type is observed in the Upper Cretaceous-Paleocene of SYSB, consistent with an evolution from semi-arid to humid paleoclimate conditions. The E1f4U and E1f2 source rocks exhibit fair to good potential, whereas poor to fair potential is present in the E1f4L and K2t2 source rocks. Compared with the Paleogene source rocks in onshore eastern China, the Upper Cretaceous-Paleocene source rocks in the SYSB probably hold good potential for generating commercial quantity of oil, although further study on hydrocarbon generation kinetics of source rocks and overall basin history are needed.

Distribution and sources of organic carbon, nitrogen and their isotopic composition in surface sediments from the southern Yellow Sea, China

The southern Yellow Sea (SYS) is a significant repository of sedimentary organic matter (SOM) and has been impacted by green tides since 2007; however, data on the distribution and quantitative contributions of different SOM sources has been scarce. TOC, TN and their δ13C and δ15N values were determined in 38 surface sediments. TOC and TN were high in central mud area and low in sand area. TOC was positively correlated with the abundance of fine-grained sediments, indicating that controlling factors of SOM were the sediment types and circulation system. The SOM included marine and terrestrial organic matter and anthropogenic nutrient inputs according to TOC/TN (5.8–14.3), δ13C (−25.1‰ to −21.0‰) and δ15N (2.6‰–6.4‰). High terrestrial contributions in northern and western parts of SYS, were influenced by terrestrial materials and eroded substances of the abandoned Yellow River delta, respectively. In the central mud area of SYS, marine organic matter was dominant.

Multi-proxy approach on the hydrocarbon generation perspective of Barjora Basin, India

Abstract Barjora Basin in India is a small basin characterized by a high organic richness of early mature nature. The present study aims to find the source of organic matter (OM) and hydrocarbon generation potential of Barjora Basin. Systematically collected coal and shale samples from R-II seam of the basin were used for proximate and ultimate analyses, Rock Eval pyrolysis along with total organic carbon (TOC) content, organo-micropetrographic framework, thermal maturity, carbon isotopic signature, biomarker composition, functional group studies and estimation of relative aliphaticity and aromaticity through Fourier Transform infrared spectroscopy (FTIR). The novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon (δ13C), biomarker signatures, thermal maturity parameters, organo-micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin. A dominant terrestrial OM input in Barjora Basin is indicated by the TOC to total nitrogen ratio (C/N), δ13C and biomarker compositions. High gelification index (GI), tissue preservation index (TPI), and carbon preference index (CPI) values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity. In addition, large liptinite content, TPI and GI designate short transportation of the OM before burial leading to organic richness of the Barjora Basin. Moreover, high liptinite content, type II-III admixed kerogen input, S2/S3 ratio, TPI and index for hydrocarbon generation (IHG) signify higher potential of the basin for hydrocarbon generation.

Distribution patterns of bacterial communities and their potential link to variable viral lysis in temperate freshwater reservoirs

Man-made reservoirs which receive substantial inputs of terrestrial organic matter are characterized by physiologically diverse and distinct bacterial communities. Here we examined bacterial community structure using Illumina MiSeq sequencing of 16S rRNA genes and evaluated the potential role of viruses in influencing them in two productive freshwater reservoirs namely, Villerest and Grangent (Central France). Two dimensional non-metric multidimensional scaling analyses indicated that bacterial communities in both reservoirs were structurally different in time and space, with Villerest harboring more diverse communities than Grangent reservoir. The bacterial communities in both reservoirs were dominated by hgcI clade (Actinobacteria) and Limnohabitans (Betaproteobacteria) which are known to have adaptive life strategies towards top-down mechanisms and resource utilization. In Villerest, thermal stratification of water column which resulted in temporary anoxia especially during summer promoted the occurrence of anoxygenic phototrophic and methanotrophic bacteria. Overall, low bacterial richness which was linked to viral lytic infection possibly suggests that a relatively small number of highly active bacterial populations sustained high bacterial activity and viral abundances. Weighted UniFrac analysis indicated that a minimum threshold viral infection and virus-to-bacteria ratio (serve as a proxy) of 10% and 10, respectively, is required to exert its impact on phylogenetic structure of bacterial community. Therefore depending on the levels of viral infection we suggest that viruses at times can prevail over other trophic or top-down factors in shaping and structuring bacterial communities in such man-made artificial freshwater systems.

Impact of hydrothermal activity on organic matter quantity and quality during deposition in the Permian Dalong Formation, Southern China

Abstract The very high temperature at the center of a hydrothermal system is detrimental for the deposition of organic-rich sediments. However, it's not known how the petroleum source rock develops at the boundary of a hydrothermal system where the seawater temperature was only slightly elevated. The petroleum generation potential, using pyrolysis-GC, GC-MS and FT-ICR MS techniques, of eight organic-rich Permian shale samples from Shangsi Section China were systematically investigated. Principal component analysis reveals that the quantity and quality of the organic matter in the shale is dominated by biomass productivity, the redox condition, and terrestrial organic matter input. Rare earth element distribution pattern reveals that the two samples with highest TOC contents show a slight Eu anomaly which indicates the sample was influenced by a hydrothermal system to some degree. A depositional model showing how the influences from hydrothermal event promote the development of petroleum source rock is summarized: (1) At the edge of a hydrothermal system, the seawater-temperature can be elevated by 5–10 °C which further promotes the development of phytoplankton and zooplankton. (2) An upwelling can be intrigued and chemical weathering will be accelerated which both introduce excessive nutrients and increase the biota productivity. (3) Flux with the terrestrial advanced plant can also be accelerated to the shelf area by the volcano-induced climate change. (4) The consumption of the extensive biomass induced by the hydrothermal activity would expand the oxygen minimum zone, and further enable more organic matter to be preserved in shale.

Reconstructing organic matter sources and rain rates in the southern West Pacific Warm Pool during the transition from the deglaciation period to early Holocene

Transient features in the organic carbon content of deep-sea sediment cores resulting from changes in the flux and/or quality of sedimentary organic matter are not uncommon. We examined the geochemical characteristics of sediments retrieved with a gravity corer from the northwestern Solomon Sea (3908 m water depth), southern West Pacific Warm Pool (WPWP). δ13C and δ15N of sedimentary organic matter, together with TOC/TN data suggest that the organic material is characterized by a mixture of marine and terrestrial origins with a higher contribution from marine algae. The data were analyzed with an inverse non-steady-state reaction-transport model to examine the variability and magnitude of particulate organic carbon (POC) flux to the seafloor during the transition between the deglaciation period and early Holocene. Measured POC content and porewater NO3−, NH4+, DIC and SO42− concentrations were used to constrain the model. Hindcast results revealed that POC flux decreased from 75 to 37.5 μg cm−2 yr−1 during the deglaciation–early Holocene transition. The rate of POC degradation in the present setting is slightly lower compared to that in the pre-Holocene setting. The synchronous decline in the relative contribution of terrestrial organic matter input and rapid sea level rise during this transition suggest that sea level, rather than surface productivity, is the dominant factor controlling the POC deposition flux in the Solomon Sea. This is conceivable because the sampling site is proximal to high-relief islands with high rainfall, a well-developed submarine canyon system and narrow and steep continental margins. Consequently, we suggest that deep-water basins in proximity to similar high-relief mountainous islands in the tropical Pacific may represent important sinks for terrestrial organic material, especially during sea level lowstands.

Spatiotemporal variation of organic geochemical properties since the mid-Miocene in the deep South China Sea (IODP Expedition 349)

We performed an extensive survey of total organic carbon (OC) and stable OC composition of in the deep South China Sea sediments from the International Ocean Discovery Program (IODP) Expedition 349 Sites U1431, U1433 and Ocean Drilling Program (ODP) Leg 184 Site 1148. Our results reveal dramatic spatial and temporal variations in organic geochemical characteristics among the three Sites. Before ~8 Ma, OC deposited at Site U1431 may be predominantly terrigenous, whereas OC deposited at Sites U1433 and 1148 is mainly of marine origin. After ~8 Ma, OC accumulation at the three Sites progressively increases, mainly due to enhancement of marine primary productivity and input of terrestrial organic matter; the three sites receive mainly marine OC, whereas Sites U1433 and 1148 receive relatively more terrestrial OC compared with Site 1431. Additionally, methane concentrations vary from ~20 to ~100,000 ppmv at Site U1433 and from ~10 to ~600 ppmv at Site 1148 with higher geothermal gradients (78 and 84 °C/km, respectively). In contrast, methane concentrations are <5 ppmv at Site U1431 with lower geothermal gradient (14.8 °C/km). Such high methane concentrations and ratios of methane to ethane at Site U1433 suggest that the gaseous hydrocarbons in the southwestern sub-basin (deep water depth, >4000 km) are primarily sourced from microbial production. Our findings suggest that the sources, trajectories, and fates of OC buried in the deep South China Sea since the mid-Miocene are spatially and temporally variable, controlled by sedimentological processes in the sub-basins, and regional tectonic evolution and long-term paleoenvironmental changes.

Multi-Substrate Radiocarbon Data Constrain Detrital and Reservoir Effects in Holocene Sediments of the Great Salt Lake, Utah

ABSTRACTThe radiocarbon (14C) content of simultaneously deposited substrates in lacustrine archives may differ due to reservoir and detrital effects, complicating the development of age models and interpretation of proxy records. Multi-substrate14C studies quantifying these effects remain rare, however, particularly for large, terminal lake systems, which are excellent recorders of regional hydroclimate change. We report14C ages of carbonates, brine shrimp cysts, algal mat biomass, total organic carbon (TOC), terrestrial macrofossils, andn-alkane biomarkers from Holocene sediments of the Great Salt Lake (GSL), Utah.14C ages for co-deposited aquatic organic substrates are generally consistent, with small offsets that may reflect variable terrestrial organic matter inputs to the system. Carbonates and long-chainn-alkanes derived from vascular plants, however, are ∼1000–400014C years older than other substrates, reflecting deposition of pre-aged detrital materials. All lacustrine substrates are14C-depleted compared to terrestrial macrofossils, suggesting that the reservoir age of the GSL was &gt; 1200 years throughout most of the Holocene, far greater than the modern reservoir age of the lake (∼300 years). These results suggest good potential for multi-substrate paleoenvironmental reconstruction from Holocene GSL sediments but point to limitations including reservoir-induced uncertainty in14C chronologies and attenuation and time-shifting of some proxy signals due to detrital effects.

Potential terrestrial influence on transparent exopolymer particle concentrations in boreal freshwaters

AbstractTransparent exopolymer particles (TEP) are ubiquitous in aquatic ecosystems and contribute, for example, to sedimentation of organic matter in oceans and freshwaters. Earlier studies indicate that the formation of TEP is related to the in situ activity of phytoplankton or bacteria. However, terrestrial sources of TEP and TEP precursors are usually not considered. We investigated TEP concentration and its driving factors in boreal freshwaters, hypothesizing that TEP and TEP precursors can enter freshwaters via terrestrial inputs. In a field survey, we measured TEP concentrations and other environmental factors across 30 aquatic ecosystems in Sweden. In a mesocosm experiment, we further investigated TEP dynamics over time after manipulating terrestrial organic matter input and light conditions. The TEP concentrations in boreal freshwaters ranged from 83 to 4940 μg Gum Xanthan equivalent L−1, which is comparable to other studies in freshwaters. The carbon fraction in TEP in the sampled boreal freshwaters is much higher than the phytoplanktonic carbon, in contrast to previous studies in northern temperate and Mediterranean regions. Boreal TEP concentrations were mostly related to particulate organic carbon, dissolved organic carbon, and optical indices of terrestrial influence but less influenced by bacterial abundance, bacterial production, and chlorophyll a. Hence, our results do not support a major role of the phytoplankton community or aquatic bacteria on TEP concentrations and dynamics. This suggests a strong external control of TEP concentrations in boreal freshwaters, which can in turn affect particle dynamics and sedimentation in the recipient aquatic ecosystem.

Sources and burial fluxes of sedimentary organic carbon in the northern Bering Sea and the northern Chukchi Sea in response to global warming

The Arctic and subarctic seas are the major CO2 sink areas on earth. In this study, the vertical variation characteristics of organic carbon, total nitrogen and their ratio (Corg/Nt), stable isotopes δ13C and δ15N, and BIT (branched and isoprenoid tetraether) index of GDGTs (glycerol dialkyl glycerol tetraethers) in combination with 210Pb-dating were used to analyze the changes in the marine and terrestrial sources of organic carbon in the northern Bering Sea (site 1), western Beaufort Sea slope (site 2) and northern Chukchi Sea (site 3). Organic carbon burial fluxes (OCBF) in the context of global warming were also explored at sites 1 and 3. The results showed that organic matter in these sediments were a mixed input of marine and terrestrial sources, and the BIT index and δ13C of site 2 suggested that the terrestrial soil organic matter was dominant. Based on a combination of 210Pb dating and Corg, the sedimentary OCBF at site 1 was 2.29–3.65 mg cm−2 y−1, and at site 3 was 0.00–0.41 mg cm−2 y−1. The temperature anomalies and sea ice changes in the Arctic in the past 100 years were compared with the burial fluxes of the terrestrial organic carbon. At site 1, the results indicated that fast melting of seasonal sea ice led to earlier arrival of ice algae bloom, enhanced zooplankton feeding and reduced carbon burial from 1947 to 2010, and the sudden increase in carbon burial after 2010 was attributed to an increase in primary productivity and terrestrial organic matter input due to an accelerated melting of sea ice. There was a smaller change in marine organic carbon content in site 3, but OCBF increased after a pre-1965 decrease, mainly controlled by terrestrial organic matter input associated with temperature rising and sea ice melting during recent decades.

Geochemistry and possible origin of crude oils from Bashituo oil field, Tarim Basin

The entire range of hydrocarbons in Bashituo oils from Devonian and Carboniferous reservoirs were investigated to determine their origin, as well as their alteration, mixing, and maturity using gas chromatography, gas chromatography–mass spectrometry, and stable carbon isotope analysis. These geochemical studies indicate that the crude oils in the Devonian and Carboniferous reservoirs share similar C15+ molecular marker compositions of marine organic matter origin, whereas their light hydrocarbon compositions show distinct differences. The Carboniferous-reservoired oils are characterized by a relatively greater abundance of cycloalkanes and methylcyclohexane, which indicate a terrestrial organic matter (OM) contribution. Based on biomarker and carbon isotope analysis, Cambrian–Ordovician (J-O) marine rocks are assumed to be the main source for both the Devonian- and Carboniferous-reservoired oils, whereas Carboniferous rocks with terrestrial OM input also contributed to the Carboniferous-reservoired oils. The coexistence of 25-norhopanes, evident humps from unresolved complex mixture, and intact n-alkanes in Devonian-reservoired oils indicate a mixture of early-charged biodegraded oils with late fresh oils, corresponding to at least two oil-generation episodes by the J-O rocks. Light hydrocarbon indicators suggest a relatively high maturity beyond peak oil generation for the J-O–sourced late fresh oil, whereas C15+ molecular marker parameters indicate a maturity equivalent to early peak oil generation for the J-O–sourced, early-charged biodegraded oil. The maturity of the Carboniferous-sourced oil is equivalent to peak oil generation. The application of the entire range of hydrocarbons is essential when assessing a mixed or altered oil system because light hydrocarbons and biomarkers may yield different source-oil–correlations and maturities.

Antecedent precipitation influences the bacterial processing of terrestrial dissolved organic matter in a North Carolina estuary

Estuaries and coastal waters ultimately receive the terrestrial dissolved organic matter (DOM) exported from coastal watersheds, more directly during extreme precipitation events. Recent work suggests DOM's degradation in coastal waters varies with its quality, which also might vary as a function of precipitation, activating contributions from different sources within a watershed. The aim of this study was to determine the extent to which microbial degradation of terrestrial DOM in the Newport River Estuary, eastern North Carolina, was influenced by precipitation events occurring within the preceding seven days from sampling. We hypothesized that DOM stored in forested wetlands (e.g., pocosins and Cypress swamps) that become connected to the main channel of the Newport River during high precipitation events was more labile than DOM flowing into the estuary under low precipitation events. DOM quality was assessed with optical and stable C isotope (δ13C) measurements, while DOM lability was assessed by measurements of bacterial production (BP) and mineralization of 14C-labeled phenanthrene (Pmin), a polyaromatic tracer compound. Aromatic content of DOM, assessed by specific ultraviolet absorbance at 254 nm (SUVA254) was highest in the river with values well over 5.0 L mg C−1 m−1, and decreased with salinity. Antecedent precipitation (AP) of at least 100 mm in the seven days prior to sampling resulted in dissolved organic carbon (DOC) concentrations >20 mg L−1, at salinities <10. Similarly, fluorescence humification index (HIX) values were highest in the estuary after the highest AP. Generally depleted δ13C-DOC values (−26 to −28‰) in the estuary up to a salinity of 30 indicated a substantial source of DOM likely originating from the forested swamps and tidal wetlands fringing the estuary. BP exhibited wide variability yet declined with salinity, while median values after higher AP (40 μg C L−1 d−1) were double that under lower AP. By contrast, aromatic mineralization (Pmin) rates increased as both DOC and CDOM concentrations, and SUVA254 and HIX values, declined with salinity. However, Pmin rates were highest after the highest AP for the three events sampled. Results indicate that flooding of coastal wetlands mobilizes a large pool of labile DOM which have a large impact on the carbon cycle in estuaries. By altering the quality, as well as quantity of terrestrial organic matter inputs to estuarine systems, extreme events may also affect utilization of aromatic organics by estuarine microbial assemblages, an intriguing research question worthy of further study.