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Global biogeochemical cycles of carbon and sulfur and atmospheric O2 over phanerozoic time
... However, this gigantic carbon reservoir might be much more dynamic than commonly realized. Considering that only a tiny fraction (0.1%) of the 15 × 10 21 g of organic carbon are cycling in active surface pools (Berner, 1989; Hedges and Keil, 1995), small variations in the interaction with the deep carbon reservoir will have a considerable impact on surface processes. Evidence of the connection between deep reservoirs of organic carbon and the surface by the transfer of methane and other hydrocarbon gasses is found all around the world in the form of gas seeps, mounds, pockmarks and mud volcanoes (e.g. ...
... The subsurface cycle involves organic matter burial and remobilization as petroleum, including methane, the most abundant subsurface gas; while in the surficial cycle, carbon moves predominantly as CO 2 . The representation of the size of carbon reservoirs at the surface and in the subsurface in Gt C and their typical δ 13 C in ‰ is after Olson et al. (1985), Berner (1989 , and Ridgwell and Edwards (2007). extrapolation from local flask measurement, space-borne nearinfrared absorption spectroscopy and methane carbon and hydrogen isotope analysis (Mikaloff-Fletcher et al., 2004; Frankenberg et al., 2005; Chen and Prinn, 2006; Lassey et al., 2007). ...
... Type III source rocks commonly have relatively low hydrogen indices and are more gas than oil prone of the three main kerogen types, type III organic material is also the least prone to be destroyed during transport and redeposition, whereas type I and II kerogens consist of quasi-autochthonous material susceptible to destruction during transport (Suess, 1980; Littke et al., 1997). Deltas, where terrestrial organic material is prevalent, are therefore a principal site of modern organic matter deposition (Berner, 1989; Hedges and Keil, 1995; Littke et al., 1997). The availability of nutrients is a limiting factor on primary marine production and therefore also on the amount of organic matter buried. ...
The mass of organic carbon in sedimentary basins amounts to a staggering 10¹⁶ t, dwarfing the mass contained in coal, oil, gas and all living systems by ten thousand-fold. The evolution of this giant mass during subsidence and uplift, via chemical, physical and biological processes, not only controls fossil energy resource occurrence worldwide, but also has the capacity for driving global climate: only a tiny change in the degree of leakage, particularly if focused through the hydrate cycle, can result in globally significant greenhouse gas emissions.
... WSBW would also be more likely to become anoxic due to the inverse relationship between O 2 solubility and water temperature and salinity, together with the anti-estuarine circulation that was likely present within WSBW source areas [12,32,39]. The development and perpetuation of anoxic conditions in the global ocean during the Early Triassic may have also been made more likely as the amount of O 2 in the atmosphere was significantly lower in the Early Triassic than the Permian (see below) [4,5,7,25,71]. Reduced atmospheric O 2 levels would have resulted in Early Triassic surface waters containing as little as twothirds as much O 2 as Permian waters [32], allowing widespread anoxia to develop more readily. ...
... Strong seasonality characterized the supercontinent [55], which was likely quite dry [16,56]. Increased levels of CO 2 in the atmosphere [4,5,7,25,71] led to global warming, resulting in an expansion of arid climates into high latitudes in the Northern Hemisphere [3,18,39,53,81,92], and the shift of deciduous forests to Southern Hemisphere polar regions [76,77]. ...
... Modeling studies suggest that atmospheric O 2 levels decreased during the Early Triassic while atmospheric CO 2 levels increased [4,5,7,25,71]. O 2 levels dropped steadily during the Triassic after reaching maximum values (up to 35% of atmospheric volume) around the Permian-Carboniferous boundary, and bottomed out near 10% of atmospheric volume close to the Triassic-Jurassic boundary [7]. ...
The Early Triassic interval is dominated by unusual oceanic and climatic conditions that are perhaps unique to the Phanerozoic. Early Triassic oceans were likely anoxic and possibly alkaline while climate during the period was dominated by the expansion of deserts and the migration of warm, moist conditions to high Southern Hemisphere latitudes. Atmospheric O2 levels apparently decreased during the period while CO2 levels increased. The unusual and severe nature of many aspects of Early Triassic oceans and climate likely played a role in determining the timing and shape of the biotic recovery from the Permian–Triassic mass extinction. To cite this article: A.D. Woods, C. R. Palevol 4 (2005).
... This storage varies in both spatial distribution of OC concentration (Battin et al., 2008;Scott & Wohl, 2018b;Sutfin et al., 2016;Wohl, Hall, et al., 2017) and residence time (Barnes et al., 2018;Marwick et al., 2015;Omengo et al., 2016). Carbon dynamics in these systems over short to moderate timescales (10 1 to 10 5 yr) can thus strongly regulate carbon emissions to and sequestration from the atmosphere (Berner, 1990;Stallard, 1998), regulating global climate. Climate change can in turn feedback on terrestrial systems that exhibit relatively rapid OC cycling, as climate influences terrestrial OC cycling (Trumbore et al., 1996). ...
... The century-scale age of much of the floodplain soil OC measured in these basins implies a close coupling between soil retention and the distribution of OC across the landscape and between the land and atmosphere. The alteration of valley bottom morphology and soil retention likely influences the fate of OC sequestered in high primary productivity (Schimel & Braswell, 2005) mountain ranges over short (Wohl, Hall, et al., 2017; and long (Berner, 1990;Molnar & England, 1990) timescales. Changes in soil retention likely alter how much OC reaches downstream water bodies that may sequester OC over longer timescales, thus altering the respiration of that OC to the atmosphere. ...
Organic carbon (OC) in valley bottom downed wood and soil that cycles over short to moderate timescales (101 to 105 yr) represents a large, dynamic, and poorly quantified pool of carbon whose distribution and residence time affects global climate. We sought to quantify this potentially important OC pool at the watershed scale to estimate its magnitude and age, as well as determine the controls on its variability within watersheds. To do this, we compared four disparate mountain river basins to show that mountain river valley bottoms store substantial estimated OC stocks in floodplain soil and downed wood (median OC of MgC/ha, n = 178). Although soil OC is generally young (exhibiting a median radiocarbon fraction modern value of , n = 121), geomorphic processes regulate soil burial and processes that limit microbial respiration, preserving aged OC in especially deep, unconfined, wet, and/or high‐elevation floodplain soils. We statistically modeled OC stocks to show that valley bottom morphology and hydrology regulate variability in floodplain soil retention and resulting variability in OC stock and age in floodplain soil throughout river networks. Comparing the distribution of OC stocks between wood and soil, we find that where floodplain soils are present, their OC stocks are generally greater than OC stocks stored in wood. Our results suggest that although mountain rivers may accumulate large OC stocks relatively rapidly, those stocks are highly sensitive to alterations in soil and wood retention, implying that human alterations to either disturb or restore floodplain wood and soil storage may have substantial impacts on OC storage in river corridors.
... atmospheric pO 2 models Variation in atmospheric pO 2 during the Phanerozoic has been modeled on the basis of sediment mass and elemental fluxes (Kump, 1988; Berner and Canfield, 1989; Van Cappellen and Ingall, 1996; Colman et al., 1997), isotope mass balances (Veizer et al., 1980; Garrels and Lerman, 1984; Kump and Garrels, 1986; Berner, 1987 Berner, , 1989 Berner and Canfield, 1989; Lasaga, 1989; Kump, 1990; Petsch and Berner, 1998; Berner, 1999; Berner et al., 2000), and, most recently, integrated global geochemical redox systems ( " COPSE, " Bergman et al., 2004; " GEOCARBSULF, " Berner, in press). The most widely cited models, the " Berner curves, " exhibit Phanerozoic atmospheric O 2 variation within the range of ∼15 to 35% (Berner and Canfield, 1989; Berner et al., 2000), or ∼12 to 30% in the most recent version (Fig. 5; Berner, in press). ...
... The atmospheric pO 2 model based on the sedimentary C org :P record of this study is broadly consonant with both the Berner and the Bergman–Lenton–Watson (subsequently " BLW2004 " ) curves. General similarities include: (1) sub-Recent O 2 levels during the Early to Middle Paleozoic; (2) a steep rise and subsequent decline in pO 2 during the Late Paleozoic (due to increased rates of burial of organic C in contemporaneous coal swamps; Berner and Raiswell, 1983; Berner, 1987 Berner, , 1989); and (3) near-modern and less variant O 2 levels during the Mesozoic–Cenozoic (Fig. 5). In detail, however, the atmospheric pO 2 model of this study differs from these earlier models in some important respects. ...
... Accumulation and subsequent burial of terrestrial organic carbon in marine sediments is a key mechanism in removing atmospheric CO 2 (Hilton et al., 2008; Stallard, 1998) and moderating global climate on geological time scales (Burdige, 2005; Galy et al., 2007; Schlünz and Schneider, 2000 ). Global burial of terrestrial organic carbon in marine sediments is estimated to be 43– 104 Â 10 12 g C with a great majority, over 80%, deposited in the large-river deltas and the broad shelf systems having highsuspended loads (Berner, 1989; Burdige, 2005; Hedges and Keil, 1995). Nevertheless, recent studies indicated that a significant fraction (up to 35% of the global budget) of terrestrial organic carbon entering the ocean could come from small mountainous rivers of the western Pacific region (Lyons et al., 2002; Schlünz and Schneider, 2000). ...
... Leithold et al. (2005) showed that the continental shelf off the Eel River hold a merely 13%. Delta and shelf have been recognized as the predominant and efficient reservoirs for organic materials originated from large rivers (Berner, 1989; Gershanovich et al., 1974; Hedges and Keil, 1995 ). Our result demonstrated that most sediment and terrigenous organic carbon did not buried efficiently in the shelf and slope region but were transported to the deep sea. ...
... Lake Nakaumi is likely to be rich in planktic organics: the water depth is shallow; the lake is easily stratified and bottom water is seasonally anoxic; and both primary productivity and sedimentation rates are high (1–2 mm year -1 ; Nakano-umi and Shinji-ko Research Group et al. 1987; Shinji-ko Research Group et al. 1986; Sampei et al. 1997a). In most settings, organic burial rate and the degree of preservation of organic matter are positively correlated with total sedimentation rate (Berner 1989). Therefore, the planktic organic matter in Lake Nakaumi may be less oxidized and have spent less time in the water column or at the sediment surface (as freshly-deposited organic matter) in comparison with the marine depositional environment (Sampei et al. 1997c). ...
... H 2 S is only detected in regions above 1.2 % sediment TS content. This suggests that the basic driving force behind iron sulfide-S formation (TS) is the amount of reactive organic matter in combination with H 2 S in the pore water (Berner 1989). This has also been documented by Lin and Morse (1991), who showed a relationship between organic carbon and sulfate reduction/ion sulfide mineral formation in anoxic sediments of the Gulf of Mexico. ...
The relationship among H2S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H2S concentrations and TOC content at the sediment water interface in a coastal brackish lake, Nakaumi, southwest Japan. In this lake, bottom water becomes anoxic during summer due to a strong halocline. Lake water has ample dissolved SO4
2− and the surface sediments are rich in planktic organic matter (C/N 7–9), which is highly reactive in terms of sulfate reduction. In this setting the amount of TOC should be a critical factor regulating the activity of sulfate reduction and H2S production. In portions of the lake where sediment TOC content is less than 3.5 %, H2S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H2S was correlated with TOC content (pore water H2S (ppm) = 13.9 × TOC (%) − 52.1, correlation coefficient: 0.72). H2S was also present in areas with sediment TS above 1.2 % (present as iron sulfide), which suggests that iron sulfide formation is tied to the amount of TOC. Based on this relationship, H2S production has progressively increased after the initiation of land reclamation projects in Lake Nakaumi, as the area of sapropel sediments has significantly increased. This TOC–H2S relationship at sediment–water interface might be used to infer H2S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO4
2− and reactive organic matter.
... The carbonate content was calculated as To characterize the depositional environment, we calculated the TOC to total sulfur ratio (C/S) (Leventhal, 1983; Berner, 1984 Berner, , 1989). To obtain information about quality and maturity of the organic matter, we applied Rock-Eval pyrolysis (Espitalié et al., 1977; Peters, 1986 ). ...
... %. The relationship between pyritic sulfur and TOC may be used to distinguish between oxic and anoxic environments (Leventhal, 1983; Berner, 1984 Berner, , 1989 Stein, 1991 ). Sediments deposited under " normal " oxic deep-water conditions display a positive correlation between organic carbon and pyritic sulfur . ...
A 290-m-thick middle Cretaceous black shale sequence in the upper Magdalena Valley, a present-day intramontane basin located between the Central and Eastern cordilleras of Colombia, was investigated with organic-geochemical and microscopic analyses. As a result of the investigation, we were able to (1) differentiate four organic facies types, (2) estimate their source rock potential, and (3) integrated these facies into a sequence stratigraphic framework. The four organic facies types were type C, BC, B, and D. Type C contains a district terrigenous organic matter component in lowstand or highstand deposits. Organic facies type BC is characterized by an increase and a better preservation of marine organic matter. BC belongs to the lower part of the transgressive systems tract. Sediments of organic facies type B have the highest amount of marine organic matter due to excellent preservation under anoxic conditions. The absence of bioturbation and the enrichment of trace metals are further implications for deposition under anoxic conditions. Facies type B is found in the upper part of the transgressive systems tract and contains the best petroleum source rock potential. Facies B occurrence coincides with sea level highstand and correlates especially with a maximum flooding in northern South America during the Turonian. Organic facies type D is also related to highstand deposits, but shows a high rate of reworking and degradation of organic matter.
... Burial fluxes of OM in modern sediments may, in some settings, comprise a mixture of ancient OM and recent primary production, contributing to increased estimates of burial efficiencies where OM burial is contrasted against autochthonous inputs (Blair et al., 2003Blair et al., , 2004). Additionally, because reconstructions of OM burial fluxes and growth of the crustal carbon inventory over geologic time depend largely on isotope mass balance models and 100% efficiency of OM remineralization during weathering (Berner, 1989), recycled ancient OM plays an important but as yet undefined role in the long-term geochemical cycles of carbon and atmospheric oxygen (Bolton et al., 2006). The age and source of OM exported to the ocean by rivers are important factors for understanding the global cycling of modern and ancient carbon. ...
... The age and source of OM exported to the ocean by rivers are important factors for understanding the global cycling of modern and ancient carbon. Approximately 90% of organic carbon burial is associated with river-dominated continental margins (Berner, 1982Berner, , 1989 Berner and Raiswell, 1983; Hedges and Keil, 1995). OM burial efficiency is at least in part related to its association with mineral particles (Mayer, 1994a,b; Hedges and Keil, 1995; Keil et al., 1997, Mayer, 1999, Kennedy et al., 2002 Dickens et al., 2006). ...
Riverine transport of organic carbon (OC) is a significant flux in the global C budget, representing major terms for both terrestrial losses and ocean margin inputs. Rivers are also dynamic systems where the chemical and isotopic character and reactivity of terrestrial OC is modified prior to its export to the margins. However, several major unknowns still exist in land-ocean OC fluxes, including: i) the amounts, ages and character of the OC reservoirs mobilized and transported; ii) the scales of variability in these parameters both within and among different systems; iii) the extent of modification of these parameters by microbial and abiotic processes during riverine and estuarine transport. The use of natural radiocarbon in aquatic and marine studies provides unique source, turnover and processing information with respect to local, regional and global carbon budgets. However, the number of C-14 analyses in most river systems is often too small, thus limiting the full potential of this isotope in carbon studies. As part of our on-going work, we are measuring the C-14 signatures and ages of dissolved and particulate organic carbon (DOC and POC, respectively), as well as dissolved inorganic carbon (DIC), in a group of northeast U.S. rivers. Here we report the ranges in radiocarbon signatures of bulk DOC, and POC, DIC and their associated 13C/12C ratios from measurements on seven different river systems. The rivers studied occupy a relatively small geographic range, yet individually they export both ancient and fully modern average-aged C to the coastal ocean. In addition, microbial heterotrophy appears to be responsible for the loss of both contemporary and highly aged OC, depending upon the dominant sources to a given system. While sample numbers still preclude an in-depth understanding of the sources and fates of different aged components in river systems in general, the data set permits some preliminary conclusions concerning the relative importance of wetlands, ancient marine organic matter, and within- system modification as key potential controls on riverine C ages.
... bottoms, requires an understanding of both the historic and modern processes shaping the 50 landscape and vegetation. Carbon dynamics in these systems over short to moderate timescales (10 1 to 10 5 yr) can thus 57 strongly regulate carbon emissions to and sequestration from the atmosphere (Berner, 1990; 58 Stallard, 1998), regulating global climate. Although numerous measurements have been made of 59 the radiocarbon age of particulate OC in transport, especially in large river basins (e.g., Barnes scale, OC export versus retention in freshwater systems is broadly controlled by sediment 64 transport dynamics (Leithold et al., 2016), whereby increased sediment retention in floodplains 65 may lead to the storage of OC over long timescales (Steger et al., 2019). ...
Carbon stored on the land has the potential to be released to the atmosphere and act as a greenhouse gas, influencing global climate. To predict future climate, it is imperative to understand where and how much carbon is stored across the landscape to understand how much carbon might be released to and/or sequestered from the atmosphere in the future. We quantify carbon storage in downed wood and soil in mountain river valley bottoms, finding that mountain river valley bottoms are high magnitude carbon storage zones on the landscape, and that the legacy of past glaciation, climate, and modern erosional and depositional processes regulate the age and quantity of stored OC. Our results imply that human actions can change how much carbon is stored in mountain river valley bottoms, and how it is stored there. Understanding the distribution of carbon across the landscape, especially in carbon-rich zones such as valley bottoms, requires an understanding of both the historic and modern processes shaping the landscape and vegetation.
... In comparison to the Amazon and Mississippi depocenters with prolonged particle residence time in oxygenated waters leading to greater remineralization of terrigenous POC inputs, the Congo appears to be likely an efficient site of POC preservation [Blair and Aller, 2012]. The Congo represents a significant fraction of the estimated total OC burial term for the South Atlantic (~1.8 Tg C yr À1 ) Mollenhauer et al., 2004] and even of the global deep-sea OC burial (10–20 Tg C yr À1 ) [Berner, 1989; Hedges and Keil, 1995]. It is apparent that the OM-rich TSS input from the Congo River and highly efficient injection of POC via the Congo Canyon to the deep ocean likely result in the Congo Fan as a globally important location for POC burial. ...
The Congo River in central Africa represents a major source of organic matter (OM) to the Atlantic Ocean. This study examined elemental (%OC, %N, C:N), stable isotopic (δ13C, δ15N) and biomarker composition (lignin phenols) of particulate OM (POM) and dissolved OM (DOM) across the seasonal hydrograph. Even though the Congo exhibits an extremely stable intraannual discharge regime, seasonal variability in OM composition was evident. DOM appears predominantly derived from vascular plant inputs with greater relative contribution during the rising limb and peak in discharge associated with the major November-December discharge maximum. Generally, POM appears to be sourced from soil-derived mineral-associated OM (low C:N, low Λ8, higher (Ad:Al)v) but the relative proportion of fresh vascular plant material (higher C:N, higher Λ8, lower (Ad:Al)v) increases with higher discharge. During the study period (September 2009-November 2010) the Congo exported 29.21 Tg yr-1 of total suspended sediment (TSS), 1.96 Tg yr-1 of particulate organic carbon (POC) and 12.48 Tg yr-1 of dissolved organic carbon (DOC). The Congo exports an order of magnitude lower TSS load in comparison to other major riverine sources of TSS (e.g. Ganges, Brahmaputra), but due to its OM rich character actually exports a comparable amount of POC. The Congo is also 2.5 times more efficient at exporting dissolved lignin per unit volume compared to the Amazon. Including Congo dissolved lignin data in residence time calculations for lignin in the Atlantic Ocean results in an approximately 10% reduction from the existing estimate, suggesting this material is more reactive than previously thought.
... Thus, AOM at the SMTZ produces additional hydrogen sulfide and enhances pyrite formation in the sediments. Variations in iron sulfide burial have affected the bioavailability of key elements Fe and S as well as the global coupled carbon-oxygensulfur biogeochemical cycles over geological timescales throughout Earth's history (Berner, 1989; Berner and Canfield, 1989; Roychoudhurya et al., 2003; Kraal et al., 2013; Tudryn et al., 2014; Lim et al., 2015). In addition, accumulation of FeS and formation of pyrite are of great environmental importance in shallow coastal systems, because sediments are relatively easily disturbed and oxidation of the highly reactive FeS can have severe negative impacts due to the potential for deoxygenation, acidification and metal release (Burton et al., 2009; Morgan et al., 2012; Kraal et al., 2013 ), especially in highly industrialized and urbanized areas where rivers become stressed by anthropogenic input of heavy metals (Diaz and Morse, 1992; Pohl et al., 1998; Neumann et al., 2005; Burton et al., 2009). ...
Sulfate reduction usually leads to the formation of iron sulfide minerals in marine sediments and strongly influences the global coupled carbon-iron-sulfur biogeochemical cycles in marine sediments. Here, we report sulfate reduction and pyrite formation from the coastal sediments near Qi'ao Island, Pearl River Estuary using a combination of sedimentary pore water and solid sediment geochemical analyses. Strong enrichments in reactive iron (276.8–358.2 μmol/g) were observed, especially at the sites located near the river outlets. High contents of reactive iron and low values of the degree of iron pyritization (DOP) indicate that the limiting effect of reactive iron on pyrite formation can be excluded at these sites. In the upper sedimentary layer, conservative mixing of river water and marine water reinforces the fact that sulfate reduction is not appreciable. The limited sulfate supply and low sulfate reduction rates lead to not enough dissolved sulfide available for formation of iron sulfide minerals. However, below this dilution-mixing layer, pore water geochemical profiles indicate that a fraction of sulfate consumption is mediated by upward-diffusing methane. An additional sulfide is produced from anaerobic oxidation of methane (AOM) and later reacts with reactive iron, resulting in enhancement of pyrite formation in the sediments. By contrast, it appears that sulfate concentration is a primary factor controlling for pyrite formation in these estuarine environments. Our study highlights the need in future work for an integrated analysis of the hydrologically driven change in the bottom seawater sulfate concentrations to better understand the regulation factors of global sulfur reservoirs in coastal sediments of estuarine environments, as sulfur burial is an important factor in determining the past atmospheric oxygen level.
... Regardless of the degradation pathway and end-products, the degradation of organic matter plays a major role in determining the chemical composition of the sediments and the organic material preserved in the sedimentary record. The amount and chemical nature of organic matter preserved in the sediments (along with carbonates and sulfur) is closely linked to the composition of the atmosphere over geologic time (Berner, 1989 ). The degradation of organic matter supplies energy to sedimentary organisms. ...
... It is, thus, a common belief that organo-mineral complexation is critical for organic C stabilization. This has led oceanographers and soil biogeochemists to postulate a connection between mineral erosion and organic C burial with implications for the global C cycle[Berner, 1989;Galy et al., 2007]. However, it is only recently that organo-mineral complexation has been recognized as potentially important for the carbon balance at the catchment level[Aufdenkampe et al., 2001[Aufdenkampe et al., , 2011Vonk et al., 2010]. ...
In fluvial ecosystems mineral erosion, carbon (C) and nitrogen (N) fluxes are linked via organo-mineral complexation, where dissolved organic molecules bind to mineral surfaces. Biofilms and suspended aggregates represent major aquatic microbial lifestyles whose relative importance changes predictably through fluvial networks. We tested how organo-mineral sorption affects aquatic microbial metabolism, using organo-mineral particles containing a mix of 13C, 15N-labelled amino acids. We traced 13C and 15N retention within biofilm and suspended aggregate biomass and its mineralisation. Organo-mineral complexation restricted C and N retention within biofilms and aggregates and also their mineralisation. This reduced the efficiency with which biofilms mineralise C and N by 30 % and 6 %. By contrast, organo-minerals reduced the C and N mineralisation efficiency of suspended aggregates by 41 % and 93 %. Our findings show how organo-mineral complexation affects microbial C:N stoichiometry, potentially altering the biogeochemical fate of C and N within fluvial ecosystems.
... The burial and storage of OC in marine sediments exerts long-term control on CO 2 concentrations in the atmosphere [Berner, 1989]. About 94% of the sedimentary OC that is preserved in the oceans is buried on continental shelves and slopes [Hedges and Keil, 1995], with the East Siberian Arctic Shelf (ESAS) constituting the largest shelf sea system of the World Ocean. ...
Given the potential for permafrost carbon (PF/C)-climate feedbacks in the Siberian-Arctic land-ocean system, there is a need for understanding the fate of thawed-out PF/C. Here we show that the sequestration of OC by reactive iron (OC-Fe) ranges between 0.5 and 22% on the Eurasian Arctic Shelf, with higher values in the Kara Sea (KS) (18 ± 6%) and the Laptev Sea (LS) (14 ± 4%). The Δ 14 C/δ 13 C signatures of the OC-Fe are substantially older and more terrestrial than the bulk sediment OC in the LS but younger and more dominated by marine plankton sources in the East Siberian Sea (ESS). Statistical source apportionment modeling reveal that reactive iron phases resequestered 15 ± 5% of thawing PF/C in the LS and 6.4 ± 5% in the ESS, derived from both coastal erosion of ice complex deposit and thawing topsoil. This Fe-associated trap of PF/C constitutes a reduction of the degradation/outgassing and thus also an attenuation of the PF/C-climate feedback.
... The TOC/TS ratio, varying from 0.86 to 48.42. TOC/TS ratio lower than 2.8 are indicative of sediments tending to anoxic conditions (Berner, 1989 ). The present values of TOC/TS ratio indicates oxic condition in the sediments except at A7. ...
The present study investigated the distribution of environmentally relevant metals and organic matter in the shelf sediments of the southeastern Arabian Sea using biogeochemical proxies for the assessment of environmental quality and trophic status. The distribution of metals in the study site followed the order: Fe>Mg>Pb>Ni>Mn>Co>Cu>Zn>Cd. High biological productivity associated with upwelling leads to significant accumulation of Cd higher than crustal abundance in the shelf region. The enrichment factor (EF) of metals demonstrate enrichment of Pb and Co which suggests the anthropogenic influence and not redox conditions. The sediment quality guidelines (SQG) in comparison with metal concentration revealed adverse effects, possibly occurring in marine benthic species. The spatial trend of metal enrichment along transects is appreciably controlled by the adsorption to fine grained sediments. The multivariate statistical analyses, such as correlations and principal component analysis (PCA) clearly indicated the control of texture, association of clay minerals in the degree of trace metal (Cd, Pb, Ni and Co) contamination from anthropogenic as well as natural sources. Low levels of Zn, preferably display scavenging by Fe/Mn metal oxides. Biochemical descriptors in sediments indicated meso-oligotrophic conditions prevailing in the summer monsoon. The ratios among various biogeochemical parameters such as total organic carbon/total nitrogen (TOC/TN<10), protein/carbohydrate (PRT/CHO<1) displayed that the organic matter deposited of marine origin which is relatively old with potentially low nutritional value. The close relationship between biochemical components and phytopigments suggest a major contribution of autochthonous phytodetritus derived organic matter. The study provides important information about sediment biogeochemistry and metal contamination from a potential fishery zone of Indian exclusive economic zone.
... The European coastal areas were found to emit 0.46–1 Tg yr −1 , but this value may underestimate the coastal input, since fluxes from estuaries and shallow seeps have not been represented adequately (Bange, 2006). Although continental margins account for only 10 % of the total ocean area and 20 % of the marine primary production (Killops and Killops, 1993), more than 90 % of all organic carbon burial occurs in sediment deposits on deltas, continental shelves, and upper continental slopes (Berner, 1989). At these locations, which are also characterized by high sedimentation rates, organic carbon is rapidly buried beneath the sulfate reduction zone and becomes available to methanogens (e.g., Cicerone and Oremland, 1988). ...
We investigated dissolved methane distributions along a 6 km transect
crossing active seep sites at 40 m water depth in the central North Sea.
These investigations were done under conditions of thermal stratification in
summer (July 2013) and homogenous water column in winter (January 2014).
Dissolved methane accumulated below the seasonal thermocline in summer with a
median concentration of 390 nM, whereas during winter, methane
concentrations were typically much lower (median concentration of 22 nM).
High-resolution methane analysis using an underwater mass-spectrometer
confirmed our summer results and was used to document prevailing
stratification over the tidal cycle. We contrast estimates of methane
oxidation rates (from 0.1 to 4.0 nM day−1) using the traditional
approach scaled to methane concentrations with microbial turnover time
values and suggest that the scaling to concentration may obscure the
ecosystem microbial activity when comparing systems with different methane
concentrations. Our measured and averaged rate constants (k') were on the
order of 0.01 day−1, equivalent to a turnover time of 100 days, even
when summer stratification led to enhanced methane concentrations in the
bottom water. Consistent with these observations, we could not detect known
methanotrophs and pmoA genes in water samples collected during both
seasons. Estimated methane fluxes indicate that horizontal transport is the
dominant process dispersing the methane plume. During periods of high wind
speed (winter), more methane is lost to the atmosphere than oxidized in the
water. Microbial oxidation seems of minor importance throughout the year.
... The coincidence may be explained as the oxygenation of the ocean triggering the evolution of animals (Nursall 1959 ). The oxygenation may have resulted from a rise in atmospheric oxygen concentrations (Berner 1989; Anbar & Knoll 2002; Algeo & Ingall 2007; Canfield et al. 2007 ). Alternatively, the evolution of increasingly complex eukaryotes, including the first animals , may have resulted in increasing organic matter transfer to bottom waters through faecal pellet delivery and benthic suspension feeding (Cremonese et al. 2013 ), thereby decreasing the consumption of oxygen in the surface waters and allowing oxygen to reach deeper waters. ...
The temporal change of redox conditions of the Yangtze ocean has been revealed by investigating the Ediacaran– Cambrian transition section at Zhalagou, South China. During the earliest Cambrian, cherts and shales were deposited under an anoxic and ferruginous bottom water with significantly increasing total organic carbon and P contents, and negative shift in kerogen δ13C values in the lowest part of the section. Euxinic bottom water conditions occurred during the earliest Cambrian Stage 2, with the surface water dominated by N2 utilization by cyanobacteria or sulphur bacteria leading to negative kerogen δ15N values. During Stage 3, dissolved oxygen and sulphate concentrations were significantly increased, and thus the oxidized surface water and the redox transition zone overlying a euxinic bottom water may have been expanded, resulting in an increase in kerogen δ15N increasing to 2–4‰, a decrease in pyrite δ34S decreasing to as low as –24.6‰ and differences in δ34S values between kerogen and pyrite as high as 37‰. This period coincided with the abrupt appearance of large-body metazoans. Thus, the expanding oxic surface water may have reinforced the evolution of animals or vice versa. Interestingly, kerogen δ34S values show negative relationships to FePy/FeHR ratios and pyrite sulphur contents, indicating that they can be used to reflect redox conditions, with the lightest values being obtained from euxinic environments.
... The study of organic matter and its storage in the subsurface of Earth has led to a greater understanding of past global biogeochemical processes. The preservation of organic matter in sedimentary deposits represents a direct link to the global cycles of carbon, oxygen and sulphur over geological timescales [1]. Fossil organic matter is primarily the product of selectively preserved biopolymers and newly generated geopolymers collectively termed kerogen, although some information-rich free organic compounds are also present in the organic inventory [2]. ...
Subcritical water extraction of organic matter containing sedimentary rocks at 300°C and 1500psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. A type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300°C and 1500psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300°C and 1500psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300°C and 1500psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300°C and 1500psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a suitable replacement for conventional solvent extraction of sedimentary rocks, but can also be used for any organic matter containing mineral matrix, including soils and recent sediments, and has the added benefit of tailored extraction for analytes of specific polarities.
Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.
... The global burial flux of OC within modern marine sediments is estimated at 0.1–0.2 Gt yr –1 (Berner, 1989; Hedges and Keil, 1995), which accounts for ~0.1% of global primary production, ~0.2% of marine plankton photosynthesis and less than half of the input of total terrestrial organic matter by rivers alone (Bianchi, 2011). Consistently, studies of deltas and adjacent coastal zones show sharp offshore increases in δ 13 C from values typical of local rivers (–25 to –– ‰ to higher values similar to marine plankton (–19 to –– ‰ ( Kao et al., 2006). ...
The global export of organic carbon (OC) is intimately linked to the total flux of terrestrial sediment to the ocean, with the continental margins receiving ~ 90% of the sediment generated by erosion on land. Recent studies suggest that a substantial amount of particulate OC (POC) might escape from the shelf and be exported to the continental slope-deep sea sector, although the mechanisms and magnitude of such deep sea POC transfer remain unknown. Here we investigate hyperpycnal flow-associated total suspended matter (TSM) collected from water depths of ~ 3000 m, near the bottom of sea floor, in the Gaoping Submarine Canyon (GSC) off southwestern Taiwan. Elemental (C, N), isotopic (δ13C, δ15N) and biomarker compositions of TSM were investigated to understand its biogeochemical characteristics. A two end-member δ13C mixing model indicates that deep sea TSM contains ~ 90% terrigenous OC, while a similar mixing model using δ15N reveals a lower proportion (~ 58%). Organic biomarkers of TSM suggest contributions from a mixture of resuspended, continental-margin derived marine organic matter (OMMAR) and terrigenous sources, revealing that terrestrial OC likely mixes with nitrogen-rich marine material during rapid transport. This study documents that rapid transfer of terrigenous organic matter (OMTERR) into the deeper regions of GSC occurred within a week of typhoon Morakot, likely through hyperpycnal injection of sediment-laden, warm freshwater from southern Taiwan. Evidence from this typhoon Morakot-induced hyperpycnal plume event in Taiwan demonstrates that extreme storm events provide an efficient way to export terrigenous OC without oxidation to hitherto unknown water depths of deep sea in the Oceania region.
... Understanding the fate of terrestrial organic carbon transported by rivers to the coastal ocean remains a critical factor for constraining the biogeochemical cycle of carbon. Rivers transport ~200–300 Tg of particulate organic carbon (POC) (Galy et al., 2007; Ludwig et al., 1996; Schlünz and Schneider, 2000 ) to the ocean, annually, representing a significant portion of the global carbon cycle and regulating global carbon and oxygen cycles (Berner, 1989; Burdige, 2005). A substantial fraction of global riverine sediment and POC fluxes occur in the tropics (Aufdenkampe et al., 2011 ), with wet tropical rivers, such as the Amazon River, dominating riverine inputs to the oceans (Milliman and Meade, 1983; Ludwig et al., 1996 ). ...
... In addition, large rivers are sites of massive fluxes of carbon, nutrients, and sediments to ocean margins (Bianchi et al. 2007a; Cai and Lohrenz 2010). Although the fate of these materials is not fully understood, much of the terrestrially derived organic material is believed to be remineralized in coastal margins (Berner 1989; Hedges and Kiel 1995 ). Paradoxically, riverinfluenced regions, and coastal margins in general, can also be strong sinks for atmospheric carbon dioxide (Chen 2004; Chen and Borges 2009; Cai 2011) (also see Chapter 7). ...
This volume provides a state-of-the-art summary of biogeochemical dynamics at major river-coastal interfaces for advanced students and researchers. River systems play an important role (via the carbon cycle) in the natural self-regulation of Earth's surface conditions by serving as a major sink for anthropogenic CO2. Approximately 90 percent of global carbon burial occurs in ocean margins, with the majority of this thought to be buried in large delta-front estuaries (LDEs). This book provides information on how humans have altered carbon cycling, sediment dynamics, CO2 budgets, wetland dynamics, and nutrients and trace element cycling at the land-margin interface. Many of the globally important LDEs are discussed across a range of latitudes, elevation and climate in the drainage basin, coastal oceanographic setting, and nature and degree of human alteration. It is this breadth of examination that provides the reader with a comprehensive understanding of the overarching controls on major river biogeochemistry.
... The bubbles may cause resuspension and destabilization of the sediment, and stripping of nutrients out of surface sediments , and subsequent reloading into the water column. It is well known from previous studies that hydrogen sulphide in anoxic lagoons is produced by the reduction of dissolved sulphate by sulphate-reducing bacteria using sedimentary organic matter as energy source, since the procedure takes place in sediment–water interface (Boudreau and Westrich 1985; Berner 1989; Sakai et al. 2013). In the above studies, it is systematically observed that the availability of dissolved sulphate and organic matter are the key factors controlling the hydrogen sulphide concentration , and it is evident that if sediment's TOC content is less than 3 %, then no hydrogen sulphide can be produced. ...
The
study area, Aetoliko Lagoon is a unique coastal Mediterranean landlocked ecosystem, controlled by tectonic activity and is characterized by permanent oxygen-depletion conditions (hypoxia/anoxia). The geological conditions, the geomorphology and the bathymetry of the lagoon, make the Aetoliko Lagoon an area of special interest for the research of the interplay between oxygen-depletion phenomena and human interference. Based on four research cruises within a time period of 1 year seasonal monitoring, in situ contemporary measurements in water column of physicochemical parameters pH, temperature (T, °C), salinity (S, ‰), dissolved oxygen (DO) and redox potential (E
h) were taken, and laboratory analyses of total organic (TOC) and inorganic carbon (IC), total nitrogen (TN) and total phosphorus were carried out. The water column is divided in three major layers: The upper layer (0–10-m depth) with seasonal salinities between 18.5 and 21.5 ‰; the middle layer (10–18.5-m depth) between 19.3 and 24.5 ‰; and the lower one (18.5–30 m) between 22.5 and 25.6 ‰. The lagoon’s lower layer was extended below 18-m depth with almost constant temperature of around 14–15 °C. Anoxic conditions were recorded below 10–11-m depth in July and November, and below 14-m depth in February and April. The vertical distributions of IC and TN values were strongly anticorrelated with the vertical distributions of DO and pH–E
h values as the result of physical, chemical and biochemical procedures. The spatial lagoon sediment characteristics such as grain size and moment measures indicate that the lagoon sediments consists mainly of poorly to very poorly sorted fine-to-coarse silt and sandy mud rich in TOC, while the geochemical parameters indicated a partition in the northern and southern parts of the lagoon. The surface sediments of the lagoon bottom act as a ‘reservoir’ for the diachronic reload of the water column with nutrients and support the assumption that the human interference plays a secondary role in the ecological status of the lagoon.
... Such settings, like recent coastal marine environments, could be characterized by high organic matter productivity. The recent environments contain up to 83% of total organic matter (Canfield et al. 1998) and up to c. 87% of total buried organic matter (Berner 1982). Coastal sediments typically contain 1 –2% of organic carbon (Canfield et al. 1998). ...
geochemical rationales source rocks in Poland: Sedimentological and Zechstein Main Dolomite (Upper Permian) petroleum Palaeoclimatic imprint, distribution and genesis of service Email alerting new articles cite this article to receive free e-mail alerts when here click request Permission part of this article to seek permission to re-use all or here click Subscribe Collection London, Special Publications or the Lyell to subscribe to Geological Society, here click Notes © The Geological Society of London 2013 by guest on December 9, 2013
... The organic matter buried within the sediments, the so-called sedimentary organic matter (SOM), represents on average 0.1–2% of the organic matter originating from primary productivity in the euphotic zone (Tissot and Welte, 1984; Berner, 1989; Hernes et al., 2001). It mainly results from the remineralization of labile components of settling particulate organic matter mediated by heterotrophic organisms during passage through the water column. ...
Although rates and mechanisms of early diagenesis have been well studied, the effects of microbial metabolism on the molecular composition of the sedimentary organic matter (SOM) over long periods of time need more investigation. In this study, we characterize the early diagenesis of marine SOM from organic-rich sediments of the Ocean Drilling Program site 1082 located off Namibia, in the vicinity of the Benguela coastal upwelling system. We used both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (13C NMR) to assess the quantitative repartition of the organic carbon into major compound classes (aliphatic, aromatic, ester, carboxylic, amide and carbons from carbohydrates). Then, we calculate the SOM composition in the main biomolecules (proteins, carbohydrates, lipids and lignin) on the basis of previous 13C NMR-based estimates of the molecular composition of the organic mixtures. Results show that the SOM is still labile at 7 m below the seafloor (mbsf) and composed of about 25% of proteins and 15% of carbohydrates. With increasing depth, the protein content exponentially decreases to 13% at 367 mbsf, whereas the carbohydrate content decreases linearly to 11%. The lignin and lipid content consistently represent around 10 and 40% of the SOM, respectively, and show an increase with depth, due mostly to selective enrichment as the more labile components are lost by degradation. Thus, these components of the SOM are considered refractory at the depth scale considered. The calculated remineralization rates are extremely slow ranging from 5.6 molC m-3 ky-1 at the top of the core to 0.2 molC m-3 ky-1 according to the organic carbon flux to the seafloor. Knowing the labile carbon losses, we propose a method to calculate the initial TOC before the diagenesis took place.
... Productivity derived organic matter and terrestrial organic rich mud input lead to lamination of the ocean floor deposits. The sedimentation rate of the slope sediments is extremely high up to 0.2 ->1 mm/a and the burial of organic matter in the sediments, particularly on continental margins provides a unique palaeo-environmental record as well as the main potential source for fossil fuels (Berner, 1989; von Rad et al., 2000). During bathymetric surveys of several cruises with the German research vessel SONNE in 1997 and 1998 (SO-122, SO-123, SO-124 and SO-130), gas seepage from shallow ridges near the OMZ were documented (Figure 13). ...
The rapidly increasing gap in the production and consumption of oil, gas and electricity in Pakistan is being felt severely at all levels of public and private sectors and even by a common man. Demand for natural gas is growing and is expected to increase substantially in the next couple of decades. Pakistan is fortunate to have some very productive gas fields on land but heavy dependence on these resources is resulting in over production and over consumption therefore, concerns about energy security are influencing energy decisions for the future. Thar coal deposits in Sindh province is one of the World’s largest coal reserves with a resource potential of about 175 billion tonnes (PPIB, 2004). However, only one per cent coal is being used for power generation in Pakistan. Compared to this, 68 per cent electricity is being generated by coal in India, 94 per cent in South Africa, 93 per cent in Poland, 76 per cent in Australia and 81 per cent in China (IEA, 2009). The unstable oil price is exerting huge burden on the economy of Pakistan because of the growing demand. We must now start looking at means to bring about a paradigm shift in dependence on oil import and look for some unconventional energy resources such as gas hydrates to meet ever increasing demand of industrial and domestic consumer to cater for the growing economic development.
The purpose of this country paper is to describe the status of direct or in-direct research on offshore gas hydrates discovered on Makran margin and that has potential to explore in detail for exploration of the gas-hydrate in Pakistan maritime area. The report attempts a holistic assessment of this important resource and tries to determine the potential of methane hydrate as an important long-term domestic and industrial energy resource, as well as to identify and understand environmental concerns associated with this resource. Production of natural gas from gas hydrates is pre-commercial and is not likely to be undertaken by industry alone due to the availability of other proven gas supplies and the long lead time necessary to prove the economic viability of this resource.
The existing knowledge of gas hydrate deposits in Pakistan offshore area is based on scientific studies and published/un-published literature as no direct or systematic study has yet been undertaken to ascertain the potential of gas hydrate deposits and thus ability to quantify the level of methane dissociating from gas hydrates in Pakistan offshore is poorly understood. Countries, such as US, Japan, India, China, and South Korea, are actively pursuing hydrates-related research. These countries are developing essential skills and knowledge that will enable them to take early advantage of whatever energy security the hydrate resource may provide.
... Modeling attempts subsequent to the Veizer et al. (1980) and Lindh (1983) data compilations are faced with a dilemma . How can the findings of Veizer et al. (1980), which have been used to explain carbon, sulfur, and oxygen mass balance calculations (and do not include fluxes associated with seafloor hydrothermal activity; e.g., Lasaga et al., 1985; Berner, 1987 Berner, , 1989 Berner and Canfield, 1989; Kump, 1989), be reconciled with the results of Lindh (1983), the 6~3C values of which have been extensively used in these models? The simultaneous use of these results seems contradictory (see Walker, 1986). ...
Original δ¹³C values of abiotically precipitated marine cements from a variety of stratigraphic intervals have been used to document secular variations in the δ¹³C values of Phanerozoic oceans. These, together with the °³⁴S values of coeval marine sulfates, are used to examine the global cycling of carbon and sulfur. It is generally accepted that secular variation in δ¹³C and δ³⁴S values of marine carbonates and sulfates is controlled by balanced oxidation-reduction reactions and that their long-term, steady-state variation can be predicted from the present-day isotopic fractionation ratio (Δc/Δs) the ratio of the riverine flux of sulfur and carbon (Fs/Fc). The predicted slope of the linear relation between δ¹³Ccarb and δ³⁴Ssulfate values is approximately −0.10 to −0.14. However, temporal variation observed in marine cement δ¹³C values and the 6345 values of coeval marine sulfates produces a highly significant linear relation (r² = 0.80; α > 95%) with a slope of −0.24; approximately twice the predicted value. This discordance suggests that either the Phanerozoic average riverine Fs/Fc was 1.6–3.3 times greater than today's estimates or that an additional source of ³⁴S-depleted sulfur or ¹³C-enriched carbon, other than continental reservoirs, was active during the Phanerozoic. This new relation between marine δ¹³C and δ³⁴S values suggests that the flux of reduced sulfur, iron, and manganese from seafloor hydrothermal systems affects oceanic O2 levels which, in turn, control the oxidation or burial of organic matter, and thus the δ¹³C value of marine DIC. Therefore, the sulfur system (driven by seafloor hydrothermal systems) controls the carbon system rather than organic carbon burial controlling the response of δ³⁴S values (via formation of sedimentary pyrite).
... Sedimentary organic matter (SOM) in aquatic environments is an essential component of the global carbon cycle and its preservation is closely related to the global cycles of sulfur and oxygen over geological timescales (Berner, 1982Berner, , 1989 Hedges and Keil, 1995). Many factors can affect its preservation, such as sediment accumulation rate, O 2 exposure time, system energy and sorption to mineral surfaces, yet the exact mechanisms remain unclear for most preservation scenarios (e.g. ...
The diagenesis of sedimentary organic matter (SOM) in three different depositional environments in south Texas and dominated by vascular plant input was investigated. Sediments were collected from McGuill Lake, a small freshwater lake, and two salt marsh sites in Nueces Delta and Copano Bay, and size-fractioned by wet sieving. Physical forcing or energy, indicated by tides, tidal current, and wind and wind fetch area, is weakest in the lake, intermediate strength at the Nueces Delta, and strongest at Copano Bay. Results from total hydrolyzable amino acid (THAA) and n-alkane analysis, and C-13 solid-state nuclear magnetic resonance spectroscopy (NMR) showed that the SOM from all three sites became more degraded towards finer size fractions, from > 300 mu m, 300-125 mu m, 125-63 mu m, 63-32 mu m to < 32 mu m. Relative to the coarse fractions, the fine fractions were enriched in the degradation indicator gamma-aminobutyric acid, and in aliphatic and proteinaceous components, as shown from NMR spectra and lower C/N ratio values. This degradation pattern of SOM with size is typical for sediments from coastal and lacustrine environments. However, the contents of organic carbon (OC), THAAs and n-alkanes were higher in sandy fractions than in silt and clay fractions from McGuill Lake sediment, suggesting that the SOM was relatively undegraded in coarse fractions. The size distribution of OM in the lake could be explained by the weak physical forcing, which may not easily break down coarser plant detritus into smaller pieces. The trend contrasted with degradation patterns for sediments from Nueces Delta and Copano Bay, where SOM was concentrated in the < 32 mu m fraction, which may be due to the strong physical forcing. The physical forcing effects could also explain the attachment of clay minerals to sand grains in both the lake and Nueces Delta because of the relatively weak physical forcing effects, while no clay attachment to sand grains was found at the Copano Bay site because of the strong physical forcing effects. Physical forcing may be an important mechanism in the processing and transport of OM from vascular plants and other organic sources in estuaries and bays before the SOM is exported to coastal oceans.
... The cycle of organic carbon in nature consists of two parts. There is a primary small " biochemical " (BIO) sub-cycle with a pool of approximately 10 6 Tg (1 Tg = 10 12 g) of organic carbon whose half-life is measured in tens of years or even days and a secondary, much larger " geochemical " (GEO) cycle comprising approximately 10 10 Tg with a half-life of several million years (Berner, 1989; atmospheric methane with respect to the total annual atmospheric methane budget to be recognized (Etiope, 2004Etiope, , 2012 Etiope et al., 2008 ). Nonetheless, the approach is challenged by the nonuniform nature of the mechanism being addressed, which hinders the accurate (a) estimation of seepage rates in areas between and around sampling locations (Etiope et al., 2008 ) and (b) extrapolation of measured rates in time, which results in the incapacity to reconstruct paleo-seepage. ...
The immense mass of organic carbon contained in sedimentary systems, currently estimated at 1.56×1010 Tg1.56×1010 Tg (Des Marais et al., 1992), bears the potential of affecting global climate through the release of thermally or biologically generated methane to the atmosphere. Here we investigate the potential of naturally-occurring gas leakage, controlled by petroleum generation and degradation as a forcing mechanism for climate at geologic time scales. We addressed the potential methane contributions to the atmosphere during the evolution of petroleum systems in two different, petroliferous geological settings: the Western Canada Sedimentary Basin (WCSB) and the Central Graben area of the North Sea. Besides 3D numerical simulation, different types of mass balance and theoretical approaches were applied depending on the data available and the processes taking place in each basin. In the case of the WCSB, we estimate maximum thermogenic methane leakage rates in the order of 10−2–10−3 Tg/yr10−2–10−3 Tg/yr, and maximum biogenic methane generation rates of 10−2 Tg/yr10−2 Tg/yr. In the case of the Central Graben, maximum estimates for thermogenic methane leakage are in the order in 10−3 Tg/yr10−3 Tg/yr. Extrapolation of our results to a global scale suggests that, at least as a single process, thermal gas generation in hydrocarbon kitchen areas would not be able to influence climate, although it may contribute to a positive feedback. Conversely, only the sudden release of subsurface methane accumulations, formed over geologic timescales, can possibly allow for petroleum systems to exert an effect on climate.
... Rivers discharge POC at a rate that is similar to the global accumulation rate of organic carbon in all marine sediments (Berner, 1989). Previous studies indicated that the annual deposition of POC in the proximal Rhône prodelta and the distal Rhône prodelta were 8.0 ± 5.0 × 10 10 g yr −1 and 2.9 ± 1.2 × 10 10 g yr −1 , respectively (De Madron et al., 2000). ...
... The cycle of organic carbon in nature consists of two parts. There is a primary small " biochemical " (BIO) sub-cycle with a pool of approximately 10 6 Tg (1 Tg = 10 12 g) of organic carbon whose half-life is measured in tens of years or even days and a secondary, much larger " geochemical " (GEO) cycle comprising approximately 10 10 Tg with a half-life of several million years (Berner, 1989; atmospheric methane with respect to the total annual atmospheric methane budget to be recognized (Etiope, 2004Etiope, , 2012 Etiope et al., 2008 ). Nonetheless, the approach is challenged by the nonuniform nature of the mechanism being addressed, which hinders the accurate (a) estimation of seepage rates in areas between and around sampling locations (Etiope et al., 2008 ) and (b) extrapolation of measured rates in time, which results in the incapacity to reconstruct paleo-seepage. ...
Around 500 to 600 Tg (1 Tg = 1012 g) of methane enter the atmosphere
every year, mainly as product of microbial processes and combustion of
fossil fuels and burning biomass. The importance of another source, the
geologic emissions of methane, is up to now only loosely constrained. In
this study, we addressed the potential methane emissions during the
geological evolution of the Western Canada sedimentary basin (WCSB),
which holds the largest oil sand accumulations in the world, and the
Central Graben area of the North Sea. In the case of the WCSB,
thermogenic gas generation and leakage at the sediment surface were
addressed through 3D petroleum systems modeling. In this basin, the
accumulated oil experienced intense biodegradation that resulted in
large masses of biogenic methane. We quantified this latter mass though
a two-step mass balance approach. Firstly, we estimated the rate of
petroleum degradation and the magnitude of petroleum loss. After this,
we calculated the mass of biogenic methane generated using a model that
assumes hexadecane (C16H34) as representative of the saturated compounds
(Zengler et al., 1999). Our 3D model suggests that 90000-150000 Tg of
dry gas (mostly methane) could have leaked during the interval from 80
Ma to 60 Ma. Therefore, uniform leakage rates would have been in the
order of 10-3-10-2 Tg yr-1. Biogenic methane generation could have taken
place at rates of 10-4 to 10-2 Tg yr-1. However, the effective mass of
thermogenic and biogenic methane reaching the atmosphere might have been
up to 90% lower than calculated here due to methanotrophic consumption
in soils (Etiope and Klusman, 2002). We addressed the thermogenic gas
generation and leakage in the Central Graben through two different
methods. The first is based on a previous 3D petroleum system modeling
of the region (Neumann, 2006). The second consisted of calculating the
mass of generated petroleum based on source rock extension and
properties (Schmoker, 1994), and then estimating the gas mass available
for leakage based on the concept of petroleum systems and the
proportions among its constituents (Hunt, 1995). We propose that a
maximum of 10-4-10-3 Tg of thermogenic gas (mostly methane) could have
leaked annually from the sediment surface. The portion of this gas that
reached the atmosphere is unconstrained, and it would depend on the
extent of oxidation through the water column. The maximum rate of
thermogenic gas generation in the WCSB is in the order of 10-2 Tg yr-1
(10-8 Tg yr-1Km-2, when normalized to area of kitchen). In the case of
the Central Graben, the maximum would be in the order of 10-3Tg yr-1
(10-8 Tg yr-1 Km-2). These results suggest that thermal maturation alone
would not be able to promote leakage rates as high as those reported for
some single sedimentary basins at present-day, these last reaching up to
3.5 Tg yr-1 (Judd, 2004). Mechanisms promoting the release of previously
accumulated gas masses in a short time span are thus a basic requisite
for petroleum systems to exert an impact on climate.
... Rivers discharge POC at a rate that is similar to the global accumulation rate of organic carbon in all marine sediments (Berner, 1989). Previous studies indicated that the annual deposition of POC in the proximal Rhône prodelta and the distal Rhône prodelta were 8.0 ± 5.0 × 10 10 g yr −1 and 2.9 ± 1.2 × 10 10 g yr −1 , respectively (De Madron et al., 2000). ...
Carbohydrates are important components of the carbon cycle and may be
used as indicators of the origin and the diagenetic status of marine and
terrestrial organic matter. Nevertheless, comprehensive studies of both
particulate (PCHO) and dissolved (DCHO) carbohydrates in rivers are
scarce, and the seasonal and interannual variability of these compounds
in relationship to the bulk particulate (POM) and dissolved organic
matter (DOM) is largely unknown. For the period 2007-2009, we sampled
once per month POM and DOM and measured the total suspended matter
(TSM), POM, DOM, PCHO, and DCHO for the Rhône River, which flows
into the Mediterranean Sea. Using these measurements, we estimated for
the above parameters annual fluxes for the period 2001-2010. The
estimated carbohydrate fluxes averaged
0.061±0.043×1010 moles Cy-1 for PCHO
and 0.041±0.0062×1010 moles Cy-1
DCHO, representing 8% and 7% of the annual flux of POC and DOC,
respectively. During flood and low-water periods, POM variations were
reflected into the PCHO pool, whereas this was not observed for DOC and
DCHO, indicating a decoupling between particulate and dissolved organic
matter. Our results also showed that flood and low-water periods may be
differentiated using the ratios PCHO/DCHO and POC/DOC, which had a
significant linear relationship. Based on the carbohydrate abundances in
both the PCHO and DCHO pools, we conclude that this material mainly
derives from allochthonous sources (vascular plants, bacteria and
soils). Moreover, during flood events, an enrichment in mannose in POM
was observed, probably reflecting an angiosperm source (leaves or
grasses). By expanding our results to the northwestern Mediterranean Sea
(Gulf of Lions), we found that the total organic carbon (TOC) fluxes of
the Rhône River accounted for ~1% of the standing stock of
seawater TOC. Considering that glucose is the most abundant carbohydrate
in both particulate and dissolved organic matter pools (~33%), its
annual flux in the northwestern Mediterranean Sea was estimated to
19.2×108 moles glucose-C.
... Although the water column conditions in deep Paleozoic oceans are difficult to determine directly due to the recycling of oceanic crust and overlying sediments, Mesozoic anoxicClaypool et al. 1980), anoxic episodes (Berner and Raiswell 1983; de Graciansky et al. 1984; Goodfellow and Jonasson 1984; Jenkyns 1988) and the total tonnage of volcanic-associated massive sulphide deposits in each period (data from Mosier et al. 1983). Three of the most important districts for VMS deposits occur in the Paleozoic (Cambrian, Ordovician, and Devonian–Carboniferous) during major δ 34 S (SO 4 ) excursions to highly positive values and when the oceans were generally considered to be stratified with anoxic and H 2 S-rich bottom waters (Berner 1990; Berry and Wilde 1978; Goodfellow 1987). The excursion to highly positive δ 34 S (SO 4 ) was generated by accelerated rates of 32 S removal from the ocean sulphur reservoir by burial in anoxic sediments that formed during periods of ocean stratification. ...
... The wash-out of organic matter (OM) from land into rivers and its subsequent transport to the ocean represents a major input of terrigenous C to the marine environment (Simoneit, 1978). This has long been recognized for its important role in the global C cycle (Berner, 1989; Degens et al., 1991; Hedges et al., 1997). The total riverine organic C carried by rivers to the sea is estimated to be $0.4 ...
Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n-alkanes (<C22) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n-alkanes, n-alkanols, n-alkan-2-ones, n-alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n-alkanoic acids (Cmax = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.
... For example, of the total amount of approximately 200 Tg terrestrially derived particulate OC delivered to the ocean by rivers each year, 58 (±17) Tg C yr À1 gets buried in continental margins, of which about 40–50% is in deltaic sediment while the rest is distributed along the shelves and margins [Blair and Aller, 2012; Burdige, 2007]. Hence, preservation of OC in large delta-front estuaries likely plays an important role in the carbon sequestration and thus global carbon cycling [Bauer and Druffel, 1998; Berner, 1989; Ludwig et al., 1996]. [3] Increased nutrient inputs to large delta-front estuaries from anthropogenic activities may cause higher primary production or eutrophication [Nixon, 1995]. ...
[1] Sediment cores were collected from the East China Sea inner shelf in 2010 to study the decay and preservation of organic carbon (OC). The highest sediment mass accumulation rate (0.61 ± 0.20 g cm−2 yr−1), derived from 210Pb, was found near the river mouth and decreased alongshore to the south (0.17 ± 0.004 g cm−2 yr−1), and in an offshore direction (0.31 ± 0.08 g cm−2 yr−1). Average total OC content was higher at inner shelf stations (0.52%) than those offshore (0.38%). The δ13C was more depleted at nearshore (−23.49‰ to −21.97‰) than offshore (−22.49‰ to −21.60‰) stations. Principal component analysis indicated that terrestrial OC, as indicated by lignin-phenols (Λ8) values, was preserved in sediment closer to the coast (0.22–0.44), while offshore sediment was more composed of lignin-poor (0.12–0.24) degraded OC that was likely hydrodynamically sorted. Marine-derived OC, as indicated by plant pigments, was significantly more abundant in the sediment mixed layer than the underlying accumulation layer. Historical flooding events were detected in Λ8 profiles in two of the six cores located at midshelf stations. Despite the magnitude of the 2010 flood in East China, we did not see any signature of this event with the chemical biomarker in these two cores. This may suggest that reduced sediment loading due to recent dam construction may have greatly decoupled river inputs with sediment loading to shelf sediment. The total OC standing stock since 1900 was approximately 1.62 ± 1.15 kg C m−2, about one tenth of all the middle and lower lakes in the Changjiang catchment basin. This work further supports the need for more research to better understand how the reduced inputs of fluvial input of sediments from Chinese rivers (due to river diversions and dams) affect carbon cycling in the East China Sea.
... Rivers discharge POC at a rate that is similar to the global accumulation rate of organic carbon in all marine sediments (Berner, 1989). Previous studies indicated that the annual deposition of POC in the proximal Rhône prodelta and the distal Rhône prodelta were 8.0 ± 5.0 × 10 10 g yr −1 and 2.9 ± 1.2 × 10 10 g yr −1 , respectively (De Madron et al., 2000). ...
Carbohydrates are important components of the carbon cycle and may be used as indicators of the origin and the diagenetic status of marine and terrestrial organic matter. Nevertheless, comprehensive studies of both particulate (PCHO) and dissolved (DCHO) carbohydrates in rivers are scarce, and the seasonal and interannual variability of these compounds in relationship to the bulk particulate (POM) and dissolved organic matter (DOM) is largely unknown. For the period 2007–2009, we sampled once per month POM and DOM and measured the total suspended matter (TSM), POM, DOM, PCHO, and DCHO for the Rhône River, which flows into the Mediterranean Sea. Using these measurements, we estimated for the above parameters annual fluxes for the period 2007–2009. The estimated carbohydrate fluxes averaged 0.064 ± 0.026 × 10<sup>10</sup> moles C yr<sup>−1</sup> for PCHO and 0.042 ± 0.008 × 10<sup>10</sup> moles C yr<sup>−1</sup> DCHO, representing 6 % and 7 % of the annual flux of POC and DOC, respectively. During flood and low-water periods, POM variations were reflected into the PCHO pool, whereas this was not observed for DOC and DCHO, indicating a decoupling between particulate and dissolved organic matter. Our results also showed that flood and low-water periods may be differentiated using the ratios PCHO/DCHO and POC/DOC, which had a significant relationship.
Based on the carbohydrate abundances in both the PCHO and DCHO pools, we conclude that this material mainly derives from allochthonous sources (vascular plants, bacteria and soils). Moreover, during flood events, an enrichment in mannose in POM was observed, probably reflecting an angiosperm source (leaves or grasses). By expanding our results to the northwestern Mediterranean Sea (Gulf of Lions), we found that the total organic carbon (TOC) fluxes of the Rhône River accounted for ~1 % of the standing stock of seawater TOC. Considering that glucose is the most abundant carbohydrate in both particulate and dissolved organic matter pools (~33 %), its annual flux in the northwestern Mediterranean Sea was estimated to 3.8 × 10<sup>8</sup> moles glucose.
... Dissolved sulphide (H 2 S)was determined using the methylene blue method (Cline, 1969). Oxygen demand units (ODUs), i.e. the amount of oxygen necessary to re-oxidize the reduced products resulting from anaerobic mineralization, were calculated using the concentration of dissolved iron, manganese, and H 2 S using the following formula: [ODU] cording to the diagenetic equations and the associated stoechiometry (Berner, 1989; Canfield et al., 1993b; Soetaert et al., 1996a), where S 2− stands for H 2 S. ...
In situ oxygen microprofiles, sediment organic carbon content, and pore-water concentrations of nitrate, am-monium, iron, manganese, and sulfides obtained in sediments from the Rhône River prodelta and its adjacent continental shelf were used to constrain a numerical diagenetic model. Results showed that (1) the organic matter from the Rhône River is composed of a fraction of fresh material associated to high first-order degradation rate constants (11– 33 yr −1); (2) the burial efficiency (burial/input ratio) in the Rhône prodelta (within 3 km of the river outlet) can be up to 80 %, and decreases to ∼20 % on the adjacent continental shelf 10–15 km further offshore; (3) there is a large contribution of anoxic processes to total mineralization in sediments near the river mouth, certainly due to large inputs of fresh organic material combined with high sedimentation rates; (4) diagenetic by-products originally produced during anoxic organic matter mineralization are almost entirely precipitated (> 97 %) and buried in the sediment, which leads to (5) a low contribution of the re-oxidation of reduced products to total oxygen consumption. Consequently, total carbon mineral-ization rates as based on oxygen consumption rates and using Redfield stoichiometry can be largely underestimated in such River-dominated Ocean Margins (RiOMar) environments.
... Rivers play an important role in both the long-term geologic and shorter term surface carbon cycles, and transport about 0.4 Gt (Gt = 10 15 g) of organic carbon from the continents to the ocean, of which *0.2 Gt is in the form of particulate organic carbon (POC) (Hedges and Keil 1995; Ludwig et al. 1996; Hedges et al. 1997). About 90% of organic carbon brought by rivers is buried within the river-dominated continental margins (Berner 1982Berner , 1989; Berner and Raiswell 1983; Hedges and Keil 1995). POC in the estuary is derived from both allochthonous (e.g., soil organic matter, higher plant debris) and autochthonous sources (e.g., phytoplankton, benthic algae) (Onstad et al. 2000; Kendall et al. 2001; Wetzel 2001), whereas riverine organic matter (OM) is mainly contributed by allochthonous terrestrial origin, including modern and ancient OM (e.g.,Longworth et al. 2007; Wu et al. 2007). ...
Spatial distribution of the carbon and nitrogen
content and their isotopic enrichment in suspended matter
and sediments were measured in the Godavari estuary to
identify the sources and transformation mechanism of
organic matter. Significant variability in isotopic distribution
was found over the entire length of the Godavari estuary,
suggesting multiple sources of organic matter. The mean
isotopic ratios (d13Csed -25.1 ± 0.9, d13Csus -24.9 ± 1,
d15Nsed 8.0 ± 2 and d15Nsus 6.5 ± 0.9%) and elemental
concentrations (Csed 0.45 ± 0.2%, Csus 0.9 ± 0.7%, Nsed
0.07 ± 0.05% and Nsus 0.16 ± 0.1%) support a predominantly
terrigenous source. Significant enrichment in the
isotopic ratios of d13Cfrom the upper to lower estuary in both
suspended (-27.5 and -24.3%, respectively) and sedimentary
(-26.2 and-24.9%, respectively) phases indicates
a decrease in the influence of terrigeneous material toward
the mouth of the estuary. A significant positive relationship
exists between the d13C of suspended and sediment, which
indicates that these two organic carbon pools are likely
coupled in the form of a significant exchange between the
two phases. A positive relationship exists between chlorophyll
a and suspended organic matter, which may mean that a
significant source of organic carbon is the in situ produced
phytoplankton. But, applying a simple mixing model to our
isotopes, data yielded about 46% as the contribution of the
terrestrial source to suspended matter, which may support the
excessive heterotrophic activity in the Godavari estuary
reported earlier.
... It has been estimated that 80% of the total organic carbon preserved in marine sediments occurs in terrigenous-deltaic regions near large-river delta front estuaries (Berner, 1989; Bianchi and Allison, 2009). The Mississippi River is the largest river in North America transporting approximately 60% of the total suspended matter and 66% of the total dissolved solids from the conterminous U.S. to the ocean (Presley et al., 1980). ...
The primary focus of this paper is to better understand carbon burial on the Louisiana continental margin using spatial scales that covered various shelf depositional areas far-field and near-field (sediment and organic carbon inputs relative to river mouth proximity) and covering a variety of sedimentation rates. Box-cores samples were collected in July 2003; cores were collected along two depositional transects extending westward and southward from the Southwest Pass (SW Pass). A key difference between the two transects sampled in this study was the greater occurrence of mobile muds derived from spillover from shallower regions along the westward 50 m isobaths. The dominant mechanism for mixing in the surface active zone (SAZ) on the inner Louisiana shelf was due to physical, not biological, forces. Burial efficiencies for organic carbon (57.2–91.5%) and total nitrogen (44.2–86.9%) ranged widely across all shelf stations. Lower burial efficiencies for bulk organic carbon, total nitrogen, and pigment biomarkers were associated with mobile muds west of Southwest Pass. Chlorophyll a concentrations were significantly higher than pheopigments at depth at the Mississippi River and Southwest Pass stations, making up 40.4 and 77.4% of total pigment concentrations in the (SAZ) and 46.2 and 63.2% in the accumulation zone (AZ), respectively. These results are in agreement with earlier plant pigment studies which showed that a large fraction of the phytodetritus delivered to the inner shelf was derived from coastal and river diatoms. The amount of lignin preserved with depth decreased with increasing residence time in the SAZ and diagenetic zone (DZ) along the canyon transect but not along the western transect. Trends for lignin concentration followed previously identified surface sediment trends indicating overall lower burial of refractory terrestrial material at depth with greater distance offshore.
... Compared to larger and/or lower-relief counterparts, POC suspended in SMR can be enriched in rock-derived organic carbon (OC), making SMR potentially significant sources of relict OC to the oceans [Kao and Liu, 1996; Masiello and Druffel, 2001; Blair et al., 2003]. The riverine flux of relict OC is a key component of the marine and global C cycles, influencing our understanding of the source of 14 C-depleted C in the oceans [Druffel et al., 1992], as well as controls on atmospheric oxygen over geologic time [Berner, 1989]. However, the controls on the isotopic composition of POC suspended in SMR are not well understood. ...
Small mountainous rivers (SMR) export globally significant quantities of particulate organic carbon (POC) to the oceans, the composition of which may be distinct from POC delivered by major world rivers. To better constrain the controls on the Δ14C signatures of POC suspended in SMR, we examined the temporal variability of Δ14C and δ13C of POC suspended in the Santa Clara River, a SMR in California, USA. Our data suggest mixing of bedrock and contemporary soil, which can be applied to other SMR in contrasting climate zones and with varying land cover. The data also suggest that chemical denudation is incomplete, but effective to the point that only the most recalcitrant moieties of the parent POC are exported. We further propose sediment yield as a potentially useful proxy for the Δ14C of riverine POC. A preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis.
... Understanding the biogeochemical processes and environmental conditions that lead to the preservation of organic matter (OM) in marine sediments has been the subject of a wealth of studies over the last decades (, and references therein). Many of these studies have been carried out on sediments deposited along the continental margins, where more than 90% of all organic carbon burial occurs (Berner, 1989). Estuarine zones are good environments for studying the origins, pathways and fates of sedimentary organic material () due to the rapid accumulation of fine sediments and consequent sealing of these materials from bacterial remineralization. ...
The vertical distribution of terrestrial and phytoplankton biomarker compounds in a sediment core from the coastal estuarine zone of the Guadiana river (southwest border between Portugal and Spain) was determined by gas chromatography–mass spectrometry. Significant downcore fluctuations were observed in the patterns of the most abundant alkyl series (n-alkanes and n-fatty acids), as well as in several biomarker ratios. In addition, a specific contribution from conifers is reflected in the presence of a resin acid series that first appears 6500 years BP. The observed changes in the lipid assemblage within the Holocene suggest recent variations in the planktonic and terrigenous supply, which are attributed mainly to the evolution of the circulation pattern in the estuary and to the alteration of vegetation cover within the Guadiana drainage basin. Our data suggest that on a 103–104 year time-scale, little or no diagenetic change occurred with respect to the compounds in question.
... Dissolved CO 2 in natural waters can be produced via various processes such as dissolution of atmospheric CO 2 , oxidation of organic carbon, and weathering of carbonate and silicate minerals (Berner, 1989; Hedges, 1992; Keller and Bacon, 1998). Determination of total dissolved CO 2 in water samples is one of the routine procedures performed in field and laboratory studies of natural waters. ...
Dissolved inorganic carbon (DIC) is one of fundamental parameters affecting physicochemical conditions of aquatic environments.
Normally, for fresh water samples, acidbase titration with Gran plot is used to determine DIC. The procedure, however, requires
more than tens of milliliters of solution volume, and CO2 in the ambient air may interfere with the titration. A monitoring system composed of a flow-through device and a CO2 coulometer was developed to measure slow CO2 production rate in an aqueous system. In this method, sample solutions are directly injected into a flow-through chamber
in which a stream of CO2-free carrier gas continuously removes dissolved CO2 from the injected solution. Degassed CO2 is delivered to the coulometer in which integrated amounts of CO2 are measured. Detection limit of the method was found to be lower than 10×10−12 molesCO2/s, which depends on factors such as flow rates, total CO2 concentrations as well as baseline drift of the coulometer. As a demonstration, the method was applied to the determination
of CO2 production rates via degradation of coal organic matter. The method can be used for monitoring of slow DIC production involved
in various geochemical processes including the weathering of silicates, dissolution of carbonates and the oxidation of sedimentary
organic carbon.
Marine sediments represent a major carbon reservoir on Earth. Dissolved organic matter (DOM) in pore waters accumulates products and intermediates of carbon cycling in sediments. The application of excitation-emission matrix spectroscopy (EEMs) in the analysis of subseafloor DOM samples is largely unexplored due to the redox-sensitive matrix of anoxic pore water. Therefore, this study aims to investigate the interference caused by the matrix on EEMs and propose a guideline to prepare pore water samples from anoxic marine sediments. The parameters determined by fluorescence spectra include 3D-index derived from EEMs after parallel factor analysis (PARAFAC), fluorescence index (FI) (contribution of terrigenous DOM), biological index (BIX) and humification index (HIX) derived from 2D emission spectra. First, we investigated the impacts of extensively-presented ions as typical electron acceptors, which are utilized by anaerobic microbes and stratified in marine sediments: Fe(II), Fe(III), Mn(II) and sulfide in anoxic pore water resulted in biases of fluorescent signals. We proposed threshold concentrations of these ions when the interference on EEMs occurred. Effective removal of sulfide from sulfide-rich samples could be achieved by flushing with N2 for 2 min. Second, the tests based on DOM standard were further verified using pristine samples from marine sediments. There was a significant change in the fluorescence spectra of DOM in anoxic sediments from the Rhône Delta. This study demonstrated that the change was caused by oxidation of the matrix rather than the intrinsic alteration of DOM. It was confirmed by extracted DOM via both EEMs analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Slight oxidation of sulfur-containing compounds (e.g., sulfhydryl) and polyphenol-like compounds occurred. Finally, a sample preparation sequence is proposed for pore water from anoxic sediments. This method enables measurement with small volumes of the sample (e.g., 50 µL in this study) and ensures reliable data without the interference of the redox-sensitive matrix. This study provides access to the rapid analysis of DOM composition in marine sediments and can potentially open a window into examining the carbon cycling of the marine deep biosphere.
The degradation of sedimentary particulate organic carbon (POC) is a key carbon cycle process that fuels the deep subseafloor biosphere. The reactivity of POC is expected to decrease with increasing sediment age, severely restricting the energy available to microorganisms. Conversely, increasing temperatures during burial have been proposed to stimulate POC degradation, possibly supplying significant energy to the deep biosphere. To test the importance of temperature, we assembled POC measurements in two global sets of drill sites where sediments underwent either relatively low or high temperatures during burial, which should have resulted in different rates of POC degradation. For ages 5-10 Ma, the decrease of the average POC content with burial is clearly more pronounced in the sites with high temperature histories. Our results support the hypothesis that temperature is one of the fundamental controls on the rate of POC degradation within deeply buried marine sediments.
Rationale
Determining the chemical constituents of natural organic matter (NOM) by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICRMS) remains the ultimate measure for probing its source material, evolution, and transport; however, lability and the fate of organic matter (OM) in the environment remain controversial. FTICRMS-derived elemental compositions are presented in this study to validate a new interpretative method to determine the extent of NOM lability from various environments.
Methods
FTICRMS data collected over the last decade from the same 9.4 tesla instrument using negative electrospray ionization at the National High Magnetic Field Laboratory in Tallahassee, Florida, was used to validate the application of a NOM lability index. Solid-phase extraction cartridges were used to isolate the NOM prior to FTICRMS; mass spectral peaks were calibrated internally by commonly identified NOM homologous series, and molecular formulae were determined for NOM composition and lability analysis.
Results
A molecular lability boundary (MLB) was developed from the FTICRMS molecular data, visualized from van Krevelen diagrams, dividing the data into more and less labile constituents. NOM constituents above the MLB at H/C ≥1.5 correspond to more labile material, whereas NOM constituents below the MLB, H/C <1.5, exhibit less labile, more recalcitrant character. Of all marine, freshwater, and glacial environments considered for this study, glacial ecosystems were calculated to contain the most labile OM.
Conclusions
The MLB extends our interpretation of FTICRMS NOM molecular data to include a metric of lability, and generally ranked the OM environments from most to least labile as glacial > marine > freshwater. Applying the MLB is useful not only for individual NOM FTICRMS studies, but also provides a lability threshold to compare and contrast molecular data with other FTICRMS instruments that survey NOM from around the world. Copyright © 2015 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.
The deep sea is often viewed as a vast, dark, remote,
and inhospitable environment, yet the deep ocean and
seafloor are crucial to our lives through the services that
they provide. Our understanding of how the deep sea functions
remains limited, but when treated synoptically, a diversity
of supporting, provisioning, regulating and cultural
services becomes apparent. The biological pump transports
carbon from the atmosphere into deep-ocean water masses
that are separated over prolonged periods, reducing the impact
of anthropogenic carbon release. Microbial oxidation
of methane keeps another potent greenhouse gas out of the
atmosphere while trapping carbon in authigenic carbonates.
Nutrient regeneration by all faunal size classes provides the
elements necessary for fueling surface productivity and fisheries,
and microbial processes detoxify a diversity of compounds.
Each of these processes occur on a very small scale,
yet considering the vast area over which they occur they become
important for the global functioning of the ocean. The
deep sea also provides a wealth of resources, including fish
stocks, enormous bioprospecting potential, and elements and
energy reserves that are currently being extracted and will
be increasingly important in the near future. Society benefits
from the intrigue and mystery, the strange life forms, and the
great unknown that has acted as a muse for inspiration and
imagination since near the beginning of civilization. While
many functions occur on the scale of microns to meters and
timescales up to years, the derived services that result are
only useful after centuries of integrated activity. This vast
dark habitat, which covers the majority of the globe, harbors
processes that directly impact humans in a variety of ways;
however, the same traits that differentiate it from terrestrial
or shallow marine systems also result in a greater need for
integrated spatial and temporal understanding as it experiences
increased use by society. In this manuscript we aim to
provide a foundation for informed conservation and management
of the deep sea by summarizing the important role of
the deep sea in society.
The burial and preservation of organic matter (OM) in marine sediments is tightly coupled to the diagenetic cycles of iron and manganese. Recently, it has been shown that approximately 20% of the sedimentary organic carbon (OC) may be bound to reducible iron oxides (Lalonde et al., 2012). These strong iron-OC complexes, formed within the oxic layer of the sediment, are transferred to the deeper anoxic sediment layers through sedimentation, physical reworking and bioturbation and are metastable over geological timescales. Using long-term (250-day) incubations under various redox and amendment conditions (Fe(II) and dissolved OM (DOM) additions), we examined the effect of iron on the early diagenetic transformations of OM in marine sediments. The fate of fresh, algal-derived DOM was monitored by tracking its stable carbon isotopic signature (δ13C). We demonstrate the incorporation of the 13C-depleted tracer into the sediment through sorption (adsorption and co-precipitation). In the presence of iron oxides, we observed increased transfer of the dissolved algal material to the solid phase, revealing the role of iron in shuttling DOM from sediment porewaters to sediment particles. Furthermore, we show that the presence of iron has a differential effect on OC and organic nitrogen (ON), with preferential preservation of OC and accelerated degradation of ON in the presence of reactive iron oxide surfaces. Hence, we propose that redox-sensitive metals may regulate the global redox balance through increased carbon preservation as well as exerting a control on the concentration of fixed nitrogen species in marine sediments.
Gas hydrates are ice-like crystalline substances occurring in nature where a solid water lattice accommodates gas molecules (primarily methane, the major component of natural gas) in a cage-like structure, also known as clathrate. Gas hydrates form under conditions of relatively high pressures and low temperatures, such as those found in the shallow subsurface under many of the world‘s oceans. Gas hydrates, which are known to occur in the marine sediments on the continental margins, are widely considered as a promising alternate energy resource. One cubic foot of hydrate at reservoir temperature and pressure yields approximately 160-180 cubic feet (ft3) of gas at atmospheric temperature and pressure. The amount of natural gas in gas hydrate worldwide is estimated to be far greater than the entire world's conventional natural gas resources. This is what makes the Gas Hydrates a potential energy resource for the future.
The diminishing fossil fuels and energy security concerns of nations have attracted international attention from governments to the scientific communities to work on gas hydrate as a potential energy resource. Energy starved SAARC countries will benefit enormously from the successful development of gas hydrates and production of natural gas from marine gas hydrates.
This document reviews the status of technology pertaining to exploration and exploitation of gas hydrates, research initiatives that have been taken by India and other SAARC countries, that has contributed significantly in the research and development of gas hydrates, and suggests a mechanism for the technology transfer and promotion of R&D activities in the SAARC region.
Gas hydrate interests are multifaceted and intertwined. Gas hydrate has been known for many years as a problem in blocking cold-region natural gas pipelines, and as a drilling hazard in the arctic. However, natural gas hydrate studies have rapidly expanded globally in recent years, with large programs in Japan and USA, and considerable efforts in Canada, India, Korea, China, and numerous other countries.
Many groups are actively participating in a wide variety of gas hydrate research. The Department of Energy (DOE) of the US is coordinating gas hydrate research activities and provides a foundation to pursue the goal of producing methane from hydrates by the year 2015. The U.S. Geological Survey (USGS) has conducted extensive geophysical surveys and established a specialized laboratory facility to model the formation and dissociation of oceanic gas hydrates.
Gas hydrate research and resource development are also underway in Japan, India, Canada, the United Kingdom, Germany, Brazil, Norway, Russia, China and Korea. India has been actively involved in the research and development of gas hydrates for more than a decade. In association with USGS and other international organizations, India‘s gas hydrates research reached a matured state. Under the National Gas Hydrates Programme, Phase II India now plans to look for sands within the GHSZ and thereafter shortlist a candidate for pilot Production test.
SAARC countries having a vast coast line and deep water environment may consider forming a consortium for exploration and development of marine gas hydrates. This will help member states to share their experience with each other. For energy deficient SAARC region an alternative energy source like methane gas from the gas hydrates will be great boost in ensuring the energy security of the region.
Resources are not estimated in any of the SAARC countries except India which recently updated the map (Figure1) which shows the Gas Hydrate Stability Thickness Map along the Indian continental margins. The occurrence of gas hydrates in the marine sediments is confirmed by direct sampling. However, worldwide, their preliminary detection over large areas is inferred based on identification of Bottom Simulating Reflector (BSR) in the conventional seismic reflection data. In view of preliminary indications the NGHP has initiated systematic exploration of gas hydrates on the continental margins of India by reprocessing the available multi-channel seismic reflection data with a specially designed sequence of processing and mapping the spatial distribution of BSR-like features. The predicted thickness map matches quite accurately with the observed depths of BSRs, marker for gas hydrates.
We have studied the net and gross metabolism of Tomales Bay, a temperate climate estuary in northern California. Tomales Bay has proved to be heterotrophic, im- plying that the bay oxidizes a subsidy of organic carbon from outside the system, in excess of inorganic nutrients supplied to it from outside and in addition to material cycling within it. Net organic oxidation releases dissolved inorganic nutrients, and the system exports these dissolved inorganic products. Dissolved inorganic phosphorus is exported to the ocean via mixing and constitutes the most direct record of net ecosystem production (NEP). Excess dissolved inorganic nitrogen is lost to denitrification. Excess dissolved inorganic carbon largely results in alkalinity elevation and hydrographic export of alkalinity due to sulfate reduction. The negative NEP of this system results in little release of CO 2 to the atmosphere, because of this alkalinity elevation. A major purpose of the study was to ascertain the relative importance of various sources of organic material supplied to the system from outside its boundaries and undergoing net reactions within it. In order to address the question, we used stoichiometrically linked whole-system budgets of carbon, nitrogen, and phosphorus. The difference between dis- solved inorganic phosphorus (DIP) fluxes to and from the bay is a measure of net internal sources or sinks of DIP and is used as a quantitative index of NEP, with the assumption that the C:P ratio of organic matter is constant (;106:1). The system is thus defined in terms of water column dissolved material composition; this definition includes time, as well as space. Net changes in the standing stocks of dissolved materials can originate from (spatial) transport to or from the system or from internal (temporal) transformations between the dissolved and particulate materials (i.e., changes in organic storage). Over the 8-yr study, the system respired 12 mmol·m 22 ·d 21 more organic C than the internal system primary production of ;100 mmol·m 22 ·d 21 . The system is thus heterotrophic by ;10%, with sub- stantial seasonality in the extent of heterotrophy. By deconvoluting the time series of NEP into a seasonal cycle and interannual variation, we infer that terrestrial and marine sources each account for about half of the carbon required to support negative NEP in this system, but with quite different turnover time scales. Temporal response of NEP to terrigenous input appears to be extremely modulated, so that there is no obvious immediate (same year) response to extreme interannual variation in terrigenous organic loading. In contrast, NEP responds both interannually and seasonally to marine organic inputs. We interpret the differences in response to loading of terrestrial vs. marine organic matter as reflecting differences in the reactivity of these carbon reser- voirs.
A B S T R A C T In order to determine the sedimentological and physico-chemical characteristics of the benthic environment and also the level, distribution and probable sources of aliphatic and polycyclic aromatic hydrocarbons, sediment samples were collected at 28 stations in the northeast portion of Todos os Santos Bay. The centre and the east region of the study area showed characteristics of depositional environments with the predominance of silt and clay and high percentages of TOC, nitrogen and sulphur. The molar C/N ratios varied between 8.8 and 27.6 indicating a mixed origin of organic matter with variable marine and continental contributions. Total aliphatic hydrocarbon concentrations ranged between 1.56 and 246.91 µg.g -1 dry weight, corresponding the high concentrations to the stations situated in the centre and in the east region of the study area. The UCM represented between 60 and 96% of the total aliphatic hydrocarbons, indicating a high degree of anthropogenic contribution and the presence of petroleum degraded residues. Total PAH concentrations varied from 8 to 4163 ng.g -1 dry weight. The highest total PAH concentration was recorded at station 5 situated adjacent to the oil refinery.
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