Formation of ammonite concretions through organic decomposition in the iron-reduction zone

Phosphorus cycling in marine sediments from the continental margin off Namibia

Interface processes of endogenous phosphorus during the freeze period: The driving role of iron dissimilation reduction and the unignorable organic phosphorus release.

Quantifying the degradation of organic matter in marine sediments: A review and synthesis

Elements, especially inorganic elements, are geochemical tracers widely used to study the evolution of various geological processes, material sources and envi-ronmental changes, especially in the fields of ocean, environment, mineral de-posits and so on. The geochemical characteristics of elements in the sedimen-tary environment are of great significance for tracing the provenance of sedi-ments. The content of elements changes with the change of rock type, sedimen-tary process and sedimentary environment. Some elements with relatively sta-ble chemical properties are basically not affected by the weathering, denudation, redeposition and diagenesis of rocks, and can well reflect the provenance char-acteristics of source rocks. Other elements have different characteristics in dif-ferent sedimentary environments. Some elements are enriched in marine sedi-ments, while others are enriched in terrigenous sediments, and are affected by sedimentary fluid environment in this process. For example, the enrichment degree of some metal elements will also change in different oxidation-reduction environments. With the process of sedimentary evolution, trace elements will also be dispersed and enriched during the formation, sedimentation and burial of sedimentary organic matter. Therefore, the analysis of the geochemical char-acteristics of elements in the sedimentary environment is of great significance for identifying the provenance and tectonic setting of sediments.

Decomposition of organic matter in marine sediments is a critical step influencing oxygen and carbon fluxes. In addition to heterotrophic bacteria and fungi, osmoheterotrophic protists may contribute to this process, but the extent of their role as decomposers is still unknown. Among saprophytic protists, the thraustochytrids have been isolated from different habitats and substrates. Recently, they have been reported to be particularly abundant in marine sediments characterized by the presence of recalcitrant organic matter such as seagrass and mangrove detritus where they can reach biomass comparable to those of other protists and bacteria. In addition, their capacity to produce a wide spectrum of enzymes suggests a substantial role of thraustochytrids in sedimentary organic decomposition. Moreover, thraustochytrids may represent a food source for several benthic microorganisms and animals and may be involved in the upgrading of nutrient-poor organic detritus. This chapter presents an overview on studies of thraustochytrids in benthic ecosystems and discusses future prospectives and possible methods to quantify their role in benthic food webs.

Using the C/N ratio to estimate terrigenous inputs of organic matter to aquatic environments

Sedimentary organic matter is a potential indicator of paleoenvironments. In this study we examine the relationship among composition of kerogen (insoluble organic matter), sedimentary environments, and sea-level changes in Miocene to Pleistocene sediments of the Niigata and Akita backarc basins, central Japan. Our primary analytical tool is a ternary diagram with apexes consisting of woody-coaly organic matter, herbaceous with pollen and spores, and amorphous organic matter (AOM) with alginite (organic-walled marine microfossils). The composition of kerogen plots into distinct regions on the ternary diagram: fluvial to estuarine, prodeltaic, shelf, slope and basin-floor submarine fans, and distal basin-floor sediments. The fluvial and estuarine sediments have high proportions of woody-coaly and herbaceous organic matter with pollen and spores, and a lesser proportion of AOM + alginite, because pollen and spores were mainly deposited in estuaries. Because abundant coarse-grained, terrigenous organic matter was supplied by delta distributaries, the prodeltaic sediments have high proportions of woody-coaly organic matter. The composition of kerogen in the shelf sediments is similar to the kerogen in slope and basin-floor submarine-fan sediments, as plotted on the ternary diagram. Both kinds of kerogen accumulations have high proportions of woody-coaly organic matter and AOM with alginite and lesser proportions of herbaceous organic matter with pollen and spores. This relationship suggests that turbidity currents supplied the terrigenous sediments. The sediments on the distal basin-floor contain high proportions of AOM. Each pattern in the ternary diagram reflects a difference in hydrodynamic behavior, distance from land, and the supply of terrigenous organic matter. The sub-ternary diagram, which has apexes of WFA (weakly fluorescent amorphous organic matter), NFA (nonfluorescent amorphous organic matter) + FA (fluorescent amorphous organic matter), and alginite, further suggests the origin of AOM. The NFA in shelf sediments and WFA in distal basin-floor sediments are inferred to consist of terrestrial higher plant and marine organic matter, respectively. A 13C value of kerogen rich in NFA (-24.6 and -27.3‰) suggests land plants, whereas kerogen rich in WFA (-20.0 to -23.6‰) suggests marine plankton. These inferences agree with those derived from the sub-ternary diagram. Furthermore, compositional changes of the kerogen in turbidites reflect relative sea-level changes, as seen by shifts in compositions on the ternary diagram. The use of ternary diagrams like those used here is recommended for future studies of kerogen, depositional environment, and sea-level relationship.

The geochemical characteristics of a 2.1 m BBW25 core, collected from the Beibu Gulf, have been investigated in terms of the major and trace elements, organic matter, and CaCO3 and AMS 14C dating by XRF, ICP-OES, ICP-MS, and more. We have found through previous research that there are issues with unclear delineation of sedimentary evolution environments and inexact responses between chemical weathering intensity and major paleoclimate events in the Beibu Gulf. The AMS 14C dating results indicate that the sedimentary age at the bottom was 19.24 ky b.p. CaCO3, δ13C, C/N, and Sr/Ba indexes show a sedimentary environment change from terrestrial to marine environments and a “jump” of ~4000 years in continent–ocean changes. The evolution of the sedimentary environment of Beibu Gulf was divided into three environments and five sub-environments. The changes in chemical weathering intensity indicators recorded by the CIX and the Fe/Al ratio respond well to the East Asian monsoon cycle, the meltwater events, and the alternation of cold and warm events. This study explains the chemical weathering intensity and sedimentary environment in the BBW25 core by geochemical characteristics and further reveals the paleoenvironmental characteristics and possible driving mechanisms over the past ~20,000 years.

<p>In order to estimate sediment organic carbon budget in coastal oceans and continental shelves, a first step is to estimate how much of the deposited organic matter is retained within a sediment matrix, for further remineralization and preservation on a geological timescale, rather being physically flushed away by benthic flow<sup>1</sup>. This question becomes more challenging for the regions where ‘mobile’ layers (e.g. fluff layer, fluid mud and nepheloid layer) are formed due to the massive organic matter inputs, and often frequent resuspension and deposition<sup>2</sup>. Organic matter remineralization and preservation in sediments has been mostly investigated but often overlooks the role of flow-induced shear stresses on suspending the organic matter. While such flow influences in sediment organic matter budget may have little influence on sediment organic matter budget in deep oceans, it cannot be neglected in shallow-water coastal seas and continental shelves where cyclic resuspension, deposition and frequent storm events occur<sup>3,4</sup>. To our knowledge, the resistance strengths of organic matter in sediments against flow resuspension has received little attention.</p><p>To investigate this knowledge gap, various organo-clay aggregates and organo-clay-sand aggregates formed under different flow conditions were investigated by a series of laboratory flume<sup>5</sup> and high resolution X-ray Microcomputed Tomography (micro-CT) experiments<sup>6</sup>. Herein, a novel methodology is proposed, which successfully establishes quantitative relationships between the resuspension resistance strengths of these organic aggregates and a wide range of flow intensities, from moderate to storm conditions. The results provide a basis for computing resuspension under a range of flow conditions and, hence improving estimates of the organic matter budget in the coastal zone.  </p><p> </p><p><strong>References</strong></p><ol><li>Burdige, D. J. Preservation of organic matter in marine sediments: Controls, mechanisms, and an imbalance in sediment organic carbon budgets? Chem. Rev. <strong>107</strong>, 467–485 (2007).</li> <li>McKee, B. A., Aller, R. C., Allison, M. A., Bianchi, T. S. & Kineke, G. C. Transport and transformation of dissolved and particulate materials on continental margins influenced by major rivers: Benthic boundary layer and seabed processes. Cont. Shelf Res. (2004). doi:10.1016/j.csr.2004.02.009</li> <li>Burdige, D. J. Burial of terrestrial organic matter in marine sediments: A re-assessment. Global Biogeochem. Cycles <strong>19</strong>, 1–7 (2005).</li> <li>Nicholls, R. J. & Cazenave, A. Sea-level rise and its impact on coastal zones. Science (2010). doi:10.1126/science.1185782</li> <li>Thompson, C. E. L., Couceiro, F., Fones, G. R. & Amos, C. L. Shipboard measurements of sediment stability using a small annular flume-core mini flume (cmf). Limnol. Oceanogr. Methods (2013). doi:10.4319/lom.2013.11.604</li> <li>Zhang, N. et al. Nondestructive 3D Imaging and Quantification of Hydrated Biofilm-Sediment Aggregates Using X-ray Microcomputed Tomography. Environ. Sci. Technol. <strong>52</strong>, 13306–13313 (2018).</li> </ol>

Abyssal food limitation, ecosystem structure and climate change

Comparative organic geochemistries of soils and marine sediments

Pore system characteristics of the Permian transitional shale reservoir in the Lower Yangtze Region, China

The purposes of the research were to know the influences of crop organic matters to diversity of soil mesofauna and macrofauna under paraserianthes stand (Paraserianthes falcataria), rate of organic matters decomposition, as well as the relationship between the rate of organic matters decomposition and diversity of soil mesofauna and macrofauna. The framework of thinking of this research was the crop organic matters which were given to the soil would influence the soil mesofauna and macrofauna diversities. The presence of soil fauna would help the decomposition process of organic matters which fertilize the soil. This research was established under paraseanthes’ stand, with 7 treatments of crop organic matters, i.e. cardamom, pineapple, cocoyam, cardamompineapple, cardamom-cocoyam, pineapple-cocoyam, cardamom-pineapplecocoyam, and the treatment without crop organic matters (control). The sampling of mesofauna data used soil extraction “Barlesse-Tulgreen” method, meanwhile the macrofauna data were obtained from “Hand- Sorting” method and “Fill-Trapp” method. The sampling of decomposition rate data used Pudjiharta’s method (1995). The data which have been obtained were analyzed by using Analysis of Variance (ANAVA) and continued with DMRT test. The Correlation test was done to find out the relationship between the rate of decomposition of crop organic matters and the soil mesofauna and macrofauna diversities. It can be concluded that the applying of crop organic matters influenced the soil mesofauna and macrofauna diversities. The highest coefficient value index of soil mesofauna diversity was 1.36 by using cardamom-cocoyam organic matters. The highest coefficient value index of the soil macrofauna diversity was 1.11 by using pineapple organic matters. The highest coefficient value index of macrofauna diversity on the surface of the soil was 1.27 by using pineapple organic matters. The crop organic matters of cardamom-cocoyam has the highest coefficient value decomposition rate, was 0.45. The crop organic matters of pineapple has the lowest coefficient value decomposition rate, was 0.15. The relation between the decomposition rate of crop organic matters and the soil mesofauna diversity index, the macrofauna in the soil, and macrofauna on the surface of the soil show the negative correlation, with the correlation coefficient value, were -0.01; -0.30; -0.001.

Riverine transport of terrestrial organic matter to the North Catalan margin, NW Mediterranean Sea

Sedimentological, mineralogical, stable carbon and oxygen isotope determinations and biomarker analyses were performed on siderite concretions occurring in terrestrial silts to understand their formation and to characterize the sedimentary and diagenetic conditions favouring their growth. High δ13C values (6·4‰ on average) indicate that siderite precipitated in an anoxic environment where bacterial methanogenesis operated. The development of anoxic conditions during shallow burial was induced by a change in sedimentary environment from flood plain to swamp, related to a rise of the ground‐water table. Large amounts of decaying plant debris led to efficient oxygen consumption within the pore‐water in the peat. Oxygen depletion, in combination with a decrease in sedimentation rate, promoted anoxic diagenetic conditions under the swamp and favoured abundant siderite precipitation. This shows how a change in sedimentary conditions can have a profound impact on the early‐diagenetic environment and carbonate authigenesis. The concretions contain numerous rhizoliths; they are cemented with calcium‐rhodochrosite, a feature which has not been reported before. The rhodochrosite cement has negative δ13C values (−16·5‰ on average) and precipitated in suboxic conditions due to microbial degradation of roots coupled to manganese reduction. The exceptional preservation of the epidermis/exodermis and xylem vessels of former root tissues indicates that the rhodochrosite formed shortly after the death of a root in water‐logged sediments. Rhodochrosite precipitated during the initial stages of concretionary growth in suboxic microenvironments within roots, while siderite cementation occurred simultaneously around them in anoxic conditions. These suboxic microenvironments developed because oxygen was transported from the overlying oxygenated soil into sediments saturated with anoxic water via roots acting as permeable conduits. This model explains how separate generations of carbonate cements having different mineralogy and isotopic compositions, which would conventionally be regarded as cements precipitated sequentially in different diagenetic zones during gradual burial, can form simultaneously in shallow burial settings where strong redox gradients exist around vertically oriented permeable root structures.