Methylated amines and sulfides are ubiquitous organic nitrogen and sulfur compounds in the marine environment and could serve as important energy substrates to methanogens inhabiting anoxic ...sediments. However, their abundance and isotopic values remain largely unconstrained in marine sediments. In this study, we investigated the distribution of trimethylamine (TMA), dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in Aarhus Bay, Denmark and provided the first report for their stable carbon isotopic composition. Simultaneous measurement of those two compounds in small volumes of pore waters and sediments was accomplished with gas chromatography in combination with either a purge and trap system for quantification or a headspace method for carbon isotopic analysis. TMA in the solid phase (exchangeable pool, 0.3–6.6μmolkg−1 wet sediment; base-extractable pool, 2–18μmolkg−1) was much more abundant than the dissolved pool (<20nM), indicating strong adsorption of TMA to sediments. Likewise, total base-hydrolyzable DMS(P)t (including DMS and base-released DMS from DMSP) in sediment was at least three orders of magnitude higher (11–65μmolkg−1) than the dissolved pool of DMS(P)d in the pore water (including DMS and dissolved DMSP; 1–12nM). TMA and DMS(P) contents in the solid phase peaked in the surface sediment, consistent with their phytodetrital origin. TMA was more 13C-depleted than DMS(P) (TMA: −36.4‰ to −39.2‰; DMS: −18.6‰ to −23.4‰), presumably due to different biological or biosynthetic origins of the respective methyl groups. Both compounds showed a downcore decrease in their solid-phase concentration, a feature that was attributed to microbial degradation, but progressive enrichment in 13C (up to 4‰) with depth was observed only for DMS(P). The considerable pool size of TMA and DMS(P) outlined in this study and geochemical evidence of their degradability suggested these two compounds could be potentially important substrates for methane production in sulfate-reducing environments.
•TMA, DMS and DMSP were measured simultaneously in marine sediment and pore waters.•The stable carbon isotopic composition of TMA and DMS(P) was reported for the first time.•TMA was more 13C-depleted than DMS(P) due to different biosynthetic origins of the respective methyl groups.
The ubiquity of microplastics (MPs) has now been demonstrated throughout Earth's geographic areas in both terrestrial and marine environments. Marine ecosystems are the end point of the plastic waste ...cycle, and marine sediments are increasingly considered to be a sink for plastic debris, with possible deleterious effects on seafloor ecosystems. However, the low concentration of MPs in a complex matrix such as marine sediment makes their reliable analysis difficult. MP concentration in marine sediments is usually determined by various extraction procedures followed by optical, spectroscopy or mass spectrometry techniques, and are therefore hard to compare. Therefore, reliable determination of MPs in sediment is a challenging task. Here we present a short review on studies dealing with analytical determination protocols and MP detection in marine sediments and discuss the advantages of the different techniques used. This analysis of the literature reveals that most of the 70 studies were carried out in European and Asian coastal environments. The use of NaCl saturated solution, hydrogen peroxide (H2O2) and Fourier transform infrared spectroscopy (FTIR) are by far the most-used techniques for the different steps of separation, digestion and identification, respectively. Based on this body of literature, we present recommendations and suggestions for future research in order to increase the reliability of results and to facilitate inter-comparison. The use of NaCl saturated and H2O2 solution is strongly recommended for the separation and digestion steps, respectively, whereas during the filtration step it is necessary to choose filter type based on the identification technique. More thorough investigation is needed to establish a systematic protocol for MP identification. A combination of techniques would permit to identify all items, and personal bias could be avoided if automatic identification was implemented. Nanoplastics (NP) occurrence in marine sediments is also discussed, although no data are available to date.
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•MPs in marine sediments have been published in at least 70 articles, at a total of 813 locations on all continents.•Areas studied are mainly in coastal environments, and the number of locations examined per study ranges from 1 to 72.•We recommend the use of a NaCl solution for the separation step.•A digestion step using an H2O2 solution and automatic identification are recommended
Sound strategies for marine chemical monitoring call for measurement systems capable of producing comparable analytical results with demonstrated quality. This work presents the development and ...validation of a new analytical procedure for the determination of the 241Am mass fraction in marine sediment and seawater samples at low levels. The procedure includes a tandem-column extraction chromatography for separation of 241Am and sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) for its determination. The separation is based on the application of two new extraction resins, TK200 and TK221. The acid leaching method was employed for the pre-treatment of marine sediments, while Fe(OH)3 co-precipitation was used for Am pre-concentration in seawater samples. The extraction behaviors of Am on TK221 resins in the different acidic mediums were investigated. The removal capabilities of the tandem TK200-TK221 columns for the 241Am in the presence of interfering elements including Pu, Pb, Hg, Bi, Tl, Pt, Hf, U, and Th were carefully investigated and the corresponding decontamination factors (DFs) estimated to be in the range from 104 to 106. The main interfering element Pu was efficiently removed with a DF of about 6 × 105. Matrix rare earth elements (REEs) in marine sediments were further removed by the application of TEVA resins. 241Am mass fraction was quantified by the application of external calibration and SF ICP-MS. Following the recommendations of the ISO/IEC 17025 guidelines, the validation of the analytical procedure was accomplished by executing it on the certified reference material (CRM) IAEA-385 (marine sediment) and the seawater IAEA-443 reference materials (RM). The obtained results showed that 241Am mass fractions were accurately determined in both reference samples, with excellent reproducibility (2.1 % and 7.6 %) and low LODs (0.4 fg g−1 and 0.2 fg g−1). The relative expanded uncertainties (k = 2) obtained were 17.1 % and 29.0 %, respectively. The overall analytical times for the application of the proposed procedure on the marine sediment and seawater samples were evaluated to be only about 9 h and 6.5 h, respectively. It shows great advantages for its potential applications for emergency monitoring of 241Am contamination in the marine environment.
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•Determination of 241Am by SF ICP-MS after tandem-column extraction separation.•Decontamination factor as high as ∼6 × 105 for Pu was obtained.•Total analytical times for marine sediment and seawater were shortened to 6–9 h.•Rapid and accurate method for 241Am monitoring for marine environmental studies.
Microplastic pollution in marine environments is of particular concern on its risk to the ecosystem. To assess and manage microplastic contaminants, their quantitative detection in environmental ...samples is a high priority. However, uncertainties of current methods still exist when estimating their abundances, particularly with fine-grained (<1 mm) microplastics. This work reports a novel thermoanalytical method for quantifying microplastics by measuring the contents of microplastic-derived carbon (MPC) in samples under the premise of nearly eliminating the limit of their particle appearances. After validating the method via samples with the spiked microplastics, we have conducted a case study on sediment core H43 that spanned 1925–2009 CE from the Yellow Sea for further illustrating the high reliability and practicability of this method for quantifying microplastics in natural samples. Our results have demonstrated that the proposed method may be a promising technique to determine the mass-related concentrations of the total microplastics in marine sediments for evaluating their pollution status and quantitative contribution to marine carbon storage.
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•A new method for quantifying microplastics was developed via analyzing MPC contents in sediments.•The method works independently of particle appearances.•The method was employed to reveal the multidecadal record of microplastic pollution in the Yellow Sea.•A microplastic contribution to sedimentary carbon storage was evaluated using this method.
•CO2 storage in heterogeneous marine sediments in investigated for the first time.•CO2 storage is possible in shallower marine sediments than previously found.•Physical and operational thresholds for ...secure CO2 storage are presented.
Global climate change is a pressing problem caused by the accumulation of anthropogenic greenhouse gas emissions in the atmosphere. Carbon dioxide (CO2) capture and storage is a promising component of a portfolio of options to stabilize atmospheric CO2 concentrations. Meaningful capture and storage requires the permanent isolation of enormous amounts of CO2 away from the atmosphere. We investigate the effectiveness of heterogeneity-induced trapping mechanism, in potential synergy with a self-sealing gravitational trapping mechanism, for secure CO2 storage in marine sediments. We conduct the first comprehensive study on heterogeneous marine sediments with various thicknesses at various ocean depths. Prior studies of gravitational trapping have assumed homogeneous (deep-sea) sediments, but numerous studies suggest reservoir heterogeneity may enhance CO2 trapping. Heterogeneity can deter the upward migration of CO2 and prevent leakage through the seafloor into the seawater. Using geostatistically-based Monte Carlo simulations of CO2 transport in heterogeneous sediment, we show that strong spatial variability in permeability is a dominant physical mechanism for secure CO2 storage in marine sediments below 1.2 km water depth (less than half of the depth needed for the gravitational trapping). We identify thresholds for sediment thickness, mean permeability and porosity, and their relationships to meaningful injection rates. Our results for the U.S. Gulf of Mexico suggest that heterogeneity-assisted trapping has a greater areal extent with more than three times the CO2 storage capacity for secure offshore CO2 storage than with gravitational trapping. These characteristics offer CO2 storage opportunities that are closer to coasts, more accessible, and likely to be less costly.
•Extractability of metals from marine sediments was investigated using various agents.•EDTA covered the strongly bound fraction of Cu and Pb to exchangeable fraction.•Potential hazard of the ...sediments was evaluated.
In this study, the feasibility of a washing process to extract Cd, Cu, Ni, Pb, and Zn from three real dredged marine sediments (Namhang (NH), Bangeojin (BE), and Haengam (HA) bay sediments, South Korea) were investigated using various washing agents (ethylenediaminetetraacetic acid (EDTA), NaCl, HCl, sodium citrate, and HNO3). Even though the removal efficiencies of heavy metals were not high, which is thought to be largely due to the high concentrations of Fe and Ca, EDTA was a more efficient extraction agent for heavy metals compared to the other agents, because EDTA formed more stable complexes with metals. EDTA removed: 30%, 43%, and 9% of Cu; 48%, 66%, and −8% of Pb; and 31%, 60%, and −14% of Zn from NH, BE, and HA sediments, respectively. Additionally, fractionation analysis showed that EDTA converted the strongly bound fractions of Cu and Pb to an exchangeable fraction. Based on the experimental results, the washing technique using EDTA is determined to be efficient for the removal Cu, Pb, and Zn from NH and BE sediment samples. On the contrary, residual concentrations of heavy metals were not decreased from HA samples compared to extraction with washing solution because of the high content of fine particles and organic matter in samples. Furthermore, the fractionations of metals highly influenced the chemical extraction of metals in sediments, and the fractionation changes after chemical washing increased the total extractable amount of metals. As a result, the fractionation change caused changes in the bioavailability and potential mobility of metals.
Dating methodologies for Quaternary marine sediments play increasingly important roles in the reconstruction of paleoenvironments and paleoclimate in (paleo)oceanography. Previous reviews or studies ...have focused mainly on one or two methodologies, and their applications in one specific environment. With the continuing technological and methodological advances in different methods over the past few decades, an up-to-date comparison of the pros and cons of each dating methodology is needed to clearly understand their applications in marine geoscience research. In this review, we first briefly summarized the common methods of absolute dating and relative dating. These are (1) radioisotope dating with different half-lives using natural nuclides of 234Th, 210Pb, 230Th, and 226Ra, cosmogenic nuclides of 7Be, 14C, 10Be, 32Si, 26Al, 36Cl and 21Ne, and the artificial radionuclides of 137Cs, 239, 240Pu, 241Am and 129I that have been induced by atmospheric nuclear tests, accidents in nuclear plants, and discharges of radioactive wastes; (2) radiation exposure dating of luminescence and electron paramagnetic resonance (ESR) dating; and (3) stratigraphic dating of δ18O and paleomagnetic sequence. Applications and limitations from the marine terraces, estuaries, to hadal trenches have been summarized to each technique in the study of Quaternary marine geoscience extending from the Anthropocene through the Pleistocene. Finally, we introduced some emerging event dating methods, namely the arrivals of microplastics, mercury isotopes, and organic pollutant deposition that all appeared after the industrial resolution in our now changing ocean influenced by acidification, global warming, and anthropogenic activities. We ended by discussing future perspectives for reliable and high-resolution chronology by interdisciplinary methods including computer programming to better understand the natural geological evolution and predict the future changes in earth science.
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•Examples of different dating methodologies in Quaternary marine sediment studies were reviewed.•Pollutant dating in the Anthropocene is emerging in the changing modern ocean.•Computer programming learning techniques provide additional ways to improve the resolution of geochronology in the future.
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