From a large number of case studies on terrestrial deposits we know that Late Holocene climate fluctuations have an important impact on the terrestrial environments. However, it is hitherto not clear how the marine se...From a large number of case studies on terrestrial deposits we know that Late Holocene climate fluctuations have an important impact on the terrestrial environments. However, it is hitherto not clear how the marine sediments can be used to shed light on the environment and climate change of the catchment. To provide such insight, we used the major element, trace element and rare earth element（REE） compositions in the southern Yellow Sea（SYS） sediments to reconstruct the changes in weathering and erosion of their source regions. The sediments originate predominantly from the upper crust of East China and are transported into the basin especially by the Yellow River（Huanghe） and to a lesser extent by the Yangtze River（Changjiang）. The chemical index of alteration（CIA; 53.7–59.7） suggests low chemical weathering of the source rocks since the Middle Holocene. This is consistent with the relatively cool and arid climate in North China after the Holocene Megathermal. Comparison of element ratios, including Al/Ca, K/Ca, Al/Na, K/Na, Rb/Sr, Li/Ba and the CIA shows that we can use the latter as a robust proxy for climate change. The CIA-based mean annual precipitation and mean annual temperature show a series of climate fluctuations in the catchment. A relatively warm and humid Period I（5.3–2.9 cal. ka BP）, a relatively cool and dry Period II（2.9–0.9 cal. ka BP） and an increasingly cool and dry Period III（0.9–0.3 cal. ka BP）. These periods can be linked to climate intervals recognized elsewhere.展开更多
Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods.These features include submarine landslides,pockmark fields,shallow free gas...Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods.These features include submarine landslides,pockmark fields,shallow free gas,gas hydrates,mud diapirs and earthquake tsunami,which are widely distributed in the continental slope and reefal islands of the South China Sea.Although the study and assessment of geohazards in the South China Sea came into operation only recently,advances in various aspects are evolving at full speed to comply with National Marine Strategy and‘the Belt and Road’Policy.The characteristics of geohazards in deep-water seafloor of the South China Sea are summarized based on new scientific advances.This progress is aimed to aid ongoing deep-water drilling activities and decrease geological risks in ocean development.展开更多
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 mat...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 N_(2)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.,50µL 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.展开更多
Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea(SCS). In...Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea(SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and overpressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.展开更多
The genus Operculina,a large symbiont-bearing benthic foraminifer,is characterized by high morphological variability showing thick involute to intermediate semi-involute to flat evolute tests.Different morphotypes are...The genus Operculina,a large symbiont-bearing benthic foraminifer,is characterized by high morphological variability showing thick involute to intermediate semi-involute to flat evolute tests.Different morphotypes are either considered as ecophenotypes or distinct species.In order to test the hypothesis of ecophenotypes versus different species,a single cell high throughput sequencing approach was applied to assess the interspecific diversity of Operculina.This results in two groups of ribotypes,one corresponding to Operculina ammonoides/Operculina discoidalis,the other containing Operculina complanata/Operculina elegans.These groups can also be separated morphologically.Therefore,O.complanata and O.elegans represent a single species and the latter can be regarded as a junior synonym of O.complanata.Operculina ammonoides and O.discoidalis also form a single species,which makes the latter a junior synonym of O.ammonoides.Because generic differences in Operculina species are manifested in morphology and molecular genetics,the genus Neoassilina with the designated species Neoassilina ammonoides is installed.Additional analysis of ribosomal SSU rDNA data of eight recent nummulitid genera confirms the obtained high troughput sequencing results and further shows that Palaeonummulites venosus builds a clade with O.complanata that branches at the base of other Nummulitidae containing Planostegina,Planoperculina,Cycloclypeus,Heterostegina,Operculinella and Neoassilina.展开更多
Surface sediment data acquired by the grab sampling technique were used in the present study to produce a high-resolution and full coverage surface grain-size mapping. The objective is to test whether the hypothetical...Surface sediment data acquired by the grab sampling technique were used in the present study to produce a high-resolution and full coverage surface grain-size mapping. The objective is to test whether the hypothetically natural relationship between the surface sediment distribution and complex bathymetry could be used to improve the quality of surface sediment patches mapping. This is based on our hypothesis that grain-size characteristics of the ridge surface sediments must be intrinsically related to the hydrodynamic condition, i.e. storm-induced currents and the geometry of the seabed morphology. The median grain-size data were obtained from grab samples with inclusive bathymetric point recorded at 713 locations on the high-energy and shallow shelf of the Spiekeroog Barrier Island at the German Bight of the Southern North Sea. The area features two-parallel shoreface-connected ridges which is situated obliquely WNW-SSE oriented and mostly sandy in texture. We made use the median grain-size (d50) as the predictand and the bathymetry as the covariable to produce a high-resolution raster map of median grain-size distribution using the Cokriging interpolation. From the cross-validation of the estimated median grain-size data with the measured ones, it is clear that the gradient of the linear regression line for Cokriging is leaning closer towards the theoretical perfect-correlation line (45°) compared to that for Anisotropy Kriging. The interpolation result with Cokriging shows more realistic estimates on the unknown points of the median grain-size and gave detail to surface sediment patchiness, which spatial scale is more or less in agreement with previous studies. In addition to the moderate correlation obtained from the Pearson correlation (r = 0.44), the cross-variogram shows a more precise nature of their spatial correlation, which is physically meaningful for the interpolation process. The present study partially contributes to the framework of habitat mapping and nature protection that is to fill the gaps in physical information in a high-energetic and shallow coastal shelf.展开更多
Archaea have unique glycerol dialkyl glycerol tetraether（GDGT） lipids that can be used to develop paleotemperature proxies such as TEX86.This research is to validate proposed GDGT-proxies for paleotemperature determ...Archaea have unique glycerol dialkyl glycerol tetraether（GDGT） lipids that can be used to develop paleotemperature proxies such as TEX86.This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea（SCS）.Samples were collected from core-top sediments （0-5 cm） in the northern SCS.Total lipids were extracted to obtain core GDGTs,which were identified and quantified using liquid chromatography-mass spectrometry（LC-MS）.The abundance of isoprenoidal GDGTs（/GDGTs） ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment,whereas the branched GDGTs（bGDGTs）,supposedly derived from terrestrial sources,ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment.The TEX_（86）-derived sea surface temperatures ranged from 20.9℃in the coast（water depth 〈 160 m） to 27.9℃offshore（water depth 〉 1000 m）.TEX86-derived temperatures near shore（〈 160 m water depth） averaged 23.1±2.5℃（n =4）,which were close to the satellite-derived winter mean sea surface temperature（average 22.6±1.0℃,n = 4）;whereas the TEX_（86）-derived temperatures offshore averaged 27.4±0.3℃（n = 7） and were consistent with the satellite mean annual sea surface temperature（average 26.8±0.4℃,n = 7）.These results suggest that TEX_（86） may record the sea surface mean annual temperature in the open ocean,while it likely records winter sea surface temperature in the shallower water.展开更多
Fracture-fissure systems found at mid-ocean ridges are dominating conduits for the circulation of metallogenic fluid.Ascertaining the distribution area of active faults on both sides of mid-ocean ridges will provide a...Fracture-fissure systems found at mid-ocean ridges are dominating conduits for the circulation of metallogenic fluid.Ascertaining the distribution area of active faults on both sides of mid-ocean ridges will provide a useful tool in the search for potential hydrothermal vents,thus guiding the exploration of modern seafloor sulfides.Considering the MidAtlantic Ridge 20°N–24°N(NMAR)and North Chile Rise(NCR)as examples,fault elements such as Fault Spacing(?S)and Fault Heave(?X)can be identified and quantitatively measured.The methods used include Fourier filtering of the multi-beam bathymetry data,in combination with measurements of the topographic slope,curvature,and slope aspect patterns.According to the Sequential Faulting Model of mid-ocean ridges,the maximal migration distance of an active fault on either side of mid-ocean ridges—that is,the distribution range of active faults—can be measured.Results show that the maximal migration distance of active faults at the NMAR is 0.76–1.01 km(the distance is larger at the center than at the ends of this segment),and at the NCR,the distribution range of active faults is 0.38–1.6 km.The migration distance of active faults on the two study areas is positively related to the axial variation of magma supply.In the NCR study area,where there is an abundant magma input,the number of faults within a certain distance is mainly affected by the variation of lithospheric thickness.Here a large range of faulting clearly corresponds to a high proportion of magmatism to seafloor spreading near mid-ocean ridges(M)value,and in the study area of the NMAR,there is insufficient magmatism,and the number of faults may be controlled by both lithospheric thickness and magma supply,leading to a less obvious positive correlation between the distribution range of active faults and M.展开更多
Sensitive skin is a clinical syndrome characterized by a hyper-reactive state of the skin,primarily on the face.It is accompanied by subjective symptoms such as burning,stinging,itching,and tightness when exposed to p...Sensitive skin is a clinical syndrome characterized by a hyper-reactive state of the skin,primarily on the face.It is accompanied by subjective symptoms such as burning,stinging,itching,and tightness when exposed to physical,chemical,or psychological stimuli.Objective signs,such as erythema,scales,and dilated blood vessels,may or may not be present.The discomfort associated with sensitive skin can be triggered by various endogenous and exogenous factors,which usually have no significant effect on the individual and do not induce irritant reactions.Sensitive skin often presents as a subjective state without clinical signs and exhibits diversity,posing challenges in sensitive skin research and care.This review summarizes the prevalence,key factors,pathophysiological mechanisms,diagnosis,and progress in daily care for sensitive skin.The aim is to provide a clearer and more systematic understanding of sensitive skin and offer guidance for sensitive skin care.展开更多
Currently, modeling studies tend to significantly underestimate observed space-based glyoxal （CHOCHO） vertical column densities （VCDs）, implying the existence of missing sources of giyoxal. Several recent studies ...Currently, modeling studies tend to significantly underestimate observed space-based glyoxal （CHOCHO） vertical column densities （VCDs）, implying the existence of missing sources of giyoxal. Several recent studies suggest that the emissions of aromatic compounds and molar yields of glyoxal in the chemical mechanisms may both be underestimated, which can affect the simulated glyoxal concentrations. In this study, the influences of these two factors on glyoxal amounts over China were investigated using the RAMS-CMAQ modeling system for January and July 2014. Four sensitivity simulations were performed, and the results were compared to satellite observations. These results demonstrated significant impacts on glyoxal concentrations from these two factors. In case 1, where the emissions of aromatic compounds were increased three-fold, improvements to glyoxal VCDs were seen in high anthropogenic emissions regions. In case 2, where molar yields of glyoxal from isoprene were increased five-fold, the resulted concentrations in July were B-B-fold higher, achieving closer agreement between the modeled and measured glyoxal VCDs. The combined changes from both cases 1 and 2 were applied in case B, and the model succeeded in further reducing the underestimations of glyoxal VCDs. However, the results over most of the regions with pronounced anthropogenic emissions were still underestimated. So the molar yields of giyoxal from anthropogenic precursors were considered in case 4. With these additional mole yield changes （a two-fold increase）, the improved concentrations agreed better with the measurements in regions of the lower reaches of the Yangtze River and Yellow River in January but not in July.展开更多
Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during ...Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during Holocene.To achieve our goals,grain size,total organic carbon,planktic and benthic foraminifera,dinoflagellate cysts have been investigated.Few micropalaentological studies have been done in the studied area and none of them used the combined proxies of benthic foraminifera and dinoflagellate cyst.Theses combined proxies reflects more comprehensive paleoenvironmental view.Biotic and abiotic data have been analysed with multivariate technique including Redundancy Analysis(RDA).Diversity indices such as:Fisher alpha index(α)and Shannon index(H)have been applied.The foraminiferal study yields 9 planktic species and 10 benthic species.Foraminiferal assemblages have low species diversity indices especially at sapropel layer S1.Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding organic poor sediments.Sapropels occur periodically in sedimentary sequences of the last millions years,which have been the subject of extensive previous study.Redundancy Analysis(RDA)yields two groups of foraminiferal assemblages depending on the changes of total organic carbon and clay content.The dinocysts study yields 15 species,the majority of cyst types belonging to the order Gonyaulacales.The association of dinoflagellate cyst shows two depositional phases in the sediment.The sapropel layer S1,with anoxic condition and warmer temperature,is recorded at depth 28-46 cm where heterotrophic taxa dominate and the post-sapropel layer is recorded at depth 0-28 cm;where autotrophic taxa dominate.展开更多
Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter(OM)can influence the mobilization of the toxic metalloid in marine envir...Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter(OM)can influence the mobilization of the toxic metalloid in marine environments.In the present study we analyze the influence of temperature and OM(particularly sulfur-containing additives)on As and S precipitation based on the recent discovery of As-rich nanoparticles in the hydrothermal system near the coast of the Greek island Milos.To this end,we experimentally recreate the formation of amorphous colloidal particles rich in As and S via acidification(pH 3–4)of aqueous precursors at various temperatures.At higher temperatures,we observe the formation of monodisperse particles within the first 24 h of the experiment,generating colloidal particles with diameters close to 160 nm.The S:As ratio and particle size of the synthetized particles closely correlates with values for As_(x)S_(y)particles detected in the hydrothermal system off Milos.Furthermore,organic sulfur containing additives(cysteine and glutathione,GSH)are a key factor in the process of nucleation and growth of amorphous colloidal As_(x)S_(y)particles and,together with the temperature gradient present in shallow hydrothermal vents,dictate the stabilization of As-bearing nanomaterials in the environment.Based on these findings,we present a simple model that summarizes our new insights into the formation and mobility of colloidal As in aquatic ecosystems.In this context,amorphous As_(x)S_(y)particles can present harmful effects to micro-and macro-biota not foreseen in bulk As material.展开更多
We reconstruct the environmental evolution of the East China Sea in the past 14 kyr based on glycerol dialkyl glycerol tetraethers(GDGTs) in a sediment core from the subaqueous Yangtze River Delta. Two primary phases ...We reconstruct the environmental evolution of the East China Sea in the past 14 kyr based on glycerol dialkyl glycerol tetraethers(GDGTs) in a sediment core from the subaqueous Yangtze River Delta. Two primary phases are recognized. Phase I(13.8–8 cal kyr BP) reflects a predominantly continental influence, showing distinctly higher concentrations of branched GDGTs(averaged 143 ng/g dry sediment weight, dsw) than isoprenoid GDGTs(averaged 36 ng/g dsw), high BIT index(branched vs. isoprenoid tetraethers) values(>0.78) and a fluctuating GDGT-0/crenarchaeol ratio(R_(0/5), varied from 0.52 to 3.81). Within this interval, temporal increases of terrestrial and marine influence are attributed to Younger Dryas(YD)(ca. 12.9–12.2 cal kyr BP) cold event and melt-water pulse(MWP)-1B(11.5–11.1 cal kyr BP), respectively. The prominent transition from 8 to 7.9 cal kyr BP shows a sharp decrease in BIT index value(<0.4) and increase in crenarchaeol, which marks the beginning of phase II. Afterwards, the proxies remain relatively constant, which indicates that phase II(7.9 cal kyr BP-present) is a shelf sedimentary environment with high stand of sea level. Overall, the BIT index in our record serves as a good marker for terrestrial influence at the site, and likely reflects the flooding history of the region. The TEX_(86)(Tetra Ether Index of tetraethers consisting of 86 carbons) proxy is not applicable in phase I because of an excess terrestrial influence; but it seems to be valid for revealing the annual SST in phase II(21.6±0.9°C, n=49). In contrast, the MBT'/CBT(Methylation of Branched Tetraethers and Cyclization of Branched Tetraethers) proxy appears to faithfully record the annual mean air temperature(MAT)(14.3±0.63°C, n=68) and presents an integrated signal over the middle and lower Yangtze River drainage basin.展开更多
Asgard is an archaeal superphylum that might hold the key to understand the origin of eukaryotes, but its diversity and ecological roles remain poorly understood. Here, we reconstructed 15 metagenomic-assembled genome...Asgard is an archaeal superphylum that might hold the key to understand the origin of eukaryotes, but its diversity and ecological roles remain poorly understood. Here, we reconstructed 15 metagenomic-assembled genomes from coastal sediments covering most known Asgard archaea and a novel group, which is proposed as a new Asgard phylum named as the "Gerdarchaeota".Genomic analyses predict that Gerdarchaeota are facultative anaerobes in utilizing both organic and inorganic carbon. Unlike their closest relatives Heimdallarchaeota, Gerdarchaeota have genes encoding for cellulase and enzymes involved in the tetrahydromethanopterin-based Wood–Ljungdahl pathway. Transcriptomics showed that most of our identified Asgard archaea are capable of degrading organic matter, including peptides, amino acids and fatty acids, occupying ecological niches in different depths of layers of the sediments. Overall, this study broadens the diversity of the mysterious Asgard archaea and provides evidence for their ecological roles in coastal sediments.展开更多
A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that...A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that the poleward advancing mid-latitude meridional temperature gradient(MTG),originating from enhanced subtropical ocean warming,plays a leading role in driving tropical expansion.However,the abrupt4xCO_(2) experiment indicates that tropical expansion occurs at a faster rate than is indicated by changes related to ocean temperature rise.The idealized amip4K experiment illustrates that without introducing any ocean warming pattern,uniform ocean surface warming also drives tropical expansion.The results based on these idealized experiments seem to contradict the hypothesis proposed by Yang et al.In this study,we revisit these 2 experiments and show that both experiments actually support the hypothesis that MTG migration is driving tropical expansion.More specifically,in the abrupt4xCO_(2) experiment,although the rate of ocean warming is relatively slow,the poleward shift of the MTG is as rapid as tropical expansion.In the amip4K experiment,although ocean surface warming is uniform,the heating effect of the ocean on the atmosphere is nonuniform because of the nonlinear relationship between temperature,evaporation,and thermal radiation.The nonuniform oceanic heating to the atmosphere introduces a poleward shift of the MTG within the upper troposphere and drives a shift in the jet streams.By conducting an additional idealized experiment in which tropical expansion occurs under both a migrating MTG and a cooling climate,we argue that the migration of the MTG,rather than global warming,is the key mechanism in driving tropical expansion.展开更多
基金funded by the"Strategic Priority Research Program"of Chinese Academy of Sciences(Nos.XDA11020102 and XDA05030402)the National Natural Science Foundation of China(No.41376090)+2 种基金the Research Fund for the Doctoral Program of Higher Education of China(No.20120145120017)the Marine Safeguard Project(No.GZH201200503)the Special Fund for Basic Scientific Research of Central Colleges,China University of Geosciences Wuhan
文摘From a large number of case studies on terrestrial deposits we know that Late Holocene climate fluctuations have an important impact on the terrestrial environments. However, it is hitherto not clear how the marine sediments can be used to shed light on the environment and climate change of the catchment. To provide such insight, we used the major element, trace element and rare earth element（REE） compositions in the southern Yellow Sea（SYS） sediments to reconstruct the changes in weathering and erosion of their source regions. The sediments originate predominantly from the upper crust of East China and are transported into the basin especially by the Yellow River（Huanghe） and to a lesser extent by the Yangtze River（Changjiang）. The chemical index of alteration（CIA; 53.7–59.7） suggests low chemical weathering of the source rocks since the Middle Holocene. This is consistent with the relatively cool and arid climate in North China after the Holocene Megathermal. Comparison of element ratios, including Al/Ca, K/Ca, Al/Na, K/Na, Rb/Sr, Li/Ba and the CIA shows that we can use the latter as a robust proxy for climate change. The CIA-based mean annual precipitation and mean annual temperature show a series of climate fluctuations in the catchment. A relatively warm and humid Period I（5.3–2.9 cal. ka BP）, a relatively cool and dry Period II（2.9–0.9 cal. ka BP） and an increasingly cool and dry Period III（0.9–0.3 cal. ka BP）. These periods can be linked to climate intervals recognized elsewhere.
基金funded by the MOST 973 program (No. 2015CB251201)the Guangzhou Marine Geology Survey project (Nos. GZH201400210 and GZH201601040) the National Natural Science Foundation of China (Nos. 91228208 and 41666012)
文摘Various geological processes and features that might inflict hazards identified in the South China Sea by using new technologies and methods.These features include submarine landslides,pockmark fields,shallow free gas,gas hydrates,mud diapirs and earthquake tsunami,which are widely distributed in the continental slope and reefal islands of the South China Sea.Although the study and assessment of geohazards in the South China Sea came into operation only recently,advances in various aspects are evolving at full speed to comply with National Marine Strategy and‘the Belt and Road’Policy.The characteristics of geohazards in deep-water seafloor of the South China Sea are summarized based on new scientific advances.This progress is aimed to aid ongoing deep-water drilling activities and decrease geological risks in ocean development.
基金The European Union’s Seventh Framework Programme—Ideas Specific Programme under contract No.247153(Advanced Grant DARCLIFEPrincipal Investigator,K.-U.)+2 种基金the Fund of the Deutsche Forschungsgemeinschaft through the Research Center/Excellence Cluster MARUM—Center for Marine Environmental Sciences,Project GB2the Fund of China Scholarship Councilthe Fund of Bremen International Graduate School for Marine Sciences.
文摘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 N_(2)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.,50µL 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.
基金supported by the National Natural Science Foundation of China (Nos. 41576049, 4166 6002)the Key Research Projects of Frontier Science of the Chinese Academy of Sciences (No. QYZDB-SSWSYS025)+1 种基金Qingdao National Laboratory for Marine Science and Technology (No. 2016ASKJ13)Key Science and Technology Foundation of Sanya (Nos. 2017PT 13, 2017PT14)
文摘Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea(SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and overpressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.
基金supported by Israel Science Foundation(No.1267/21)to Sigal Abramovichthe Swiss National Science Foundation(No.31003A_179125)to Jan PawlowskiOpen Access funding provided by University of Geneva。
文摘The genus Operculina,a large symbiont-bearing benthic foraminifer,is characterized by high morphological variability showing thick involute to intermediate semi-involute to flat evolute tests.Different morphotypes are either considered as ecophenotypes or distinct species.In order to test the hypothesis of ecophenotypes versus different species,a single cell high throughput sequencing approach was applied to assess the interspecific diversity of Operculina.This results in two groups of ribotypes,one corresponding to Operculina ammonoides/Operculina discoidalis,the other containing Operculina complanata/Operculina elegans.These groups can also be separated morphologically.Therefore,O.complanata and O.elegans represent a single species and the latter can be regarded as a junior synonym of O.complanata.Operculina ammonoides and O.discoidalis also form a single species,which makes the latter a junior synonym of O.ammonoides.Because generic differences in Operculina species are manifested in morphology and molecular genetics,the genus Neoassilina with the designated species Neoassilina ammonoides is installed.Additional analysis of ribosomal SSU rDNA data of eight recent nummulitid genera confirms the obtained high troughput sequencing results and further shows that Palaeonummulites venosus builds a clade with O.complanata that branches at the base of other Nummulitidae containing Planostegina,Planoperculina,Cycloclypeus,Heterostegina,Operculinella and Neoassilina.
文摘Surface sediment data acquired by the grab sampling technique were used in the present study to produce a high-resolution and full coverage surface grain-size mapping. The objective is to test whether the hypothetically natural relationship between the surface sediment distribution and complex bathymetry could be used to improve the quality of surface sediment patches mapping. This is based on our hypothesis that grain-size characteristics of the ridge surface sediments must be intrinsically related to the hydrodynamic condition, i.e. storm-induced currents and the geometry of the seabed morphology. The median grain-size data were obtained from grab samples with inclusive bathymetric point recorded at 713 locations on the high-energy and shallow shelf of the Spiekeroog Barrier Island at the German Bight of the Southern North Sea. The area features two-parallel shoreface-connected ridges which is situated obliquely WNW-SSE oriented and mostly sandy in texture. We made use the median grain-size (d50) as the predictand and the bathymetry as the covariable to produce a high-resolution raster map of median grain-size distribution using the Cokriging interpolation. From the cross-validation of the estimated median grain-size data with the measured ones, it is clear that the gradient of the linear regression line for Cokriging is leaning closer towards the theoretical perfect-correlation line (45°) compared to that for Anisotropy Kriging. The interpolation result with Cokriging shows more realistic estimates on the unknown points of the median grain-size and gave detail to surface sediment patchiness, which spatial scale is more or less in agreement with previous studies. In addition to the moderate correlation obtained from the Pearson correlation (r = 0.44), the cross-variogram shows a more precise nature of their spatial correlation, which is physically meaningful for the interpolation process. The present study partially contributes to the framework of habitat mapping and nature protection that is to fill the gaps in physical information in a high-energetic and shallow coastal shelf.
基金supported by the South China Sea-Deep program of the National Science Foundation of China #91028005(CLZ)the State Key Laboratory of Marine Geology of Tongji UniversityHD was supported by NSFC(Grant Nos.91028011 and 41076091)
文摘Archaea have unique glycerol dialkyl glycerol tetraether（GDGT） lipids that can be used to develop paleotemperature proxies such as TEX86.This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea（SCS）.Samples were collected from core-top sediments （0-5 cm） in the northern SCS.Total lipids were extracted to obtain core GDGTs,which were identified and quantified using liquid chromatography-mass spectrometry（LC-MS）.The abundance of isoprenoidal GDGTs（/GDGTs） ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment,whereas the branched GDGTs（bGDGTs）,supposedly derived from terrestrial sources,ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment.The TEX_（86）-derived sea surface temperatures ranged from 20.9℃in the coast（water depth 〈 160 m） to 27.9℃offshore（water depth 〉 1000 m）.TEX86-derived temperatures near shore（〈 160 m water depth） averaged 23.1±2.5℃（n =4）,which were close to the satellite-derived winter mean sea surface temperature（average 22.6±1.0℃,n = 4）;whereas the TEX_（86）-derived temperatures offshore averaged 27.4±0.3℃（n = 7） and were consistent with the satellite mean annual sea surface temperature（average 26.8±0.4℃,n = 7）.These results suggest that TEX_（86） may record the sea surface mean annual temperature in the open ocean,while it likely records winter sea surface temperature in the shallower water.
基金supported by the grant of China Ocean Mineral Resources R&D Association(DY135-S2-1-01)
文摘Fracture-fissure systems found at mid-ocean ridges are dominating conduits for the circulation of metallogenic fluid.Ascertaining the distribution area of active faults on both sides of mid-ocean ridges will provide a useful tool in the search for potential hydrothermal vents,thus guiding the exploration of modern seafloor sulfides.Considering the MidAtlantic Ridge 20°N–24°N(NMAR)and North Chile Rise(NCR)as examples,fault elements such as Fault Spacing(?S)and Fault Heave(?X)can be identified and quantitatively measured.The methods used include Fourier filtering of the multi-beam bathymetry data,in combination with measurements of the topographic slope,curvature,and slope aspect patterns.According to the Sequential Faulting Model of mid-ocean ridges,the maximal migration distance of an active fault on either side of mid-ocean ridges—that is,the distribution range of active faults—can be measured.Results show that the maximal migration distance of active faults at the NMAR is 0.76–1.01 km(the distance is larger at the center than at the ends of this segment),and at the NCR,the distribution range of active faults is 0.38–1.6 km.The migration distance of active faults on the two study areas is positively related to the axial variation of magma supply.In the NCR study area,where there is an abundant magma input,the number of faults within a certain distance is mainly affected by the variation of lithospheric thickness.Here a large range of faulting clearly corresponds to a high proportion of magmatism to seafloor spreading near mid-ocean ridges(M)value,and in the study area of the NMAR,there is insufficient magmatism,and the number of faults may be controlled by both lithospheric thickness and magma supply,leading to a less obvious positive correlation between the distribution range of active faults and M.
基金supported by the Key-Area Research and Development Program of Guangdong Province[grant numbers 21202107201900005,21202107201900003].
文摘Sensitive skin is a clinical syndrome characterized by a hyper-reactive state of the skin,primarily on the face.It is accompanied by subjective symptoms such as burning,stinging,itching,and tightness when exposed to physical,chemical,or psychological stimuli.Objective signs,such as erythema,scales,and dilated blood vessels,may or may not be present.The discomfort associated with sensitive skin can be triggered by various endogenous and exogenous factors,which usually have no significant effect on the individual and do not induce irritant reactions.Sensitive skin often presents as a subjective state without clinical signs and exhibits diversity,posing challenges in sensitive skin research and care.This review summarizes the prevalence,key factors,pathophysiological mechanisms,diagnosis,and progress in daily care for sensitive skin.The aim is to provide a clearer and more systematic understanding of sensitive skin and offer guidance for sensitive skin care.
基金supported by the National Natural Science Foundation of China (No. 91544221)the National Key R&D Programs of China (Nos. 2017YFC0209803, 2017YFC0210000)the CAS Strategic Priority Research Program Grant (No. XDB05020000)
文摘Currently, modeling studies tend to significantly underestimate observed space-based glyoxal （CHOCHO） vertical column densities （VCDs）, implying the existence of missing sources of giyoxal. Several recent studies suggest that the emissions of aromatic compounds and molar yields of glyoxal in the chemical mechanisms may both be underestimated, which can affect the simulated glyoxal concentrations. In this study, the influences of these two factors on glyoxal amounts over China were investigated using the RAMS-CMAQ modeling system for January and July 2014. Four sensitivity simulations were performed, and the results were compared to satellite observations. These results demonstrated significant impacts on glyoxal concentrations from these two factors. In case 1, where the emissions of aromatic compounds were increased three-fold, improvements to glyoxal VCDs were seen in high anthropogenic emissions regions. In case 2, where molar yields of glyoxal from isoprene were increased five-fold, the resulted concentrations in July were B-B-fold higher, achieving closer agreement between the modeled and measured glyoxal VCDs. The combined changes from both cases 1 and 2 were applied in case B, and the model succeeded in further reducing the underestimations of glyoxal VCDs. However, the results over most of the regions with pronounced anthropogenic emissions were still underestimated. So the molar yields of giyoxal from anthropogenic precursors were considered in case 4. With these additional mole yield changes （a two-fold increase）, the improved concentrations agreed better with the measurements in regions of the lower reaches of the Yangtze River and Yellow River in January but not in July.
文摘Paleontological and sedimentological analyses were carried out in sediment core from southeastern Mediterranean Sea,offshore Egypt to reconstruct the past environmental changes in trophic state and temperature during Holocene.To achieve our goals,grain size,total organic carbon,planktic and benthic foraminifera,dinoflagellate cysts have been investigated.Few micropalaentological studies have been done in the studied area and none of them used the combined proxies of benthic foraminifera and dinoflagellate cyst.Theses combined proxies reflects more comprehensive paleoenvironmental view.Biotic and abiotic data have been analysed with multivariate technique including Redundancy Analysis(RDA).Diversity indices such as:Fisher alpha index(α)and Shannon index(H)have been applied.The foraminiferal study yields 9 planktic species and 10 benthic species.Foraminiferal assemblages have low species diversity indices especially at sapropel layer S1.Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding organic poor sediments.Sapropels occur periodically in sedimentary sequences of the last millions years,which have been the subject of extensive previous study.Redundancy Analysis(RDA)yields two groups of foraminiferal assemblages depending on the changes of total organic carbon and clay content.The dinocysts study yields 15 species,the majority of cyst types belonging to the order Gonyaulacales.The association of dinoflagellate cyst shows two depositional phases in the sediment.The sapropel layer S1,with anoxic condition and warmer temperature,is recorded at depth 28-46 cm where heterotrophic taxa dominate and the post-sapropel layer is recorded at depth 0-28 cm;where autotrophic taxa dominate.
基金supported by Conicyt through a fellowship to VDT(Programa de Capital Humano Avanzado,BECASChile,CONICYT,72160570 Res.Convenio 7359/2015)by the Deutsche Forschungsgemeinschaft(DFG,Germany)through the Emmy Noether Program(grant BU 2606/1-1 to SIB)。
文摘Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter(OM)can influence the mobilization of the toxic metalloid in marine environments.In the present study we analyze the influence of temperature and OM(particularly sulfur-containing additives)on As and S precipitation based on the recent discovery of As-rich nanoparticles in the hydrothermal system near the coast of the Greek island Milos.To this end,we experimentally recreate the formation of amorphous colloidal particles rich in As and S via acidification(pH 3–4)of aqueous precursors at various temperatures.At higher temperatures,we observe the formation of monodisperse particles within the first 24 h of the experiment,generating colloidal particles with diameters close to 160 nm.The S:As ratio and particle size of the synthetized particles closely correlates with values for As_(x)S_(y)particles detected in the hydrothermal system off Milos.Furthermore,organic sulfur containing additives(cysteine and glutathione,GSH)are a key factor in the process of nucleation and growth of amorphous colloidal As_(x)S_(y)particles and,together with the temperature gradient present in shallow hydrothermal vents,dictate the stabilization of As-bearing nanomaterials in the environment.Based on these findings,we present a simple model that summarizes our new insights into the formation and mobility of colloidal As in aquatic ecosystems.In this context,amorphous As_(x)S_(y)particles can present harmful effects to micro-and macro-biota not foreseen in bulk As material.
基金supported by the National Key Basic Research Program of China (Grant No. 2013CB955703), National Key Basic Research Program of China (Grant No. 2013CB429701)the National Natural Science Foundation of China (Grant No. 91028005)+4 种基金the China Geological Survey (Grant No. GZH201100203)the Fundamental Research Funds for the Central Universitiesthe "National Thousand Talents" Program through the State Key Laboratory of Marine Geology at Tongji Universitythe DFG to GJMV Heisenberg Grant (Grant No. VE486/2-2)the Project of Shanghai Engineering Research Center of Hadal Science and Technology (Grant No. 14DZ2250900)
文摘We reconstruct the environmental evolution of the East China Sea in the past 14 kyr based on glycerol dialkyl glycerol tetraethers(GDGTs) in a sediment core from the subaqueous Yangtze River Delta. Two primary phases are recognized. Phase I(13.8–8 cal kyr BP) reflects a predominantly continental influence, showing distinctly higher concentrations of branched GDGTs(averaged 143 ng/g dry sediment weight, dsw) than isoprenoid GDGTs(averaged 36 ng/g dsw), high BIT index(branched vs. isoprenoid tetraethers) values(>0.78) and a fluctuating GDGT-0/crenarchaeol ratio(R_(0/5), varied from 0.52 to 3.81). Within this interval, temporal increases of terrestrial and marine influence are attributed to Younger Dryas(YD)(ca. 12.9–12.2 cal kyr BP) cold event and melt-water pulse(MWP)-1B(11.5–11.1 cal kyr BP), respectively. The prominent transition from 8 to 7.9 cal kyr BP shows a sharp decrease in BIT index value(<0.4) and increase in crenarchaeol, which marks the beginning of phase II. Afterwards, the proxies remain relatively constant, which indicates that phase II(7.9 cal kyr BP-present) is a shelf sedimentary environment with high stand of sea level. Overall, the BIT index in our record serves as a good marker for terrestrial influence at the site, and likely reflects the flooding history of the region. The TEX_(86)(Tetra Ether Index of tetraethers consisting of 86 carbons) proxy is not applicable in phase I because of an excess terrestrial influence; but it seems to be valid for revealing the annual SST in phase II(21.6±0.9°C, n=49). In contrast, the MBT'/CBT(Methylation of Branched Tetraethers and Cyclization of Branched Tetraethers) proxy appears to faithfully record the annual mean air temperature(MAT)(14.3±0.63°C, n=68) and presents an integrated signal over the middle and lower Yangtze River drainage basin.
基金the National Natural Science Foundation of China (91851105, 31622002, 31970105, 31600093, and 31700430)the Shenzhen Science and Technology Program (JCYJ20170818091727570 and KQTD20180412181334790)+3 种基金the Key Project of Department of Education of Guangdong Province (2017KZDXM071)the China Postdoctoral Science Foundation (2018M633111)the DFG (Deutsche Forschungsgemeinschaft) Cluster of Excellence EXC 309 “The Ocean in the Earth System - MARUM - Center for Marine Environmental Sciences” (project ID 49926684)the University of Bremen。
文摘Asgard is an archaeal superphylum that might hold the key to understand the origin of eukaryotes, but its diversity and ecological roles remain poorly understood. Here, we reconstructed 15 metagenomic-assembled genomes from coastal sediments covering most known Asgard archaea and a novel group, which is proposed as a new Asgard phylum named as the "Gerdarchaeota".Genomic analyses predict that Gerdarchaeota are facultative anaerobes in utilizing both organic and inorganic carbon. Unlike their closest relatives Heimdallarchaeota, Gerdarchaeota have genes encoding for cellulase and enzymes involved in the tetrahydromethanopterin-based Wood–Ljungdahl pathway. Transcriptomics showed that most of our identified Asgard archaea are capable of degrading organic matter, including peptides, amino acids and fatty acids, occupying ecological niches in different depths of layers of the sediments. Overall, this study broadens the diversity of the mysterious Asgard archaea and provides evidence for their ecological roles in coastal sediments.
基金supported by the AWI INSPIRES program of“Changing Earth-Sustaining our Future”and the Deutsche Forschungsgemeinschaft(Excellence Cluster“EXC 2077:The Ocean Floor-Earth’s Uncharted Interface”,project no.390741603)。
文摘A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that the poleward advancing mid-latitude meridional temperature gradient(MTG),originating from enhanced subtropical ocean warming,plays a leading role in driving tropical expansion.However,the abrupt4xCO_(2) experiment indicates that tropical expansion occurs at a faster rate than is indicated by changes related to ocean temperature rise.The idealized amip4K experiment illustrates that without introducing any ocean warming pattern,uniform ocean surface warming also drives tropical expansion.The results based on these idealized experiments seem to contradict the hypothesis proposed by Yang et al.In this study,we revisit these 2 experiments and show that both experiments actually support the hypothesis that MTG migration is driving tropical expansion.More specifically,in the abrupt4xCO_(2) experiment,although the rate of ocean warming is relatively slow,the poleward shift of the MTG is as rapid as tropical expansion.In the amip4K experiment,although ocean surface warming is uniform,the heating effect of the ocean on the atmosphere is nonuniform because of the nonlinear relationship between temperature,evaporation,and thermal radiation.The nonuniform oceanic heating to the atmosphere introduces a poleward shift of the MTG within the upper troposphere and drives a shift in the jet streams.By conducting an additional idealized experiment in which tropical expansion occurs under both a migrating MTG and a cooling climate,we argue that the migration of the MTG,rather than global warming,is the key mechanism in driving tropical expansion.
