New Benthic Fossils from the Late Ediacaran Strata of Southwestern China

The Jiangchuan Biota from the Jiucheng Member(Mb.)of the Dengying Formation(Fm.),discovered in Jiangchuan,eastern Yunnan,China,is marked by copious macrofossils at the apex of the Ediacaran strata.This fauna features benthic algae with varied holdfasts and other fossils of indeterminate taxonomic affinity and is compositionally unique compared to the Shibantan and Gaojiashan biotas of the Dengying Fm.and the Miaohe and Wenghui biotas of the Doushantuo Fm.,elsewhere in China.One novel benthic saccular macroalgal fossil,named here Houjiashania yuxiensis gen.and sp.nov.,from the Jiangchuan Biota is based on fossils that are sausage-shaped,elongate,tubular,ranging from 0.3 to 4 cm in length,and up to 0.8 cm in diameter.One terminus is blunt and rounded to an obtuse angle,the other is bent with a spread-out surface resembling a holdfast,suggesting a three-dimensional thallus.Thin,stipe-shaped outgrowths,likely vestiges of sessile saccular life forms,are prevalent in macroalgal fossils of analogous size and shape,as well as present brown algae Scytosiphonaceae,such as Colpomenia and Dactylosiphon.The new findings augment the diversity of benthic algae,such as those known from the Early Neoproterozoic Longfengshan Biota in North China.The benthic algal macrofossils in the Jiucheng Mb.add to knowledge of Late Ediacaran metaphyte diversification and offer more clues about the evolutionary positioning of primitive macroalgae.The co-occurrence of numerous planktonic and benthic multicellular algae and planktonic microbes might have facilitated ecologically the more extensive later Cambrian explosion evidenced by the Chengjiang Biota in Yunnan.

Small molecule deoxynyboquinone triggers alkylation and ubiquitination of Keap1 at Cys489 on Kelch domain for Nrf2 activation and inflammatory therapy

Activation of nuclear factor erythroid 2-related factor 2(Nrf2)by Kelch-like ECH-associated protein 1(Keap1)alkylation plays a central role in anti-inflammatory therapy.However,activators of Nrf2 through alkylation of Keap1-Kelch domain have not been identified.Deoxynyboquinone(DNQ)is a natural small molecule discovered from marine actinomycetes.The current study was designed to investigate the anti-inflammatory effects and molecular mechanisms of DNQ via alkylation of Keap1.DNQ exhibited significant anti-inflammatory properties both in vitro and in vivo.The pharmacophore responsible for the anti-inflammatory properties of DNQ was determined to be theα,β-unsaturated amides moieties by a chemical reaction between DNQ and N-acetylcysteine.DNQ exerted anti-inflammatory effects through activation of Nrf2/ARE pathway.Keap1 was demonstrated to be the direct target of DNQ and bound with DNQ through conjugate addition reaction involving alkylation.The specific alkylation site of DNQ on Keap1 for Nrf2 activation was elucidated with a synthesized probe in conjunction with liquid chromatography-tandem mass spectrometry.DNQ triggered the ubiquitination and subsequent degradation of Keap1 by alkylation of the cysteine residue 489(Cys489)on Keap1-Kelch domain,ultimately enabling the activation of Nrf2.Our findings revealed that DNQ exhibited potent anti-inflammatory capacity throughα,β-unsaturated amides moieties active group which specifically activated Nrf2 signal pathway via alkylation/ubiquitination of Keap1-Kelch domain,suggesting the potential values of targeting Cys489 on Keap1-Kelch domain by DNQ-like small molecules in inflammatory therapies.

New record of the feather star Palaeocomatella hiwia(Echinodermata:Crinoidea:Comatulida)from Zhenbei Seamount in South China Sea:new insights into the taxonomic position of Palaeocomatella

One specimen belonging to the family Comatellinae was collected from the Zhenbei Seamount(332.5–478.2 m)in the South China Sea in July 2022.Based on the morphological characters,the specimen was identified as Palaeocomatella hiwia McKnight,1977.It is first recorded from China Sea and redescribed in detail.This specimen differs from the original description from New Zealand for never showing syzygy at br4+5 or br5+6 on interior and br1+2 on exterior arms.However,it is much conform to the redescription to specimens from Indonesia,with only differences in position of the second syzygy and distalmost pinnule comb.Specimen is deposited in the Institute of Oceanology,Chinese Academy of Sciences.Phylogenetic analyses based on the mitochondrial c oxidase subunit I(COI)and 16S rRNA genes indicated that P.hiwia was nested within the tribe Phanogeniini and clustered with Aphanocomaster pulcher.Furthermore,P.hiwia showed same morphological features in terms of mouth placement,comb location,and number of comb teeth rows as other genera of Phanogeniini.Therefore,we suggest that the genus Palaeocomatella should be put in the tribe Phanogeniini.

Integrated biomarker response to assess toxic impacts of iron and manganese on deep-sea mussel Gigantidas platifrons under a deep-sea mining activity scenario

Deep-sea mining activities can potentially release metals,which pose a toxicological threat to deep-sea ecosystems.Nevertheless,due to the remoteness and inaccessibility of the deep-sea biosphere,there is insufficient knowledge about the impact of metal exposure on its inhabitants.In this study,deep-sea mussel Gigantidas platifrons,a commonly used deep-sea toxicology model organism,was exposed to manganese(100,1000μg/L)or iron(500,5000μg/L)for 7 d,respectively.Manganese and iron were chosen for their high levels of occurrence within deep-sea deposits.Metal accumulation and a battery of biochemical biomarkers related to antioxidative stress in superoxide dismutase(SOD),catalase(CAT),malondialdehyde(MDA);immune function in alkaline phosphatase(AKP),acid phosphatase(ACP);and energy metabolism in pyruvate kinase(PK)and hexokinase(HK)were assessed in mussel gills.Results showed that deep-sea mussel G.platifrons exhibited a high capacity to accumulate Mn/Fe.In addition,most tested biochemical parameters were altered by metal exposure,demonstrating that metals could induce oxidative stress,suppress the immune system,and affect energy metabolism of deep-sea mussels.The integrated biomarker response(IBR)approach indicated that the exposure to Mn/Fe had a negative impact on deep-sea mussels,and Mn demonstrated a more harmful impact on deep-sea mussels than Fe.Additionally,SOD and CAT biomarkers had the greatest impact on IBR values in Mn treatments,while ACP and HK were most influential for the low-and high-dose Fe groups,respectively.This study represents the first application of the IBR approach to evaluate the toxicity of metals on deep-sea fauna and serves as a crucial framework for risk assessment of deep-sea mining-associated metal exposure.

Small temporal variation in abundance of virioplankton compared to bacterioplankton and phytoplankton in two bays in the northern South China Sea

Variations of picoplankton groups were investigated over a one-month period in Daya Bay and Sanya Bay,in the northern South China Sea.The two coastal regions exhibited different variation patterns in physicochemical parameters.Moreover,the diel variations of picoplankton groups were different between the two bays.The abundance of the picoplankton in Sanya Bay displayed a pronounced diel variation,while it was not significant in Daya Bay.In addition,some similar patterns of picoplankton abundance were discovered.In the two bays,virioplankton exhibited the smallest fluctuation range,whereas picocyanobacteria fluctuated most markedly.The fluctuation range of picoplankton groups was larger in spring tide than in neap tide,especially in Sanya Bay.Random forest model analysis demonstrated that the variation of picoplankton groups was attributed to physical and chemical factors in Sanya Bay and Daya Bay,respectively.Therefore,our findings suggest that virioplankton abundance can persist more stably in response to changing environmental conditions compared to bacterioplankton and picophytoplankton.

Impacts of central-Pacific El Niño and physical drivers on eastern Pacific bigeye tuna

Bigeye tuna Thunnus obesus is an important migratory species that forages deeply,and El Niño events highly influence its distribution in the eastern Pacific Ocean.While sea surface temperature is widely recognized as the main factor affecting bigeye tuna(BET)distribution during El Niño events,the roles of different types of El Niño and subsurface oceanic signals,such as ocean heat content and mixed layer depth,remain unclear.We conducted A spatial-temporal analysis to investigate the relationship among BET distribution,El Niño events,and the underlying oceanic signals to address this knowledge gap.We used monthly purse seine fisheries data of BET in the eastern tropical Pacific Ocean(ETPO)from 1994 to 2012 and extracted the central-Pacific El Niño(CPEN)indices based on Niño 3 and Niño 4indexes.Furthermore,we employed Explainable Artificial Intelligence(XAI)models to identify the main patterns and feature importance of the six environmental variables and used information flow analysis to determine the causality between the selected factors and BET distribution.Finally,we analyzed Argo datasets to calculate the vertical,horizontal,and zonal mean temperature differences during CPEN and normal years to clarify the oceanic thermodynamic structure differences between the two types of years.Our findings reveal that BET distribution during the CPEN years is mainly driven by advection feedback of subsurface warmer thermal signals and vertically warmer habitats in the CPEN domain area,especially in high-yield fishing areas.The high frequency of CPEN events will likely lead to the westward shift of fisheries centers.

Spatial patterns of zooplankton abundance,biovolume,and size structure in response to environmental variables:a case study in the Yellow Sea and East China Sea

The Yellow Sea(YS)and East China Sea(ECS)are highly dynamic marginal seas of the northwestern Pacific Ocean.To gain an in-depth understanding of zooplankton community structure,zooplankton abundance,biovolume,and size structure in summer 2017 in the YS and ECS were assessed using ZooScan imaging analysis.Zooplankton abundance and biovolume ranged 2.94–1187.14 inds./m^(3)and 3.13–3438.51 mm^(3)/m^(3),respectively.Based on the biovolume data of the categorized size classes of 26 identified taxonomic groups,the zooplankton community was classified into five groups,and each group was coupled with distinctive oceanographic features.Under the influence of the Yellow Sea Cold Water Mass,the Yellow Sea offshore group featured the lowest bottom temperature(10.84±3.42℃)and the most abundant Calanoids(mainly in the 2–3 mm size class).In the Yellow Sea inshore group,Hydrozoans showed the largest biovolume and dominated in the 3–4-mm and>5-mm size classes.The East China Sea offshore group,which was affected by the Kuroshio Branch Current,featured high temperature and salinity,and the lowest bottom dissolved oxygen(2.58±0.5 mg/L).The lowest values of zooplankton abundance and biovolume in the East China Sea offshore group might be attributed to the bottom dissolved oxygen contents.The East China Sea inshore group,which was mainly influenced by the Zhejiang-Fujian Coastal Current and Changjiang Diluted Water,was characterized by high chlorophyll a and the largest biovolume of carnivorous Siphonophores(280.82±303.37 mm^(3)/m^(3)).The Changjiang River estuary offshore group showed the most abundant Cyclopoids,which might be associated with the less turbid water mass in this region.Seawater temperature was considered the most important factor in shaping the size compositions of Calanoids in different groups.

Molybdenum isotope composition of the upper mantle and its origin:insight from mid-ocean ridge basalt

The molybdenum(Mo)isotope system is pivotal in reconstructing marine redox changes throughout Earth’s history and has emerged as a promising tracer for igneous and metamorphic processes.Understanding its composition and variation across major geochemical reservoirs is essential for its application in investigating high-temperature processes.However,there is debate regarding theδ^(98/95)Mo value of the Earth’s mantle,with estimates ranging from sub-chondritic to super-chondritic values.Recent analyses of global mid-ocean ridge basalt(MORB)glasses revealed significantδ^(98/95)Mo variations attributed to mantle heterogeneity,proposing a two-component mixing model to explain the observed variation.Complementary studies confirmed the sub-chondriticδ^(98/95)Mo of the depleted upper mantle,suggesting remixing of subduction-modified oceanic crust as a plausible mechanism.These findings underscore the role of Mo isotopes as effective tracers for understanding dynamic processes associated with mantle-crustal recycling.

Distribution,abundance,and realized niches of meroplankton by two different mesh size nets during spring 2017 in the Southern Yellow Sea,China

Meroplankton play a crucial role in both benthic and pelagic ecosystems.Existing quantitative research on estimating the quantities of meroplankton groups is both underrepresented and inaccurate.To investigate and evaluate the influence of varying mesh sizes(505 and 160μm)on the sampling efficiency of meroplankton,we conducted an examination using two commonly used plankton nets during the spring season in the Southern Yellow Sea(SYS).Our study revealed a total of 12 meroplankton groups,with 9 groups identified in the 505-μm mesh nets and 11 groups in the 160-μm mesh nets.The results demonstrated the superior collection efficiency of the 160-μm net compared to the 505-μm net across the majority of meroplankton groups.Furthermore,we focused on exploring the abundance,distribution patterns,and realized niches of meroplankton collected by the two mesh size nets,and observed that the distribution of meroplankton closely resembled the distribution of possible benthic adults in the SYS.Correlation analysis of the six dominant groups collected in the 160-μm mesh nets revealed that seawater temperature and salinity emerged as the key environmental factors driving variations in meroplankton abundance within the SYS.This study also found that a smaller mesh size net does not necessarily capture meroplankton more comprehensively.A comprehensive understanding of the ecological characteristics of meroplankton requires the combination of two types of nets for research.Our research significantly advances our understanding of the quantification,abundance,and distribution of meroplankton,serving as a valuable contribution to the broader landscape of detailed quantitative meroplankton studies.

Contrasting physical mechanisms of yellowfin tuna fluctuations between the western and eastern Indian Ocean

As an economically critical pelagic migratory species,yellowfin tuna(Thunnus albacores,YFT)is very sensible to physical and environmental conditions,such as sea surface temperature(SST),ocean heat content(OHC),and the mixed layer depth(MLD).We investigated the impact of SST,OHC,and MLD on fluctuations of YFT catch in the western/eastern Indian Ocean using the long time series of 63-year environmental and YFT datasets.We found that the impact of SST on YFT was heavily overestimated in the past,and MLD plays a more critical role in the YFT catch fluctuation.When the MLD deepens(>34.8 m),SST was more influential in predicting the catches of YFT than OHC in the western Indian Ocean,and OHC was more critical to YFT than SST in the eastern Indian Ocean.However,when the MLD shallows(<34.8 m),MLD was more vital to predict the catch per unit effort(CPUE)of YFT than SST/OHC in the western.After 2000,there was an asynchronous pattern of YFT CPUE induced by higher frequency variations and ocean hiatus of SST/OHC signals in the western and eastern Indian Oceans basins.The impact of the subsurface hiatus may induce the decrease of YFT in the eastern Indian Ocean.The above findings clarified a non-stationary relationship between the environmental factors and catches of YFT and provided new insights into variations in YFT abundance.

Morphological and molecular analyses of a Philine kinglipini outbreak in summer of 2022 in Jiaozhou Bay,China

A sudden and unprecedented outbreak of molluscan Philine kinglipini occurred in summer 2022 in Jiaozhou Bay,Shandong,China,causing substantial damage to local mariculture industry of the Manila clam Ruditapes philippinarum.Although P.kinglipini has been found in many coastal regions of China,the molecular research of P.kinglipini has not been extensively studied,making it difficult to accurately identify and track P.kinglipini samples in field using molecular methods.Samples were collected during the outbreak and their morphological features and molecular sequences were analyzed.Results show that the causative species of the outbreak was P.kinglipini.The mitochondrial genome(mt DNA)of P.kinglipini was constructed for the first time,based on which phylogenetic analysis of the mt DNAs of P.kinglipini and related species in the order Cephalaspidea was carried out.As revealed by metabarcoding analysis of 18S rDNA V4,the seasonal change of P.kinglipini and closely related Philine species was striking with peaks between April and August.Therefore,metabarcoding analysis is applicable tool for monitoring the bloom development of P.kinglipini and related species.This study generated for the first time essential molecular marker sequences and mtDNA of P.kinglipini,which provided a reference for future characterization and monitoring of its outbreaks and for phylogenetic analysis of Philine species.

Species composition and distribution of common Crassostrea and Saccostrea oysters along the coast of Hainan Island

Oyster cultivation is a pivotal economic industry in Hainan Island,South China,where a high oyster species diversity is shown.However,the specific distribution and biodiversity of oyster resources in the island have remained unclear.To elucidate the diversity of oyster species and their distribution there,307 oyster samples were collected from 29 sites in the intertidal zone around the island,and were identified using both morphological and molecular approaches.A minimum of 12 oyster species were identified in taxonomy,including Crassostrea species(C.gigas angulata,C.sikamea,C.iredalei,C.dianbaiensis,C.talonata,C.ariakensis,and C.hongkongensis),and Saccostrea species(S.malabonensis,S.mordax,S.echinata,S.circumsuta,and S.mordoides).The results revealed a remarkable diversity of oyster species along the coast of the island.Particularly noteworthy are that S.malabonensis and S.mordax constituted 36%and 22%of the collected specimens,respectively.This study provided a comprehensive overview on current state of oyster biodiversity in Hainan,serving as a valuable reference for conservation and research on species distribution and resource dynamics in oyster populations.

Shells in the cabinet:four new species of Tellinidae(Mollusca:Bivalvia:Tellinoidea)identified from existing South China Sea collections

Four species new to science were identified in the Tellinidae museum collections in the Marine Biological Museum of Chinese Academy of Sciences.Pinguitellina triquetra sp.nov.,collected in 1981,has not previously been described or reported.It differs from other Pinguitellina species by its trigonal shape,rose-colored valve interior,and deep and wide pallial sinus,which is confluent with the pallial line.Pinguitellina protuberangla sp.nov.has a broad and deep dorsal corner,short and straight posterodorsal margin,comparatively large adductor scars,depressed and fragile shells,and deep socket at the anterior edge of the right valve.Pinguitellina minuta sp.nov.was previously misidentified as Arcopella casta in China.It is a new species based on its unique characteristics,which include small,fragile,inflated,translucent,and triangularly ovate-shaped shells with acuminated and convex umboes.As the first species described in China within the genus Abranda Iredale,1924,Abranda xui sp.nov.has internal ligaments and thin,fragile,and translucent elliptical shells with fine radials on the surface.In this study,we reorganized the species currently contained in the two genera Pinguitellina and Abranda and created keys to the known species.We believe that numerous collected bivalve specimens have been overlooked in the South China Sea,and to date,mollusk has not been adequately sampled.Thus,further exploration and analysis are required to understand species diversity in this area.

Genome-wide SNP markers provided insights into the reproductive strategy and genetic diversity of the green tide causative species Ulva prolifera in China

Ulva prolifera is the causative species of the annually occurring large-scale green tides in China since 2007.Its specific biological features on reproductivity strategies,as well as intra-species genetic diversity,are still largely unknown,especially at the genome level,despite their importance in understanding the formation and outbreak of massive green tides.In the present study,the restriction site-associated DNA genotyping approach(2b-RAD)was adopted to identify the genome-wide single-nucleotide polymorphisms(SNPs)of 54 individual thalli including samples collected from Subei Shoal in 2019 and Qingdao coast from 2019 to 2021.SNPs genotype results revealed that most of the thalli in 2019 and 2020 were haploid gametophytes,while only half of the thalli were gametophytes in 2021,indicating flexibility in the reproductive strategies for the formation of the green tides among different years and the dominance of asexual and vegetative reproductive mode for the floating period.Besides,population analysis was conducted,and it revealed a very low genetic diversity among samples from Subei Shoal and the Qingdao coast in the same year and a higher divergence among samples in different years.The results showed the efficiency of 2b-RAD in the exploration of SNPs in U.prolifera and provided the first genome-wide scale evidence for the origin of the large-scale green tides on the Qingdao coast.This study improved our understanding of the reproductive strategy and genetic diversity of the green tide causative species and will help further reveal the biological causes of the green tide in China.

Comparative Transcriptome Analysis of Shell-Matrix-Protein Genes and Observation of the Shell Microstructure in the Deep-Sea Clam Calyptogena marissinica

The deep-sea clam Calyptogena marissinica is widely distributed in the Haima cold seep ecosystem on the northwes-tern slope of the South China Sea with low pH values,low temperature and high pressure.Limited information is available on the biomineralization of this species.In this research,we generated a comprehensive transcript dataset of C.marissinica’s mantle tissue,and a total of 19821 unigenes were assembled.Fourteen shell matrix proteins(SMP)-related genes were identified.The qPCR results showed that four out of six prismatic matrix genes(MSP2,MSP5,prisilkin-39,and shematrin),four out of the six nacreous matrix genes(perlucin,pif,pif97,and papilin),and two extrapallial fluid proteins(SPARC and calmodulin)were significantly expressed in the mantle.Both the nacreous and the prismatic layers are chrysanthemum-shaped,which are stacked on the top of each other to form a laminated nacreous structure.The alignment and phylogenetic analysis of MSP-5,Prisilkin-39,Perlucin,and Pif homologues showed that some amino acids of C.marissinica that differed from those detected in other molluscs may cause the different shape of the nacreous and prismatic layers,but do not lead to a change in the species’evolutionary status.These results indicated the conservation of the functions of SMP-related genes in C.marissinica,and the specific shape of the prismatic and nacreous layers of this deep-sea mollusc,which will contribute to the research on the molecular regulation mechanisms of biomineralization in C.marissinica and provide a new perspective to investigate biomineralization in deep-sea clams in general.

Comparative transcriptomic analysis of ovary and testis reveals sex-related genes in roughskin sculpin Trachidermus fasciatus

The mechanisms underlying sex determination and differentiation have long intrigued researchers in the fields of development and evolutionary biology.The roughskin sculpin(Trachidermus fasciatus Heckel),displaying sexual dimorphism,provides an ideal model for studying the mechanisms.However,both genetic and genomic information concerning sex determination and differentiation,such as gonadal transcriptome data in roughskin sculpin,are lacking.Here,we present the first gonadal transcriptomes of roughskin sculpin and identify sex-related genes.We identified 8531 differentially expressed genes(DEGs),among them 4065 were upregulated in the ovary and 4466 upregulated in the testis.Several sex-related gene ontology(GO)terms were enriched in ovary-biased genes,including“binding of sperm to zona pellucida”,“egg coat formation”,“positive regulation of acrosome reaction”,“cell division”,and“cell cycle”,while the GO terms such as“spermatogenesis”,“sperm axoneme assembly”,“cilium assembly”,“cilium movement”,and“cilium movement involved in cell motility”were enriched in testis-biased genes.Moreover,six KEGG pathways were significantly enriched in the ovary,whereas only one was enriched in the testis.Of these DEGs,40 sex-related genes were identified,which including 26 testis-biased genes(such as Dmrtb 1,Gsdf,Sox 9 b,Wnt 4 b,Tcp 11 l 2,and Efhb),and 14 ovary-biased genes(such as Cyp 19 a 1 a,Foxh 1,Foxr 1,Gdf 3,Hsd 17 b 12,and Igf 2 bp 3).This gonadal transcript dataset would broaden our understanding of sex determination and differentiation mechanisms in roughskin sculpin,expand the genomic database,support future studies on sex-related gene functions,and facilitate molecular biology research into roughskin sculpin.

Characterization of Nutrients,Heavy Metals,Petroleum and Their Impact on Phytoplankton in Laizhou Bay:Implications for Environmental Management and Monitoring

The Laizhou Bay(LB)represents a substantial ecological area that is vulnerable to human activities and confronts diverse environmental challenges.This study provides a comprehensive characterization of nutrients,petroleum,heavy metals,and phytoplankton community structure across seven distinct areas in LB.The results indicate relatively high concentrations of NO_(2)-N,SiO_(4)-Si,and NO_(3)-N in the Southwest Laizhou Bay(SWLB)and Huanghe River Estuary(HRE).In contrast,the East Laizhou bay(ELB)and the North of Huanghe River Estuary(NHRE)exhibit the highest concentrations of heavy metals(As,Cr and Hg).The areas with high phytoplankton density and community diversity are mainly located in the SWLB.After adjusting for basic environmental factors,phytoplankton density and Margalef richness index D are significantly associated with nutrients(NO_(3)-N,NO_(2)-N,NH_(4)-N,SiO_(4)-Si),and heavy metal(Cr)concentrations.We highlight that,in addition to Xiaoqinghe River,nutrients brought by the Mihe River in the SWLB and heavy metal(Cr)pollution in the ELB resulting from industrial and mining activities along the coast significantly influence phytoplankton growth and community structure.Therefore,it is recommended that more monitoring and management efforts be focused on these regions in the future.

Satellite observations of coastal upwelling in the northern Arafura Sea

Coastal upwelling is significant for marine ecosystems by lifting nutrient-rich deep waters into the euphotic zone,thereby increasing primary and secondary productivity.The satellite observations show that the northern Arafura Sea(NAS),especially in the coastal region,features high chlorophyll-a(chl-a)concentrations,implying a strong coastal upwelling.However,coastal upwelling in the NAS has not received much attention.Based on a semi-automatic image processing technology,the seasonal and interannual variability of coastal upwelling in the NAS are investigated in this study using satellite-observed sea surface temperature(SST)and wind data.The results suggest that there are seasonal coastal upwelling events in the NAS modulated by upwelling-favorable southeast monsoon(SEM).The annual mean days,mean area,and annual mean intensity of coastal upwelling events during the SEM season are 92 days,6514 km^(2),and-5.31×10^(5),respectively,while the corresponding values during the northwest monsoon(NWM)season are 32 days,5569 km^(2),and-1.41×10^(5).It is also found that the SEM coastal upwelling in the NAS displays prominent interannual variability.The strong upwelling events are found in 2010,2013,2016,and 2017 when the southeast monsoon winds were weaker.Further analysis suggests that at the interannual scale,the upwelling index(UI)averaged in the SEM season is negatively correlated with that of three upwelling indicators.This can be attributed to the limitation of onshore geostrophic flow which is evidenced by the negative correlation between the UI and the alongshore difference in sea surface height.This study highlights the important role of the southeast monsoon in the temporal variability of coastal upwelling in the NAS.

The corrosion characteristic and mechanism of Mg-5Y-1.5Nd-xZn-0.5Zr(x=0,2,4,6 wt.%)alloys in marine atmospheric environment

The microstructure and precipitated phases of as-cast Mg-5Y-1.5Nd-x Zn-0.5Zr(x=0,2,4,6 wt.%)alloys were investigated by optical microscopy,scanning electron microscopy,energy-dispersive spectrometry and X-ray Diffraction.The exposure corrosion experiment of these magnesium alloys was tested in South China Sea and KEXUE vessel atmospheric environment.The corrosion characteristic and mechanism of magnesium alloys of Mg-5Y-1.5Nd-x Zn-0.5Zr(x=0,2,4,6 wt.%)alloys were analyzed by weight loss rate,corrosion depth,corrosion products and corrosion morphologies.The electrochemical corrosion tests were also measured in the natural seawater.The comprehensive results showed that Mg-5Y-1.5Nd-4Zn-0.5Zr magnesium alloy existed the best corrosion resistance whether in the marine atmospheric environment and natural seawater environment.That depended on the microstructure,type and distribution of precipitated phases in Mg-5Y-1.5Nd-4Zn-0.5Zr magnesium alloy.Sufficient quantity anodic precipitated phases in the microstructure of Mg-5Y-1.5Nd-4Zn-0.5Zr alloy played the key role in the corrosion resistance.

Identification of the Caroline Plate boundary:constraints from magnetic anomaly

The Caroline Plate is located among the Pacific Plate,the Philippine Sea Plate,and the India Australia Plate,and plays a key role in controlling the spreading direction of the Philippine Sea Plate.The Caroline Submarine Plateau(or Caroline Ridge)and the Eauripik Rise on the south formed a remarkable T-shaped large igneous rock province,which covered the northern boundary between the Caroline Plate and the Pacific Plate.However,relationship between these tectonic units and magma evolution remains unclear.Based on magnetic data from the Earth Magnetic Anomaly Grid(2-arc-minute resolution)(V2),the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)technique was used to study the boundary of the Caroline Plate.Results show that the northern boundary is a transform fault that runs 1400 km long in approximately 28 km wide along the N8°in E-W direction.The eastern boundary is an NNW-SSE trending fault zone and subduction zone with a width of tens to hundreds of kilometers;and the north of N4°is a fracture zone of dense faults.The southeastern boundary may be the Lyra Trough.The area between the southwestern part of the Caroline Plate and the Ayu Trough is occupied by a wide shear zone up to 100 km wide in nearly S-N trending in general.The Eauripik transform fault(ETF)in the center of the Caroline Plate and the fault zones in the east and west basins are mostly semi-parallel sinistral NNW-SSE–trending faults,which together with the eastern boundary Mussau Trench(MT)sinistral fault,the northern Caroline transform fault(CTF),and the southern shear zone of the western boundary,indicates the sinistral characteristics of the Caroline Plate.The Caroline hotspot erupted in the Pacific Plate near the CTF and formed the west Caroline Ridge,and then joined with the Caroline transform fault at the N8°.A large amount of magma erupted along the CTF,by which the east Caroline Ridge was formed.At the same time,a large amount of magma developed southward via the eastern branch of the ETF,forming the northern segment of the Eauripik Rise.Therefore,the magmatic activity of the T-shaped large igneous province is obviously related to the fault structure of the boundary faults between the Caroline Plate and Pacific Plate,and the active faults within the Caroline Plate.