The formation of explosive volcanos at the circum-Pacific convergent margin during the last century

The circum-Pacific convergent margin is known as"the Ring of Fire",with abundant volcano eruptions.Large eruptions are rare but very disastrous.It remains obscure how are large explosive volcanos formed and where are the danger zones.Three largest eruptions since 1900,the Hunga Tonga-Hunga Ha’apai,the Mt.Pinatubo,and the Novarupta were found to be associated with subductions of volatile-rich sediments and located close to slab windows.Among them,the Hunga Tonga-Hunga Ha’apai is close to subducting seamount chains;the Mt.Pinatubo is right next to subducting fossil ridges.Both seamount chains and fossil ridges have water depths much shallower than the carbonate compensation depths(CCD)in the Pacific Ocean.Seismic image shows that a seamount is subducting towards the Novarupta volcano.Subduction of volatile-rich sediments and a slab window nearby are the two most important favorable conditions for catastrophic eruptions.Slab windows expose the mantle wedge to the hot asthenosphere,which increases the temperature and dramatically promotes the partial melting of the carbonate-fluxed domains,forming volatile-rich magmas that powered explosive eruptions.

Variations in nano-and pico-eukaryotic phytoplankton assemblages in the Qinhuangdao green-tide area

Qinhuangdao coastal waters have been frequently hitting by nano-and pico-eukaryotic phytoplankton(NPEP)blooms and green tides(macroalgal blooms)in the recent decade.However,understanding about the impacts of environmental factors and the green tides on the NPEP assemblages in this area is limited.In this study,the composition of NPEP assemblages and their variations were analyzed via amplicon sequence variants(ASVs)assay based on amplicon high-throughput sequencing data with the 18S V4 region as a targeted gene in the Qinhuangdao green-tide area during the green tide.Consequently,average NPEP effective sequences and ASVs of 178000 and 200 were obtained from each sample,respectively.Although there were 25 classes,110 genera,and 97 species of NPEP were identified and annotated,the proportions of annotated ASVs at genus and species levels were only 44.7%and 17.8%,respectively.The NPEP communities had a seasonal succession from diatom-dominated to dinoflagellate-dominated.During the three investigations,Skeletonema,Karlodinium,and Gonyaulax were the most dominant genera in May,August,and September,respectively.Species diversity and the abundance of NPEP communities could be increased by a high content of dissolved organic nitrogen(DON)and dissolved organic phosphorus(DOP)but inhibited by low dissolved inorganic phosphorus content.The outbreak of green tides could alter the composition and content of nutrients and accelerate the succession of the NPEP communities from diatom-dominated to dinoflagellate-dominated under the background of a seasonal increase in seawater temperature.These results preliminarily revealed the impacts of the recurrent occurrences of green tides on the NPEP assemblages in the Qinhuangdao green-tide area exhibiting high DON content and dissolved inorganic nitrogen/phosphorus ratio.

Plume-ridge interaction induced migration of the Hawaiian-Emperor seamounts

The history of the Hawaiian hotspot is of enduring interest in studies of plate motion and mantle flow,and has been investigated by many researchers using the detailed history of the Hawaiian-Emperor Seamount chain.One of the unexplained aspects of this history is the apparent offset of several Emperor seamounts from the Hawaii plume track.Here we show that the volcanic migration rates of the Emperor seamounts based on existing data are inconsistent with the drifting rate of the Pacific plate,and indicate northward and then southward “absolute movements”of the seamounts.Numerical modeling suggests that attraction and capture of the upper part of the plume by a moving spreading ridge led to variation in the location of the plume’s magmatic output at the surface.Flow of the plume material towards the ridge led to apparent southward movement of Meiji.Then,the upper part of the plume was carried northward until 65 Ma ago.After the ridge and the plume became sufficiently separated,magmatic output moved back to be centered over the plume stem.These changes are apparent in variations in the volume of seamounts along the plume track.Chemical and isotopic compositions of basalt from the Emperor Seamount chain changed from depleted(strong mid-ocean ridge affinity)in Meiji and Detroit to enriched(ocean island type),supporting declining influence from the ridge.Although its surface expression was modified by mantle flow and by plume-ridge interactions,the stem of the Hawaiian plume may have been essentially stationary during the Emperor period.

The formation of deep sea plastic biotas

Deep sea plastic biotas are formed by floating plastics that sank after biofouling.Plastics with nutrition and high biodiversity attract deep sea creatures and act as stepping-stone for biological striding.Plastics are cheap,light,water proof,sturdy and durable,with high insulativity.It is easy to shape and resistant to chemical corrosion.Therefore,plastics are widely used in the modern society,representing a major progress in human civilization.Global production of plastics has increased considerably over the last few decades from 1.7 million metric tons per year in the 1950s to 370 million metric tons per year in 2019[1].As a result,plastic wastes also increase quickly,e.g.,by~10%every year in the last decades.Around 6.3 billion metric tons of plastic wastes were generated between 1950 and 2015[2].Given that its degradation takes hundreds of years,plastic is even proposed as the No.1 environmental challenge.More than tens of thousands metric tons of plastics are dumped into the ocean every year[3].Fishing thread,microplastics and other plastics are indeed an increasing threat to ocean lives:ingestions and entanglements by the marine life[4].Nevertheless,the impact of such large amount of plastic garbage on ocean environment remains to be fully explored.

Reply to "Is‘plume interaction induced migration of the Hawaiian-Emperor Seamounts’a step too far?"

Thanks to Sager,who founded our paper on plume-ridge interaction of the oldest seamounts of the Hawaiian-Emperor chain is interesting and plausible[1,2].Surprisingly,he argued that our paper“may be misleading”due to the“sparse data representing complex phenomena”[2].

冲绳海槽超临界二氧化碳热液的形成

冲绳海槽超临界二氧化碳热液喷口位于俯冲的加瓜海岭之上.菲律宾海盆水深通常超过5000 m,在碳酸盐补偿深度之下,因此洋壳上碳酸盐不稳定.而加瓜海岭的水深在碳酸盐补偿深度之上,碳酸盐稳定.加瓜海岭俯冲携带的碳酸盐被俯冲板片释放的流体所溶解,向上运移、聚焦,高浓度的二氧化碳在冲绳海槽形成超临界二氧化碳喷口.结合高温高压实验结果,我们推断携带富碳酸盐沉积物的俯冲板片可以直接释放大量二氧化碳.被动陆缘是富碳酸盐沉积物形成和存储的最主要的构造背景,其俯冲可能对气候变化起了重要作用.鉴于此,我们认为新生代大气二氧化碳的长期增加是由于新特提斯洋关闭期间,被动大陆边缘富碳酸盐沉积物俯冲造成的.

A deep‐sea sulfate‐reducing bacterium generates zero‐valent sulfur via metabolizing thiosulfate

Zero‐valent sulfur(ZVS)is a crucial intermediate in the sulfur geobiochemical circulation and is widespread in deep‐sea cold seeps.Sulfur‐oxidizing bacteria are thought to be the major contributors to the formation of ZVS.However,ZVS production mediated by sulfate‐reducing bacteria(SRB)has rarely been reported.In this study,we isolated and cultured a typical SRB designated Oceanidesulfovibrio marinus CS1 from deep‐sea cold seep sediment in the South China Sea.We show that O.marinus CS1 forms ZVS in the medium supplemented with thiosulfate.Proteomic and protein activity assays revealed that thiosulfate reductase(PhsA)and the sulfide:quinone oxidoreductase(SQR)played key roles in driving ZVS formation in O.marinus CS1.During this process,thiosulfate firstly was reduced by PhsA to form sulfide,then sulfide was oxidized by SQR to produce ZVS.The expressions of PhsA and SQR were significantly upregulated when O.marinus CS1 was cultured in a deep‐sea cold seep,strongly indicating that strain CS1 might form ZVS in the deep‐sea environment.Notably,homologs of phsA and sqr were widely identified from microbes living in sediments of deep‐sea cold seep in the South China Sea by the metagenomic analysis.We thus propose that SRB containing phsA and sqr genes potentially contribute to the formation of ZVS in deep‐sea cold seep environments.