Preliminary study on community structures of meiofauna in the middle and eastern Chukchi Sea

Sediment core samples were collected from 17 stations in the middle and eastern Chukchi Sea during the sixth Chinese National Arctic Research Expedition(CHINARE-Arctic)in summer 2014.The samples were analyzed for composition,abundance,biomass,vertical distribution,size spectra,and ecological indexes of meiofauna.A total of 14 meiofauna taxa were detected,and the free-living marine nematodes comprised the most dominant taxon,accounting for 97.21%of the average abundance.The abundance and biomass of meiofauna were within ranges of(218.12±85.83)-(7239.38±1557.15)ind./(10 cm^(2))and(130.28±52.17)-(3309.56±1751.80)μg/(10 cm^(2)),with average values of(2391.90±1966.19)ind./(10 cm^(2))and(1549.73±2042.85)μg/(10 cm^(2))(according to dry weight)respectively.Furthermore,91.26%of the individuals were distributed in the top layer of 0-5 cm of surface sediment,and 90.84%had sizes of 32-250μm.Group diversity index of meiofauna in the survey area was low,and the variation of abundance was the main difference in meiofauna communities among all stations.Abundance and biomass of meiofauna were not significantly correlated with environmental factors except concentration of nutrient Si in bottom seawater.Abundance of meiofauna in shallow water of marginal seas in the Pacific sector of the Arctic Ocean is likely at a same level and higher than that in most of China sea areas,suggesting that the shallow water of the summer Chukchi Sea is a continental shelf area with rich resources of meiofauna.The Chukchi Sea is important for studying the ecosystem of the Arctic Ocean and environmental responses.However,studies on meiofauna in the Chukchi Sea are still not enough,and in the future,natural and human disturbances may increase due to global warming,the Arctic channel opening,and other factors.Thus,more studies on meiofauna should be required,in order to know more about how the Arctic benthic community would alter.

Dual Strengthened Control of Recrystallization Behavior on CVCDE Magnesium Alloy Containing Characteristic Structure

Various characteristic structures in typical magnesium alloys,including dislocation cells,substructures and twins,have an important influence on the dynamic recrystallization behavior,and the DRX(dynamic recrystallization)behavior is closely related to the grain refinement and texture weakening of the hot deformed structure.Therefore,this study reveals the influence of the above characteristic structures on the dynamic recrystallization behavior of magnesium alloys,which have great significance for regulating the high-performance hot deformed microstructure of magnesium alloys and optimizing the macro mechanical properties.In this study,continuous variable channel direct extrusion(CVCDE)magnesium alloy was prepared by CVCDE,and its macro mechanical properties including hardness and uniaxial tension were characterized.The thermoplastic deformation behavior and texture evolution of magnesium alloy with characteristic structure were analyzed by electron back-scattering diffraction technology.It is found that the dislocation recombination was realized by deformation mechanism(slip,climb and cross slip),the formation of grain substructure in coarse grains and the induction of recrystallization by twins promote the recrystallization behavior in hot deformed structures more adequate,which effectively improves the degree of microstructure refinement and deformation uniformity.