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Nitrogen uptake regime regulated by ice melting during austral summer in the Prydz Bay, Antarctica
Run Zhang, Qiang Ma, Min Chen, Minfang Zheng, Jianping Cao, Yusheng Qiu
doi: 10.1007/s13131-019-1434-2
Using a combination of stable isotope (15N) and radionuclide (226Ra) analyses, we examine possible controls on the interactions between melting ice and the uptake of nitrogen in the Prydz Bay during the 2006 austral summer. We find that specific rates of uptake for nitrate and ammonium correlate positively to their concentrations, thus suggesting a substrate effect. In the study area, we observe that regions along open, oceanic water have high f-ratios (nitrate uptake/nitrate+ammonium uptake), while areas near the Amery Ice Shelf have significantly low f-ratios. Further analysis reveals a negative correlation between the f-ratio and the melt water fraction, thus implying that the melting of ice plays an essential role in regulating pelagic N dynamics in the Southern Ocean (SO). Stratification, produced by melting ice, should profoundly affect the efficiency of the SO’s biological pump and consequently affect the concentration of CO2 in the atmosphere. Results presented in this study add information to an already significant base of understanding of the controls on pelagic C and N dynamics in the SO. This provides unique insights for either interpreting past changes in geologic records or for predicting future climate change trends.
key words: nitrogen uptake regime, ice melting, Prydz Bay, Antarctica
Diatom distribution and its relationship to sediment property in the Minjiang Estuary, southeast China
Linnan SHEN, Aiguo GAO, Chao LI, Min CHEN
doi: 10.1007/s13131-017-1070-7
The distribution of diatoms in surface sediments in the Minjiang Estuary, southeast China, was investigated in 2009. Total 56 species and other species belonging to 25 genera were identified, among them 11 species were dominant over 5%. Dominant species included Actinocyclus ehrenbergii, Coscinodiscus curvatulus, C. divisus, C. jonesianus, C. radiatus, C. rothii, C. subtilis, Cyclotella stylorum, Epithemia hyndmanii, Hydrosera whampoensis, and Trachyneis aspera. Diatom abundance varied spatially, with the absolute abundance of diatoms ranging from 13 valves/g to 11×104 valves/g, and averaging 2.5×104 valves/g. A canonical correspondence analysis (CCA) was used to explain the relationships between diatom distribution and sediment properties in the Minjiang Estuary. CCA revealed that the major elements (Fe2O3, Na2O, CaO, MgO, TiO2, SiO2, Al2O3, and K2O) were closely related to diatom abundance. Four diatom assemblages were distinguished, representing different sediment properties, which may assist late Quaternary palaeoceanographic reconstructions of the Minjiang Estuary.
key words: diatom, surface sediment, Minjiang Estuary, canonical correspondence analysis, sediment properties
The spatial distribution of major and trace elements of surface sediments in the northeastern Beibu Gulf of the South China Sea
Qian GE, George Z XUE, Liming YE, Dong XU, Jianru ZHAO, Fengyou CHU
doi: 10.1007/s13131-019-1402-x
A multi-index analysis including grain size, major and trace elements is performed on the surface sediments from the northeastern Beibu Gulf to trace the sources of the sediments and to understand the controlling factors for elements distribution. The mean grain size exhibits a wide variation ranging from 0.09Φ to 8.05Φ with an average value of 5.33Φ. The average contents of major elements descend in an order of c(SiO2)>c(Al2O3)>c(Fe2O3)>c(CaO)>c(MgO)>c(K2O)>c(Na2O)>c(TiO2)>c(P2O5)>c(MnO), while those of trace elements exhibit a descending order of c(Sr)>c(Rb)>c(V)>c(Zn)>c(Cr)>c(Pb)>c(Ni)>c(Cu)>c(As). On the basis of elementary distribution characteristics and statistical analyses, the study area is divided into the four zones: Zone I is located in the northeastern coastal area of the gulf, which receives large amount of fluvial materials from local rivers in Guangxi and Guangdong, China, and the Qiongzhou Strait; Zone II is located in the center of the study area, where surface sediments exhibits a multiple source; Zone III is located in the Qiongzhou Strait, where surface sediments are dominated by materials from the Zhujiang River and Hainan; Zone IV is located in the southwest of the study area, where surface sediments are mainly originated from the Red River and Hainan. The statistical analyses of sediment geochemical characteristics reveal that the grain size, which is mainly influenced by hydrodynamics and mineral composition of terrigenous materials, is the leading factor controlling the elementary distribution. Meanwhile, impacts from anthropogenic activities and marine biogenic process will also be taken into consideration.
key words: grain size, major and trace elements, Beibu Gulf, spatial distribution, sediment source

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