The composition and concentration of dissolved free amino acid (DFAA) of seawater samples collected in May 2016 from the surface to the hadal zone of the northern region of the Yap Trench were analyzed by pre-column derivatization of o-phthalaldehyde. Results show that the average concentration of DFAA in the study area was 0.47±0.36 µmol/L. In different sampling stations, the concentrations of DFAA with water depth showed complex variation patterns. At the sediment-seawater interface, the concentrations of DFAA in the western side of the trench were obviously higher than that in its eastern side. In the study area, there were no significant correlations between the concentrations of DFAA and the environmental parameters such as concentrations of chlorophyll a (Chl a), dissolved oxygen (DO), pH, and dissolved inorganic nitrogen (DIN), indicating that the concentrations of DFAA in seawater of the trench are affected by many factors, such as photosynthesis, respiration, temperature, pressure, illumination, and circulation. The dominant DFAA are similar in different water layers of sampling stations, including aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), and serine (Ser). The composition of different amino acids, and the relative abundance of acidic, basic, and neutral amino acids might be related to the sources and consumption of various amino acids. Nine pairs of amino acids in the DFAA showed significantly positive relationship by correlation matrix analysis, suggesting that they might share similar biogeochemical processes. The degradation index (DI) of the DFAA in seawater of the Yap Trench could reflect the degradation, source, and freshness of DFAA in the trench to some extents. This is a preliminary study of amino acids from sea surface to hadal zone in the ocean, more works shall be done in different trenches to reveal their biogeochemical characteristics in extreme marine environments.
After the 2015 MS8.1 Nepal earthquake, a strong and moderate seismicity belt has formed in Tibet gradually spreading along the northeast direction. In this paper, we attempt to summarize the features and investigate the primary mechanism of this behavior of seismic activity, using a 2-D finite element numerical model with tectonic dynamic settings and GPS horizontal displacements as the constraints. In addition, compared with the NE-trending seismicity belt triggered by the 1996 Xiatongmoin earthquake, we discuss the future earthquake hazard in and around Tibet. Our results show that:the NE-directed seismicity belt is the response of enhanced loading on the anisotropic Qinghai-Tibetan plateau from the Indian plate and earthquake thrusting. Also, this possibly implies that a forthcoming strong earthquake may fill in the gaps in the NE-directed seismicity belt or enhance the seismic hazard in the eastern (the north-south seismic zone) and western (Tianshan tectonic region) parts near the NE-directed belt. 相似文献
An important supplement for ocean observing systems, the Northwestern Tropical Pacific Ocean (NWTPO) mooring array including 15 moorings equipped with Acoustic Doppler Current Profilers (ADCP) devices was developed by the Chinese Academy of Sciences and deployed in 2013. This study assessed the performance of this mooring array in monitoring the intra-seasonal and low-frequency (above 91 days) variability of oceanic currents by conducting targeted observation analyses using an ensemble-based method. Key regions for monitoring intra-seasonal variability of the NWTPO circulation are the equator, Indonesian throughflow (ITF), headstream of the North Equatorial Countercurrent (NECC), and Subtropical Countercurrent (STCC). For monitoring intra-seasonal variability, the range of each mooring is confined to a local scale. Therefore, NWTPO moorings cannot adequately resolve intra-seasonal variability in areas of the ITF, the headstream of the NECC, and STCC due to location constraints of the moorings. For monitoring low-frequency variability of NWTPO circulation, the key regions are the Western Boundary Current (WBC), NECC, and the Equatorial Undercurrent (EUC). NWTPO moorings performed relatively well in monitoring the low-frequency variability, as indicated by the strong background correlations between each of the currents. The NWTPO mooring array plays an important role in monitoring the location and intensity of background currents. Because moorings are costly and require a high-density distribution for optimal performance, understanding the multi-timescale dynamical nature of the NWTPO current system is critical for the deploying future moorings in this region. 相似文献
