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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. [ABSTRACT FROM AUTHOR]

By analyzing the variability of global SST (sea surface temperature) anomalies, we propose a unified Niño index using the surface thermal centroid anomaly of the region along the Pacific equator embraced by the 0.7°C contour line of the standard deviation of the SST anomalies and try to unify the traditional Niño regions into a single entity. The unified Niño region covers almost all of the traditional Niño regions. The anomaly time series of the averaged SST over this region are closely correlated to historical Niño indices. The anomaly time series of the zonal and meridional thermal centroid have close correlation with historical TNI (Trans-Niño index) indices, showing differences among El Niño (La Niña) events. The meridional centroid anomaly suggests that areas of maximum temperature anomaly are moving meridionally (although slightly) with synchronous zonal movement. The zonal centroid anomalies of the unified Niño region are found helpful in the classification of the Eastern Pacific (EP)/Central Pacific (CP) types of El Niño events. More importantly, the zonal centroid anomaly shows that warm areas might move during a single warming/cooling phase. All the current Niño indices can be well represented by a simple linear combination of unified Niño indices, which suggests that the thermal anomaly (SSTA) and thermal centroid location anomaly of the unified Niño region would yield a more complete image of each El Niño/La Niña event. [ABSTRACT FROM AUTHOR]