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2,4,6-Tripyridine-s-triazine (TPTZ) spectrophotometric method was applied to determine the concentrations of dissolved monosaccharides (MCHO), polysaccharides (PCHO), and total carbohydrate (TCHO) in seawater samples collected from sea surface to hadal zone and sediment-seawater interface of the Southern Yap Trench in the Western Pacific Ocean. Results show that the concentrations of MCHO, PCHO, and TCHO ranged from 6.3 to 22.3 µmol C/L, 1.1 to 25.4 µmol C/L, and 12.1 to 44.9 µmol C/L, respectively, from the euphotic layer to the hadal zone of the trench. At different sampling stations, the concentrations of MCHO, PCHO, and TCHO in the seawater showed complex vertical variation characteristics, but the overall variation trends were decreasing with water depth. In the Southern Yap Trench, the maximum concentration of MCHO in the seawater appeared in the euphotic layer, and the minimum in the hadal zone. The maximum concentration of PCHO appeared in the euphotic layer, and the minimum in the bathypelagic layer. The water layer where the maxima and minima of the average concentration of TCHO appeared was consistent with that of PCHO. PCHO was the major component of TCHO in the seawater of the Southern Yap Trench. In the seawater from the sediment-seawater interface, the concentrations of MCHO, PCHO, and TCHO ranged from 8.4 to 10.6 µmol C/L, 3.8 to 5.8 µmol C/L, and 12.2 to 15.2 µmol C/L, respectively, and MCHO was the major component of TCHO. The key factors affecting the concentration and existing forms of dissolved sugars in the seawater of the Southern Yap Trench included photosynthesis, respiration, polysaccharide hydrolysis, adsorption and desorption of particulate matter, trench "funnel effect", deep ocean currents, sediment resuspension, and etc. This study provided fundamental data about labile organic matter in abyss and hadal zone of marine environment, which is significant for further understanding of deep-sea organic carbon cycle. [ABSTRACT FROM AUTHOR]

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]

The global surge in demand for metals such as cobalt and nickel has created unprecedented interest in deep-sea habitats with mineral resources. The largest area of activity is a 6 million km 2 region known as the Clarion-Clipperton Zone (CCZ) in the central and eastern Pacific, regulated by the International Seabed Authority (ISA). Baseline biodiversity knowledge of the region is crucial to effective management of environmental impact from potential deep-sea mining activities, but until recently this has been almost completely lacking. The rapid growth in taxonomic outputs and data availability for the region over the last decade has allowed us to conduct the first comprehensive synthesis of CCZ benthic metazoan biodiversity for all faunal size classes. Here we present the CCZ Checklist, a biodiversity inventory of benthic metazoa vital to future assessments of environmental impacts. An estimated 92% of species identified from the CCZ are new to science (436 named species from a total of 5,578 recorded). This is likely to be an overestimate owing to synonyms in the data but is supported by analysis of recent taxonomic studies suggesting that 88% of species sampled in the region are undescribed. Species richness estimators place total CCZ metazoan benthic diversity at 6,233 (+/-82 SE) species for Chao1, and 7,620 (+/-132 SE) species for Chao2, most likely representing lower bounds of diversity in the region. Although uncertainty in estimates is high, regional syntheses become increasingly possible as comparable datasets accumulate. These will be vital to understanding ecological processes and risks of biodiversity loss., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

The abyss (3500-6500 m) covers the bulk of the deep ocean floor yet little is known about the extent of plastic debris on the abyssal seafloor. Using video imagery we undertook a quantitative assessment of the debris present on the abyssal seafloor (5700-5800 m depth) beneath the Kuroshio Extension current system in the Northwest Pacific. This body of water is one of the major transit pathways for the massive amounts of debris that are entering the North Pacific Ocean from Asia. Shallower sites (1400-1500 m depth) were also investigated for comparison. The dominant type of debris was single-use plastics - mainly bags and food packaging. The density of the plastic debris (mean 4561 items/km 2 ) in the abyssal zone was the highest recorded for an abyssal plain suggesting that the deep-sea basin in the Northwest Pacific is a significant reservoir of plastic debris., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The seafloor contains valuable mineral resources, including polymetallic (or manganese) nodules that form on offshore abyssal plains. The largest and most commercially attractive deposits are located in the Clarion Clipperton Fracture Zone (CCZ), in the eastern Pacific Ocean (EP) between Hawaii and Mexico, where testing of a mineral collection system is set to start soon [1]. The requirement to establish pre-mining environmental management plans has prompted numerous recent biodiversity and DNA barcoding surveys across these remote regions. Here we map DNA sequences from sampled ophiuroids (brittle stars, including post-larvae) of the CCZ and Peru Basin onto a substantial tree of life to show unprecedented levels of abyssal ophiuroid phylogenetic diversity including at least three ancient (>70 Ma), previously unknown clades. While substantial dark (unobserved) biodiversity has been reported from various microbial meta-barcoding projects [2, 3], our data show that we have considerably under-estimated the biodiversity of even the most conspicuous mega-faunal invertebrates [4] of the EP abyssal plain., (Copyright © 2019 Elsevier Ltd. All rights reserved.)