Probing the sedimentary DOM in the deepest sector of Earth’s surface (original) (raw)
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High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth
Nature Geoscience, 2013
Microbes control the decomposition of organic matter in marine sediments. Decomposition, in turn, contributes to oceanic nutrient regeneration and influences the preservation of organic carbon 1 . Generally, rates of benthic decomposition decline with increasing water depth, although given the vast extent of the abyss, deep-sea sediments are quantitatively important for the global carbon cycle 2,3 . However, the deepest regions of the ocean have remained virtually unexplored 4 . Here, we present observations of microbial activity in sediments at Challenger Deep in the Mariana Trench in the central west Pacific, which at almost 11,000 m depth represents the deepest oceanic site on Earth. We used an autonomous micro-profiling system to assess benthic oxygen consumption rates. We show that although the presence of macrofauna is restricted at Challenger Deep, rates of biological consumption of oxygen are high, exceeding rates at a nearby 6,000-m-deep site by a factor of two. Consistently, analyses of sediments collected from the two sites reveal higher concentrations of microbial cells at Challenger Deep. Furthermore, analyses of sediment 210 Pb profiles reveal relatively high sediment deposition in the trench. We conclude that the elevated deposition of organic matter at Challenger Deep maintains intensified microbial activity at the extreme pressures that characterize this environment.
Hadal trenches are dynamic hotspots for early diagenesis in the deep sea
Communications Earth & Environment, 2021
The deepest part of the global ocean, hadal trenches, are considered to act as depocenters for organic material. Relatively high microbial activity has been demonstrated in the deepest sections of some hadal trenches, but the deposition dynamics are thought to be spatially and temporally variable. Here, we explore sediment characteristics and in-situ benthic oxygen uptake along two trenches with contrasting surface primary productivity: the Kermadec and Atacama trenches. We find that benthic oxygen consumption varies by a factor of about 10 between hadal sites but is in all cases intensified relative to adjacent abyssal plains. The benthic oxygen uptake of the two trench regions reflects the difference in surface production, whereas variations within each trench are modulated by local deposition dynamics. Respiratory activity correlates with the sedimentary inventories of organic carbon and phytodetrital material. We argue that hadal trenches represent deep sea hotspots for early di...
Sediment Accumulation and Carbon Burial in Four Hadal Trench Systems
2022
Hadal trenches are considered to act as depocenters for organic material, although pathways for the material transport and deposition rates are poorly constrained. Here we assess focusing, deposition and accumulation of material and organic carbon in four hadal trench systems underlying different surface ocean productivities; the eutrophic Atacama and Kuril-Kamchatka trenches, the mesotrophic Kermadec trench and the oligotrophic Mariana Trench. The study is based on the distributions of naturally occurring 210 Pb ex , 137 Cs and total organic carbon from recovered sediment cores and by applying previously quantified benthic mineralization rates. Periods of steady deposition and discreet mass-wasting deposits were identified from the profiles and the latter were associated with historic recorded seismic events in the respective regions. During periods without mass wasting, the estimated focusing factors along trench axes were elevated, suggesting more or less continuous downslope focusing of material toward the interior of the trenches. The estimated organic carbon deposition rates during these periods exhibited extensive site-specific variability, but were generally similar to values encountered at much shallower settings such as continental slopes and margins. Organic carbon deposition rates during periods of steady deposition were not mirrored by surface ocean productivity, but appeared confounded by local bathymetry. The inclusion of deposition mediated by mass-wasting events enhanced the sediment and organic carbon accumulations for the past ∼150 years by up to a factor of ∼4. Thus, due to intensified downslope material focusing and infrequent mass-wasting events, hadal trenches are important sites for deposition and sequestration of organic carbon in the deep sea. Plain Language Summary Hadal trenches (>6,000 m water depth) occupy ∼1% of the world's ocean floor yet are largely underexplored, but recent studies have shown that these environments are depocenters for organic material and microbial activity is intensified when compared to shallower abyssal plains. However, transport and accumulation of sediment material to these hadal trenches is poorly understood. This study investigates sedimentation and accumulation dynamics of organic carbon in trenches using results of radionuclide analysis (in sediment from the Atacama, Kuril-Kamchatka, Kermadec, and Mariana trenches). The analysis shows that trench sediments consist of discreet layers representing both periods of continuous deposition and sudden mass-wasting events often triggered by historic earthquakes. Down slope focusing of material, intensified the deposition along the trench axes. However, the deposition rates exhibited extensive site-specific variations that were partly related to mass-wasting events which greatly enhanced not only mass accumulation but also organic carbon accumulation at the trench axes. Our results illustrate that mass-wasting events play an important role on supplying organic carbon to hadal communities and suggest that hadal trenches might be quantitatively important for sediment and organic carbon sequestration in the deep sea. OGURI ET AL.
2019
Hadal trench bottom (>6,000 m below sea level) sediments harbor higher microbial cell abundance compared to adjacent abyssal plain sediments. This is supported by the accumulation of sedimentary organic matter (OM), facilitated by trench topography. However, the distribution of benthic microbes in different trench systems has not been explored yet. Here, we carried out small subunit ribosomal RNA gene tag sequencing for 92 sediment subsamples of seven abyssal and seven hadal sediment cores collected from three trench regions in the northwest Pacific Ocean: the Japan, Izu-Ogasawara, and Mariana Trenches. Tag-sequencing analyses showed specific distribution patterns of several phyla associated with oxygen and nitrate. The community structure was distinct between abyssal and hadal sediments, following geographic locations and factors represented by sediment depth. Co-occurrence network revealed six potential prokaryotic consortiums that covaried across regions. Our results further s...
Microbes control the decomposition of organic matter in marine sediments. Decomposition, in turn, contributes to oceanic nutrient regeneration and influences the preservation of organic carbon1. Generally, rates of benthic decomposition decline with increasing water depth, although given the vast extent of the abyss, deep-sea sediments are quantitatively important for the global carbon cycle2,3. However, the deepest regions of the ocean have remained virtually unexplored4. Here, we present observations of microbial activity in sediments at Challenger Deep in the Mariana Trench in the central west Pacific, which at almost 11,000mdepth represents the deepest oceanic site on Earth. We used an autonomous micro-profiling system to assess benthic oxygen consumption rates. We show that although the presence of macrofauna is restricted at Challenger Deep, rates of biological consumption of oxygen are high, exceeding rates at a nearby 6,000-m-deep site by a factor of two. Consistently, analy...
Biogeochemistry of hadal trenches: Recent developments and future perspectives
Deep Sea Research Part II: Topical Studies in Oceanography, 2018
Hadal trenches with water depth ranging from 6000 to 11000 meters are the deepest biogeochemical province in the world's oceans. Due to technological challenges of sampling and observation at such extreme depths, these trenches are one of the least exploited habitats on our planet. Recent findings show high sedimentation rates, high biomass, intense microbial activity and chemosynthetic communities in hadal trenches, suggesting that they may play a more important role in global ocean biogeochemical cycles than previously recognized. Here we review the hadal biogeochemistry in four aspects: food supply and its effect on hadal life; hadal carbon cycle; microbial-mediated stable carbon isotope fractionation in biosynthesis of lipids under high hydrostatic pressures; and pollution in the hadal trenches. Our current knowledge of hadal biogeochemistry is rudimentary and many fundamental questions remain to be answered. However, with the rapid development of the full-ocean-depth exploration and sampling technologies, it is very likely hadal scientists will make significant breakthroughs in hadal biogeochemistry research in the coming decades.
Vertically distinct microbial communities in the Mariana and Kermadec trenches
PloS one, 2018
Hadal trenches, oceanic locations deeper than 6,000 m, are thought to have distinct microbial communities compared to those at shallower depths due to high hydrostatic pressures, topographical funneling of organic matter, and biogeographical isolation. Here we evaluate the hypothesis that hadal trenches contain unique microbial biodiversity through analyses of the communities present in the bottom waters of the Kermadec and Mariana trenches. Estimates of microbial protein production indicate active populations under in situ hydrostatic pressures and increasing adaptation to pressure with depth. Depth, trench of collection, and size fraction are important drivers of microbial community structure. Many putative hadal bathytypes, such as members related to the Marinimicrobia, Rhodobacteraceae, Rhodospirilliceae, and Aquibacter, are similar to members identified in other trenches. Most of the differences between the two trench microbiomes consists of taxa belonging to the Gammaproteobac...
Bulk and Active Sediment Prokaryotic Communities in the Mariana and Mussau Trenches
Frontiers in Microbiology, 2020
Surprisingly high rates of microbial respiration have recently been reported in hadal trench sediment, yet the potentially active microorganisms and specific microbemicrobe relationships in trench sediment are largely unknown. We investigated the bulk and active prokaryotic communities and co-occurrence interactions of different lineages in vertically sectioned sediment cores taken from the deepest points of the Mariana and Mussau Trenches. Analysis on species novelty revealed for the first time the high rate of novel lineages in the microbial communities of the hadal trenches. Using 95, 97, and 99% similarity as thresholds, averagely 22.29, 32.3, and 64.1% of total OTUs retrieved from sediments of the two trenches were identified as the potentially novel lineages, respectively. The compositions of the potentially active communities, revealed via ribosomal RNA (rRNA), were significantly different from those of bulk communities (rDNA) in all samples from both trenches. The dominant taxa in bulk communities generally accounted for low proportions in the rRNA libraries, signifying that the abundance was not necessarily related to community functions in the hadal sediments. The potentially active communities showed high diversity and composed primarily of heterotrophic lineages, supporting their potential contributions in organic carbon consumption. Network analysis revealed high modularity and non-random cooccurrence of phylogenetically unrelated taxa, indicating highly specified micro-niches and close microbial interactions in the hadal sediments tested. Combined analysis of activity potentials and network keystone scores revealed significance of phyla Chloroflexi and Gemmatimonadetes, as well as several potentially alkane-degrading taxa in maintaining microbial interactions and functions of the trench communities. Overall, our results demonstrate that the hadal trenches harbor diverse, closely interacting, and active microorganisms, despite the extreme environmental conditions.
Microbial Diversity in Sediments from the Bottom of the Challenger Deep, the Mariana Trench
Microbes and Environments
The Challenger Deep is the deepest ocean on Earth. The present study investigated microbial community structures and geochemical cycles associated with the trench bottom sediments of the Challenger Deep, the Mariana Trench. The SSU rRNA gene communities found in trench bottom sediments were dominated by the bacteria Chloroflexi (SAR202 and other lineages), Bacteroidetes, Planctomycetes, "Ca. Marinimicrobia" (SAR406), and Gemmatimonadetes and by the archaeal α subgroup of MGI Thaumarchaeota and "Ca. Woesearchaeota" (Deep-sea Hydrothermal Vent Euryarchaeotic Group 6). The SSU rRNA gene sequencing analysis indicated that the dominant populations of the thaumarchaeal α group in hadal water and sediments were similar to each other at the species or genus level. In addition, the co-occurrence of nitrification and denitrification was revealed by the combination of pore water geochemical analyses and quantitative PCR for nitrifiers.