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The South Sandwich Trench is a 965 km long arcuate subduction trench spanning the South Atlantic and Southern oceans, isolated from most other hadal (areas where water depths exceed 6000 m) environments by thousands of kilometres. This feature represents the coldest known hadal ecosystem with ambient sub-zero temperatures recorded from bathyal depths to over 7000 m water depth. Very little research has been carried out into the hadal fauna of this trench since the Russian expeditions of the 1960s and 70s. Here, we report the first visual assessment of hadal fauna from the South Sandwich Trench from a series of seven baited camera and trap deployments between 6044 m and the deepest point at 8265 m water depth, a location called Meteor Deep. Three species of hadal fish (Liparidae), with very low population densities were observed at depths shallower than expected, likely due to the piezo-thermal effect decreasing their depth range. Four species of scavenging amphipods were recovered, extending the known distribution of Eurythenes andhakarae, Hirondellea dubia, and Bathycallisoma schellenbergi to the South Sandwich Trench. Large densities of brittle stars (Ophiuroidea) were seen in the shallower hadal depths, while dense aggregations of holothurians (Elpididae) were observed within trench-fill basins located along the deep trench axis coincident with a visible surficial layer of surface derived detritus. In addition, gastropods, sponges, and stalked crinoids were observed. Importantly, this study highlights the endemic community present at hadal depth within this somewhat unique high pressure-low temperature environment.

Mercury (Hg) is a non-essential metal that can have toxic effects on the fitness of organisms and tends to bioaccumulate with age and to biomagnify in higher trophic levels. Few studies have assessed oxidative stress and neurotoxicity in deep-water sharks. This study evaluated early ontogenetic changes and physiological effects (antioxidant defences, oxidative damage, aerobic metabolism and neurotransmission functions) of Hg accumulation in the white muscle and brain tissues of the velvet belly lantern shark Etmopterus spinax from the southern Iberian coast (NE Atlantic). Results suggested that the low mercury concentrations observed may induce acute effects in E. spinax before they reach sexual maturity. We found different Hg concentrations in E. spinax: [Hg] males > [Hg] females; [Hg] muscle > [Hg] brain. Females appeared to have higher redox capability translated into higher activities and levels of antioxidant defences than males. However, higher levels of oxidative damage were also observed in females. Whilst the mechanisms underlying these effects remain unknown, these results suggest differences in mercury accumulation between tissues and sex, and potentially deleterious effects on oxidative stress status and neurophysiology of E. spinax, potentially impairing swimming performance and reproduction, which could subsequently impact on the health of both individuals and population. info:eu-repo/semantics/publishedVersion

Deepwater circulation significantly changed during the last deglaciation from a shallow to a deep-reaching overturning cell. This change went along with a drawdown of isotopically light waters into the abyss and a deep ocean warming that changed deep ocean stratification from a salinity-to a temperature-controlled mode. Yet, the exact mechanisms causing these changes are still unknown. Furthermore, the long-standing idea of a complete shutdown of North Atlantic deepwater formation during Heinrich Stadial 1 (HS1) (17.5–14.6 kyr BP) remains prevalent. Here, we present a new compilation of benthic δ13C and δ18O data from the North Atlantic at high temporal resolution with consistent age models, established as part of the international PAGES working group OC3, to investigate deepwater properties in the North Atlantic. The extensive compilation, which includes 105 sediment cores, reveals different water masses during HS1. A water mass with heavy δ13C and δ18O signature occupies the Iceland Basin, whereas between 20 and 50°N, a distinct tongue of 18O depleted, 13C enriched water reaches down to 4000 m water depths. The heavy δ13C signature indicates active deepwater formation in the North Atlantic during HS1. Differences in its δ18O signature indicate either different sources or an alteration of the deepwater on its southward pathway. Based on these results, we discuss concepts of deepwater formation in the North Atlantic that help to explain the deglacial change from a salinity-driven to a temperature-driven circulation mode. Highlights • Spatial analyses of benthic δ13C and δ18O data from OC3 Atlantic compilation for HS1. • Heavy δ13C, light δ18O waters migrated into deep western North Atlantic basin during HS1. • Active deepwater formation between 30 and 60°N in the North Atlantic during HS1. • New concepts for transport of isotopically light δ18O into deep ocean. • Major contribution of North Atlantic waters to deglacial deep ocean stratification changes.

Summary Myoglobin (Mb) is highly concentrated in the myocytes of diving mammals such as whales and seals, in comparison with land animals, and its molecular evolution has played a crucial role in their deep-sea adaptation. We previously resurrected ancestral whale Mbs and demonstrated the evolutional strategies for higher solubility under macromolecular crowding conditions. Pinnipeds, such as seals and sea lions, are also expert diving mammals with Mb-rich muscles. In the present study, we resurrected ancestral pinniped Mbs and investigated their biochemical and structural properties. Comparisons between pinniped and whale Mbs revealed the common and distinctive strategies for the deep-sea adaptation. The overall evolution processes, gaining precipitant tolerance and improving thermodynamic stability, were commonly observed. However, the strategies for improving the folding stability differed, and the pinniped Mbs exploited the shielding of hydrophobic surfaces more effectively than the whale Mbs., Graphical abstract, Highlights • Ancestral pinniped myoglobins (Mbs) were resurrected to analyze deep-sea adaptation • The structural and biochemical parameters of pinniped and whale Mbs were compared • Electrostatic repulsion, fold stabilization, and surface entropy increment were common • Hydrophobic patch shielding was detected as a unique strategy of pinniped Mbs, Biomolecules; Evolutionary biology; Evolutionary mechanisms.

67 Ocean Drilling Program and Deep Sea Drilling Project sites were investigated to determine the relationship between temperature and time for silica diagenesis. The selected sites cover a variety of settings where the opal-A to opal-CT transition zone lies in Cenozoic sediments. The opal-A to opal-CT transition leads to abrupt changes in the sediment petrophysics which are used to identify the diagenetic interval at the study sites. This transition zone is a thin interval ranging in thickness from 10 to 40 m. Controls on transition zone thickness are analysed and temperature was found to be the fundamental driver. This study extends “the time–temperature stability field of Hein et al. (1978)” for the onset of opal-CT precipitation more generally. Active silica diagenesis persists over a long period of time (>35 m.y.) at low temperatures (55 °C) regardless of burial depth. Geothermal gradients and sediment accumulation rates are the principal controls of the rate of silica diagenesis transformation. Sites 794 and 795 in the Japan Sea, as typical cases of deep-sea boreholes capturing active transitions, were selected for further understanding the temperature–time control on silica diagenesis. The reconstructed thermal evolution of sediments from these representative sites demonstrates that the rapid increase in temperatures from the Late Miocene onwards occurred in response to high accumulation rates in the opal-A interval. The higher burial temperatures achieved for the opal-A sediment under higher sedimentation rates and a steeper thermal gradient led to an earlier transition at Site 795 (~5 m.y.) as compared to Site 794 (~8 m.y.). Kinetic-based models are formulated to illustrate the time–temperature dependence of biogenic silica diagenesis. One of the main findings based on this model is that although opal-CT precipitation reaches its peak levels across the transition zone at 8 and 5 m.y. after initial deposition of opal-A at Sites 794 and 795, respectively, the transformation is not completed until 14 m.y. at Site 794 and ca. 9.5 m.y. at Site 795 after initial sedimentation. Given the temperature and elapsed time, the model allows the transformation state of opal-containing sediments to be successfully predicted at any depth in these two sites.

Exploration vehicles can introduce vast quantities of single-use, plastic-coated tether that have been deliberately discarded as observed at the deepest site of all Earth's oceans. Manned submersible dives to Challenger Deep (10,925 m deep) in the Mariana Trench in 2019 and 2020 revealed hundreds of metres of yellow and white tether strewn across the seafloor. Due to its composition, these fibre-optic tethers will not only persist environmentally, but form a significant risk to equipment and life should unmanned and manned craft become entangled. As a result, the site of the iconic first descent to the deepest place on Earth by Piccard and Walsh in 1960 is unlikely to be safely explored again if this practise continues.

Highlights • In-situ temperature measurements were conducted at the Danube deep sea fan. • Operations were performed with the MARUM-MeBo200 seafloor drill rig. • The BSR is located ∼20 m below the current gas hydrate stability zone. • Seismic data suggest presence of shallower BSR-like events. Abstract Coring, geophysical logging, and in-situ temperature measurements were performed with the MARUM-MeBo200 seafloor rig to characterize gas hydrate occurrences in sediments of the Danube deep sea fan, off Romania, Black Sea. The new drilling data showed no evidence for significant gas hydrate saturations within the sediments but the presence of free gas at the depth of the bottom-simulating reflector (BSR). In-situ temperature and core-derived geochemical data suggest that the current base of the gas hydrate stability zone (BGHSZ) is ∼20 m shallower than the BSR. Investigation of the seismic data around the drill sites shows several locations where free gas previously trapped at a former BGHSZ migrated upwards forming a new reflection above the BSR. This shows that the gas hydrate system in the Danube deep sea fan is still responding to climate changes initiated at the end of the last glacial maximum.

An annotated species list of all macrobenthic invertebrates inhabiting the Siberian sector of the Arctic Ocean is presented. The area considered includes the Kara, Laptev and East Siberian seas and the adjacent region of the deep-sea Central Arctic. Entries on species occurrences in the database are supported by corresponding references. Species of Polychaeta, Crustacea and Echinodermata in addition contain information on bathymetric distribution. Apart from published data, 12 taxa were identified in the area for the first time. In total 1574 macrobenthic species were recorded within the considered area. The most species rich was the Kara Sea with 1184 species. The Laptev and East Siberian seas and the Central Arctic showed lower species richness with correspondingly 1105, 780 and 268 species. The much smaller numbers of species in the East Siberian Sea and in the deep-sea Central Arctic can be related to taxonomic impoverishment or/and much smaller study effort in those regions.

Investigation of Kinorhyncha from Senghor Seamount (tropical northeastern Atlantic Ocean) and the adjacent deep-sea floor revealed seven species of Echinoderes. Of these, Echinoderes kaempfae sp. nov. and Echinoderes schwieringae sp. nov. are described as new species. Echinoderes multiporus originally found on Eratosthenes Seamount, Mediterranean Sea, and Echinoderes cf. adrianovi originally found off Florida, northwestern Atlantic Ocean, were also recovered. In addition, three additional species, which possibly represent undescribed species, occurred on Senghor Seamount. Because of the low number of available specimens or necessity of further observations of closely related congeners for these three undescribed species, we provide only a brief description of them without naming them as new species. The comparison of each species with morphologically similar congeners is also provided. Based on all records of kinorhynchs from seamounts and the adjacent deep-sea floor in the Northeastern Atlantic Ocean, Mediterranean Sea, and Arctic Sea, it is suggested that (1) the kinorhynch fauna on seamounts is partly unique, (2) seamount kinorhynchs originate both from shallow waters and the deep sea, and (3) a few kinorhynch species diversified on seamounts.

Deep-sea regions provide vast ecosystem services such as biological habitat and nutrient cycling. Even though being threatened by climate change and facing possible biodiversity loss, these deep-sea ecosystems are poorly understood. So are macrobenthic communities and their functions within these ecosystems. Biodiversity and ecosystem function relationships as well as their link to environmental drivers can be assessed with the biological trait analysis. We used this approach for the first time for macrofauna assemblages across the deep Fram Strait between Greenland and Svalbard (1000–5500 m water depth) to evaluate their community-specific function from the upper continental slope down to the deepest known Arctic depression, the Molloy Deep. We aimed to investigate whether there are changes in benthic functioning along the bathymetric gradient and if so, which environmental stressors may drive these changes. In total, 16 stations were sampled with a giant box corer (0.25 m2) in 2016 and 2018. Sediments were sieved through a 0.5 mm mesh size sieve and fauna was identified to lowest possible taxonomic entity. Functions of species were characterized by using six traits split in 24 modalities gathered in a fuzzy coded species × traits array. Environmental parameters shaping the benthic habitat and reflecting food availability were gathered from remote sensing, mooring deployments, and sediment sampling. A distance-based redundancy analysis indicated near-bottom water temperature, seabed inclination, water depth as well as phytodetritial matter at the sea surface and seafloor (indicating food availability) to be the best variables explaining the trait and station distribution. Stations clustered into three groups based on their trait composition. Shallower stations characterized by high chlorophyll a concentration with large organisms, living within the sediment as well as predating specimens clustered in one group. A second group was characterized by stations with low chlorophyll a concentration and medium-sized, suspension feeding, epifaunal living macrofauna. A third group comprised stations with water depths ≥ 3000 m and was dominated by medium sized, surface deposit feeding and infaunal living specimens. Overall, the functional structure of macrofauna communities in the Fram Strait followed a food availability-driven gradient. Based on the relationship between sea ice, surface water primary production and food availability at the seafloor, these results point to macrobenthos being sensible to predicted anthropogenically generated environmental variations in polar regions. Alterations in benthic ecosystem functions might be expected when environmental conditions change.

Trehalose, a non-reducing disaccharide (α-D-glucopyranosyl-(1→1)-α-D-glucopyranoside) is a natural compound, which serves as a protective substance in halophilic bacterial cells. Trehalose biosynthesis genes (otsA and otsB) were PCR amplified from the genomic DNA of deep sea actinobacteria, Streptomyces qinglanensis NIOT-DSA03. The amplified genes were cloned and nucleotide sequences were determined. In silico sequence and phylogenetic analysis of nucleotides and amino acids of otsA and otsB sequences of S. qinglanensis were also determined. The experimental data described in this study will be helpful to develop a recombinant expression system to produce trehalose for biotechnological applications.

Oligotrophic areas cover about 75% of the ocean’s surface, and these ocean regions are predicted to expand under global warming scenarios. To evaluate impacts on global marine biogeochemical cycles and changes in ocean-atmosphere carbon fluxes, it is essential to understand particulate matter fluxes and determine the amount of organic carbon that is exported to the ocean’s interior. The oligotrophic Indian Ocean subtropical gyre (IOSG) is one of the least explored ocean regions in terms of particulate matter fluxes. Sediment trap-based particulate matter fluxes determined during a 4-year time series provide new information on the nature of export fluxes, their controlling factors, and on the spatial and temporal variability of oceanic processes in the IOSG. Trap-averaged total mass fluxes (∼9.8 ± 3.7 mg m-2 day-1), as well as particulate organic carbon (POC) fluxes (0.50 ± 0.15 mg m-2 day-1) measured at 500–600 m above bottom (2600–3500 m water depth) are among the lowest fluxes recorded worldwide. These low flux values are a result of strongly stratified and nutrient-depleted upper waters in the gyre. Such oligotrophic conditions lead to low primary production rates in a relatively homogeneous and isolated ocean region. Consequently, we observe an almost constant rain of POC fluxes in space and time, although minor variations in the net primary production (NPP) and in the sea surface temperature (SST) are seen in satellite surveys and model estimations. Factors contributing to the lack of seasonality in the POC fluxes are intense organic matter degradation, variations in the ocean mixed layer depth (OMLD), and impacts of physical mixing (surface wind stress, cyclonic eddies). Preliminary estimates indicate that the average POC export efficiency (e = 0.03 ± 0.01) is extremely low in the IOSG. Assuming that the IOSG, as well as comparable ocean regions, will expand under climate warming conditions, it is of major importance to investigate POC export fluxes to the deep ocean in order to predict changes in the global carbon cycle during the next decades.

The ocean dominates the Earth's surface, but despite decades of exploration it remains poorly explored, with major geological, oceanographic and biological discoveries frequently being made. The majority of the ocean floor is underlain by relatively young, mafic oceanic crust, which is covered by modern sediments. A complex interplay between geological processes, related seafloor geomorphology, and a multitude of oceanographic processes controls the distribution of oceanic mineral deposit-forming environments in time and space. The most important deep ocean mineral deposits are ferromanganese crusts and nodules, and sulfide-rich deposits that are linked to submarine hydrothermal activity. Submarine hydrothermal systems are associated with magmatism and seafloor volcanism, which is principally concentrated along tectonic plate boundaries. In these environments circulation of seawater through the crust results in heating and chemical modification of the water to generate metal-rich hydrothermal fluids that may precipitate sulfide minerals at or below the seafloor. The resulting seafloor massive sulfide (SMS) deposits typically comprise a near-surface massive sulfide mound, underlain by sulfide-rich veins and disseminated mineralization. The chemical composition, morphology, rate of formation and size of SMS deposits varies as a function of geodynamic setting, the style of volcanism and tectonics, and water depth. Once an SMS deposit has accumulated on the seafloor it may be altered by a variety of hydrothermal, diagenetic and seafloor weathering and erosion processes. Geological understanding of the seafloor and the formation of SMS deposits is continuously evolving, and will help to focus ocean exploration in those areas likely to have the greatest mineral potential.

On the basis of occurrence of the features of a type A homogenite, it is inferred that erosion (stir-up) or non-erosion of deep-sea sediments by a tsunami depends essentially on the depth of the seafloor. It has been suggested that the maximum depth where erosion occurred was between 2000 and 3000 m in the case of the Santorini tsunami event. The grain-size distribution and the fossil and chemical contents of the Mediterranean homogenites reflect essentially the constituents of the calcareous sediments in their provenance area. The homogeneous nature of the homogenites is attributed to settling from a high suspension cloud. The transport and depositional processes of the homogeneous fine-grained upper part of type B homogenites resemble the depositional process from a cloud formed by a pyroclastic flow. Thus, homogenites provide a good opportunity for investigating the important role that settling of suspended load plays in the genesis of the sedimentary structures in turbidites. The repeated occurrence of tsunami waves is revealed by a faint vertical change in the grain-size distribution and the fossil content.

20 pages, 8 figures, 2 tables, Recent work using compound-specific stable isotopes of amino acids (CSI-AA) in proteinaceous deep-sea corals opens a new realm of high-fidelity reconstruction for biogeochemical and ecological changes in the ocean. However, underlying these CSI-AA paleoceanographic applications are a series of fundamental assumptions, which hold first that baseline-proxy AA isotope values fixed at the base of food webs represent integrated δ13C and δ15N values of primary production, and second they are unaltered during subsequent export and incorporation from particles into corals. We explored long-term δ13C and δ15N CSI-AA data on a sediment trap time series together with contemporaneous, geographically close deep-sea bamboo corals (Isidella sp.) in the California margin, directly testing these assumptions for the first time. Our data show that isotope values of essential (δ13CEAA) and source AAs (δ15NPhe) in sinking particles quantitatively track bulk δ13C and δ15N values of export production. These CSI-AA baseline proxies varied independently of carbon flux, trophic position (TPCSI-AA) and microbial alteration, suggesting that they were well preserved in the sinking particles consumed by corals. Paired comparisons between sinking particles and corals revealed minor elevations of δ13CEAA (by ∼2‰) and δ15NPhe (by ∼1‰) in available coral specimens. We hypothesize that the difference in δ13CEAA is due to the geographic offset in δ13C values of primary production expected between the (more offshore) sediment trap site and (more onshore) coral specimens, whereas the δ15NPhe offset is likely related to expected minor trophic fractionation. Using empirical models derived from the sediment trap time series, we demonstrate for the first time that CSI-AA in proteinaceous deep-sea corals can reconstruct known bulk δ15N values of export production, source nitrogen δ15N values, and exported TPCSI-AA values with very good fidelity. Together, these findings represent a major advance in our understanding of AA isotope behavior in modern and paleoarchives, and can be used to underpin the rapidly evolving use of CSI-AA-based tools in multiple paleoceanographic studies and archives, This study was supported by National Science Foundation (OCE 1635527 to T.G. and M.M). A portion of this work was performed under the auspices of the U.S. Department of Energy (DE-AC52-07NA27344)

16 pages, 9 figures, 4 tables, supplementary data https://doi.org/10.1016/j.dsr.2021.103593, Deep-sea habitats are home for a variety of yet poorly known fish species, some of which display specialized life strategies, as is the case of Bythitidae and Zoarcidae. With the purpose of elucidating biological and ecological aspects of representatives of these families in NW Mediterranean waters, a large dataset based on 599 specimens of Cataetyx alleni, 30 C. laticeps and 284 Melanostigma atlanticum captured during the last 30 years within the framework of different research projects was used to address their geographical and bathymetric distribution, population structure, reproduction, trophic ecology, parasitism and enzymatic markers in the Balearic basin. Present outcomes revealed a patchy distribution mostly for M. atlanticum, possibly related to aggregation during reproduction and to the association with specific sediments. For the three species, higher densities occurred in the mainland vs. the insular margin, and a diminishing trend in estimated densities over the last decades was observed for C. alleni and M. atlanticum likely linked to climatic oscillations. Trophic data indicated that the two Cataetyx species inhabit the water-sediment interface and mainly feed on suprabenthic prey, while M. atlanticum inhabits the water column near the bottom preying on pelagic organisms and moving towards the seabed during reproduction. These results were supported by the parasitological assessment, which revealed that parasite communities were moderately diverse and abundant for Cataetyx spp. while being highly depauperate for M. atlanticum. Present outcomes from the Mediterranean Sea confirmed reproduction of C. alleni during autumn-winter and of M. atlanticum during autumn. Spawning of the former species may occur in winter-spring, as suggested by the finding, by the first time, of two females captured in March with fully-developed embryos inside. Levels of enzymatic markers quantified in muscle were provided for C. alleni and M. atlanticum for the first time. The special interactions found between the distribution and biology of Bythitidae and Zoarcidae and the sedimentary bottoms that they inhabit indicates that such conventional habitats are more heterogeneous than it is generally assumed and deserve higher attention for future protection, This work was supported by the Spanish National Research Council (CSIC) and the Spanish Scientific and Technic Research Assessing Commission (CAICYT) projects BATIMAR (grant number PAC 86–008/ID 821) and RETRO (grant number MAR90/757), and by the Spanish Ministry of Science and Innovation (MICYT) projects BIOMARE (grant number CTM2006-13508-C02-01/MAR), ANTROMARE (grant numbers CTM2009–12214–C02–01/MAR and CTM2009–12214–C02–02/MAR) and RECOMARES (gran number RTI2018-094066-B-100)

29 pages, 10 figures, 4 tables, This article offers an overview of the main sedimentary systems defining the geomorphology of deep sea environments from low to high latitudes. Mass-transport deposits, turbidite systems, contourites, volcaniclastic aprons, glacial trough mouth systems, carbonate mounds and other bathyal systems, such as pelagites, hemipelagites, mid-ocean channels and polymetallic mineral deposits, are presented with special attention to their morphology, sediments, processes and controlling factors. The integration of the main systems on the continental margins and adjacent abyssal plains in the North Atlantic and westernmost Mediterranean allows to characterize different sedimentation models

Highlights • Overview on geochemical composition of pore water and solid phase of sediments on the Azores Plateau. • Evidence for deep marine hydrothermal activity on the Azores Plateau. • Pore water data suggest ongoing anaerobic oxidation of methane and carbonate recrystallization. The Azores Plateau is an active magmatic region in the Central North Atlantic Ocean. In this study, we present a comprehensive data set of major element compositions and 87Sr/86Sr ratios of pore waters from surface sediments (0–9 mbsf) of the Azores Plateau. Based on distinct geochemical signatures we can separate normal marine from hydrothermally affected sediments. Normal marine sediments can further be differentiated by their ash content. Pore waters of ash rich gravity cores (GCs) do not show any deviations from seawater values except of a minor increase in Sr. In contrast, ash poor GCs generally show a trend for decreasing Ca with increasing depth, accompanied by a minor SO4 decrease and a more pronounced Sr increase. We suggest that these deviations are caused by processes such as anaerobic oxidation of methane and carbonate recrystallization. At four additional sample locations we observed a decrease in Mg and SO4 accompanied by a Ca increase in the pore waters, a pattern typical for hydrothermal fluids. The existence of hydrothermal systems in this region are corroborated by multi-channel seismic data, suggesting that sill or dyke intrusions are present in the subsurface close to the core locations. Overall, our observations offer preliminary indications for the existence of submarine hydrothermal systems on the Azores Plateau away from the Mid- Atlantic Ridge.

The early Cambrian was a critical interval for the Earth system, during which a rise in oceanic and atmospheric oxygen levels coincided with the rapid diversification of metazoans. A variety of contrasting models have been proposed for the spatiotemporal redox evolution of the early Cambrian ocean. These include the development of a well-oxygenated deep ocean at the base of Cambrian Stage 3 (commencing at ~521 Ma), or alternatively, persistent and widespread anoxic (ferruginous) conditions throughout the early Cambrian ocean. Here, we present redox sensitive trace element (RSTE), Fe speciation, and N and C isotope (δ15Nsed and δ13Corg) data for samples from a section (Zhongnancun) of the early Cambrian Niutitang Formation, which was deposited on the outer-shelf of the Yangtze Block, South China. The Fe speciation and RSTE data provide evidence of a transition from euxinic, through ferruginous, to oxic conditions during deposition of the Niutitang Formation. The combination of these new data with existing data from the inner-shelf to basin environment, implies regional redox stratification across the Yangtze Block during Cambrian stages 2 and 3, with oxic shallow waters above ferruginous deep waters, and spatial variability in the degree of mid-depth euxinia. Oxygenation of deeper waters may have occurred by early Cambrian Stage 4 (~514 Ma). A compilation of δ15N values from multiple early Cambrian sections of the Yangtze Block indicate that N2 fixation dominated the nitrogen cycle during late Cambrian Stage 2. Low δ15N values (

Summary Nitrous oxide (N2O) is a potent greenhouse gas and has significantly increased in the atmosphere. Deep-sea hydrothermal fields are representative environments dominated by mesophilic to thermophilic members of the class Campylobacteria that possess clade II nosZ encoding nitrous oxide reductase. Here, we report a strain HRV44T representing the first thermophilic campylobacterium capable of growth by H2 oxidation coupled to N2O reduction. On the basis of physiological and genomic properties, it is proposed that strain HRV44T (=JCM 34002 = DSM 111345) represents a novel species of the genus Nitratiruptor, Nitratiruptor labii sp. nov. The comparison of the N2O consumption ability of strain HRV44T with those of additional Nitratiruptor and other campylobacterial strains revealed the highest level in strain HRV44T and suggests the N2O-respiring metabolism might be the common physiological trait for the genus Nitratiruptor. Our findings provide insights into contributions of thermophilic Campylobacteria to the N2O sink in deep-sea hydrothermal environments., Graphical Abstract, Highlights • A N2O-reducing thermophile strain HRV44 was isolated from the deep-sea hydrothermal vent • Strain HRV44T shows strong exogenous N2O reduction at pH 6.0 and 53°C • We propose the name Nitratiruptor labii sp. nov. for strain HRV44T • Members of the genus Nitratiruptor possibly contribute to the capacity of N2O mitigation, Earth Sciences; Geology; Geomicrobiology; Microbiology; Biocatalysis

Financial support to DJW, TS, and TvdF was provided by the Natural Environment Research Council (NE/N001141/1), the Leverhulme Trust (RPG-398), the Grantham Institute for Climate Change and the Environment, and a Marie Curie Reintegration grant (IRG 230828). LFR acknowledges support from the Natural Environment Research Council (NE/N003861/1) and the European Research Council (278705). The sequence of deep ocean circulation changes between the Last Glacial Maximum and the Holocene provides important insights for understanding deglacial climate change and the role of the deep ocean in the global carbon cycle. Although it is known that significant amounts of carbon were sequestered in a deep overturning cell during glacial periods and released during deglaciation, the driving mechanisms for these changes remain unresolved. Southern Ocean sea-ice has recently been proposed to play a critical role in setting the global deep ocean stratification and circulation, and hence carbon storage, but testing such conceptual and modelling studies requires data constraining past circulation changes. To this end, we present the first deglacial dataset of neodymium (Nd) isotopes measured on absolute-dated deep-sea corals from modern Lower Circumpolar Deep Water depths in the Drake Passage. Our record demonstrates deglacial variability of 2.5 εNd units, with radiogenic values of up to during the Last Glacial Maximum providing evidence for a stratified glacial circulation mode with restricted incorporation of Nd from North Atlantic Deep Water in the lower cell. During the deglaciation, a renewed Atlantic influence in the deep Southern Ocean is recorded early in Heinrich Stadial 1, coincident with Antarctic sea-ice retreat, and is followed by a brief return to more Pacific-like values during the Antarctic Cold Reversal. These changes demonstrate a strong influence of Southern Ocean processes in setting deep ocean circulation and support the proposed sea-ice control on deep ocean structure. Furthermore, by constraining the Nd isotopic composition of Lower Circumpolar Deep Water in the Southern Ocean, our new data are important for interpreting deglacial circulation changes in other ocean basins and support a spatially asynchronous return of North Atlantic Deep Water to the deep southeast and southwest Atlantic Ocean. Postprint Postprint

11 pages, 4 figures, 4 tables, supplementary material https://doi.org/10.1016/j.pocean.2020.102321.-- All environmental data are available in Supplementary Tables S1.1 to S1.4. All raw images are archived and can be downloaded from the Oceans 2.0 Ocean Networks Canada online database, using the following link: https://data.oceannetworks.ca/DataSearch?location=BACWL.V3&deviceCategory=VIDEOCAM, The spatio-temporal distribution of seven abundant morphospecies (i.e. taxa identified based on morphological traits) and the diversity of the benthic megafaunal community at the Barkley Canyon hydrates site (870 m, Vancouver Island, BC, Canada) were assessed in 18 linear imaging transects (each transect ~30 m long), conducted with an Internet Operated Deep-sea Crawler in November 2016. Faunal counts (as proxy for local abundances) were treated as Poisson-behaving variables and were modeled and correlated to habitat quality (i.e. level of physical seafloor disturbance, as previously induced by the crawler), fluctuating oceanographic conditions (i.e. tides and currents, seasonal transitions and episodic particle fluxes) and temporally and spatially varying food availability (i.e. elevated chlorophyll levels, proximity to the hydrate mounds as additional energy sources). The model outcome was used to establish a potential trigger-notification procedure for substrate disturbance monitoring when ratios of faunal abundances exceed the expected range for any morphospecies. Finally, a quality assessment of the crawler’s performance as a multidisciplinary monitoring platform was performed using individual and morphospecies accumulation curves, which aids in optimizing and standardizing data collection protocols. We showed that the abundances and diversity of hydrates megafaunal community differed in relation to physical seafloor disturbance, proximity to the hydrate mounds and episodic food input, at varying degrees. Our work sets a solid base for the future real-time, long-term monitoring of ecosystem functioning and health status in deep-sea areas exposed to industrial substrate alterations (i.e. mining, fisheries, etc.), This study was conducted within the framework of Ocean Networks Canada and NEPTUNE Canada, Helmholtz Alliance and Tecnoterra (ICM-CSIC/UPC) and the following project activities: ROBEX (HA-304), ARIM (Autonomous Robotic sea-floor Infrastructure for benthopelagic Monitoring; MartTERA ERA-Net Cofound) and RESBIO (TEC2017-87861-R; Ministerio de Ciencia, Innovación y Universidades), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Highlights • Nd isotope records from the South Atlantic and Southern Ocean. • New Early Cretaceous general circulation model. • Opening history of gateways on the Falkland Plateau. • Gateway opening controlled organic carbon burial. Organic carbon burial is an important driver of carbon cycle and climate dynamics on geological and shorter time scales. Ocean basins emerging during the Early Cretaceous break-up of Gondwana were primary sites of organic carbon burial, implying that their tectonic and oceanographic evolution may have affected trends and perturbations in global climate via changes in local organic carbon burial. Assessing the role of individual ocean basins in the global carbon-climate context requires a sound understanding of the processes that induced large-scale changes in carbon burial and the timing of these changes. Here we reconstruct the oceanographic evolution, and its links to organic carbon burial, in the Barremian to Albian South Atlantic and Southern Ocean basins, which may have acted as carbon sinks of global importance. Our reconstruction is based on combined seawater neodymium isotope and sedimentological records obtained from multiple deep sea drill sites and a new general circulation model. Deep water circulation within and between those basins was primarily controlled by the opening of the shallow Falkland Plateau Gateway (between ∼118 Ma and ∼113 Ma) and the deep Georgia Basin Gateway (by ∼110 Ma), for which we provide new age constraints based on biostratigraphic and carbon isotope data. The opening of these gateways was accompanied by local to basin-wide decreases in organic carbon burial, suggesting that ocean circulation affected the oxygenation state via changes in deep water ventilation. Although our data do not provide quantitative information on the impact of changes in regional organic carbon burial on the global carbon cycle, the synchronicity between the reduction of organic carbon burial in the South Atlantic basin and global warming during the Early Albian points to a strong causal relationship.