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In Kongsfjorden (Spitsbergen), we quantified the zonation of visually dominant macroalgal taxa and of detached macroalgae from underwater videos taken in summer 2009 at six transects between 2 and 138 m water depth. For the first time, we provide information on the occurrence of deep water red algae below the kelp forest and of detached macroalgae at water depth > 30 m. The presence and depth distribution of visually dominant red algae were especially pronounced at the outer fjord, decreased with proximity to the glacial front and they were absent at the innermost locations. Deepest crustose coralline red algae and foliose red algae were observed at 72 and 68 m, respectively. Brown algae were distributed along the entire fjord axis at 2–32 m. Green algae were only present at the middle to inner fjord and at areas influenced by physical disturbance at water depths of 2–26 m. With proximity to the inner fjord the depth distribution of all macroalgae became shallower and only extended to 18 m depth at the innermost location. Major recipients of detached macroalgae were sites at the shallower inner fjord and at the middle fjord below the photic zone at depths to 138 m. They may either fuel deep water secondary production, decompose or support carbon sequestration. Univariate and community analyses of macroalgal classes including detached macroalgae across transects and over depths reveal a considerable difference in community structure between the outermost sites, the central part and the inner fjord areas, reflecting the strong environmental gradients along glacial fjords.

International audience; Plastic and microplastic pollutions are known to be widespread across the planet in all types of environments. However, relatively little about microplastic quantities in the deeper areas of the oceans is known, due to the difficulty to reach these environments. In this work, we present an investigation of microplastic (

In this article we report on a hexactinellid sponge new to science, Walteria demeterae sp. nov. , which was collected from the northwestern Pacific seamounts at depths of 1 271–1 703 m. Its tubular and basiphytous body, extensive lateral processes, numerous oval lateral oscula which are irregularly situated in the body wall, the presence of microscleres with oxyoidal, discoidal and onychoidal outer ends, and the absence of anchorate discohexasters, indicate it belongs to the genus Walteria of family Euplectellidae, which is also supported by molecular phylogenetic evidence from 18S, 28S, 16S and COI sequences. The unique morphotype, which is structured by a thin and rigid framework of body wall and lateral processes consisting of diactins, characterizes it as a new species. Local aggregations of individuals of this new species coupled with their associated macrofauna in the Suda Seamount are reported, highlighting its functional significance in providing biogenic microhabitats in the deep sea.

The 2010 Deepwater Horizon spill remains the largest catastrophic release of oil and gas into the deep sea. The irrupted oil and gas substantially impact a marine ecosystem, cause human injury, and have high societal opinions. Therefore, understanding the transport and dispersion of subsurface hydrocarbon provides an imperative substratum for the practical assessment and response of marine oil spill accidents. In this review, we summarize the major advances since the Deepwater Horizon accident, with emphasis on the observation and modeling of the droplet and the formation and dynamics of the plume. Additional complexity including more than the investigation of gas-saturated oil at high-pressure and the effect of Earth's rotation on near field plume is also outlined. We end with a few outlooks on key priorities for more precisely estimations on future oil spills.

The flow field in the Toyama Deep-Sea Channel (TDSC) in the Japan Sea was investigated based on mooring observations. An asymmetric current system accompanying offshore and onshore currents over the east- and west-side slopes in the channel, respectively, is suggested. A bottom intensified flow characteristic was observed at the offshore stations in the Yamato Basin. The asymmetric current system in the channel is also suggested by the asymmetric distribution of water characteristics across the TDSC in Toyama Bay; a cold dense water mass with higher dissolved oxygen (DO) and higher transmittance (Tr) was found over the west-side slope of the channel, whereas a water mass with lower DO and lower Tr was distributed over the east-side slope, suggesting a turbidity current from the head of Toyama Bay. The currents facing the shallower depth on their right-hand-side, along with the density distribution in the TDSC, suggest a density current system under the influence of the earth’s rotation. The dissolved oxygen concentration in the TDSC was significantly lower than that in the offshore region of the same temperature range. This suggests that the water mass over the west-side slope in the TDSC is a modified offshore water mass which experienced significant mixing with the low DO water mass over the east-side slope in the TDSC, probably due to strong shear between the offshore and onshore currents in the narrow channel.

This study presents a systematic analysis of double-frequency (DF) microseisms recorded on the unconsolidated sediments in the eastern and southeastern coasts of United States. For all recordings, the site effect parameters (predominant frequency (f0), amplification factor and unconsolidated sediment thickness (UST)) are obtained by Nakamura method and the DF spectra are classified into five groups in terms of the DF peak patterns and the recording locations relative to the coastline. The frequencies and energy levels of the DF peaks in horizontal direction and the amplification factors are associated with the UST which is resulted from seismic site effect. By polarization analysis, the primary vibration directions of the DF peaks are identified and presented as great circles passing through the recording stations intersecting mainly along the continental slope. Correlation analyses of time histories of the DF energy and the ocean wave climate observed at buoys show that the low ( 0.2 Hz) frequency DF microseisms are generated in the deep ocean and the continental shelf respectively. It is concluded that the continental slope plays a significant role in the generation of DF microseisms as it causes reflection of waves from the open ocean, initiating standing waves.

The mechanism that controls particulate organic carbon (POC) flux in the deep sea differs depending on the season and sea. The POC produced in the western subarctic North Pacific are known to be transported to the deep sea efficiently, but the direct relationship between the POC flux and physical processes is still unclear. In this study, we evaluated the effect of mesoscale eddies on POC flux in the western subarctic North Pacific. The seasonal and interannual variabilities of POC flux were investigated using data from a time-series sediment trap deployed at 4810 m at station K2 (47°N, 160°E) from 2005 to 2018. POC flux was high during May–November, appearing to reflect spring and fall blooms at the ocean surface. POC flux also showed interannual variability, with twelve peaks that were mostly affected by enhanced bloom just before the peak. Nine peaks of the twelve peaks were affected by mesoscale eddies, which enhanced bloom around K2 by extending the area with a high chlorophyll-a concentration along the coastal region into the offshore region, suggesting that mesoscale eddies strongly impact the interannual variability of POC flux at K2.

The effective climate sensitivity estimates the equilibrium response of near-surface temperature to doubling atmospheric carbon dioxide concentration and is a widely used metric to characterize potential global warming. Earth system models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) exhibit considerable spread in effective climate sensitivity estimates. Cloud feedbacks are thought to be the cause of this, with marine boundary layer clouds over the Southern Ocean playing an important role. Here, we show that Southern Ocean deep convection is a major contributor to the CMIP6 intermodel spread in effective climate sensitivity. By comparing two Earth system models with very different sensitivities, we find that greater storage of heat at depth can delay the Southern Ocean surface warming and associated cloud response, thereby delaying global surface warming by centuries. The link between Southern Ocean convection and effective climate sensitivity is seen across 41 CMIP6 models, with low-sensitivity models exhibiting substantial deep ocean warming. Our results reveal the influence of Southern Ocean convection on potential long-term climate warming. Southern Ocean deep convection governs the magnitude of long-term warming in response to greenhouse gases, according to an analysis of Earth system models.

To investigate the nature of gas hydrates in the Makran area, new high-resolution geophysical data were acquired between 2018–2019. The data collected comprise multibeam and two-dimensional multi-channel seismic reflection data. The multibeam bathymetry data show East-North-East (ENE) ridges, piggy-back basins, canyon and channel systems, and the morphology of the abyssal plain. Continuous and discontinuous bottom simulating reflectors (BSRs) occur in the piggy-back basins on most of the seismic profiles available. The BSRs cut the dipping layers with strong amplitude and reversed polarity. Discontinuous BSRs indicate a transition along a dipping high-permeable sand layers from gas-rich segment to the gas hydrate-bearing segment and suggest alternating sediments of fine and relatively coarse grain size. Double BSRs are highly dynamic and attributed to slumps occurring in the study area. The BSRs induced by slumps are located both at deep and shallow depths, responding to the temperature or pressure variation. For the first time, BSRs are observed in the abyssal plain of the Makran area, being associated with anticline structures, which do not show large spatial continuity and are strongly conditioned by structural conditions such as anticlines and fluid migration pathways, including deep fault, gas chimney, and high-permeable sedimentary layer. Our results may help to assess the gas hydrate potential within the piggy-back basins and to determine the most promising target areas. Moreover, results about the abyssal plain BSR may help to locate hydrocarbon reservoirs in the deep ocean.

The climate variability induced by the El Nino-Southern Oscillation (ENSO) cycle drives significant changes in the physical state of the tropical Western Pacific, which has important impacts on the upper ocean carbon cycle. During 2015–2016, a super El Nino event occurred in the equatorial Pacific. Suspended particulate matter (SPM) data and related environmental observations in the tropical Western Pacific were obtained during two cruises in Dec. 2014 and 2015, which coincided with the early and peak stages of this super El Nino event. Compared with the marine environments in the tropical Western Pacific in Dec. 2014, an obviously enhanced upwelling occurred in the Mindanao Dome region; the nitrate concentration in the euphotic zone almost tripled; and the size, mass concentration, and volume concentration of SPM obviously increased in Dec. 2015. The enhanced upwelling in the Mindanao Dome region carried cold but eutrophic water upward from the deep ocean to shallow depths, even into the euphotic zone, which disrupted the previously N-limited conditions and induced a remarkable increase in phytoplankton blooms in the euphotic zone. These results reveal the mechanism of how nutrient-limited ecosystems in the tropical Western Pacific respond to super El Nino events. In the context of the ENSO cycle, if predicted changes in biogenic particles occur, the proportion of carbon storage in the tropical Western Pacific is estimated to be increased by more than 52%, ultimately affecting the regional and possibly even global carbon cycle. This paper highlights the prospect for long-term prediction of the impact of a super El Nino event on the global carbon cycle and has profound implications for understanding El Nino events.

This study investigated 20 elements in the muscle of 11 cephalopod species caught in the Canary Islands inhabiting from coastal to meso-bathypelagic habitats. Among them, trace element contents from large and elusive cephalopods such as Architeuthis dux, Taningia danae, Lepidoteuthis grimaldii, and Haliphron atlanticus were determined. Statistically significant differences in element concentration were found among class sizes and habitat. Large species that are inhabiting in deepest waters such as Loligo forbesii, A. dux, T. danae, H. atlanticus, and L. grimaldii showed a high load and variability in Fe and Al, while coastal species were characterized by a homogeneous element composition, being the Zn loads highest than other elements. Metal contents in large and elusive cephalopod species were dominated by Fe, Ni, Al, Zn, and Sr, with these species being able to carry important amounts of these elements to predators such as deep-diving odontocetes that reside around the Canary waters.

Laetmonice Kinberg, 1856 is a remarkable genus characterized by having harpoon notochaetae in the polychaete family Aphroditidae. We describe a new species of Laetmonice, Laetmonice iocasica sp. nov., found from seamounts on the Caroline Ridge in the tropical Western Pacific. The new species is readily distinguished from congeners, particularly those distributed in the Indo-Pacific Ocean by possessing 45 segments with 18 pairs of elytra, and the tuberculated harpoon notochaetae in the elytrigerous segments, which are replaced by tuberculated notochaetae without recurved fangs on segments 4 and 5. Laetmonice iocasica sp. nov. is closely related to L. producta Grube, 1877, but differs in both morphology and the genetic distance of the mitochondrial cytochrome oxidase subunit I (COI) sequences. Laetmonice producta Grube, 1877 contained five varieties reported in various marine areas, which have been raised to species level. However, the records of L. producta from the Sagami Bay and Suruga Bay in Japan and in the south-eastern Australia remain obscure and probably represent a different species. The data indicate that L. producta, which was originally described from Kerguelen Islands in the Southern Ocean and later commonly found on the Antarctic shelf, is probably distributed only at high latitudes of the Southern Hemisphere.

The ocean is an important inventory of anthropogenic mercury (Hg), yet the history of anthropogenic Hg accumulation in the ocean remains largely unexplored. Deep-sea corals are an emerging archive of past ocean chemistry, which take in sinking or suspended particulate organic matter as their food sources. Such organic matter would exchange Hg with the local seawater before being consumed by the deep, sea corals. As such, the organics preserved in the coral skeleton may record the Hg evolution of the ambient seawater during the time of coral growth. Here, we report the first data on Hg concentrations variability of a deep-sea proteinaceous coral in the oligotrophic North Pacific at the water depth of 1 249 m, in attempt to understand the transfer of anthropogenic Hg into the deep Pacific ocean over the last seven centuries. We find that the Hg concentrations of different coral growth layers have remained relatively constant albeit with considerable short-term variability through time. The overall stable Hg concentration of the last seven centuries recorded in our sample suggests that anthropogenic pollution is not yet a clearly resolvable component in the deep oligotrophic North Pacific waters, in agreement with recent estimation from modelling works and observational studies of modern seawater profiles. As there is hardly an unambiguous way to separate anthropogenic Hg from the natural background based on recent seawater profiles, our historical data provide valuable information helping to understand the oceanic cycle of Hg through time.

Two new species of Chrysogorgia Duchassaing & Michelotti, 1864 collected from the Caroline seamounts in the tropical Western Pacific Ocean are described. Chrysogorgia pinniformis sp. nov. belongs to Versluys' group C (Squamosae typicae) with only scales in polyp body wall and tentacles. C. pinniformis sp. nov. is characterized by large branches pinnately branched and forming multiple fans with its small branches regularly and quasi-dichotomous branched, and scales and rods present in the polyp mouth area. It is most similar to C. pinnata Cairns, 2007 by the pinnate trait, but differs from the latter by its group C pattern (vs. group A, Spiculosae) and having sclerites present in the polyp mouth area (vs. absent). Chrysogorgia varians sp. nov. belongs to the Chrysogorgia group A (Spiculosae) with rods distributed in the polyp body wall and tentacles. It is characterized by warty rods and elongated scales in the tentacles, many warts and ridges on the scales, conspicuously toothed margins at the rounded ends in the pinnules, and small rods with ridge-like warts in the polyp mouth area. This species was frequent and abundant in the Caroline seamounts during our cruises and its morphological variability in growth period was obvious. The phylogenetic analyses based on mtMutS and 28S rDNA regions supported the assignment of the new species to the genus Chrysogorgia. However, the mtMutS marker showed very limited usefulness for species delimitation and inner relationship inference of Chrysogorgia. In contrast, the 28S rDNA showed much higher level of genetic variation, and it may be a potential barcode for this genus. In the 28S rDNA trees, the two new species clustered together. Additionally, compilation of our data showed that 42 of 78 (ca. 54%) Chrysogorgia species were found in the Indo-West Pacific convergent region, indicating that this area may be a hotspot of deep-water Chrysogorgia species.

The present study reports an unusual caligid copepod, Anchicaligus nautili (Willey, 1896) infesting the deep-water chambered nautilus Nautilus pompilius Linnaeus, 1758 from the Indian Ocean. Both male and female are redescribed and illustrated based on the materials recovered from the museum collection of the Department of Aquatic Biology & Fisheries, University of Kerala, collected in March, 1985 from the Andaman region of the Indian Ocean as a trawl bycatch. The species is characterised by the presence of a pair of large lenses (conspicillae) in the median eyes, postanal-protrusions and the displacement of the caudal rami. It appears to be the first record of the species from Indian waters.

Since its discovery, the deep-sea glass sponge Euplectella aspergillum has attracted interest in its mechanical properties and beauty. Its skeletal system is composed of amorphous hydrated silica and is arranged in a highly regular and hierarchical cylindrical lattice that begets exceptional flexibility and resilience to damage. Structural analyses dominate the literature, but hydrodynamic fields that surround and penetrate the sponge have remained largely unexplored. Here we address an unanswered question: whether, besides improving its mechanical properties, the skeletal motifs of E. aspergillum underlie the optimization of the flow physics within and beyond its body cavity. We use extreme flow simulations based on the 'lattice Boltzmann' method, featuring over fifty billion grid points and spanning four spatial decades. These in silico experiments reproduce the hydrodynamic conditions on the deep-sea floor where E. aspergillum lives. Our results indicate that the skeletal motifs reduce the overall hydrodynamic stress and support coherent internal recirculation patterns at low flow velocity. These patterns are arguably beneficial to the organism for selective filter feeding and sexual reproduction11,12. The present study reveals mechanisms of extraordinary adaptation to live in the abyss, paving the way towards further studies of this type at the intersection between fluid mechanics, organism biology and functional ecology., Comment: 23 pages, 4 figures, 9 extended data figures, 3 extended data tables

Two deep-sea eels collected from the Western Pacific Ocean are described in this study. Based on their morphological characteristics, the two deep-sea eel specimens were assumed to belong to the cusk-eel family Ophidiidae and the cutthroat eel family Synaphobranchidae. To accurately identify the species of the deep-sea eel specimens, we sequenced the mitochondrial genes (cytochrome c oxidase subunit I [COI] and 16S ribosomal RNA [16S rRNA]). Through molecular phylogenetic analysis based on mtDNA COI and 16S rRNA gene sequences, these species clustered with the genera Bassozetus and Synaphobranchus, suggesting that the deep-sea eel specimens collected are two species from the genera Bassozetus and Synaphobranchus in the Western Pacific Ocean, respectively. This is the first study to report new records of the genera Bassozetus and Synaphobranchus from the Western Pacific Ocean based on COI and 16S rRNA genes

The deep-sea is considered as the most extensive ecosystem on the Earth. It is meaningful for elucidating the life origins by exploring the origin and adaptive genetic mechanisms of the large deep-sea organisms. Caridean shrimps have colonized and successfully adapted to deep-sea environments. They provide an ideal model to analyze the origin and adaptive evolution of modern deep-sea fauna. Here, we conducted the phylogenetic analyses of mitochondrial genomes (mitogenomes) from carideans, including 11 newly sequences reported in this investigation to explore the habitat origins, divergence times, and adaptive evolution of deep-sea (seamounts and hydrothermal vents) caridean shrimps. The results showed that the species of deep-sea Caridea formed a monophyletic group. Phylogenetic analysis supported that the deep-sea caridean shrimps may originated from shallow sea. The hydrothermal vents alvinocaridid shrimps and Lebbeus shinkaiae from Thoridae underwent a second range expansion from seamounts to vent ecosystems. Estimates of divergence time showed that the caridean shrimps invaded into deep-sea at 147.75 Ma. The divergence of most of the modern seamount and hydrothermal vent species are in the late Cretaceous/early Tertiary. This may associate with the geological events of the Western Pacific, the climate change, and the global deep-water anoxic/dysoxic events during this period. Twenty-two potentially important adaptive residues were detected in the deep-sea shrimp lineage, which were located in atp6, atp8, cox1, cox3, cytb, nad2, nad4l, and nad5. This investigation adds our understanding of the evolutionary history of deep-sea caridean shrimps, and provides insights into the mitochondrial genetic basis of deep-sea adaptation in this group.

Metal-enriched minerals have been widely observed near hydrothermal vent fields. However, the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained. Here, radioactive 234Th in both dissolved and particulate phases were used to examine the kinetics of particle-reactive metal adsorption, removal, and residence in a newly found hydrothermal plume over the Southwest Indian Ridge. The results showed a relatively low value on 234Th/238U ratios (i.e., 0.73–0.88) compared to the deep oceans, indicating an enhanced adsorption of particle-reactive metals onto particulate matter in the plume. Based on the 234Th-238U disequilibria, the adsorption and sinking rate constants of 234Th averaged (0.009±0.001) d−1 and (0.113±0.024) d−1 in the hydrothermal plume, corresponding to the residence times of (115±19) d and (16±5) d for dissolved and particulate 234Th, respectively. This timescale allows vent-discharged particle-reactive metals to disperse hundreds to thousands of miles away. Thus, hydrothermal activities might influence the metal distribution in deep ocean over a very large scope. Also, a high sinking flux of (36.2±5.4) Bq/(m2·d) for 234Th was observed for the plume, suggesting an enrichment of metal in particles deposited close to the vent. The enhancement of particle sinking could also benefit the transport of organic carbon and nitrogen and fuel the benthic ecosystems under the plume regimes. Thus, hydrothermal plumes may have an impact on both the elemental geochemistry and/or ecosystem to the deep oceans interior than previous expectation.

Simulations from seven global coupled climate models performed at high and standard resolution as part of the high resolution model intercomparison project (HighResMIP) are analyzed to study deep ocean mixing in the Labrador Sea and the impact of increased horizontal resolution. The representation of convection varies strongly among models. Compared to observations from ARGO-floats and the EN4 data set, most models substantially overestimate deep convection in the Labrador Sea. In four out of five models, all four using the NEMO-ocean model, increasing the ocean resolution from 1° to 1/4° leads to increased deep mixing in the Labrador Sea. Increasing the atmospheric resolution has a smaller effect than increasing the ocean resolution. Simulated convection in the Labrador Sea is mainly governed by the release of heat from the ocean to the atmosphere and by the vertical stratification of the water masses in the Labrador Sea in late autumn. Models with stronger sub-polar gyre circulation have generally higher surface salinity in the Labrador Sea and a deeper convection. While the high-resolution models show more realistic ocean stratification in the Labrador Sea than the standard resolution models, they generally overestimate the convection. The results indicate that the representation of sub-grid scale mixing processes might be imperfect in the models and contribute to the biases in deep convection. Since in more than half of the models, the Labrador Sea convection is important for the Atlantic Meridional Overturning Circulation (AMOC), this raises questions about the future behavior of the AMOC in the models. This work has been funded by the PRIMAVERA project, which is funded by the European Union's Horizon 2020 programme, Grant Agreement No. 641727PRIMAVERA. D. V. Sein was also supported by the state assignment of the Ministry of Science and Higher Education of Russia (theme No. 0128-2021-0014). PO was supported by the Spanish Ministry of Economy, Industry and Competiveness through the Ramon y Cajal grant (RYC-2017-22772). The global ocean heat flux and evaporation products were provided by the WHOI OAFlux project (http://oaflux.whoi.edu) funded by the NOAA Climate Observations and Monitoring (COM) program. Peer Reviewed "Article signat per 12 autors/es: Torben Koenigk, Ramon Fuentes-Franco, Virna L. Meccia, Oliver Gutjahr, Laura C. Jackson, Adrian L. New, Pablo Ortega, Christopher D. Roberts, Malcolm J. Roberts, Thomas Arsouze, Doroteaciro Iovino, Marie-Pierre Moine & Dmitry V. Sein "

Three-hundred and thirty-one sediment cores, including six sediment types (clayey- and sandy-silt, silty- and sandy-clay, clayey- and silty-sand) were collected from the shallow and semi-deep seas of the South China Sea, and the P-wave velocities and physical properties of core sediments were measured under standard laboratory conditions. To eliminate the influence of environmental factors, the empirical sound speed ratio equations were established. Compared with several equations from literature, the porosity and wet bulk density empirical equations established in this paper agree well with Richardson and Briggs (2004)’s in-situ equations, which implies that our empirical equations can be used in the similar region of world’s oceans under certain conditions and will be useful in areas lacking first-hand P-wave speed data. However, the mean grain size equations established in this study, similar to the previous studies, have low accuracy, which may be due to the different particle arrangements and degrees of compaction in sediments. The results also show that for different sediment types, the equation based on all sediment data is in good agreement with the measured data in the study area, as there are both siliciclastic and carbonate sediments on the studied seabed. It is suggested that appropriate empirical equations should be selected according to sediment types and sedimentary environment in future works, and the empirical equation of porosity or the two-parameter equation of porosity and grain size should be preferred.

We measured the north–south transactional distributions of nutrients, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM) in the East Sea (Japan Sea) in November 2019. The humic-like (C peak and M peak) and protein-like (T peak) components were identified using the parallel factor analysis model. The concentrations of C peak, M peak, and nutrients increased with depth, while T peak and DOC concentrations decreased with depth. However, unusually higher DOC concentrations were observed in the deep layer of some stations near the Ulleung Basin, relative to those in the other stations, perhaps by internal oceanic waves driven by a combination of the anti-cyclonic eddy and the unique bottom topography. The humic-like FDOM in the deep layer was found to be produced mainly by aerobic degradation of sinking organic matter in the water column and additionally by anaerobic processes in the sediments, based on its plot against apparent oxygen utilization. Although the concentrations of M peak were almost constant in the entire depth, C peak decreased gradually from 1000 m to the surface, suggesting relatively ineffective production of M peak in the deep ocean and/or more effective UV degradation of C peak in the surface layer. The labile portion of FDOM, T peak, was observed only in the euphotic layer, indicating its rapid removal before reaching the deep ocean. Our results observed in the East Sea, a miniature of the global ocean, provide new insights into the production and removal mechanisms regarding the FDOM distributions in the ocean.

Deep-sea scleractinian cup corals are prominent members of Southern Ocean megabenthic communities, though little is known about their life history. This study used paraffin histology and scanning electron microscopy to characterize the reproduction of the scleractinian coral Balanophyllia malouinensis (Squires, 1961) from Burdwood Bank in the Drake Passage. Samples were taken in April and May via otter trawls, Blake trawls, and dredges on three separate cruises: one on the RV Lawrence M. Gould in 2006, and two on the RV Nathaniel B. Palmer in 2008 and 2011. B. malouinensis is gonochoric with rare hermaphroditism. All four spermatocyst stages were seen simultaneously in males; similarly, most females contained oocytes at varying stages of development, though seasonality or periodicity could not be determined without a wider range of sample dates. Average fecundity was 241 ± 184 oocytes/individual (n = 38) and not correlated to cup size. Maturing larvae were found in the mesenteries and coelenteron of females, indicating B. malouinensis broods its larvae. This study was the first to characterize the reproduction of a deep-sea Balanophyllia species and adds to a small but growing body of work seeking to understand the unique benthic communities of Burdwood Bank.

Diversity of microbial eukaryotes is estimated largely based on sequencing analysis of the hypervariable regions of 18S rRNA genes. But the use of different regions of 18S rRNA genes as molecular markers may generate bias in diversity estimation. Here, we compared the differences between the two most widely used markers, V4 and V9 regions of the 18S rRNA gene, in describing the diversity of epipelagic, bathypelagic, and hadal picoeukaryotes in the Challenger Deep of the Mariana Trench, which is a unique and little explored environment. Generally, the V9 region identified more OTUs in deeper waters than V4, while the V4 region provided greater Shannon diversity than V9. In the epipelagic zone, where Alveolata was the dominant group, picoeukaryotic community compositions identified by V4 and V9 markers are similar at different taxonomic levels. However, in the deep waters, the results of the two datasets show clear differences. These differences were mainly contributed by Retaria, Fungi, and Bicosoecida. The primer targeting the V9 region has an advantage in amplifying Bicosoecids in the bathypelagic and hadal zone of the Mariana Trench, and its high abundance in V9 dataset pointed out the possibility of Bicosoecids as a dominant group in this environment. Chrysophyceae, Fungi, MALV-I, and Retaria were identified as the dominant picoeukaryotes in the bathypelagic and hadal zone and potentially play important roles in deep-sea microbial food webs and biogeochemical cycling by their phagotrophic, saprotrophic, and parasitic life styles. Overall, the use of different markers of 18S rRNA gene allows a better assessment and understanding of the picoeukaryotic diversity in deep-sea environments.

The statistical characteristics and vertical thermohaline properties of mesoscale eddies in the Bay of Bengal are studied from the view of satellite altimetry data and Argo profiles. Eddy propagation preferences in different lifetimes, eddy evolution process, and geographical distribution of eddy kinetic properties are analyzed in this area. Eddies exist principally in the western Bay of Bengal, and most of them propagate westward. There is a clear southward (equatorward) preference for eddies with long lifetimes, especially for cyclones. Moreover, the eddies in different areas of the bay show different north-southward preferences. Evolution of eddy kinetic properties with lifetime shows that eddies have the significant three-stage feature: the growth period in the former one-fifth lifetime, the stable period in the middle two-fifth to four-fifth lifetime, and the dying period in the last one-fifth lifetime. Large-amplitude and high-intensity eddies occur only in the relatively confined regions of highly unstable currents, such as the East Indian Coastal Current and eastern Sri Lanka. Based on Argo profile data and climatology data, the eddy synthesis method was used to construct three-dimensional temperature and salt structures of eddies in this area. The mean temperature anomaly is negative/positive to the cyclonic/anticyclonic eddies in the upper 300×104 Pa, and below this depth, the anomaly becomes weak. The salinity structures of positive anomalies inside cyclonic eddies and negative anomalies inside anticyclonic eddies in the Bay of Bengal are not consistent with other regions. Due to the special characteristics of the water mass in the bay, especially under the control of the low-salinity Bay of Bengal water at the surface and the Indian equatorial water in the deep ocean, the salinity of seawater shows a monotonic increase with depth. For regional varieties of temperature and salinity structures, as the eddies move westward, the temperature anomaly induced by the eddies increases, the effecting depth of the eddies deepens, and the salinity structures are more affected by inflows. In the north-south direction, the salinity structures of the eddies are associated with the local water masses, which comprise low-salinity water in the northern bay due to the inflow of freshwater from rivers and salty water in the southern bay due to the invasion of Arabian Sea high-salinity water from the north Indian Ocean.

Observations of the diversity, distribution and abundance of pelagic fauna are absent for many ocean regions in the Atlantic, but baseline data are required to detect changes in communities as a result of climate change. Gelatinous fauna are increasingly recognized as vital players in oceanic food webs, but sampling these delicate organisms in nets is challenging. Underwater (in situ) observations have provided unprecedented insights into mesopelagic communities in particular for abundance and distribution of gelatinous fauna. In September 2018, we performed horizontal video transects (50–1200 m) using the pelagic in situ observation system during a research cruise in the southern Norwegian Sea. Annotation of the video recordings resulted in 12 abundant and 7 rare taxa. Chaetognaths, the trachymedusa Aglantha digitale and appendicularians were the three most abundant taxa. The high numbers of fishes and crustaceans in the upper 100 m was likely the result of vertical migration. Gelatinous zooplankton included ctenophores (lobate ctenophores, Beroe spp., Euplokamis sp., and an undescribed cydippid) as well as calycophoran and physonect siphonophores. We discuss the distributions of these fauna, some of which represent the first record for the Norwegian Sea.

Breakdown of skeletal and lithic hard substrates by organisms, a process referred to as bioerosion, is part of the global carbon cycle and receives increased attention, but little is known about bioerosion in polar environments. Here, we study bioerosion traces (addressed by their respective ichnotaxa) recorded in the barnacle Bathylasma corolliforme from the Ross Sea, Antarctica. Traces were visualized via scanning electron microscopy of epoxy casts prepared with the vacuum cast-embedding technique. In 50 samples from shallow 37 m to bathyal 1680 m water depths, 16 different bioerosion traces were found, classified into microborings presumably produced by cyanobacteria (1), chlorophytes (1), fungi (9), foraminifera (1), unknown organotrophs (5), and macroborings produced by cirripeds (1). Statistical ichnodiversity analysis resulted in a significant (p = 0.001) ANOSIM with moderate differences (R = 0.5) between microbioerosion trace assemblages at different water depths and revealed two main clusters (NMDS, SIMPROF) corresponding to the photic and aphotic stations. A comparison between this study and a corresponding study from the Svalbard archipelago, Arctic Ocean, shows that the ichnodiversity in calcareous barnacle skeletons is similar in polar waters of both hemispheres. This includes several ichnotaxa that are indicative for cool- to cold-water environments, such as Flagrichnus baiulus and Saccomorpha guttulata. Nine of the investigated ichnotaxa occur in both polar regions and seven ichnotaxa show an extensive bathymetrical range down to the deep sea at bathyal 1680 m water depth.

In the Southern Ocean, pteropods play an important role in biogeochemical cycling, and sediment traps are a valuable tool for investigating this role through the collection of passively sinking matter from productive surface waters to deep sea layers. Observations of ‘swimmers’ (e.g. organisms that actively swim into traps) can also prove valuable for studying zooplankton community structure. In this study, we used two separate sediment trap studies during the 2016–2017 summer to study pteropod population structure over time scales of 24 h and 28 days. In both studies, highest densities were measured for veliger-stage Limacina helicina antarctica (0.09–0.3 mm) relative to all species and age classes. Increases in shell diameters of veligers in all traps over time enabled the calculation of an intraseasonal potential growth rate of 0.0068 mm d−1. Swimmer flux rates ranged from 121 to 2674 ind. m−2 d−1 at 53 m depth, and the 24-h vertical flux study measured 960 ind. m−2 d−1 at 57 m depth and 6692 m−2 d−1 at 90 m depth. Among a suite of environmental and biological covariates tested, fluorescence and sinking particulate organic and inorganic carbon (POC and PIC) possessed the most predictive power to explain abundances of near-surface pteropod age class and species composition. Gymnosome abundances were largely influenced by increasing adult L. helicina antarctica counts. Changes to pteropod population and community dynamics in response to climate change will have cascading effects throughout Antarctic epipelagic food webs, and these results provide a regional snapshot of patterns in structure and sedimentation from an under-surveyed region of the Southern Ocean.

In the present study, the coal-rock organic facies of Oligocene Yacheng Formation of the marginal basin in the South China Sea were classified and divided. In addition, through the correlations of the large-scale coal-bearing basins between the epicontinental sea and the South China Sea, it was concluded that the coal forming activities in the South China Sea presented particularity and complexity. Furthermore, the coal forming mechanisms also presented distinctiveness. The marginal basins in the South China Sea consist of several large and complex rift or depression basins, which are distributed at different tectonic positions in the South China Sea. Therefore, the marginal basins in the South China Sea are not simple traditional units with onshore continental slopes extending toward the deep sea. The marginal basins are known to consist of multi-level structures and distinctive types of basins which differ from the continental regions to the sea. During the Oligocene, the existing luxuriant plants and beneficial conditions assisted in the development of peat. Therefore, the Oligocene was the significant period for the formation and aggregation of the peat. However, the peat did not form in unified sedimentary dynamic fields, but instead displayed multi-level geographical units, multiple provenance areas, instability, and nonevent characteristics. As a result, the marginal basins in the South China Sea are characterized by non-uniform peat aggregation stages. In another words, the majority of the peat had entered the marine system in a dispersive manner and acted as part of the marine deposits, rather than during one or several suitable coal-forming stages. These peat deposits then became the main material source for hydrocarbon generation in all of the marginal basins of the South China Sea. The study will be of much significance for the hydrocarbon exploration in the marginal basins of the South China Sea.

In this review, we primarily address the present state of the arts and latest progresses in a few frontier issues mostly relevant to free surface/interface in ocean engineering. They include TC (tropical cyclone) induced extreme surface wave, sloshing of LNG (liquefied natural gas), cavitation/bubble dynamics and VIM (vortex-induced motion) and VIV (vortex-induced vibration). In addition to general description, we mainly focus on the recent advances and challenging aspects of above-mentioned topics. Inspired by the achievements in the previous 70 years, mankind starts a new round of ocean exploration activities. Then, we can find obvious trends: the realm of ocean engineering is expanding from sea surface to deep sea, from low and middle latitude to polar region and from fossil to renewable energy in near future.

An optimization experiment was conducted to reproduce the climatological distribution of water properties with an ocean general circulation model in which interior vertical mixing below the surface mixed layer is represented by tidally induced near- and far-field vertical-mixing schemes. Globally constant parameters in the tidally induced mixing schemes along with other physical parameters are optimally estimated based on the Green’s function method. The optimized model performs reasonably well in reproducing the deep-water properties of the Pacific Ocean, suggesting that the combination of tidally induced vertical-mixing schemes is useful in providing a reliable simulation of the deep-ocean state, consistent with both observed broad-scale hydrographic characteristics and recent knowledge of mixing. Adjustment of the parameters in the near-field mixing scheme was effective in improving simulation of the deep-ocean state. These results suggest that the adjustment of a small number of globally constant parameters in tidally induced and other mixing schemes based on recent knowledge of mixing through data assimilation may enable improvements in ocean state estimation throughout the entire water column, including the deep ocean.

This study presents the length-weight relationships (LWRs) for six deep-sea fish species from the deep-waters of Andaman and Nicobar archipelago of India (70 29’130’’N − 120 44’ 480’’N and 920 19’ 580’’E − 930 24’ 440’’E). We employed bottom trawl using High Speed Demersal Trawl (HSDT-II CV, mesh size of 30 mm in the cod end) between March-April 2017, off the Indian coast between 295 and 650m depth. The speed of the vessel kept as average 3.5 knots, with ~ 1-hour duration. The specimens were collected from each haul, the samples sorted in to species level, and then we have taken few species for LWR study, in which previous reports are not available. We estimated the values for the parameter b of the length-weight relationship together with Coefficient of determination scores using ordinary least squares regression method. LWRs were significant with r2 values ranged from 0.94 to 0.96 and ‘b’ values are 2.55 for Apristurus indicus, 2.97 for Benthobatis moresbyi, 2.55 for Epigonus elongates, 3.43 for Gavialiceps taeniola, 2.96 for Polymixia fusca and 2.92 for Ostracoberyx dorygenys. In addition, a t-test was applied to test b value to verify the significant difference from the isometric value (b = 3). We also compared the current estimate with the Bayesian length-weight in the Fishbase. The parameters have a wide application such as biology, ecology, species management and stock assessment. However, the current estimate of the LWR restricted to the given length range and geographical region. Therefore, we recommend more studies to confirm the growth pattern of these fishes. Moreover, this study provides significant inputs to the knowledge on the least explored deep-water fishes of Andaman and Nicobar Archipelago of India.

Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.

We assessed fungal diversity in deep-sea sediments obtained from different depths in the Southern Ocean using the internal transcribed spacer 2 (ITS2) region of nuclear ribosomal DNA by metabarcoding through high-throughput sequencing (HTS). We detected 655,991 DNA reads representing 263 fungal amplicon sequence variants (ASVs), dominated by Ascomycota, Basidiomycota, Mortierellomycota, Mucoromycota, Chytridiomycota and Rozellomycota, confirming that deep-sea sediments can represent a hotspot of fungal diversity in Antarctica. The community diversity detected included 17 dominant fungal ASVs, 62 intermediate and 213 rare. The dominant fungi included taxa of Mortierella, Penicillium, Cladosporium, Pseudogymnoascus, Phaeosphaeria and Torula. Despite the extreme conditions of the Southern Ocean benthos, the total fungal community detected in these marine sediments displayed high indices of diversity and richness, and moderate dominance, which varied between the different depths sampled. The highest diversity indices were obtained in sediments from 550 m and 250 m depths. Only 49 ASVs (18.63%) were detected at all the depths sampled, while 16 ASVs were detected only in the deepest sediment sampled at 1463 m. Based on sequence identities, the fungal community included some globally distributed taxa, primarily recorded otherwise from terrestrial environments, suggesting transport from these to deep marine sediments. The assigned taxa included symbionts, decomposers and plant-, animal- and human-pathogenic fungi, suggesting that deep-sea sediments host a complex fungal diversity, although metabarcoding does not itself confirm that living or viable organisms are present.

This work reports on a preliminary taxonomic study of epibenthic macroinvertebrates collected or observed by underwater video at the Haima cold seeps and in adjacent deep-sea habitats, including a mud volcano field and Ganquan Plateau, during an expedition in the South China Sea by the Chinese-manned submersible Shenhai Yongshi in May 2018. A total of 41 species belonging to 6 phyla were identified, among which 34 species were collected from the Haima cold seeps. Mollusks and crustaceans that are specialized in reducing habitats were predominant in biotopes of the Haima cold seeps, whereas sponges and cold-water corals and their commensals were prominent in communities of the mud volcano field and the slopes of Ganquan Plateau. The distribution and faunal composition of each taxonomic group are discussed.

The oceanic crustal aquifer is one of the largest habitable volumes on Earth, and it harbors a reservoir of microbial life that influences global-scale biogeochemical cycles. Here, we use time series metagenomic and metatranscriptomic data from a low-temperature, ridge flank environment representative of the majority of global hydrothermal fluid circulation in the ocean to reconstruct microbial metabolic potential, transcript abundance, and community dynamics. We also present metagenome-assembled genomes from recently collected fluids that are furthest removed from drilling disturbances. Our results suggest that the microbial community in the North Pond aquifer plays an important role in the oxidation of organic carbon within the crust. This community is motile and metabolically flexible, with the ability to use both autotrophic and organotrophic pathways, as well as function under low oxygen conditions by using alternative electron acceptors such as nitrate and thiosulfate. Anaerobic processes are most abundant in subseafloor horizons deepest in the aquifer, furthest from connectivity with the deep ocean, and there was little overlap in the active microbial populations between sampling horizons. This work highlights the heterogeneity of microbial life in the subseafloor aquifer and provides new insights into biogeochemical cycling in ocean crust.

In this study, to meet the need for accurate tidal prediction, the accuracy of global ocean tide models was assessed in the South China Sea (0°–26°N, 99°–121°E). Seven tide models, namely, DTU10, EOT11a, FES2014, GOT4.8, HAMTIDE12, OSU12 and TPXO8, were considered. The accuracy of eight major tidal constituents (i.e., Q1, O1, P1, K1, N2, M2, S2 and K2) were assessed for the shallow water and coastal areas based on the tidal constants derived from multi-mission satellite altimetry (TOPEX and Jason series) and tide gauge observations. The root mean square values of each constituent between satellite-derived tidal constants and tide models were found in the range of 0.72–1.90 cm in the deep ocean (depth>200 m) and 1.18–5.63 cm in shallow water area (depth

Over half of the organic carbon on Earth’s surface is trapped in marine sediment as methane hydrates. Ocean warming causes hydrate dissociation and methane leakage to the water column, rendering the characterization of microbes from hydrate depositions a pressing matter. Through genomic, phylogenetic, and biochemical assays, we characterize the first microorganisms isolated from the Rio Grande Cone (Brazil), reservoir responsible for massive methane releases to the water column. From sediment harboring rich benthic communities, we obtained 43 strains of Brevibacillus sp., Paenibacillus sp. and groups of Bacillus sp. Methane-enriched samples yielded strains of the Pseudomonas fluorescens complex, exhibiting fluorescent siderophore production and broad multi-carbon catabolism. Genomic characterization of a novel Pseudomonas sp. strain indicated 32 genes not identified in the closest related type-species, including mercury resistance proteins. Our results provide phylogenetic and genomic insights on the first bacterial isolates retrieved from a poorly explored region of the South Atlantic Ocean.

Transparent exopolymer particles (TEP) are the central mechanism by which carbon is shuttled from the surface to the deep ocean. Despite the importance of these particles, the magnitude and drivers of temporal variability in the concentration and production rate of TEP in the ocean are not well resolved, especially in highly dynamic and productive regions like estuaries. Here, TEP dynamics were evaluated across weekly, tidal, and diel time scales within the Skidaway River Estuary (GA, USA) and adjacent coastal waters in the South Atlantic Bight. No significant trends in TEP concentration or production rates were observed over weekly time scales, though over tidal cycles, TEP concentration varied between tide stage and TEP:chlorophyll ratios were always lower at low relative to high tides. Over sequential diel cycles, TEP concentrations were two times higher at night relative to midday. Different biological and environmental variables were correlated with TEP dynamics (Spearman ρ) depending on the time scale considered, reinforcing the importance of time-specific drivers of TEP. These results emphasize the importance in considering the temporal variability of field-based TEP measurements, with implications for accurate assessments of carbon cycling in coastal ecosystems and the incorporation of TEP into carbon export models.

Fish species classifiction is an important task for biologists and marine ecologists to frequently estimate the relative abundance of fish species in their natural habitats and monitor changes in their populations. Traditional methods used for fish species classifiction were laboriuos, time consuming and expensive. So, there is need for an automated system that can not only detect and track but also categorize fish as well as other aquatic species in underwater imagery, minimizing the manual interference. Absorption and scattering of light in deep sea environment leads to low resolution images making fish species recognition and classification a challenging task. Further, performance of traditional computer vision techniques tends to degrade in underwater conditions due to the presence of high background clutter and highly indistinct features of marine species. For such classification problems, Artificial Neural Networks (ANN) or deep neural network are being increasingly employed for improved performance. But the limited dataset of fish images makes it difficult to train such networks as they require huge datasets for training. Thus to reduce the requirement for a huge amount of training data, an algorithm using cross convolutional layer pooling on a pre-trained Convolutional Neural Networks (CNN) is proposed. The present paper focuses on the development of automatic system for classification, which can detect and classify fish from underwater images captured through videos. Thorough analysis on image dataset of 27,370 fish images gives a validation accuracy of 98.03%. The proposed method will be an efficient replacement to strenuous and time consuming method of manual recognition by marine experts and thus be advantageous for monitoring fish biodiversity in their natural habitats.

Deep-sea hydrothermal plumes are considered natural laboratories for understanding ecological and biogeochemical interactions. Previous studies focused on interactions between microorganisms and inorganic, reduced hydrothermal inputs including sulfur, hydrogen, iron, and manganese. However, little is known about transformations of organic compounds, especially methylated, sulfur-containing compounds, and petroleum hydrocarbons. Here, we reconstructed nine gammaproteobacterial metagenome-assembled genomes, affiliated with Methylococcales, Methylophaga, and Cycloclasticus, from three hydrothermal ecosystems. We present evidence that these three groups have high transcriptional activities of genes encoding cycling of C(1)-compounds, petroleum hydrocarbons, and organic sulfur in hydrothermal plumes. This includes oxidation of methanethiol, the simplest thermochemically-derived organic sulfur, for energy metabolism in Methylococcales and Cycloclasticus. Together with active transcription of genes for thiosulfate and methane oxidation in Methylococcales, these results suggest an adaptive strategy of versatile and simultaneous use of multiple available electron donors. Meanwhile, the first near-complete MAG of hydrothermal Methylophaga aminisulfidivorans and its transcriptional profile point to active chemotaxis targeting small organic compounds. Petroleum hydrocarbon-degrading Cycloclasticus are abundant and active in plumes of oil spills as well as deep-sea vents, suggesting that they are indigenous and effectively respond to stimulus of hydrocarbons in the deep sea. These findings suggest that these three groups of Gammaproteobacteria transform organic carbon and sulfur compounds via versatile and opportunistic metabolism and modulate biogeochemistry in plumes of hydrothermal systems as well as oil spills, thus contributing broad ecological impact to the deep ocean globally.

The International Monitoring System (IMS) hydroacoustic network consists of six hydrophone stations and 5 T-stations. The IMS T-stations are high-frequency seismic stations (sample rates of 100 Hz) situated on islands or coastal stations and intended primarily to capture impulsive signals from in-water explosions. However, while there are numerous recordings of impulsive-like signals from in-water explosions at the hydrophone stations, recordings of this type of signal at the T-stations are rare. This is because the conversion of the hydroacoustic to a seismic signal as it propagates from ocean to land is inefficient, characterized both by complex geologic and topographic features and by strong attenuation. To improve the understanding of this signal conversion at T-stations, we performed numerical calculations using the spectral element code SPECFEM2D, modelling the acoustic signal as it propagates from the deep ocean through the ocean/land interface and finally, as an elastic signal, to the T-station. Environmental information from a variety of sources was gathered to construct the earth and ocean models used in the calculations. The goal of this work is to provide a set of calculated waveforms to complement the limited set of observed waveforms and to assist in the characterization of arrivals from explosion-generated hydroacoustic waves recorded at the T-stations.

This study documents simulated oceanic circulations and sea ice by the coupled climate system model FGOALS-f3-L developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, under historical forcing from phase 6 of the Coupled Model Intercomparison Project (CMIP6). FGOALS-f3-L reproduces the fundamental features of global oceanic circulations, such as sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), vertical temperature and salinity, and meridional overturning circulations. There are notable improvements compared with the previous version, FGOALS-s2, such as a reduction in warm SST biases near the western and eastern boundaries of oceans and salty SSS biases in the tropical western Atlantic and eastern boundaries, and a mitigation of deep MLD biases at high latitudes. However, several obvious biases remain. The most significant biases include cold SST biases in the northwestern Pacific (over 4°C), freshwater SSS biases and deep MLD biases in the subtropics, and temperature and salinity biases in deep ocean at high latitudes. The simulated sea ice shows a reasonable distribution but stronger seasonal cycle than observed. The spatial patterns of sea ice are more realistic in FGOALS-f3-L than its previous version because the latitude-longitude grid is replaced with a tripolar grid in the ocean and sea ice model. The most significant biases are the overestimated sea ice and underestimated SSS in the Labrador Sea and Barents Sea, which are related to the shallower MLD and weaker vertical mixing.

Deep-water column micronekton play a key role in oceanic food webs and represent an important trophic link between deep- and shallow-water ecosystems. Thus, the potential impacts of sub-surface hydrocarbon plumes on these organisms are critical to developing a more complete understanding of ocean-wide effects resulting from deep-sea oil spills. This work was designed to advance the understanding of hydrocarbon toxicity in several ecologically important deep-sea micronekton species using controlled laboratory exposures aimed at determining lethal threshold exposure levels. The current study confirmed the results previously determined for five deep-sea micronekton by measuring lethal threshold levels for phenanthrene between 81.2 and 277.5 μg/L. These results were used to calibrate the target lipid model and to calculate a critical target lipid body burden for each species. In addition, an oil solubility model was used to predict the acute toxicity of MC252 crude oil to vertically migrating crustaceans, Janicella spinacauda and Euphausiidae spp., and to compare the predictions with results of a 48-h constant exposure toxicity test with passive-dosing. Results confirmed that the tested deep-sea micronekton appear more sensitive than many other organisms when exposed to dissolved oil, but baseline stress complicated interpretation of results.

Iron (Fe) is a productivity-limiting nutrient in the ocean. However, the sources of dissolved Fe (dFe) in the deep ocean and how they respond to tectonic and climate changes are still poorly understood. In the northern hemisphere, dust flux to the low-latitude western Pacific has increased dramatically since the late Miocene associated with intense aridification of the Asian inland. Meanwhile, the terrigenous material supply to the open ocean might have also changed as a result of the reorganization of the Pacific circulation due to the gradual closure of seaways in the low latitudes. Therefore, the western Pacific is a characteristic region for understanding the sources of dFe in the deep ocean and their responses to long term climate changes. Here, we present data on isotopic evolution of dFe and dissolved Pb since ∼8 Ma based on ferromanganese crust METG-03 (16.0°N, 152.0°E, 3850 m water depth) in the western Pacific deep water. Our results show that δ56Fe of the crust remains fairly stable since the late Miocene, i.e., about −0.32±0.08‰ (2SD). We infer that δ56Fe of dFe in the deep western Pacific is relatively invariant at ∼0.45 ±0.1‰ based on the Fe isotopic fractionation between hydrogenetic crust and the seawater dissolved component. The reconstructed isotope signature is similar to the measured δ56Fe value (0.37±0.15‰) of the intermediate to deep waters in the modern low-latitude western Pacific region close to the island arcs, but is significantly higher than that of the eastern Pacific deep waters near South America which is controlled by the reductive dissolution of continental shelf sediments and the hydrothermal inputs (δ56Fe

The annual cycle of the Dead Sea surface temperature was investigated using band 10 onboard Landsat 8 during 2017–2018 and thermodynamic concepts. Retrieved Dead Sea temperatures are congruent with field observations with a mean square error of 1.22 °C and a correlation coefficient of 0.983. A new method employing thermodynamic concepts is presented in this paper to address the influence of buoyant plumes generated by freshwater influx on evaporation from hypersaline lakes/lagoons. Thermal images reveal a distinct spatial temperature pattern across the Dead Sea which reflects differential heating and cooling caused by variations in thermophysical characteristics of the deep sea compared with the shallow shoreline. The temperature patterns are negatively skewed in winter and positively skewed in summer. These temporal and spatial temperature patterns were illustrated using observed hourly data combined with energy balance calculations. The presence of buoyant plumes is found to alter evaporation compared with the undisturbed sea brine, and the effect of these plumes on evaporation is controlled by the simultaneous departure of temperature and activity compared with the undisturbed sea brine. Analysis shows that evaporation from buoyant plumes is more likely to be smaller than that from the open sea in winter and larger than its corresponding part from the open sea in summer. Thermal images can be used as surrogates to intensive field campaigns to examine temperature and evaporation regimes of lakes/salt flats.

Geothermal energy provides an important resource in Antarctic marine ecosystems, exemplified by the recent discovery of large-sized chemosymbiotic vesicomyid bivalves (subfamily Pliocardiinae) in the Southern Ocean. These clams, which we identified as Archivesica s.l. puertodeseadoi, have been reported as dead shells in areas previously covered by Larsen A and B ice shelves (eastern Antarctic Peninsula) and as live animals from active hydrothermal sites in the Kemp Caldera (South Sandwich Arc) at depths of 852–1487 m. Before, A. puertodeseadoi was known only from its type locality in the Argentine Sea, so we considerably extend the range of the species. Observations taken by remotely operated vehicle (ROV) footage show that the clams can live buried in sediment, or epilithically on the surface of rocks in diffuse geothermal flow. Experimental respirometry was conducted at surface pressure on individual bivalves acclimated to either their habitat temperature (4 °C) or elevated temperature (10 °C). The range of standard metabolic rates, from 3.13 to 6.59 (MO2, μmol O2 h−1 g−1 dry tissue mass), is similar to rates measured ex situ for other species in this clade, and rates did not differ significantly between temperature groups. Taken together, these data indicate a range of ecophysiological flexibility for A. puertodeseadoi. Although adapted to a specialist mode of life, this bivalve exploits a relatively broad range of habitats in the Southern Ocean: within sulphidic sediments, epilithically in the presence of diffuse sulphidic flow, or in deep methane-enriched seawater trapped under ice.

Marine invertebrates can display several reproductive strategies, from external reproduction to parental care. Internal brooding is particularly relevant in harsh conditions, like Antarctic/sub-Antarctic waters and deep-sea, since it maximizes the survival of the young. Actinostola crassicornis is an abundant and widely distributed sea anemone from the southwestern Atlantic Ocean. It can be found all along the Argentinean sea down to 1200 m depth, usually in large numbers. It is a unique species in the area, since it is a large white brooding sea anemone. We studied 75 specimens collected by the O/V Walther Herwig and the O/V Puerto Deseado all along its distribution, from about 60 m to 800 m depth, in different seasons of the year. All the specimens were sexed, and the presence of free oocytes and juveniles inside the coelenteron were assessed. Large oocytes (over 500 μm) and juveniles were found in samples from most of the sampled months. We found a larger number of female specimens, and most of the brooding specimens were female. No early developmental stages were found smaller than a sea anemone with about 12 tentacles. We conclude that A. crassicornis reproduces continuously throughout the year and that although most of the juveniles were found in females, male specimens can breed. Brooding has great benefits in terms of protecting the offspring, since predation upon the juveniles is prevented, but dispersal of the offspring is low, shown by the aggregated distribution of the species. Fil: Lauretta, Daniel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Vidos, Camila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Martinez, Mariano Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina