Abyssal Plain Research Articles

Composition of deep-sea polychaetes from the SokhoBio expedition with a description of a new species of Labioleanira (Annelida: Sigalionidae) from the Sea of Okhotsk

During the SokhoBio expedition in 2015, deep-sea benthic invertebrate fauna of the Kuril Basin of the Sea of Okhotsk and the Pacific Ocean between the Bussol Strait and the Kuril-Kamchatka Trench was sampled on board of the R/V Akademik M.A. Lavrentyev. Over 18,400 polychaetes belonging to 48 families, 139 genera, and 189 species were found in the studied area. The abyssal zone of the Sea of Okhotsk and the Pacific slope of the Kuril-Kamchatka Trench are the areas of high polychaete diversity and species richness. The diversity of the Kuril Basin is higher than that in the deep-sea basin of the Sea of Japan and is comparable to that in the abyssal plain adjacent to Kuril-Kamchatka Trench. A total of 160 polychaete species belonging to 124 genera and 47 families were identified from depths of 1676–3366 m in the Kuril Basin. Over half of these (93 species, 58%) occur on the Pacific slope of the Kuril-Kamchatka Trench. The records of widespread and eurybathic species common to both the Kuril Basin and the Pacific slope confirm the relationship between the abyssal fauna of the Kuril Basin and deep sea North-West Pacific. Nine genera and 18 species have been reported for the North-West Pacific for the first time. One family, 36 genera and 49 species were first records for the Sea of Okhotsk. More than 40% of the collected polychaete species were new to science. Among these, a sigalionid Labioleanira okhotica sp. nov. described herein, is the deepest (3211–4803 m) record for the genus Labioleanira. This species is easily recognized by the lack of eyes, the presence of nodular auricles instead of ear-shaped ones, and the presence of small dorsal tubercles on chaetiger 3. The genus Labioleanira Pettibone, 1992 is newly recorded in the North-West Pacific. An updated key to the species of the genus Labioleanira is provided.

Geomorphological and sedimentary processes of the glacially influenced northwestern Iberian continental margin and abyssal plains

The offshore region of northwestern Iberia offers an opportunity to study the impacts of along-slope processes on the morphology of a glacially influenced continental margin, which has traditionally been conceptually characterised by predominant down-slope sedimentary processes. High-resolution multibeam bathymetry, acoustic backscatter and ultrahigh-resolution seismic reflection profile data are integrated and analysed to describe the present-day and recent geomorphological features and to interpret their associated sedimentary processes. Seventeen large-scale seafloor morphologies and sixteen individual echo types, interpreted as structural features (escarpments, marginal platforms and related fluid escape structures) and depositional and erosional bedforms developed either by the influence of bottom currents (moats, abraded surfaces, sediment waves, contourite drifts and ridges) or by gravitational features (gullies, canyons, slides, channel-levee complexes and submarine fans), are identified for the first time in the study area (spanning ~90,000 km2 and water depths of 300 m to 5 km). Different types of slope failures and turbidity currents are mainly observed on the upper and lower slopes and along submarine canyons and deep-sea channels. The middle slope morphologies are mostly determined by the actions of bottom currents (North Atlantic Central Water, Mediterranean Outflow Water, Labrador Sea Water and North Atlantic Deep Water), which thereby define the margin morphologies and favour the reworking and deposition of sediments. The abyssal plains (Biscay and Iberian) are characterised by pelagic deposits and channel-lobe systems (the Cantabrian and Charcot), although several contourite features are also observed at the foot of the slope due to the influence of the deepest water masses (i.e., the North Atlantic Deep Water and Lower Deep Water). This work shows that the study area is the result of Mesozoic to present-day tectonics (e.g. the marginal platforms and structural highs). Therefore, tectonism constitutes a long-term controlling factor, whereas the climate, sediment supply and bottom currents play key roles in the recent short-term architecture and dynamics. Moreover, the recent predominant along-slope sedimentary processes observed in the studied northwestern Iberian Margin represent snapshots of the progressive stages and mixed deep-water system developments of the marginal platforms on passive margins and may provide information for a predictive model of the evolution of other similar margins.

Nematode communities in sediments of the Kermadec Trench, Southwest Pacific Ocean

Hadal trenches are characterized by environmental conditions not found in any other deep-sea environment, such as steep topography and periodic disturbance by turbidity flows, which are likely responsible for the distinct nature of benthic communities of hadal trenches relative to those of the abyssal plain. Nematodes are the most abundant metazoans in the deep-sea benthos, but it is not yet clear if different trenches host distinct nematode communities, and no data are yet available on the communities of most trenches, including the Kermadec Trench in the Southwest Pacific. Quantitative core samples from the seafloor of the Kermadec Trench were recently obtained from four sites at 6000–9000 m depth which allowed for analyses of meiofauna, and nematodes in particular, for the first time. Nematode community and trophic structure was also compared with other trenches using published data. There was a bathymetric gradient in meiofauna abundance, biomass, and community structure within the Kermadec Trench, but patterns for species richness were ambiguous depending on which metric was used. There was a change in community structure from shallow to deep sites, as well as a consistent change in community structure from the upper sediment layers to the deeper sediment layers across the four sites. These patterns are most likely explained by variation in food availability within the trench, and related to trench topography. Together, deposit and microbial feeders represented 48–92% of total nematode abundance in the samples, which suggests that fine organic detritus and bacteria are major food sources. The relatively high abundance of epigrowth feeders at the 6000 and 9000 m sites (38% and 31%, respectively) indicates that relatively freshly settled microalgal cells represent another important food source at these sites. We found a significant difference in species community structure between the Kermadec and Tonga trenches, which was due to both the presence/absence of species as well as differences in relative abundances of shared species. The cluster and SIMPROF analyses of nematode genus community data across Pacific and Atlantic trenches identified two statistically significant natural groupings: the first group comprised all three Puerto Rico Trench samples, and the second comprised all remaining trenches (South Sandwich, Atacama, Tonga, and Kermadec). Our analyses show that differences in nematode between the adjacent Kermadec and Tonga trenches are observable when analyses are conducted with species-level identifications, but genera-based and trophic structure analyses revealed only limited heterogeneity among trenches. The present study contributes to the growing amount of information on hadal trench environments, which ultimately will build a greater understanding of these rarely sampled deep-sea habitats.

Decorrelation scales for Arctic Ocean hydrography – Part I: Amerasian Basin

Abstract. Any use of observational data for data assimilation requires adequate information of their representativeness in space and time. This is particularly important for sparse, non-synoptic data, which comprise the bulk of oceanic in situ observations in the Arctic. To quantify spatial and temporal scales of temperature and salinity variations, we estimate the autocorrelation function and associated decorrelation scales for the Amerasian Basin of the Arctic Ocean. For this purpose, we compile historical measurements from 1980 to 2015. Assuming spatial and temporal homogeneity of the decorrelation scale in the basin interior (abyssal plain area), we calculate autocorrelations as a function of spatial distance and temporal lag. The examination of the functional form of autocorrelation in each depth range reveals that the autocorrelation is well described by a Gaussian function in space and time. We derive decorrelation scales of 150–200 km in space and 100–300 days in time. These scales are directly applicable to quantify the representation error, which is essential for use of ocean in situ measurements in data assimilation. We also describe how the estimated autocorrelation function and decorrelation scale should be applied for cost function calculation in a data assimilation system.

Palaeomagnetic time and space constraints of the Early Cretaceous Rhenodanubian Flysch zone (Eastern Alps)

The Rhenodanubian Flysch zone (RDF) is a Lower Cretaceous-lower Palaeocene turbidite succession extending for similar to 500 km from the Danube at Vienna to the Rhine Valley (Eastern Alps). It consists of calcareous and siliciclastic turbidite systems deposited in a trench abyssal plain. The age of deposition has been estimated through micropalaeontologic dating. However, palaeomagnetic studies constraining the age and the palaeolatitude of deposition of the RDF are still missing. Here, we present palaeomagnetic data from the Early Cretaceous Tristel and Rehbreingraben Formations of the RDF from two localities in the Bavarian Alps (Rehbrein Creek and Lainbach Valley, southern Germany), and from the stratigraphic equivalent of the Falknis Nappe (Liechtenstein). The quality of the palaeomagnetic signal has been assessed by either fold test (FT) or reversal test (RT). Sediments from the Falknis Nappe are characterized by a pervasive syntectonic magnetic overprint as tested by negative FT, and are thus excluded from the study. The sediments of the Rehbreingraben Formation at Rehbrein Creek, with positive RT, straddle magnetic polarity Chron M0r and the younger M'-1r' reverse event, with an age of similar to 127-123 Ma (late Barremian-early Aptian). At Lainbach Valley, no polarity reversals have been observed, but a positive FT gives confidence on the reliability of the data. The primary palaeomagnetic directions, after correction for inclination shallowing, allow to precisely constrain the depositional palaeolatitude of the Tristel and Rehbreingraben Formations around similar to 28 degrees N. In a palaeogeographic reconstruction of the Alpine Tethys at the Barremian/Aptian boundary, the RDF is located on the western margin of the Brianconnais terrain, which was separated from the European continent by the narrow Valais Ocean.

Unusually diverse, abundant and endemic deep–sea sponge fauna revealed in the Sea of Okhotsk (NW Pacific Ocean)

The deep–sea sponge fauna of the NW (North–West) Pacific has been re–examined with new and previously collected specimens. In total, 555 new sponge specimens were collected in the under–explored deep Kuril Basin (Sea of Okhotsk), Bussol Strait and adjacent NW Pacific Ocean sites during the Russian–German expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) in 2015. Our knowledge of Sea of Okhotsk deep–sea sponge species has nearly tripled (additional 19 spp.) as a result of this expedition, taking the total of known deep–sea species to 32 for this region. Close to half of species collected were either new to science or new to this region, and two–thirds of species were only found at one site during this study. The Sea of Okhotsk is unlikely to be a sink population, and could be considered a source population for several species due to the large numbers of individuals found. The NE Kuril Basin (Sea of Okhotsk) harboured nearly half of all sponge individuals found during this expedition, and is more species diverse than other Kuril Basin sectors, highlighting the variability in abundance and diversity found in this basin; and is also far richer than the Bussol Strait and NW Pacific sites explored. These differences are potentially due to the presence of productive currents, variable substrates, and niche differences in throughout this region. The semi–enclosed abyssal sector of the Sea of Okhotsk is partially connected with the adjacent NW Pacific abyssal plains through the Bussol and Krusenstern straits, and these straits have enabled faunal connectivity. The long–term partial isolation of the Sea of Okhotsk, low population density of deep–sea sponges, high productivity, and its unusual marine environment, could be key to understanding the exceptional levels of regional deep–sea sponge endemism and diversity.

Echo-character of the NW Iberian continental margin and the adjacent abyssal plains

ABSTRACTThe acoustic facies analyses have provided an important basis for sedimentary processes in the deep-sea environments. The echo-character mapping, through the interpretation and correlation of very high-resolution seismic profiles, is a very useful tool for the characterization of the recent sedimentary processes and their distribution. This work presents the first echo-character map at 1:800,000 scale of the Galicia Continental Margin and the adjacent abyssal plains elaborated by the Geological Survey of Spain. The map was carried out on the basis of the analysis and interpretation of the bathymetry and reflectivity data from the SIMRAD EM12, EM120 and EM1002 echosounders, and the high-resolution seismic profiles from the SIMRAD TOPAS PS18 parametric echosounder. On the basis of seafloor morphology, surface bedforms, backscatter and sub-bottom acoustic echo-characters, 26 echo-types were identified in the uppermost sedimentary sequence. These echo-types have been grouped into four main echoes: Distinct, Irregular, Hyperbolic and Undulated, according to their main acoustic characteristics. This information has been acquired in the framework of the ‘Scientific Research Program of the Economic Exclusive Zone of Spain’, which is coordinated and leaded by the Defense Ministry of Spain, during the oceanographic cruises carried out on board of the R/V Hesperides in 2001–2003 and 2006–2009.

Understanding the Evolution of an Oceanic Intraplate Volcano From Seismic Reflection Data: A New Model for La Réunion, Indian Ocean

AbstractHigh‐resolution seismic reflection profiles gathered in 2006 on La Réunion submarine flanks and surrounding abyssal plain, enabled characterization of the seismostratigraphy architecture of the volcaniclastic apron. Four seismic units are defined beyond the edifice base: (1) a basal unit, interpreted as pelagic sediment predating La Réunion volcanism; (2) a second unit showing low‐ to medium‐amplitude reflections, related to La Réunion emergence including the submarine explosive phase; (3) a high‐amplitude seismic unit, associated with subaerial volcanic activity (i.e., mature island stage); and (4) an acoustically transparent unit, ascribed to erosion that currently affects the volcanic complex. Two prominent horizons delineate the base of the units II and III marking, respectively, the onset of La Réunion seamount explosive activity and the Piton des Neiges volcanic activity. Related isopach maps demonstrate: (1) the existence of a large proto‐Piton des Neiges volcano during the first building phase of the volcanic complex, and (2) the central role of the Piton des Neiges volcano during the second phase. Shield growth stage of the Piton de la Fournaise volcano is also captured in the upper part of the volcaniclastic apron, attesting to its recent contribution. Seismic facies identified in the apron highlight a prevalence of sedimentary and reworking processes since the onset of the volcanism compared to catastrophic flank collapses. We present here a new model of evolution for La Réunion volcanic complex since the onset of the volcanism and argue that a major proto Piton des Neiges‐Piton des Neiges volcanic complex controls La Réunion present‐day morphology.

Habitat heterogeneity of hadal trenches: Considerations and implications for future studies

The hadal zone largely comprises a series of subduction trenches that do not form part of the continental shelf-slope rise to abyssal plain continuum. Instead they form geographically isolated clusters of deep-sea (6000–11,000 m water depth) environments. There is a growing realization in hadal science that ecological patterns and processes are not driven solely by responses to hydrostatic pressure, with comparable levels of habitat heterogeneity as observed in other marine biozones. Furthermore, this heterogeneity can be expressed at multiple scales from inter-trench levels (degrees of geographical isolation, and biochemical province), to intra-trench levels (variation between trench flanks and axis), topographical features within the trench interior (sedimentary basins, ridges, escarpments, ‘deeps’, seamounts) to the substrate of the trench floor (seabed-sediment composition, mass movement deposits, bedrock outcrop). Using best available bathymetry data combined with the largest lander-derived imaging dataset that spans the full depth range of three hadal trenches (including adjacent slopes); the Mariana, Kermadec and New Hebrides trenches, the topographic variability, fine-scale habitat heterogeneity and distribution of seabed sediments of these three trenches have been assessed for the first time. As well as serving as the first descriptive study of habitat heterogeneity at hadal depths, this study also provides guidance for future hadal sampling campaigns taking into account geographic isolation, total trench particulate organic matter flux, maximum water depth and area.

The Central Canyon depositional patterns and filling process in east of Lingshui Depression, Qiongdongnan Basin, northern South China Sea

Central canyons are considered to be important conduits for the transfer of sediment to the abyssal plains. High‐resolution 3D seismic data and logging data from the east of Lingshui Depression are used to investigate the depositional elements, patterns, and filling processes of central canyon in the Qiongdongnan Basin, northern South China Sea. The Central Canyon in this segment is 30 km wide and more than 1,000 m deep. It was found to be characterized by being subparallel to the continental shelf. In this study, 6 types of deep‐water gravity flow depositional elements were identified, including erosion surfaces, basal lags, turbidite channel complexes, mass transport deposits, lobe complex, and pelagic deposits. Each type of these depositional elements was found to have distinct external features, internal structures, and lateral characteristics in the seismic profiles. Meanwhile, these different assemblages of depositional elements could be composed of 5 depositional units. And in a vertical direction, the evolutionary history could be divided into 5 stages as follows: (a) a repeated cut and fill stage; (b) high net‐to‐gross channel complex dominated stage; (c) low high net‐to‐gross channel and pelagic shale dominated stage; (d) lobe complex deposition stage; and (e) mass transport deposit dominated stage. During Stage 3, the development of small‐scale turbidite channels is the indicators of northern sediment supply. During Stage 4, 7 lobes have been identified in the lobe complexes. The evolution and depositional processes in the study area were most likely controlled by the negative relief induced by the palaeo‐seafloor morphology, as well as the structural inversions of the Red River Fault and the basement faults. Additionally, the sediment supply, sea‐level fluctuations, and tectonic activities also controlled and influenced the depositional processes, along with the internal architecture of the canyon.The results of this study have potentially important implications for the improved understanding the vertical evolution of submarine canyons and also shed a new light on the reservoir potential of the Lingshui section of the Central Canyon.

An Overview of Seabed Mining Including the Current State of Development, Environmental Impacts, and Knowledge Gaps

Rising demand for minerals and metals, including for use in the technology sector, has led to a resurgence of interest in exploration of mineral resources located on the seabed. Such resources, whether seafloor massive (polymetallic) sulfides around hydrothermal vents, cobalt-rich crusts on the flanks of seamounts or fields of manganese (polymetallic) nodules on the abyssal plains, cannot be considered in isolation of the distinctive, in some cases unique, assemblages of marine species associated with the same habitats and structures. In addition to mineral deposits, there is interest in extracting methane from gas hydrates on continental slopes and rises. Many of the regions identified for future seabed mining are already recognised as vulnerable marine ecosystems. Since its inception in 1982, the International Seabed Authority (ISA), charged with regulating human activities on the deep-sea floor beyond the continental shelf, has issued 27 contracts for mineral exploration, encompassing a combined area of more than 1.4 million km2, and continues to develop rules for commercial mining. At the same time, some seabed mining operations are already taking place within continental shelf areas of nation states, generally at relatively shallow depths, and with others at advanced stages of planning. The first commercial enterprise, expected to target mineral-rich sulfides in deeper waters, at depths between 1,500 and 2,000 metres on the continental shelf of Papua New Guinea, is scheduled to begin early in 2019. In this review, we explore three broad aspects relating to the exploration and exploitation of seabed mineral resources: (1) the current state of development of such activities in areas both within and beyond national jurisdictions, (2) possible environmental impacts both close to and more distant from mining activities and (3) the uncertainties and gaps in scientific knowledge and understanding which render baseline and impact assessments particularly difficult for the deep sea. We also consider whether there are alternative approaches to the management of existing mineral reserves and resources, which may reduce incentives for seabed mining.

The transport and accumulation processes of the anthropogenic radionuclides in the Black Sea

The mechanism of transport and accumulation of anthropogenic radionuclides (137Cs) in the Black Sea is analyzed on the basis of data obtained within the framework of the IAEA international project RER/2/003. The features of the sedimentation of the contaminated suspended matter to the shelf, the continental slope and the abyssal plain. The estimation of the value of 137Cs accumulated on different parts of the sea bottom is given. On the example of transport and sedimentation patterns of radionuclides, analogies with a similar process in passive suspensions entering the sea are carried out. The influence of extreme natural phenomena on the described processes is noted.

Greater Role of Geostrophic Currents in Ekman Dynamics in the Western Arctic Ocean as a Mechanism for Beaufort Gyre Stabilization

AbstractSeven different methods, with and without including geostrophic currents, were used to explore Ekman dynamics in the western Arctic Ocean for the period 1992–2014. Results show that surface geostrophic currents have been increasing and are much stronger than Ekman layer velocities in recent years (2003–2014) when the oceanic Beaufort Gyre (BG) is spinning up in the region. The new methods that include geostrophic currents result in more realistic Ekman pumping velocities than a previous iterative method that does not consider geostrophic currents and therefore overestimates Ekman pumping velocities by up to 52% in the central area of the BG over the period 2003–2014. When the BG is spinning up as seen in recent years, geostrophic currents become stronger, which tend to modify the ice‐ocean stress and moderate the wind‐driven Ekman convergence in the Canada Basin. This is a mechanism we have identified to play an important and growing role in stabilizing the Ekman convergence and therefore the BG in recent years. This mechanism may be used to explain three scenarios that describe the interplay of changes in wind forcing, sea ice motion, and geostrophic currents that control the variability of the Ekman dynamics in the central BG during 1992–2014. Results also reveal several upwelling regions in the southern and northern Canada Basin and the Chukchi Abyssal Plain which may play a significant role in physical and biological processes in these regions.

Dominant Circulation Patterns of the Deep Gulf of Mexico

AbstractThe large-scale circulation of the bottom layer of the Gulf of Mexico is analyzed, with special attention to the historically least studied western basin. The analysis is based on 4 years of data collected by 158 subsurface floats parked at 1500 and 2500 m and is complemented with data collected by current meter moorings in the western basin during the same period. Three main circulation patterns stand out: a cyclonic boundary current, a cyclonic gyre in the abyssal plain, and the very high eddy kinetic energy observed in the eastern Gulf. The boundary current and the cyclonic gyre appear as distinct features, which interact in the western tip of the Yucatan shelf. The persistence and continuity of the boundary current is addressed. Although high variability is observed, the boundary flow serves as a pathway for water to travel around the western basin in approximately 2 years. An interesting discovery is the separation of the boundary current over the northwestern slope of the Yucatan shelf. The separation and retroflection of the along-slope current appears to be a persistent feature and is associated with anticyclonic eddies whose genesis mechanism remains to be understood. As the boundary flow separates, it feeds into the westward flow of the deep cyclonic gyre. The location of this gyre—named the Sigsbee Abyssal Gyre—coincides with closed geostrophic contours, so eddy–topography interaction via bottom form stresses may drive this mean flow. The contribution to the cyclonic vorticity of the gyre by modons traveling under Loop Current eddies is discussed.

Abyssal Solenogastres (Mollusca, Aplacophora) from the Northwest Pacific: Scratching the Surface of Deep-Sea Diversity Using Integrative Taxonomy

Solenogastres (Aplacophora) is a small clade of marine, shell-less worm-molluscs with close to 300 valid species. Their distribution ranges across all oceans, and whereas the vast majority of species has been collected and described from the continental shelf and slope, only few species are known from depths below 4000 m. Following traditional taxonomy, identification of specimens to species level is complex and time-consuming and requires detailed investigations of morphology and anatomy – often resulting in the exclusion of the clade in biodiversity or biogeographic studies. During the KuramBio expedition (Kuril-Kamchatka Biodiversity Studies) to the abyssal plain of the Northwest Pacific and the Kuril-Kamchatka trench, 33 solenogaster specimens were sampled from 4830 m to 5397m. Within this study we present an efficient workflow to address solenogaster diversity, even when confronted with a high degree of singletons and minute body sizes, hampering the use of single individuals for multiple morphological and molecular approaches. We combine analyses of external characters and scleritome with molecular barcoding based on a self-designed solenogaster specific set of mitochondrial primers. Overall we were able to delineate at least 19 solenogaster lineages and identify 15 species to family level and beyond. Based on our approach we identified three key lineages from the two regionally most species-rich families (Acanthomeniidae and Pruvotinidae) for deeper taxonomic investigations and describe the novel abyssal species Amboherpia abyssokurilensis sp. nov. (Cavibelonia, Acanthomeniidae) using microanatomical 3D-reconstructions. Our study more than doubles the previous records of solenogaster species from the Northwest Pacific and its marginal seas. Almost all lineages are reported for the first time from the region of the (Northwest) Pacific, vastly expanding distribution ranges of the respective clades. Moreover it doubles the number of Solenogastres collected from abyssal depths on a global scale and underlines the lack of exploratory α-diversity work in the abyssal zone for reliable species estimates in marine biodiversity.

First insights into the solenogaster diversity of the Sea of Okhotsk with the description of a new species of Kruppomenia (Simrothiellidae, Cavibelonia)

Solenogastres form a small clade of worm-shaped molluscs distributed world-wide with most of the approx. 300 species occurring in the deep sea. A recent diversity study from the abyssal plain in the Northwest Pacific has revealed a wealth of new abyssal solenogaster lineages highlighting the need for further alpha-taxonomic work. During the ‘Sea of Okhotsk Biodiversity Studies’ (SokhoBio) expedition, 93 specimens were collected at overall eight stations ranging from depths of 1696–3377 m. Preliminary investigations revealed twelve clearly distinguishable morphospecies, including one relatively common species present at six of eleven stations. All morphospecies are characterized externally via light microscopy and identified to the best possible taxonomic level via scleritome characters. Molecular barcodes (16S rRNA) are provided as a first step towards establishment of a barcoding library to enable fast and accurate re-identification of these taxonomically challenging molluscs in future studies. The most wide-spread and abundant cavibelonian Solenogastres Kruppomenia genslerae sp. nov. (Simrothiellidae) is exemplarily described in full microanatomical detail based on 3D-reconstructions from histological semithin section series and scanning electron microscopy. We discuss our results in comparison to the solenogaster diversity of the neighbouring abyssal plain of the Northwest Pacific, which is connected with the Kuril Basin via two straits. Our initial characterization of the diversity boosts the hitherto poorly known diversity of Solenogastres in the Far Eastern Seas, but also underlines the taxonomic impediment for proper taxonomic descriptions of the wealth of new discovered material.

Near-Surface and Deep Circulation Coupling in the Western Gulf of Mexico

AbstractThe coupling between the upper (z < 1000-m depth) and deep (z > 1500 m) circulation in the western Gulf of Mexico (WGoM) driven by the arrival of Loop Current eddies (LCEs) is analyzed from moorings measuring horizontal velocity in the full water column during a 5-yr period (October 2008–October 2013). Nine LCEs crossing the mooring array are documented. A composite of these events shows that strong northward currents at depth having speeds of 0.1–0.2 m s−1 precede (~10–20 days) the strong northward near-surface currents (~0.5 m s−1) characteristic of the western rim of the LCEs. These deep northward flow intensifications are followed by southward deep flows coupled with the surface-intensified southward current of the eastern (rear) part of the LCEs crossing the array. These results are consistent with the existence of a deep anticyclone leading and a cyclone trailing the upper-layer LCEs. Objectively interpolated regional maps of velocities and vertical vorticity obtained from up to 30 moorings indicate the mean circulation at 100-m depth in the northern WGoM is mostly anticyclonic and enhanced by the arrival of the westward-propagating LCEs, while the southern part is dominated by the presence of a semipermanent cyclonic structure (Bay of Campeche cyclonic gyre). At 1500-m depth, the mean circulation follows the slope in a cyclonic sense and shows a cyclonic vorticity maximum on the abyssal plane consistent with the LCE deep flow composites. This suggests the LCEs strongly modulate not only the upper-layer circulation but also impact the deep flow.

Predicting Sediment Thickness on Vanished Ocean Crust Since 200 Ma

AbstractTracing sedimentation through time on existing and vanished seafloor is imperative for constraining long‐term eustasy and for calculating volumes of subducted deep‐sea sediments that contribute to global geochemical cycles. We present regression algorithms that incorporate the age of the ocean crust and the mean distance to the nearest passive margin to predict sediment thicknesses and long‐term decompacted sedimentation rates since 200 Ma. The mean sediment thickness decreases from ∼220 m at 200 Ma to a minimum of ∼140 m at 130 Ma, reflecting the replacement of old Panthalassic ocean floor with young sediment‐poor mid‐ocean ridges, followed by an increase to ∼365 m at present‐day. This increase reflects the accumulation of sediments on ageing abyssal plains proximal to passive margins, coupled with a decrease in the mean distance of any parcel of ocean crust to the nearest passive margin by over 700 km, and a doubling of the total passive margin length at present‐day. Mean long‐term sedimentation rates increase from ∼0.5 cm/ky at 160 Ma to over 0.8 cm/ky today, caused by enhanced terrigenous sediment influx along lengthened passive margins, superimposed by the onset of ocean‐wide carbonate sedimentation. Our predictive algorithms, coupled to a plate tectonic model, provide a framework for constraining the seafloor sediment‐driven eustatic sea‐level component, which has grown from ∼80 to 210 m since 120 Ma. This implies a long‐term sea‐level rise component of 130 m, partly counteracting the contemporaneous increase in ocean basin depth due to progressive crustal ageing.

Prodigious submarine landslides during the inception and early growth of volcanic islands

Volcanic island inception applies large stresses as the ocean crust domes in response to magma ascension and is loaded by eruption of lavas. There is currently limited information on when volcanic islands are initiated on the seafloor, and no information regarding the seafloor instabilities island inception may cause. The deep sea Madeira Abyssal Plain contains a 43 million year history of turbidites among which many originate from mass movements in the Canary Islands. Here, we investigate the composition and timing of a distinctive group of turbidites that we suggest represent a new unique record of large-volume submarine landslides triggered during the inception, submarine shield growth, and final subaerial emergence of the Canary Islands. These slides are predominantly multi-stage and yet represent among the largest mass movements on the Earth’s surface up to three or more-times larger than subaerial Canary Islands flank collapses. Thus whilst these deposits provide invaluable information on ocean island geodynamics they also represent a significant, and as yet unaccounted, marine geohazard.

Four new species of the family Propeamussiidae (Mollusca: Bivalvia) from the abyssal zone of the northwestern Pacific, with notes on Catillopecten squamiformis (Bernard, 1978)

Based on the material collected from 1949 to 2015 by nine deep-sea expeditions, four new species of the family Propeamussiidae (Mollusca: Bivalvia) and Catillopecten squamiformis (Bernard, 1978) were found in the abyssal zone (2,901-5,680 m depths) of the Bering Sea, the Sea of Okhotsk, and the northwestern Pacific. Parvamussium pacificum sp. nov., Catillopecten brandtae sp. nov., Catillopecten malyutinae sp. nov., and Catillopecten natalyae sp. nov. are described from the abyssal plain (4,860-5,680 m depths) adjacent to the Kuril-Kamchatka and Japan trenches (Pacific Ocean). Catillopecten squamiformis was found in the Bering Sea, the Sea of Okhotsk, and at the abyssal plain near the southeastern coast of Kamchatka and Aleutian Trench (Pacific Ocean) at 2,901-5,020 m depth. This is the first record of C. squamiformis from the northwestern Pacific. An expanded description of C. squamiformis with new data on its morphology and geographic distribution is given. To date, 12 species of the genus Catillopecten are known from the different regions of the World Ocean. A table with the main differences among all known species in the genus is provided.