Trough Slope Research Articles

Bacterioplankton of the Western Part of the Kara Sea

Data on the structural and production characteristics of bacterioplankton in the western part of the Kara Sea at the beginning and in the middle of summer are presented. In the region of the St. Anna Trough slope, the average abundance of prokaryotes for the water column was (594–708) × 103 cells/ml (26.4–36.5 mgC/m3) in June and (247–517) × 103 cells/ml (12–28 mgC/m3) at the beginning of August. On the transect along Novaya Zemlya, the average abundance of bacterioplankton in the water column was (186–554) × 103 cells/mL (8.5–30 mgC/m3) within a week after the seasonal ice and (169–443) × 103 cells/mL (8–21 mgC/m3) in the midsummer. Bacterial specific growth rate did not exceed 1.28 day–1; its high values were observed in the upper warm water layer, above the halocline, and also at the near-bottom depths. At the beginning of summer, the production of bacterioplankton tended to decrease in the northeast direction. The distribution of prokaryotes abundance was determined by temperature and water saturation with oxygen, possibly as an indirect indicator of past phytoplankton “bloom”.

Structural analysis and evolution of large Venusian coronae: Insights from low-angle faults at coronae rims

We analyzed topography, fracture patterns, and faults of the asymmetric Atahensik Corona (700 × 900 km diameter), formerly known as Latona Corona, and their surrounding troughs using Magellan SAR imagery, and compare the results with the smaller, ovoid Didilia (400 × 450 km diameter) and Pavlova coronae (550 × 650 km diameter) to get insights on corona formation on Venus. Atahensik contains a high density of radial, oblique, and concentric fractures, the latter are inferred to be the youngest fractures. A high density of concentric fractures particularly occurs along the outer rise and indicates elastic downward bending of this part of the lithosphere in the later stage of corona formation. Along the steep inner slopes of Atahensik's arcuate troughs, large-scale faults are exposed that dip gently towards the corona center and crosscut all fractures. We propose that these low-angle faults were initially formed as thrust planes but subsequently became reactivated as low-angle normal faults, thereby exposing parts of their fault surfaces. Such faults have been identified not only along the arcuate troughs of Atahensik but also occur in Dali Chasma, northwest of Atahensik Corona.A phenomenological formation model of large coronae is presented: corona initiation starts with radial fracturing, which is caused by the dike emplacement and thermal uplift of the corona center due to the rise of a hot asthenospheric mantle plume. Uplift and lateral plume spreading steepen the outer rim of the uplift and cause intense radial fracturing of a central volcanic edifice and the corona's outer rim. This intermediate stage is preserved in several less-evolved coronae such as Didilia and Pavlova Coronae. The fractured ridge thrusts outward onto an intact and cooler lithosphere along strongly localized thrust planes. The overthrusted, cooler lithosphere is elastically bent downward and forms arcuate troughs and associated outer rises with numerous concentric fractures along their crest line. The fractured ridge annulus of the corona is supported by the intact and thickened lithosphere surrounding the corona. The present morphology of Atahensik Corona indicates subsequent subsidence in its central part due to declining plume activity and reduced thermal buoyancy. Reactivation of the thrusts as low-angle normal faults results from the subsidence of the corona interior, a gravitational instability of the elevated corona annulus, and a lack of shortening. The evolutionary sequence derived on the basis of structural data is in agreement with geodynamic models on corona formation involving a bending lithosphere at the plume margin.

Occurrence and Sources of Polycyclic Aromatic Hydrocarbons and Factors Influencing Their Accumulation in Surface Sediment of a Deep-Sea Depression, Namely, the Tatar Trough (Tatar Strait, the Sea of Japan)

The concentrations of 14 polycyclic aromatic hydrocarbons (PAHs) in the sediment of the Tatar Trough were studied. Despite the increase in PAH concentrations over recent decades, which is likely the result of the handling and transportation of fossil fuels, PAH levels and ecological risk were found to be low. The spatial pattern revealed that higher PAH concentrations were mainly in the deeper water sites, suggesting that trough slope failure transported the PAHs to the deeper part of the basin. There was no correlation between the PAHs and grain size or the PAHs and organic carbon that is related to the PAH input from a variety of sources and the heterogeneity of organic matter. The PAH composition, isomer ratio, and PCA identified two areas with different PAH sources. The most northern part of the Tatar Trough received petrogenic PAHs that are probably transported downslope from the northern Tatar Strait where fossil fuels are handled in some ports. Another trough part was polluted by the PAHs from the combustion of coal and biomass and the exhaust of marine vehicles. The minor presence of genes responsible for aerobic PAH destruction can be explained by the anaerobic degradation of PAHs or the spontaneous creation of favorable conditions that promote bacterial PAH oxidation.

Diagenetic Geochemistry of Iron, Sulfur, and Molybdenum in Sediments of the Middle Okinawa Trough Impacted by Hydrothermal Plumes and/or Cold Seeps

AbstractIron (Fe), sulfur (S), and molybdenum (Mo) geochemistry in marine sediments impacted by hydrothermal plumes and/or cold seeps is complex and has not been systematically documented. Here we characterize Fe, S, and Mo diagenesis in sediments between the Minami‐Ensei Knoll hydrothermal field and a cold‐seep site of the middle Okinawa Trough. Results show that distances away from the hydrothermal field and the steep trough slope may significantly affect the transport of hydrothermal Fe. The transformation of hydrothermal reactive Fe to poorly reactive or unreactive Fe‐bearing phyllosilicates decreased the relative fractions of highly reactive Fe (FeHR) in total Fe (FeHR/FeT). Despite this, the standing stocks of Fe oxides in the methane‐free sediments have not been dampened, indicating no net impacts of hydrothermal Fe inputs on the size of Fe oxides. In the methane‐free sediments, low ratios of total reduced inorganic sulfide (TRIS) to total organic carbon (TOC) (TRIS/TOC), highly 34S‐depleted pyrite, and low Mo contents suggest that organoclastic sulfate reduction is at low rates and plays a limited role in carbon cycle. In the cold‐seep sediments, however, intense sulfate reduction coupled to anaerobic methane oxidation significantly elevate TRIS/TOC ratios, Mo enrichment, and isotope compositions of Mo and pyrite‐S. This pathway is expected to be important in carbon cycle in the basin due to the wide occurrence of cold seeps. Our results highlight the important controls of the local extreme depositional/diagenetic conditions on sedimentary S and Mo records, with implications for the reconstruction of paleoredox states of the past earth's surface.

Methane seepage intensity distinguish microbial communities in sediments at the Mid-Okinawa Trough

Shallow methane/sulfate transition zones in cold seeps are hotspots to study microbially mediated geochemical cycles due to high methane fluxes. However, our knowledge about the microbial communities in remote seafloor cold seep ecosystems with different methane seepage intensity is still sparse due to the challenge for sampling and visual observations. In this work, three remotely operated vehicle (ROV) video-guided push sediment cores were sampled from cold seep fields with different methane seepage intensity (low-intensity seepage, R5-C1; moderate-intensity seepage, R6-C2; high-intensity seepage, R6-C3) at the western slope of Mid-Okinawa Trough (Mid-OT) and subjected to high throughput sequencing of 16S rRNA genes for bacteria and archaea. Vesicomyid clams and white microbial mats are visible by video at R6-C3 with methane bubbles. The high relative abundances of anaerobic methanotrophic archaea (ANME-1, -2, and -3), δ-Proteobacteriacea and Campylobacteria in R6-C3 indicated that the processes of anaerobic methane oxidation (AOM), sulfate reduction and sulfur oxidation might occur in this active seeping site. In contrast, Bathyarchaeia, Nitrosopumilales, Sphingomonadales, and Burkholderiales were enriched in bubble-free sites, which commonly involved in the degradation of organic compounds. Principal coordinate analysis showed that both bacterial and archaeal communities were clustered according to sampling sites, also indicating the impact of methane seepage intensity on microbial communities. The co-occurrence network analysis revealed that microbes at the site with high methane fluxes mainly cooperated with each other to sustain the ecosystems, whereas competition enhanced at sites with low methane fluxes. Detection of thermophiles Thermoanaerobaculia and Hydrothermarchaeota may indicate microbial transmission from nearby hydrothermal vents, suggesting potential interactions between cold seepage and hydrothermal vent ecosystems. These results expand our knowledge about the composition and distribution of bacteria and archaea with different methane seepage intensity in cold seep field at the Mid-OT, contributing to the ongoing efforts in understanding carbon cycling in the cold seep ecosystems.

Design of partial cross-sectional geometry and prediction of separation performance in the spiral separator

ABSTRACT Understanding the influence mechanism of the partial cross-sectional geometry of a spiral separator on the flow field characteristics and particle separation performance is conducive to the design of a combined cross-section profile. The impact of the trough slope in the inner and middle troughs on the flow field characteristics and particle separation performance was investigated by CFD methods. The results show that the average depth of the flow film, the average tangential velocity, and the average radial velocity in the partial radial region are linearly related to the trough slope. With the increase in the trough slope in the inner and middle troughs (r = 30–110 mm), the radial velocity reversal position will decline, resulting in an enlarged proportion of the outward flow. Adjusting the trough slopes of the two straight segments in the inner and middle troughs will have a positive effect on the precise segregation of particles. In comparison, changing the trough slope in the middle trough containing the miscible band had a more significant effect on particle separation. A maximum separation efficiency of 80.80% was obtained with a trough slope in the middle trough of 5°and a splitter position of 95 mm.

Induced Seismic Events—Distribution of Ground Surface Displacements Based on InSAR Methods and Mogi and Yang Models

In this article, we present a possible approach to use satellite radar data for a complete description of the formation process of a subsidence trough resulting from an induced seismic event—a mining tremor. Our main goal was to verify whether SAR data allow for the calculation of the basic indicators for the trough (w—subsidence, T—trough slope, K—curvature, u—horizontal displacements, ε—horizontal deformations). We verified the extent to which the Mogi and Yang models can be fitted to match the actual displacements recorded after an induced seismic tremor. The calculations were performed for the Legnica-Glogow Copper Belt (LGCB) area in southwest Poland. Due to intensive mining operations and specific geological and tectonic conditions, the area shows a high level of induced seismic activity. Our detailed analysis focused on four powerful mining tremors: the first tremor occurred on 29 November 2016 (MW3.4), the second on 7 December 2017 (MW3.3), the next on 26 December 2017 (MW3.6) and the last tremor on 29 January 2019 (MW3.7). For each analyzed event, we determined the displacements based on the Differential Interferometric Synthetic Aperture Radar (DInSAR) method and Sentinel 1 synthetic aperture radar (SAR) data from two paths (22 and 73). Additionally, for the period from November 2014 to October 2020, we calculated the displacements using the Small Baseline Subset method (SBAS) time series method. In all cases, the tremor was followed by the development of long-lasting surface deformations. The obtained results allowed us to conclude that it is possible to calculate indicators that result from a specific induced mining event. Considering the full moment tensor and nature of the tremor source, we demonstrated that the Mogi and Yang models can be employed to describe the influence of an induced tremor on the surface in an area of mining activity. We also confirmed the global character of the influence of the reduced troposphere on SAR data calculations. Our conclusions indicate that accounting for the tropospheric correction does not distort horizontal and vertical displacement values in regions influenced by mining activity/tremors.

Effects of cross-sectional geometry on flow characteristics in spiral separators

ABSTRACT As flowing film gravity concentrators, spiral separators are extensively used in the processing of numerous minerals. Appropriate design of their cross-sectional geometries has been known as an effective method to improve the performance of spiral separators. However, limited work has been published on the impact of cross-sectional geometry on flow field characteristics in spiral separators. In this study, the effects of cross-sectional geometries with various parabolic profiles (|x|=m|y| n ) of a spiral separator on the flow film thickness, flow pattern and flow regime were investigated by numerical simulation. The validity of the simulation approach was confirmed by the reasonably good agreement between the predicted and measured flow film thickness in the own laboratory spiral separator. Results have shown that the flow film thickness and the mean primary velocity in the inner and middle troughs are reduced by decreasing downward bevel angle or increasing parabolic index. The dominant region of the secondary flow can be expended inward by increasing the downward bevel angle and decreasing the parabolic index. As the radial position extends inward, a larger downward bevel angle is more conducive to improving the intensity of secondary flow. A wider laminar flow region can be obtained with a smaller downward bevel angle or a larger parabolic index. The flow film thickness has a significant positive correlation with the trough slope in the inner and middle troughs. It is recommended that the matching relationship between material properties and flow field characteristics should be fully considered when selecting the cross-sectional geometry. Thus, this study aids the structural design of the cross-sectional geometries of spiral separators.

A Persistent Deep Anticyclonic Vortex in the Rockall Trough Sustained by Anticyclonic Vortices Shed From the Slope Current and Wintertime Convection

AbstractThe presence of a persistent surface anticyclone centered at approximately 55°N, 12°W in the Rockall Trough, northeast North Atlantic, has been previously noted in satellite altimetry data. Here, we show that this surface anticyclone is the imprint of a deep, persistent, non‐stationary anticyclonic vortex. Using wintertime 2007 and 2011 ship‐board data, we describe the anticyclone's vertical structure for the first time and find that the anticyclone core is partly made of warm and salty Mediterranean Overflow Water. The anticyclone has a radius of ~40 km, it stretches down to 2,000 m, with a velocity maximum around 500 m. To analyze the anticyclone's generating mechanism, we use a mesoscale‐resolving (~2 km) simulation, which produces a realistic pattern of the Rockall Trough anticyclone. The simulation indicates that the anticyclone is locally formed and sustained by two types of processes: wintertime convection and merger with anticyclonic vortices shed from the slope current flowing poleward along the eastern Rockall Trough slope. Intense negative vorticity filaments are generated along the Rockall Trough south‐eastern slope, and they encapsulate Mediterranean Overflow Water as they detach and grow into anticyclonic vortices. These Mediterranean Overflow Water‐rich vortices are advected into the trough, consequently merging with the Rockall Trough anticyclone and sustaining it. We suggest that the Rockall Trough anticyclone impacts regional intermediate water masses modifications, heat and salt budgets locally, and further afield into the neighboring subpolar northeast North Atlantic.

Sedimentation rates (data on 210pb and 137cs radionuclides) in different facial-genetic types of the Kara sea bottom sediments

In the article original data on isotope composition of natural excess Pb-210 and artificial Cs-137 radionuclides in upper 2550-cm layer of sea-bottom sediments at the Kara Sea (from Ob and Yenisei estuaries, Eastern-Novaya-Zemlya trough, Voronin trough, as well as Sedov bay (Novaya Zemlya)) are presented. The research results showed close tie between sedimentation rates and facial-genetic types of the sea-bottom sediments. Highest sedimentation rates are typical for the terrigenic-estuarine type. The type is divided on tractional load with sedimentation rate 0.40.7 cm per year and mud bank sediments with sedimentation rate 0.71.0 cm per year. The terrigenic-shallow-marine type is characterized by lowest sedimentation rate 0.10.3 cm per year. The background terrigenic-marine type has a broadest spectrum of the sedimentation rates: on trough slope the rates are minimal (likely to terrigenic-shallow-marine type), within central parts of the trough (as a result of gravity creep) the rates may increase up to 0.9 cm per year. Single facial-genetic type is glacial sediments of Navaya Zemlya bays. Measured recent sedimentation rate within inner depression of the Sedov bay is 0.10.2 cm per year.

Species Composition and Peculiarities of the Distribution of Benthic Peracarida (Crustacea, Malacostraca) in the Barents Sea, Based on Surveys 2003–2008

According to the results of surveys performed in the years 2003–2008, the species composition of the Peracarida (Crustacea, Malacostraca) fauna of the Barents Sea was determined. In total, 323 species were identified within the study area. Sixty-four species of Peracarida were noted for the Barents Sea for the first time. The most significant refinements concerned the orders Isopoda, Cumacea, and Tanaidacea. The main features of the quantitative distribution of Peracarida were revealed; it was found that the richest accumulations were confined to mixed silty–sandy bottom sediments of the shallow waters and the slopes of troughs. In the Barents Sea, eight Peracarida faunistic complexes have been identified, which are confined to specific environmental conditions. Generally, boreal–arctic species prevail in the biogeographic structure, the share of the boreal species exceeds that of the arctic species (28 and 21%, respectively). The zone of combining the ranges of the arctic and boreal species has shifted eastwards and northwards compared to the period of 1968–1970; this is a consequence of the ongoing “warm” hydrological period in the Barents Sea.

Sedimentation Rates in Different Facies–Genetic Types of Bottom Sediments in the Kara Sea: Evidence from the 210Pb and 137Cs Radionuclides

The paper presents authors' original data on the isotope composition of the natural “excess” Pb‑210 and artificial Cs-137 radionuclides in the upper 25- to 50-cm layer of sea-bottom sediments in the Kara Sea (from the Ob and Yenisei estuaries, Eastern Novaya Zemlya trough, Voronin trough, and Sedov bay at the Novaya Zemlya). Sediment cores were collected during Cruises AMK-63 and AMK-66 of the R/V Akademik Mstislav Keldysh in 2015 and 2016. Results of this research show strong correlations between the sedimentation rates and facies-genetic types of the sea-bottom sediments. The highest sedimentation rates are typical of the terrigenous–estuarine sediments, which are subdivided into tractional load, whose sedimentation rate is 0.4–0.7 cm per year, and “mud bank” sediments, whose sedimentation rate is 0.7–1.0 cm per year. The terrigenous shallow marine sediments are characterized by the lowest sedimentation rate of 0.1–0.3 cm per year. The background terrigenous marine sediments show broad variations in the sedimentation rates: these rates are at a minimum (and comparable to the sedimentation rates of the terrigenous shallow marine sediments) on trough slopes and can increase to 0.9 cm per year in the central parts of the trough (as a result of gravity creep). The glacial sediments of Novaya Zemlya bays belong to a separate individual type. The measured “current” sedimentation rate within the inner depression of the Sedov bay is 0.1–0.2 cm per year.

Platform Session – NIBS: An open-loop TMS study evaluating the impact of mu and beta oscillations on motor-evoked potential amplitudes

Neuronal networks exhibit oscillatory activity at various frequencies, which are thought to coordinate local neuronal processing and cortico-cortical communication through alternating periods of excitation and inhibition. In the motor cortex, single neuron spiking rates (Haegens et al., 2011) and neuronal population activity (Miller et al., 2012) are highest at mu and beta oscillatory troughs (maximum surface negativity) and lowest at peaks (maximum surface positivity). This relationship is strongest when subjects are at rest, when power in these frequency bands is known to be high (Pfurtscheller and Da Silva, 1999). Yet, how sensorimotor oscillatory phase and power interact to influence corticospinal excitability in intact humans is not known. Here, we explored this issue in an open-loop TMS design (i.e., timing of TMS delivery was determined by the passage of time, but not brain oscillatory state), focusing on mu and beta oscillatory activity due to their relevance to human motor control. We collected 600 MEPs for each of 20 healthy subjects using single-pulse TMS (Magstim, UK) at 120% or resting motor threshold delivered to the scalp hotspot for the right first dorsal interosseous during simultaneous EEG recordings (BrainProducts GmbH, Germany). Subsequently, data from the C4 sensor were Hjorth-transformed (central: C4; surround: FC2, FC6, CP2, CP6) and the instantaneous oscillatory phase and pre-stimulus power within 150 ms of the TMS pulse in the mu and beta bands was calculated. Peak and trough trials were defined as trials where TMS occurred at maximum surface positivity (45–135°) and maximum surface negativity (225–315°) of the oscillatory cycle, respectively. The influence of sensorimotor oscillatory phase (categorical variable, peak vs. trough), power (continuous variable) and their interaction on MEP amplitudes was statistically evaluated using separate trial-by-trial linear mixed-effects models for each frequency band. For mu activity, there was a significant PHASE x POWER interaction (p = 0.001), evident as a significantly more positive relationship between pre-stimulus mu power and MEP amplitudes for troughs than peaks (mu peak slope = −0.001 [95% CI = −0.029 to 0.027]; mu trough slope = 0.063 [95% CI = 0.034 to 0.090]). Notably, when mu power was high, MEPs were larger at troughs versus peaks, while the opposite was true when mu power was low. For beta activity, there was a significant main effect of POWER (p = 0.007), revealing a positive relationship between pre-stimulus beta power and MEP amplitudes independent of beta phase. Corticospinal excitability was highest at mu troughs during periods of high mu power, and during periods of high beta power regardless of beta phase. We conclude that sensorimotor oscillatory power and phase interact to shape human motor function, supporting the view that sensorimotor rhythms dynamically gate corticospinal excitability.

Analysis of Horizontal Displacements Measured over the Mining Operations in Longwall No. 537 at the Girondelle 5 Seam of the Bw Friedrich Heinrich-Rheinland Coal Mine

Abstract The article presents an analysis of the horizontal land surface displacements taking place as an effect of coal exploitation on the Girondelle 5 seam in the Friedrich Heinrich-Rheinland mine in Germany. The paper presents changes in displacement vectors measured on the surface following the progress of the exploitation face and an analysis of horizontal displacement measurements assuming that their magnitude is proportional to the profile of subsidence trough slope. Then, the values of horizontal displacement coefficient B are assessed for selected longitudinal and transversal calculation cross-sections of longwall No. 537.

The structure and distribution of the phytoplankton community in the deep region of the Northern Kara Sea

The phytoplankton community and its distribution were investigated in the eastern branch of the St. Anna Trough and over the adjacent Kara Sea shelf in September 2011 and in August 2014. The spatial and seasonal differences in the phytoplankton structure were analyzed in connection with ice melting and changes in the temperature, salinity, and biogenic regime. Four 4 zones were defined: the Kara Sea shelf, the upper part of the St. Anna Trough slope, the lower part of the St. Anna Trough slope, and its deep part. It was shown that over the Kara Sea shelf where riverine runoff influence was observed, the phytoplankton community differs from the community of the St. Anna Trough in both investigated periods: in September and August. Rearrangement of the phytoplankton community was observed in the frontal zone associated with the upper part of the slope in September of 2011. The main features of this rearrangement were a change in dominant species composition and a 1.5–2-fold increase in the number and biomass of algae. Over the lower part of the slope and deep area of the St. Anna Trough in August 2014 and September 2011, the phytoplankton community was at different successive stages: in August, at the late spring and summer stage, and in September, at the summer–autumn stage.

Numerical Modelling of the Mining Induced Horizontal Displacement

Abstract The paper presents results of numerical calculations and modeling of mining-induced surface deformation based on Finite Element Method (FEM). Applying the numerical method discussed to calculations allows us to assume a larger number of factors, such as rock mass structure, fracture network, rock properties, etc., which essentially affect the results obtained. On the basis of an elastic transversely isotropic model, an analysis of horizontal displacement distribution and surface subsidence was carried out for two sample regions of mines. The results of numerical calculations were later compared with the measured values. Such an analysis proved that the applied numerical model properly described distribution and values of subsidence and slope of subsidence trough, though there were serious differences in the values of calculated horizontal displacement, especially in areas of far influence range. In order to improve the matching, the influence of boundary conditions of the model on the value of calculated horizontal displacement was analyzed. The results are presented in graphs.

Some Considerations on Horizontal Displacement and Horizontal Displacement Coefficient B

Abstract Mining-induced deformations of the ground surface and within the rock mass may pose danger not only for surface constructions but also for underground objects (e.g., tunnels, underground storages, garages), diverse types of pipelines, electric cables, etc. For a proper evaluation of hazard for surface and underground objects, such parameters as horizontal displacement and horizontal deformations, especially their maximum values, are of crucial importance. The paper is an attempt at a critical review of hitherto accomplished studies and state of the art of predicting horizontal displacement u, in particular the coefficient B, whose value allows determination of the value of maximum displacement if the value of maximum slope is known, or the value of maximum deformation if the value of maximum trough slope is recognized. Since the geodesic observations of fully developed subsidence troughs suggest that the value of the coefficient depends on the depth H, radius of main influences range r and properties of overburden rock, in particular the occurrence of sub-eras Paleogene and Neogene layers (old name: Quaternary and Tertiary) with low strength parameters, therefore a formula is provided in the present paper allowing for the estimation of the influence of those factors on the value of coefficient B.

TO THE PROBLEM OF PROSPECTING FOR HYDROCARBON DEPOSITS WITHIN MONOKLІNAL SLOPES OF TROUGHS

The analysis of structural-geological structure for promising oil and gas anticlinal objects of Dnieper-Donets depression was done. Based on the analysis of geological and geophysical studies it is recommends to works realization on the northern slopes of Yarivskyi and South-Serednyakivsky troughs.

In situ thermal excursions detected in the Nankai Trough forearc slope sediment at IODP NanTroSEIZE Site C0008

At Integrated Ocean Drilling Program (IODP) Site C0008 in the Nankai Trough slope sediment, we discovered in situ temperature anomalies at 80 to 160 m below the seafloor, where pore fluid Cl and δ 18O excursions were identified and interpreted as pore fluid refreshing due to hydrate dissociation. The volume fraction of hydrates is estimated to be approximately 3% and approximately 40% maximum at Holes C0008A and C0008C, respectively. In the vicinity of these anomalies, we discovered negative and positive temperature excursions of up to 1 K measured in situ using the Advanced Piston Corer Temperature (APC-T) tool attached to the shoe of a hydraulic piston corer. They are significantly larger than the uncertainties caused during data acquisition and processing. Frictional heat due to penetration increased the temperature by >10 K, exceeding the gas/hydrate stability temperature at that depth. This heat is partly consumed by hydrate dissociation, which disturbs the thermal decay curve after penetration, but 2D numerical modeling revealed that hydrate dissociation does not significantly change the extrapolated equilibrium temperature. So far, we cannot suggest any acceptable explanation for the observed thermal anomalies, although we strongly suspect that it is related to hydrate dissociation.

The macro- and megabenthic fauna on the continental shelf of the eastern Amundsen Sea, Antarctica

In 2008 the BIOPEARL II expedition on board of RRS James Clark Ross sailed to the eastern Amundsen Sea Embayment and Pine Island Bay, one of the least studied Antarctic continental shelf regions due to its remoteness and ice cover. A total of 37 Agassiz trawls were deployed at depth transects along the continental and trough slopes. A total of 5469 specimens, belonging to 32 higher taxonomic groups and more than 270 species, were collected. Species richness per station varied from 1 to 55. The benthic assemblages were dominated by echinoderms and clearly different to those in the Ross, Scotia and Weddell seas. Here we present the macro- and megafaunal assemblage structure, its species richness and the presence of several undescribed species.