Gravity Cores Research Articles

Detection and Identification of Sediment Layer to Discover the Marine Mineral Resources Potential in Aruah Islands

<p>Aruah Islands is located on an international shipping line adjacent to Malaysia. The important aspect in borderline management is the maritime resource potential, one of which is sea minerals. In order to dig the information about marine mineral resources in Aruah Islands, a high-resolution seismic reflection with low frequency was applied, which capable to detect the depth and identify the sedimentary layers clearly and accurately. The depth of water and sediment layers were detected using an echosounder, reason Navi sound type 210 with a tow fish 100 kHz and shallow seismic boomer with a single channel type and wave energy 200 Joules. Gravity core and grab sampler were used to collect the sediment sample. There were three stages on seismic interpretation: sequence analysis, facies analysis, and reflection character identification. Furthermore, sediments containing coarse sand-sized minerals were observed using a microscope. The measurement result of Aruah Islands water depth was ranging from 0-80 m, the deepest part is on the Northern of Batu Mandi island which was 80 m depth. Seismic profiles indicated that the upper layer of tertiary sedimentary as the youngest rocks. Based on sediment thickness, the thickest area was found on the Western (approx. 50 m) and the Northern (approx. 32 m). In line with the island’s Southern part condition, which was plain or shallow sea exposure, the Southeastern island sediment thickness ranged only about 10-18 m. Generally, based on the analyzed sediment sample, quartz was the main mineral found, which was 60-80% of the composition. Other minerals were zircon, tin, hematite, magnetite, limonite, biotite, and dolomite.</p>

Holocene sedimentation in the Hupo Trough of the southwestern East Sea (Japan Sea) and development of the East Korea Warm Current

Various sediment properties, such as mean grain size, total organic carbon, total nitrogen, C/N ratio, CaCO3, and biogenic opal content, were analyzed for a box core (BC02; 45 cm long) and a gravity core (GC02; 628 cm long), which were collected from the western margin of the Hupo Trough located off the eastern coast of Korea. The study area has been affected by the East Korea Warm Current (EKWC), a branch of the Tsushima Warm Current (TWC). The analytical results obtained for BC02 and the upper part of GC02 were in agreement, affirming the core-top preservation of GC02. Based on the corrected calibrated AMS 14C dates, the sedimentation rate of GC02 changed abruptly at ~8.2 ka from ~4.0–10.2 cm/kyr in the lower part to ~56.6–91.0 cm/kyr in the middle to upper part. This corresponds to the lithologic change from sandy mud to mud sediments showing the mean grain size change from 6.9 to 46.0 μm. Diverse paleoceanographic proxies representing the surface water condition exhibited varying degree of change at ~8.2 ka, after which all the properties remain almost unchanged, implying stable and continuous depositional conditions following the complete development of the EKWC. Furthermore, it indicated that the sediment depositional conditions in the Hupo Trough in response to the EKWC might have stabilized at ~8.2 ka since the opening of the Korea Strait during the Holocene sea level rise. Moreover, microfossil data from previous studies on the establishment of the TWC in the East Sea (Japan Sea) support our interpretation that the sediment properties revealed the Holocene development of the EKWC in the Hupo Trough.

Implementation of comparative detection approaches for the accurate assessment of sediment thickness and sediment volume in the Passaúna Reservoir

Siltation has significant economic and social impacts as it directly reduces the useable amount of water in reservoirs. Giving a solution to the issue of sedimentation is a complicated task and maybe one of the most important engineering and environmental challenges of the 21st century. The deposited volume and the distribution pattern of the sediment are often unknown and not easy to assess. The sedimentation process is highly dynamic, initially due to the hydrological conditions of the incoming rivers, but also due to common internal phenomena like resuspension or density currents. Sediment remediation measures such as mechanical sediment removal or flushing are planned based on the sediment thickness distribution and the overall sediment volume/mass. Often, the sediment thickness is calculated through topographic differencing between the pre-impoundment reservoir lake bottom and the actual lake bottom. However, it is common that the previous depth distribution map is not available or in insufficient quality. In this regard, alternative measurement techniques have to be taken into consideration. In this study, we assessed the best possible approach depending on the characteristics of the sediment and of the reservoir. We combined three different acoustic systems (a multibeam, a sub-bottom profiler, and a single beam dual frequency system) with sediment coring and dynamic free fall penetrometer measurements for an improved assessment of sediment stock and sediment distribution in the Passaúna Reservoir. Our results showed that topographic differencing could not be applied, as the data for the pre-impoundment lake bottom was insufficiently accurate. The parametric sub-bottom profiler could detect the sediment thickness in high accuracy, but significant limitations were recorded in areas with high gas contents. The dual-frequency echosounder derived the sediment thickness with a normalized mean absolute error of 56% due to the high volumetric gas content in the sediment. The dynamic free-fall penetrometer showed satisfying results compared to the other systems. The normalized mean absolute error was 22%, and sediment thickness could be detected in areas with up to 1.8 m of sediment. Sediment coring is also a reliable technique for sediment thickness determination. However, the results showed that if only traditional coring devices are used (gravity corer), the limited penetration depth of the equipment combined with sampling disturbances often prevent a correct assessment of the sediment thickness. The overall results of this study can help for an improved decision-making regarding reservoir management. The accurate assessment of sediment volume and distribution can reduce costs for sediment removal and assist in having a precise overview of the reservoir lifetime.

The Late-Quaternary deposits of the Piedra Buena Terrace (Patagonian continental slope, SW Atlantic): An example of interaction between bottom currents and seafloor morphology

The Piedra Buena Terrace (PBT), situated in the Patagonian continental slope, is swept by the vigorous flow of Antarctic-sourced bottom water masses, and intersected by a considerable submarine canyon system. It thus represents a world-class natural laboratory to investigate the sedimentary dynamics of deep-ocean settings influenced by both, along-slope, and down-slope sedimentary processes. In the framework of the Pampa Azul project, the PBT was surveyed with swath bathymetry and a high-resolution parametric sub-bottom seismic profiler and sampled at several locations with a 7 m long gravity corer. Through the integration of the acoustic data, grain size results from a sediment core and two AMS 14C ages this work attempts to: (1) describe for the first time the detailed geomorphology of a poorly known region of the Patagonian continental slope; (2) depict the principal sub-surface seismic units, illustrating their internal structure, geometry, and distribution; (3) establish a correlation between sub-surface seismic facies and sediment deposits using the first age constraints for this region; (4) propose a model with the depositional history of the PBT, focusing on the interaction between along-slope and down-slope processes and seafloor morphology. The acquired bathymetric data imaged with unprecedent detail the geomorphology of the southern part of the PBT revealing the presence of a field of kilometric-sized, sub-circular, crater-like depressions, and a submarine canyon. The analyzed seismic sub-bottom profiles showed that the shallow sedimentary structure of the study area is represented by patchy-mounded deposits characterized by three distinctive features: cyclic stacks of two seismic facies (FA and FB), mounded shape, and preferential location northwards the morphological depressions and the submarine canyon. Integration of a seismic sub-bottom profile with one sediment core indicates that the alternation of seismic facies reflects variations in the hydrodynamic conditions. FA is related to a high to moderate energy medium with input of terrigenous material and FB is related to a low energy environment with a limited contribution of sediments from the continent. The patchy distribution, mounded shape and preferential location are associated with hydrodynamic processes occurring between the geomorphological features and the north-flowing Antarctic bottom currents, which result in the deposition of mounded contourites in the northern flank of depressions and hybrid along-slope down-slope deposits northwards a submarine canyon. The 14C ages constrain the chronological framework of these sediments to the Late-Pleistocene. This is in contrast with previous investigations that have suggested much older ages (Late Miocene) for the sub-surface sediments of PBT. Finally, a conceptual model is here proposed to illustrate the Late Quaternary sediment depositional history of the PBT where the interaction between north-flowing bottom contouritic currents and seafloor relief played an important role in the deposition and preservation of sediments in this area.

Millennial-Scale Environmental Variability in Late Quaternary Deep-Sea Sediments from the Demerara Rise, NE Coast of South America

We carried out a rock magnetic study of two deep-sea gravity cores from the Demerara Rise, NE South America. Our previous studies provided radiocarbon and paleomagnetic chronologies for these cores. This study presents detailed rock magnetic measurements on these cores in order to characterize the rock magnetic mineralogy and grain size as indicators of the overall clastic fraction. We measured the magnetic susceptibility, anhysteretic remanence, and isothermal remanence and demagnetized the remanences at several alternating field demagnetization levels. The magnetic intensities estimate the magnetic material concentration (and indirectly the overall clastic fraction) in the cores. Ratios of rock magnetic parameters indicate the relative grain size of the magnetic material (and indirectly the overall clastic grain size). Rock magnetic intensity parameters and rock magnetic ratios both vary systematically and synchronously over the last 30,000 years in both cores. There is a multi-millennial-scale cyclicity, with intervals of high magnetic intensity (high magnetic and clastic content) with low magnetic ratios (coarser magnetic and clastic grain size), alternating in sequence with intervals of low magnetic intensity with high magnetic ratios (finer grain size). There is also a higher-frequency millennial-scale variability in intensity superposed on the multi-millennial-scale variability. There are nine (A–I) multi-millennial-scale intervals in the cores. Intervals A, C, E, G, and I have high magnetic and clastic content with coarser overall magnetic and clastic grain size and are likely intervals of enhanced rainfall and runoff from the NE South American margin to the coastal ocean. In contrast, intervals B, D, F, and H have lower clastic flux with finer overall grain size, probably indicating lower continental rainfall and runoff. During the Holocene, high rainfall and runoff intervals can be related to cooler times and low rainfall and runoff to warmer times. The opposite pattern existed during the Pleistocene, with higher rainfall and runoff during interstadial conditions and lower rainfall and runoff during stadial conditions. We noted a similar pattern of Pleistocene multi-millennial-scale variability in a transect of deep-sea sediment cores along the NE Brazilian margin, from the Cariaco Basin (~10 N) to the NE Brazilian margin (~1° N–4° S). However the NW part of this transect (Cariaco Basin, Demerara Rise, Amazon Fan) has an out-of-phase relationship with the SE part of the transect (NE Brazilian margin) between warm–cold and wet–dry conditions. One possible cause of the high–low rainfall and runoff patterns might be oscillation of the Intertropical Convergence Zone (ITCZ), with higher rainfall and runoff associated with a more southerly average position of the ITCZ and lower rainfall and runoff associated with a more northerly average position of the ITCZ.

Dinoflagellate cyst assemblages in surface sediment from Jakarta Bay

Dinoflagellate cysts play an essential role in the initiation, recurrence and geographical expansion of harmful algal blooms (HABs). The horizontal distribution and abundance of dinoflagellate cysts in marine sediments provide essential information in giving early warnings of the presence of toxic species and possible continuing recurrence of HABs in a given area. This research carried out in the waters of Jakarta Bay. Sediment samples collected from thirteen sampling stations using TFO gravity corer 2.1 cm diameter from sediment thickness 0-4 cm. The results showed that resting cysts belong to Gonyaulax, Alexandrium, Scrippsiella, Protoperidinium, Gymnodinium, Gyrodinium. Two of them, namely Gymnodinium sp and Alexandrium sp, known as toxic species. Cysts in the sediment thickness 0-4 cm mainly dominated by the group of Gonyaulax (Gonyaulacoid). Cyst abundance in the sediment depth-layer 0-2 cm is higher than in depth-layer 2-4 cm. The number of dino-cysts in sediment layer 0-2 cm ranged from 2.984 – 22.298 cysts cm−3 while in the layer 2-4 cm the amount varies from 1.063 – 8.132 cysts cm−3 of wet sediment. The result revealed that dino-cyst abundance is higher in the deposit collected from locations near to the coast. The assemblages of dinoflagellate resting cysts seemed to have a relation with some hydrological parameters.

Late Holocene lagoon succession and its response to environmental variations at Yongle atoll, Xisha Islands, South China Sea

Tropical coral reef lagoons that are characterized by high deposition rates are potentially useful for high‐resolution palaeoenvironmental reconstructions. We present the geochemical and accelerator mass spectrometry (AMS) 14C‐dating data of a 113‐cm gravity core obtained from the Yongle atoll lagoon in the South China Sea. The core record preserves a continuous 1,500‐year depositional history of the back‐reef lagoon environment, with sedimentation rates varying from 0.55 to 1.55 mm yr−1 (mean of 0.74 mm yr−1). Calcium carbonate (CaCO3) production was calculated based on the sediment accumulation rates and sediment density to be 807 g m−2 yr−1. The geochemical records of the studied core displayed a progressively increasing trend of storms over the past 1,500 years. The stable carbon and oxygen isotopes of the lagoon sediment have the potential to record monsoon intensity. The lagoon system of the Yongle atoll appears to have been influenced by minor terrestrial input from 1,500 calendar years before present (cal yr BP) to 500 cal yr BP, and by a strong anthropogenic influence over the past 200 years.

Response of a wave-dominated coastline and delta to antecedent conditioning and fluctuating rates of postglacial sea-level rise

In the context of rising sea levels, wave-dominated coasts and deltas are among the most threatened of coastal landforms. The study of submerged deltas, in tandem with other drowned wave-dominated shoreline sequences, can shed light on the long-term coastal behaviour of these threatened shorelines when subject to high-end scenarios of relative sea-level rise. Using ultra high-resolution seismic reflection data and gravity core samples, this paper investigates the post-glacial stratigraphic development and architecture of the shelf off southern Mozambique. We document several well-preserved beachrock/aeolianite palaeo-shoreline complexes from water depths of −100, −75 and −60 m, interpreted as representing the positions of former sea-level slowstands or stillstands. These overlie the regional subaerial unconformity associated with the last glacial maximum and are linked to two phases of deltaic deposition. Pro-deltaic deposits on the outer shelf were linked with the period of sea-level stability attributed to the −100 m shoreline, while proximal delta front deposits on the inner- to mid-shelf are linked to a slowstand evident in the local sea level record at −40 m. Well-developed lower delta plain facies overlie both shoreline and delta front facies and show evidence of strong channelisation during normal regression of the delta. These are overlain across the shelf by isolated and stranded pieces of the now relict shoreface, trapped to seaward by the shoreline complexes. The more proximal parts of the shelf are in turn overlain by fluvial-derived muddy facies of the current prodeltas of the area.The preservation of shoreline and delta deposits was enhanced by intervening rapid increments in sea-level rise associated with meltwater pulses 1A (−100 m) and 1B,(−60 m) though the preservation of the −75 shoreline feature, in spite of modest rates of Older Dryas base-level change, points toward other factors such as rapid cementation as dominant in this instance. The region's high sediment supply exerted a primary control on shelf preservation by dampening the erosive extent of wave-ravinement. Variations in antecedent gradient are responsible for much of the documented along-shelf and down-dip depositional variability: low-gradient settings promoted the development of broad coastal plains and strongly wave-dominated deltaic facies, while steeper areas of the shelf favoured the development of coastal landforms in relatively narrow complexes fronted by deep-water deltaic deposits. Steeper areas of the shelf also tend be characterised by an embayed along-coast profile that locally mitigates wave-energy, reinforcing the influence of inherited gradient.Once preserved, drowned coastal barriers introduced an additional geological control as post-glacial sediment became trapped between these features on the outer shelf. The dispersal of modern sediments is strongly influenced by the hydrodynamic regime Delagoa Bight, under which fluvial muds are transported northeastward along the shelf by a persistent inner-mid shelf counter-current. A considerable proportion of the modern sediment budget is lost off-shelf where the shelf narrows.This study shows that low antecedent gradients foster gentle coastal profiles predisposed to delta overstepping. Though local topographic knickpoints can aid in preserving the delta during submergence, they do not buffer the delta from the general effects of inundation which include drowning of the delta top. Once overstepped, the former delta can be overlain by distal deltaic sediments associated with the higher sea level and associated fluvial and oceanographic forcing quite different from earlier phases of delta construction.

Pleistocene magnetostratigraphy of four cores in the West Philippian Basin and regional sedimentary shift during the Mid‐Pleistocene transition

The Philippine Sea is a well‐preserved, extinct, marginal basin, and due to generally deeper than the carbonate compensation depth, the geochronology and its geological significance of the abyssal sediments are less studied in previous researches. In this work, we studied the magnetostratigraphy of four gravity cores from the centre of the West Philippian Basin and establish a reliable chronology for sedimentary sequences in the Pleistocene. The main results include: (a) several magnetozones are recognized in the studied four cores, which can be correlated to the geomagnetic polarity timescale from chrons C1n to C2An (0–3.0 Ma); (b) since ~1.2 Ma, the depositional rates across the West Pacific are relatively consistent, about 160–250 cm/Myr; (c) a transition in depositional rates around ~1.2 Ma was identified in the studied area, from a spatial variety in the Early Pleistocene to a persistent pattern since the Middle Pleistocene. Based on these findings, we report that this sedimentary shift in the Philippian Sea can be correlated to global climate changes during the Mid‐Pleistocene transition, representing a major change in the studied area. Therefore, we suggest that the sedimentary processes in the studied area can be linked to a common shift in palaeoclimatology across the inner Asian continent, the Philippian Sea, and the tropical Pacific during the late Early Pleistocene.

Glacio-eustatic variations and sapropel events as main controls on the Middle Pleistocene-Holocene evolution of the Cabliers Coral Mound Province (W Mediterranean)

Cold-water coral mounds are key hot-spots of deep ocean biodiversity and also important archives of past climatic conditions. Nonetheless, the paleo-oceanographic setting in which coral mounds developed in the Mediterranean Sea during the last 500 ka still needs to be properly understood. This study describes the coral deposits and corresponding ages of two on-mound gravity cores acquired from opposite sectors of the newly discovered Cabliers Coral Mound Province (CMP, Alboran Sea, W Mediterranean). U–Th data revealed Pleistocene-aged corals covering mound formation periods from >389 to 9.3 ka BP and from 13.7 to 0.3 ka BP in the southern and northern mounds respectively. The coral-rich deposits of the cores were mainly dominated by Desmophyllum pertusum, although in some sections concurrent with the Middle Pleistocene and the Holocene, other corals such as Dendrophyllia cornigera and Madrepora oculata also appeared as dominating species. Coral mound formation stages generally occurred during deglacials and temperate interstadial (3.5–4.1 δ18O‰) periods, whereas during interglacials (<3.5 δ18O‰) coral mound formation only occurred in the northern and shallower mound. We interpret this to indicate that the shoaling of the interface between Atlantic (AW) and Levantine Intermediate Waters (LIW) during interglacial periods prevented the corals in the southern CMP from acquiring sufficient food supply, thus causing periods of coral mound stagnation. Similarly, the interruption in LIW formation throughout sapropel events also coincides with coral mound stagnation phases. This suggests that sapropel-derived processes, which originated in the eastern Mediterranean, likely affected the entire Mediterranean basin and further supports the role of LIW as a conveyor belt facilitating cold-water coral growth in the Mediterranean Sea. Overall, we show that these coral mounds yield important insights into how local changes in oceanographic conditions can influence coral mound development.

Assuring Integrity of CO2 Storage Sites Through Ground Surface Monitoring (SENSE)

Monitoring of geological CO2 storage is crucial for large-scale injection to gain public acceptance. Monitoring plans for large-scale operations need to include both the injection and post-injection phases to assure CO2 is safely stored permanently. The SENSE project aims to develop reliable, continuous, and cost-efficient monitoring based on ground movement detection combined with geomechanical modeling and inversion, utilizing new technology developments, data processing optimization, and interpretation algorithms. The proposed research activities include: • demonstration of continuous monitoring of surface deformation and subsurface pressure distribution using satellite data, water pressure sensors and fiber optics; • quantitative characterization of critical geomechanical and hydraulic parameters and automatization routine for data processing and interpretation; • optimization of sampling arrays in order to offer storage site operators a cost-effective monitoring option as part of an effective site assurance program. The SENSE project brings together experts from 14 international institutions of nine different countries to solve challenges in CO2 storage site monitoring and to provide solutions for safe and successful injection and post-closure phases of site operation. The project is organized in five Work Packages (WPs); WP1: Quantification of ground movement, WP2: Geomechanical modeling and rock strain assessment, WP3: History matching inversion and coupled flow-mechanics, WP4: Integration of results for cost-effective monitoring and WP5: Project management. The ultimate goal of SENSE is to offer storage site operators a cost-effective monitoring option that can form part of an effective site assurance/monitoring program and feed into workflows for an early alert system to detect unexpected changes in the subsurface. The SENSE project has four demonstration sites for monitoring technologies and developing concepts and procedures. These sites are both onshore and offshore. The onshore sites include In Salah (Algeria) and Hotfield Moors (UK). For these sites, the project will use satellite data to explore the response of the surface to pressure changes in the subsurface. Algorithms for automatic satellite data processing to facilitate quick access to ground elevation data for site operators are under development at the British Geological Survey (BGS) and Norwegian Geotechnical Institute (NGI). The offshore sites include Bay of Mecklenburg (Germany) and the Gulf of Mexico (USA). In addition, the SENSE partners have requested access to data from the Troll Gas Field, the North Sea, to study its subsidence due to production-related pressure reduction. The Troll Gas Field is located next to the storage site considered for the Norwegian Long Ship project, and its data will provide a good understanding of the geomechanics of the area. In this paper, we present the work on the In Salah and the Bay of Mecklenburg sites. New InSAR data from the In Salah are used to evaluate the ground movement during the post-injection period and thus to assess the behaviour of the storage site after completion of the injection phase. Bay of Mecklenburg is an offshore site for field experiment to inject a gas underground, build-up pressure, uplift the seafloor and measure the resulted uplift. The first field campaign at the Bay of Mecklenburg was completed in late 2019. It provided both gravity cores from the seabed and geophysical data acquisition for characterizing the shallow subsurface layers. The gravity cores were characterized for physical and mechanical properties. The material properties were used for simulating injection and response of the seafloor to induced pressure. Geomechanical 2D and 3D simulations show that the reservoir may sustain very low overpressure before it fails. Hence, this magnitude of overpressure may create a seafloor uplift of about a few millimeters to a couple of centimeters. The monitoring techniques are therefore being designed to capture uplift in this order of magnitude during the injection operation.

Spatio-temporal sublittoral macrobenthic distribution and dominant species in Guanabara Bay, Rio de Janeiro, Brazil.

Soft-bottom macrobenthic invertebrates are sensitive to natural or anthropogenic changes in aquatic ecosystems. The distribution patterns of sublittoral macrobenthic species in Guanabara Bay were studied from 2005 to 2007. Samples were collected at ten stations during six surveys throughout the rainfall regime (dry, early and late rainy). Ten replicates were collected at each station by Gravity corer or skin diving. Van Dorn bottles (bottom water) and by Ekman sediment sampler (granulometry) provided material for abiotic data. Stations were grouped into sectors (Entrance, Intermediary and Inner) based on abiotic data and location. The Redundancy Analysis (RDA) and Parsimonious RDA for all years and each annual cycle showed indicator taxa with high dominance in each sector. PERMANOVA indicated a regular seasonality between the surveys for the first annual cycle (p <0.05), and an atypical pattern for the second (p> 0.05), possibly due the low rainfall observed during this period. The mosaic of soft-bottom substrates infers structural variables, and patterns of temporal distribution were basically influenced by parameters those indicating pollution and the SACW (South Atlantic Central Water) intrusion, as well as ecological attributes among species, such as: predation, competition. The Ervilia concentrica and Cypridinidae could be used as indicators for anthropic and natural impacts in the Guanabara Bay for the Entrance sector, while Cyprideis salebrosa and Cyprideis sp. for the Intermediary sector and Heleobia australis for the Inner sector.

A Hybrid Lister‐Outrigger Probe for Rapid Marine Geothermal Gradient Measurement

AbstractWe have successfully constructed and tested a new, portable, Hybrid Lister‐Outrigger (HyLO) probe designed to measure geothermal gradients in submarine environments. The lightweight, low‐cost probe is 1–3 m long and contains 4–12 semiconductor temperature sensors that have a temperature resolution of 0.002°C, a sample rate of &lt;2 s, and a maximum working depth of ~2,100 m below sea level (mbsl). Probe endurance is continuous via ship power to water depths of ~700 mbsl or up to ~1 week on batteries in depths &gt;500 mbsl. Data are saved on solid‐state disks, transferred directly to the ship during deployment via a data cable, or transmitted via Bluetooth when the probe is at the sea surface. The probe contains an accelerometer to measure tilt, internal pressure, temperature, and humidity gauges. Key advantages of this probe include (1) near‐real‐time temperature measurements and data transfer; (2) a low‐cost, transportable, and lightweight design; (3) easy and rapid two‐point attachment to a gravity corer, (4) short (3–5 min) thermal response times; (5) high temporal/spatial resolution; and (6) longer deployment endurance compared to traditional methods. We successfully tested the probe both in lakes and during sea trials in May 2019 offshore Montserrat during the R/V Meteor Cruise 154/2. Probe‐measured thermal gradients were consistent with seafloor ocean‐drilling temperature measurements. Ongoing probe improvements include the addition of real‐time bottom‐camera feeds and long‐term (6–12 months) deployment for monitoring.

РАСПРЕДЕЛЕНИЕ ГАЗОВ В ДОННЫХ ОТЛОЖЕНИЯХ ЮГО-ЗАПАДНОГО СУББАССЕЙНА ЮЖНО-КИТАЙСКОГО МОРЯ

For the first time, this paper presents the distribution of gases (CO2, hydrocarbon C1-C4, H2, He) in 39 gas samples in bottom sediments from 19 gravity cores located in the southwestern sub-basin of the South China Sea (known as Bien Dong). The surface sediments in the studied area are mostly silty clay. In general, the concentration of methane varies in a wide range of 0.5–440 ppm. Anomalous values of methane were detected at many locations along the slope area of the southwest sub-basin of the South China Sea. The value of 2.2 ppm could be considered as a background concentration of methane in the studied region. The presence of a large-scale degassing zone of methane in the studied area was proposed. Besides, heavy hydrocarbon gases (ethylene, ethane, propane, and butane) were also determined with the highest values up to 70 ppm, 124 ppm, and 50 ppm for ethylene, ethane and propane, respectively. In addition, data of carbon dioxide, hydro and helium suggest some anomalous values of H2 up to 56.7 ppm.

ELEMENTAL ANALYSIS OF MARINE CORE SEDIMENT BELONG TO CENTRAL WESTERN BAY OF BENGAL BY USING PIXE

The aim of the present work is to estimate the accumulation of various elements related to the core sediment belong to the Krishna-Godavari marginal area with a nuclear analytical technique. Hence, a 4.12 m long marine sediment gravity core was collected from near to Nizampatnam Bay that related to Bay of Bengal and by using particle induced X-ray emission (PIXE) elemental concentrations have been determined. The concentrations of major elements like Fe, Ca, K, Ti, Mn and minor (trace) elements such as Sr, Co, V, Zn, Ni, Cu, Rb, Sc and Cr have been evaluated with the obtained PIXE spectra. These values are interpreted based on the monsoonal runoff coming from the rivers causing to play an important role for bring lot of sedimentary material of the coastal waters to the Bay of Bengal. Further results are interpreted to understand biological and anthropogenic activities, chemical reactions etc during Holocene and Pleistocene periods.

The Influence of Hydrothermal Fluids on the REY-Rich Deep-Sea Sediments in the Yupanqui Basin, Eastern South Pacific Ocean: Constraints from Bulk Sediment Geochemistry and Mineralogical Characteristics

Rare earth elements (REEs) and yttrium (Y), together known as REY, are extremely enriched in deep-sea pelagic sediments, attracting much attention as a promising new REY resource. To understand the influence of hydrothermal processes on the enrichment of REY in deep-sea sediments from the eastern South Pacific Ocean, we conducted detailed lithological, bulk sediment geochemical, and in situ mineral geochemical analyses on gravity core sample S021GC17 from the Yupanqui Basin of eastern South Pacific. The REY-rich muds of S021GC17 are dark-brown to black zeolitic clays with REY contents (ΣREY) ranging from 1057 to 1882 ppm (average 1329 ppm). The REY-rich muds display heavy rare earth elements (HREE) enriched patterns, with obvious depletions in Ce, and positive anomalies of Eu in Post-Archean Australian Shale (PAAS)-normalized REE diagrams. In contrast, the muds of S021GC17 show light rare earth elements (LREE) enriched patterns and positive anomalies of Ce and Eu in the seawater-normalized REE diagrams. Total REY abundances in the core show positive correlations with CaO, P2O5, Fe2O3, and MnO concentrations. In situ analyses of trace element contents by laser ablation-inductively coupled plasma–mass spectrometry (LA-ICP-MS) demonstrate that bioapatite fossils contain high REY concentrations (998 to 22,497 ppm, average 9123 ppm), indicating that they are the primary carriers of REY. The in situ Nd isotope values of bioapatites are higher than the average values of seawater in Pacific Ocean. Fe–Mn micronodules are divided into hydrogenetic and diagenetic types, which have average REY concentrations of 1586 and 567 ppm, respectively. The high contents of Fe-Mn-Ba-Co-Mo, the positive correlations between ΣREY and Fe-Mn, the ratios of Fe/Ti and Al/(Al + Fe + Mn), and the LREE-enriched patterns in the REY-rich muds, combined with high Nd isotope values shown by bioapatite fossils, strongly indicate that the hydrothermal fluids have played an important role in the formation of the REY-rich sediments in the eastern South Pacific Ocean.

Characterising sediment physical property variability for bench-scale dewatering purposes

A field sampling programme was undertaken to assess the variability of physical characteristics of contaminated sediments in a large (160 ha) effluent stabilisation lagoon. The objective of this paper is to use this ‘field lab’ as a basis for comparing different sampling techniques (i.e. discrete and composite) for remediation-based evaluations (i.e. sediment volume estimates and bench-scale dewatering studies). The distribution of sediment thickness measured throughout the lagoon by gravity core sampling is presented for context. Selected gravity core sediment samples are evaluated with respect to physical property (water/solids content, bulk density and particle size) variability in both the vertical (i.e. within a single gravity core) and spatial directions (among gravity cores). Composite samples are created by way of homogenisation of a single entire gravity core to compare their properties to the discrete and average physical properties of a nearby gravity core. Vacuum-based samples are also compared to gravity core samples in terms of particle size. It is demonstrated that by understanding sediment variability, composite samples can be shown to be an efficient method of obtaining representative samples. When large samples for dewatering trials are required, vacuum sampling can produce samples with similar mean particle size to discrete and composite samples.

An Improved Cleaning Protocol for Foraminiferal Calcite from Unconsolidated Core Sediments: HyPerCal—A New Practice for Micropaleontological and Paleoclimatic Proxies

Paleoclimatic and paleoceanographic studies routinely rely on the usage of foraminiferal calcite through faunal, morphometric and physico-chemical proxies. The application of such proxies presupposes the extraction and cleaning of these biomineralized components from ocean sediments in the most efficient way, a process which is often labor intensive and time consuming. In this respect, in this study we performed a systematic experiment for planktonic foraminiferal specimen cleaning using different chemical treatments and evaluated the resulting data of a Late Quaternary gravity core sample from the Aegean Sea. All cleaning procedures adopted here were made on the basis of their minimum potential bias upon foraminiferal proxies, such as the faunal assemblages, degree of fragmentation, stable isotope composition (δ18O and δ13C) and/or Mg/Ca ratios that are frequently used as proxies for surface-ocean climate parameters (e.g., sea surface temperature, sea surface salinity). Six different protocols were tested, involving washing, sieving, and chemical treatment of the samples with hydrogen peroxide and/or sodium hexametaphosphate (Calgon®). Single species foraminifera shell weighing was combined with high-resolution scanning electron microscopy (SEM) and synchrotron X-ray microtomography (SμCT) of the material processed by each of the cleaning protocols, in order to assess the decontamination degree of specimen’s ultrastructure and interior. It appeared that a good compromise between time and cleaning efficiency is the simultaneous treatment of samples with a mixed hydrogen peroxide and Calgon solution, while the most effective way to almost completely decontaminate the calcareous components from undesirable sedimentary material is a two-step treatment—initially with hydrogen peroxide and subsequently with Calgon solutions.

Last glacial ice sheet dynamics offshore NE Greenland – a case study from Store Koldewey Trough

Abstract. The presence of a grounded Greenland Ice Sheet on the northeastern part of the Greenland continental shelf during the Last Glacial Maximum is supported by new swath bathymetry and high-resolution seismic data, supplemented with multi-proxy analyses of sediment gravity cores from Store Koldewey Trough. Subglacial till fills the trough, with an overlying drape of maximum 2.5 m thick glacier-proximal and glacier-distal sediment. The presence of mega-scale glacial lineations and a grounding zone wedge in the outer part of the trough, comprising subglacial till, provides evidence of the expansion of fast-flowing, grounded ice, probably originating from the area presently covered with the Storstrømmen ice stream and thereby previously flowing across Store Koldewey Island and Germania Land. Grounding zone wedges and recessional moraines provide evidence that multiple halts and/or readvances interrupted the deglaciation. The formation of the grounding zone wedges is estimated to be at least 130 years, while distances between the recessional moraines indicate that the grounding line locally retreated between 80 and 400 m yr−1 during the deglaciation, assuming that the moraines formed annually. The complex geomorphology in Store Koldewey Trough is attributed to the trough shallowing and narrowing towards the coast. At a late stage of the deglaciation, the ice stream flowed around the topography on Store Koldewey Island and Germania Land, terminating the sediment input from this sector of the Greenland Ice Sheet to Store Koldewey Trough.

Assessing methane cycling in the seep sediments of the mid-Okinawa Trough: Insights from pore-water geochemistry and numerical modeling

The methane-enriched fluids in cold seeps are likely to crystallize as gas hydrates and serve as crucial sources of carbon to seawater. In this research, we analyzed the pore-water composition in terms of CH4, dissolved inorganic carbon (DIC), Cl−, Br−, SO42−, Na+, Mg2+, Ca2+, Sr2+, and NH4+, and the δ13CDIC, δ13CCH4, and δDCH4 values of two gravity cores and six remotely operated vehicle (ROV) video-guided push cores retrieved from fault scarps and dome-like structures (DSs) on the western slope of the mid-Okinawa Trough. In addition, a reaction–transport model was applied to quantify the methane fluxes and related biogeochemical processes. Active seepage of biogenic (δ13CCH4 ~ –70‰ V-PDB) and thermogenic (δ13CCH4 = −40‰ to −56‰ V-PDB) methane was identified on fault scarps and dome structures, respectively. Methane seepage was controlled by the transport and dissolution of the ascending gas rather than by clay dehydration or gas hydrate dissociation-induced fluid advection. The high methane concentrations and shallow sulfate–methane transition zones (SMTZs; between 0.1 and 0.4 mbsf) at sites R3-C2, R4-C4, and R6-C1 suggest strong methane seepage at three of the four studied DS (the highest gas dissolution rates are 6450, 1475, and 515 mmol m−2yr−1). Site GC08, located along a fault scarp, exhibits a moderate methane seepage; the SMTZ is located at ~2.5mbsf, and the rate of anaerobic oxidation of methane (AOM) is 130 mmol m−2yr−1. The methane migrating from depth is mainly consumed by AOM. However, ~12%–66% of the methane released from the two most intensive seep sites escapes to the water column. The precipitation of high–Mg calcite (at all sites) and aragonite (only at site R3-C2) has fixed 27%–50% (average = 39%) of the DIC. Therefore, the carbon outputs to the water column have been reduced. In the study area, the area-weighted seafloor CH4 and DIC fluxes are ~30 and 20 mmol m−2yr−1, respectively. Together, they correspond to ~7%–14% of the organic carbon burial rate, indicating that sediments could not be simply regarded as a stable carbon sink because they provide methane and a certain amount of DIC to the water column. Our findings contribute to the results of the ongoing efforts in understanding carbon cycling in submarine cold seep systems.