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Verfahren zur Analyse der chemischen Zusammensetzung eines Gewässerbodens umfassend folgende Schritte a. Bereitstellen einer Vorrichtung umfassend eine Eindringsonde umfassend ein Messfenster mit einer Scheibe und Mittel zur Durchführung eines Röntgenfluoreszenz- Verfahrens, welche über die Verbindungsvorrichtung mit einem Wasserfahrzeug verbunden ist, wobei die Eindringsonde in einer Wassertiefe bis zu 6000 m vorliegt, b. Initialisierung eines schwerkraftbedingten Falls der Vorrichtung, c. zumindest teilweises Eindringen der Eindringsonde in den Gewässerboden, in eine Tiefe von bis zu 18 m, bevorzugt in eine Tiefe von bis zu 12 m, d. Herausziehen der der Eindringsonde aus dem Gewässerboden, mit einer bevorzugten Geschwindigkeit von 0,1 m/s, e. Durchführung eines Röntgenfluoreszenz-Verfahrens während des gesamten Herausziehens, wobei in der Eindringsonde erzeugte Röntgenstrahlung durch das Messfenster abgestrahlt wird und im Gewässerboden generierte Fluoreszenzstrahlung durch das Messfenster einfällt und detektiert wird, g. Verbleiben der Vorrichtung in einem gewässerbodennahen Arbeitsbereich von bevorzugt 10 m über dem Gewässerboden.

10 páginas, 4 tablas, 3 figuras., Cold seep ecosystems can support enormous biomasses of free-living and symbiotic chemoautotrophic organisms that get their energy from the oxidation of methane or sulfide. Most of this biomass derives from animals that are associated with bacterial symbionts, which are able to metabolize the chemical resources provided by the seeping fluids. Often these systems also harbor dense accumulations of non-symbiotic megafauna, which can be relevant in exporting chemosynthetically fixed carbon from seeps to the surrounding deep sea. Here we investigated the carbon sources of lithodid crabs (Paralomis sp.) feeding on thiotrophic bacterial mats at an active mud volcano at the Costa Rica subduction zone. To evaluate the dietary carbon source of the crabs, we compared the microbial community in stomach contents with surface sediments covered by microbial mats. The stomach content analyses revealed a dominance of epsilonproteobacterial 16S rRNA gene sequences related to the free-living and epibiotic sulfur oxidiser Sulfurovum sp. We also found Sulfurovum sp. as well as members of the genera Arcobacter and Sulfurimonas in mat-covered surface sediments where Epsilonproteobacteria were highly abundant constituting 10% of total cells. Furthermore, we detected substantial amounts of bacterial fatty acids such as i-C15:0 and C17:1v6c with stable carbon isotope compositions as low as 253% in the stomach and muscle tissue. These results indicate that the white microbial mats at Mound 12 are comprised of Epsilonproteobacteria and that microbial mat-derived carbon provides an important contribution to the crab’s nutrition. In addition, our lipid analyses also suggest that the crabs feed on other 13C-depleted organic matter sources, possibly symbiotic megafauna as well as on photosynthetic carbon sources such as sedimentary detritus., Financial support for the M66-Subflux cruise came through the Collaborative Research Center (SFB) 574 (‘‘Volatiles and Fluids in Subduction Zones’’) at Kiel University funded by the DFG. This work was further supported by NSF (OCE-0242034 and OCE-0242091), the Max Planck Society, the Helmholtz Association and the University of Basel. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

IFM-GEOMAR Report No 49

Submarine slope failures occur at all continental margins, but the processes generating different mass wasting phenomena remain poorly understood. Multibeam bathymetry mapping of the Middle America Trench reveals numerous continental slope failures of different dimensions and origin. For example, large rotational slumps have been interpreted to be caused by slope collapse in the wake of subducting seamounts. In contrast, the mechanisms generating translational slides have not yet been described. Lithology, shear strength measurements, density, and pore water alkalinity from a sediment core across a slide plane indicate that a few centimeters thick intercalated volcanic tephra layer marks the detachment surface. The ash layer can be correlated to the San Antonio tephra, emplaced by the 6000 year old caldera-forming eruption from Masaya-Caldera, Nicaragua. The distal deposits of this eruption are widespread along the continental slope and ocean plate offshore Nicaragua. Grain size measurements permit us to estimate the reconstruction of the original ash layer thickness at the investigated slide. Direct shear test experiments on Middle American ashes show a high volume reduction during shearing. This indicates that marine tephra layers have the highest hydraulic conductivity of the different types of slope sediment, enabling significant volume reduction to take place under undrained conditions. This makes ash layers mechanically distinct within slope sediment sequences. Here we propose a mechanism by which ash layers may become weak planes that promote translational sliding. The mechanism implies that ground shaking by large earthquakes induces rearrangement of ash shards causing their compaction (volume reduction) and produces a rapid accumulation of water in the upper part of the layer that is capped by impermeable clay. The water-rich veneer abruptly reduces shear strength, creating a detachment plane for translational sliding. Tephra layers might act as slide detachment planes at convergent margins of subducting zones, at submarine slopes of volcanic islands, and at submerged volcano slopes in lakes.

We report total dissolved inorganic carbon (DIC) abundances and isotope ratios, as well as helium isotope ratios (3He/4He), of cold seep fluids sampled at the Costa Rica fore arc in order to evaluate the extent of carbon loss from the submarine segment of the Central America convergent margin. Seep fluids were collected over a 12 month period at Mound 11, Mound 12, and Jaco Scar using copper tubing attached to submarine flux meters operating in continuous pumping mode. The fluids show minimum 3He/4He ratios of 1.3 RA (where RA is air 3He/4He), consistent with a small but discernable contribution of mantle-derived helium. At Mound 11, δ13C∑CO2 values between −23.9‰ and −11.6‰ indicate that DIC is predominantly derived from deep methanogenesis and is carried to the surface by fluids derived from sediments of the subducting slab. In contrast, at Mound 12, most of the ascending dissolved methane is oxidized due to lower flow rates, giving extremely low δ13C∑CO2 values ranging from −68.2‰ to −60.3‰. We estimate that the carbon flux (CO2 plus methane) through submarine fluid venting at the outer fore arc is 8.0 × 105 g C km−1 yr−1, which is virtually negligible compared to the total sedimentary carbon input to the margin and the output at the volcanic front. Unless there is a significant but hitherto unidentified carbon flux at the inner fore arc, the implication is that most of the carbon being subducted in Costa Rica must be transferred to the (deeper) mantle, i.e., beyond the depth of arc magma generation.

R/V POSEIDON cruise P388 was the fourth expedition to the West Nile Delta taking place within the West Nile Delta project. It was also the third time the WND project was using R/V POSEIDON. From 13 July to 4 August 2009, a team of 10 scientists and technicians was on board to deepen our insights on the mud volcanoes "Giza" and "North Alex". During the cruise, project leader Dr. Warner Brückmann (WB) and P388 chief scientist Dr. Jörg Bialas (JB) put the latest information and pictures into this expedition log.

IFM-GEOMAR Report No 27

Vom 1. bis 20. Dezember 2007 fand die POSEIDON-Fahrt P362 unter der Fahrtleitung von Dr.Warner Brückmann statt. Ziel der Ausfahrt ist die Untersuchung von Schlammvulkanen im West-Nil-Delta.

METEOR 66/3a Caldera - Caldera Wochenberichte Erster Wochenbericht, 24.10 – 30.10. 2005

METEOR 66/3b Caldera - Corinto Wochenberichte Dritter Wochenbericht, 7.11. – 13.11. 2005

METEOR 66/3a Caldera - Caldera Wochenberichte Zweiter Wochenbericht, 31.10 – 6.11. 2005

METEOR 66/3b Caldera - Corinto Wochenberichte Vierter Wochenbericht, 14.11. – 20.11. 2005

In the northern Barbados accretionary wedge, several Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) legs (DSDP Leg 78 and ODP Legs 110, 156, and 171A) targeted the décollement and the seaward extension of the décollement, the proto-décollement. During Leg 171A, the logging while drilling (LWD) technique was used to determine the physical properties variations along a profile across the deformation front. Because of the unstable borehole conditions in accretionary wedges, LWD is the most effective method for the measurements of physical properties in these poorly consolidated sediments. LWD data are acquired just above the drill bit a few minutes after the formation has been drilled, yielding measurements as close to in situ conditions as possible. The large amount of LWD data and the demand for a quick, objective, and reliable evaluation calls for the application of multivariate statistical methods. The multivariate factor analysis is a method of reducing the amount of logging data while giving them a new integrated meaning with no loss of important information, resulting in factor logs that are helpful tools for further interpretation. The cluster analysis of the two or three most significant factors proved to be a useful and objective method to identify and confirm significant logging units. The main objective of the application of multivariate statistical methods in this study is twofold. First, Leg 171A was a stand-alone logging leg, where no cores were retrieved. The factor analysis was used as an objective tool for a classification of the drilled sequences based on their physical and chemical properties. The new factor logs mirror the basic processes behind the measured geophysical properties and make them easier to interpret. Second, in the succeeding cluster analysis, similar geophysical properties are grouped into one cluster, reflecting one logging unit. These objectively defined logging units can be compared to statistical electrofacies, which are helpful in differentiating lithologic characterizations. In particular for LWD measurements, the multivariate statistical methods of factor and cluster analysis are helpful tools for a fast, reliable, and objective definition of logging units, which should be considered for future legs.

Low-gradient flow tests and one-dimensional consolidation tests were performed on four samples from Ocean Drilling Program (ODP) Leg 156, northern Barbados Ridge, Hole 949B, to provide direct as well as indirect measures of permeability and stress history. All samples tested show a significant degree of underconsolidation, with overconsolidation ratio (OCR) values decreasing with depth from 0.4 to 0.2 to 0.1. These low ratios were used to approximate the excess pore pressures within the accreted sediment and the décollement. The largest estimated excess pore-pressure values lie within the interpreted décollement zone at Site 949 and range from 1600 to 1900 kPa. Combining results from this study with previous data from Leg 110, two generalized functions of void ratio vs. hydraulic conductivity for high and low permeability sediments are developed that are characteristic for sediments of low and high smectite content. By applying these functions to the Site 671 (ODP Leg 110) porosity profile, it is possible to demonstrate the occurrence of a zone of low permeability immediately above the décollement. This is consistent with the concept that low permeability sediments will develop higher excess pore pressures, and therefore, are more susceptible to shear failure.

In situ and laboratory studies of permeability, conducted by Ocean Drilling Program scientists from Leg 156, provide constraints on parameters controlling the hydrogeologic system in the Barbados accretionary prism. Results from these studies indicate that core-scale and formation-scale permeability values differ by at least several orders of magnitude and are dependent on pore-fluid pressure and effective stress conditions. Direct measurement from packer experiments and indirect evidence from consolidation tests suggest that pore-fluid pressures are commonly above hydrostatic values and approach lithostatic values within the décollement zone. Permeability and fluid pressure conditions in the Barbados accretionary prism reflect the complexity of the hydrogeologic system of such an active tectonic environment.

Ocean Drilling Program (ODP) Leg 156 revisited the northern Barbados Ridge, where the previous Deep Sea Drilling Program Leg 78A and ODP Leg 110 studied the frontal part of this accretionary prism. Drilling and logging-while-drilling at Sites 947, 948, and 949 successfully identified major thrust faults and the décollement, which was the target of several downhole experiments. Two of the eight holes drilled were equipped with borehole observatories that will monitor temperature, pressure, and fluid flow over the next years. Coring at Hole 948C recovered 180 m of sediment, centered around the décollement, which was positively identified based on structural information. The aim of this study is the evaluation of the possible correlation of preferred orientation of acoustic properties and the direction of maximum compressive strain in the frontal part of the accretionary prism. For this purpose, shipboard P-wave velocities from Holes 948C and 949B were reoriented. This information was then used to compare the directional properties of accreted and subducted sediments. In Hole 948C, lowest transverse velocities (Tmin ) were observed to be consistently oriented perpendicular to the maximum horizontal compressive stress, believed to be parallel to the convergence vector. In the underthrust domain of Hole 948C, several preferred orientations for Tmin were detected, but no correlation with the geotectonic reference frame could be identified. Acoustic anisotropy does not show a comparable pattern in Hole 948C. It is concluded that the observed directional dependence of P-wave velocity in the accreted sediment domain in Hole 948B is the result of moderate to steeply inclined bedding, although this conclusion can not adequately be tested due to the lack of corrected structural data.

Deep-sea sediments deposited at or near an actively spreading mid-ocean ridge experience a distinctly different thermal history than sediments deposited in other marine geotectonic settings. For sediments of a given age the impact of high heat flow decreases with increasing distance from the ridge. This simple relation is superimposed in the active spreading ridge along the margin of Southern Chile—the Chile Triple Junction—by the process of sediment accretion. Both processes, heat flow and lateral thrusting, strongly modify the mechanical behavior of sediment accreted. The original intent was to study the mechanical state of accreted sediment recovered during Ocean Drilling Program (ODP) Leg 141, both unaltered and altered diagenetically by hydrothermal fluids, to differentiate the effects of thermal and mechanical diagenesis. The research program included high-pressure oedometer as well as triaxial testing to quantify the relative importance of both diagenetic processes for shear strength and consolidation behavior. Unfortunately, whole-round core samples available from Leg 141 appeared to be inadequately preserved and only a limited number of specimens could be used for mechanical testing. Therefore, most of the pre-cruise goals could not be attained. This paper reports the results of oedometer as well triaxial tests obtained from a restricted testing program.

Complete penetration of frontal thrust and décollement of the Nankai Trough accretionary complex in Site 808 during ODP Leg 131 provided a wealth of structural observations and physical property data. In this paper possible mechanisms are discussed that could be responsible for the development of irregular downhole trends in acoustic anisotropy observed in Site 808. After various steps of data reduction and screening, a paleomagnetic reorientation procedure is applied to a selected group of physical property data sets. This facilitates the integration of the observed changes in physical properties with the geotectonic framework at the deformation front of the Nankai Trough accretionary complex. The paleomagnetic database was employed in the reconstruction of directional properties of acoustic velocities of the Lower Shikoku Basin sedimentary sequence, which is divided by a sharply defined décollement into an accreting and a subducting portion. P-wave velocity anisotropies derived from paleomagnetically oriented samples in the upper part of this 420-m-thick hemipelagic sequence show maximum values in the direction parallel and normal to the inferred vector of plate convergence (31O°-315°). No preferred orientation of P-wave velocity anisotropy is found in the subducting part of the sequence. The preferred direction of maximum anisotropy parallel to the convergence vector is also in accordance with the true direction of the observed macro- to mesoscale structural features in Site 808. Microfractures and microcracks forming as stress relief and tensile fractures in cores of semilithified sediment normal and perpendicular to the maximum horizontal stress are discussed as control mechanisms for the development of the observed anisotropy pattern.

Sediments undergoing accretion in trench-forearc systems are subjected to conditions of large lateral thrusting. This stress regime controls the mechanism of faulting as well as the yield and strength properties of the sediment. Understanding them is therefore crucial for the construction of quantitative models of sediment dynamics in convergent margin settings. For this purpose triaxial and oedometer tests were performed on six whole-round core samples recovered from Site 808 from depths between 173 and 705 mbsf. Samples from five depth intervals were subjected to a triaxial test program that was primarily designed to define yield and strength behavior. Test specimens were cut parallel and normal to the core axis. Additional five oedometer tests with similarly prepared specimens were performed on samples from four depth intervals to evaluate the directional state and degree of sediment compaction. Test results show that the degree of sediment compaction is higher than expected from overburden. This overcompaction increases with depth. A well-developed mechanical anisotropy is evident in all samples tested, regardless of their depth and lithology. Values of yield limit, stiffness, and shear strength are up to 40% higher in the horizontal direction compared to the vertical direction. In addition the test data demonstrate that the axis of the volumetric yield loci have rotated into extensional stress field. This verifies that the mechanical state of sediment in the accretionary wedge is controlled by in-situ stress conditions of extensional nature. The coefficients of lateral stress inferred suggest that the extensional stress regime becomes increasingly effective with depth.

Structural, physical property, and magnetic data from Ocean Drilling Program Site 808 in the Nankai Trough, Japan, indicate that both sediment loading and plate convergence have driven dewatering and consolidation in this region. Evidence for this interpretation is provided by a migrated seismic reflection profile, computed tomography of core-scale structures, magnetic susceptibility and P-wave velocity data, and experimental studies of Site 808 samples. These data also show that the strain (including volume change) resulting from plate convergence is partitioned into both penetrative deformation structures as well as more discrete, core-scale structures with finite displacements. These core-scale structures range from relatively subtle, kink-like deflections of the primary phyllosilicate fabric to sharp discontinuities with probable displacements much greater than the dimensions of the core barrel. Although all of the structures acted at least in part as dewatering conduits, evidence of concentrated fluid flow in this region of the prism is limited to a narrow interval almost 150 m above the décollement (located at between 946 and 965 mbsf). This interval correlates with the middle of a hemipelagic sequence above the décollement that appears to have thinned, apparently through dewatering, relative to a more seaward section. Thinning and dewatering appear to have been induced by deposition of a more clastic sedimentary sequence (the outer marginal trench-wedge sediments) that grades upward into a coarse-grained trench-fill sequence. Importantly, the hemipelagic sequence below the décollement appears to have thinned very little, suggesting that these sediments are underconsolidated and overpressured. This interpretation is consistent with porosity measurements from below the décollement. Microscopic and submicroscopic studies of sediments from within the décollement record a cyclic deformation sequence of displacement-brecciation-porosity collapse and compaction that may also reflect deformation of an overpressured sequence. Finally, the structural, physical property, and magnetic data also yield kinematic and geometric results consistent with the present convergent vector between the Philippine Sea Plate and Eurasia. These data indicate a shortening direction that trends between 308° and 315°, consistent with plate convergent vectors that trend between 310° and 314°.