Distinct expressions of the BSR using various frequencies offshore Uruguay and its correspondence with the gas hydrate stability zone

At the Uruguayan continental margin, seismic evidence for the occurrence of gas hydrate has been identified based on the presence of BSRs in densely spaced 2D reflection seismic sections from different surveys. Mapping of BSRs based on 2D seismic data acquired in 2007 and 2008 suggested the presence of gas hydrates in areas that were not previously identified; hence hydrate occurrence offshore Uruguay is more widespread than previously thought. Recently ANCAP has digitized offshore seismic data acquired between 1970 and 1982. Being able to work on this data using interpretation software, and integrating results with the latest interpretations performed on the seismic collected in 2007 and 2008, the BSR extends over an area of approximately 25.000 km2. It is present in water depths greater than 500 m and has high continuity in Pelotas Basin but is more discontinuous at Punta del Este Basin and southern part of Oriental del Plata Basin. In offshore basins around the world the base of GHSZ can have different seismic expressions such as continuous, segmented, and high-relief BSRs depending on the stratigraphic, fluid and geothermal setting. Here, we present examples of the influence of the acquisition parameters on the acoustic expression of the BSR, comparing commercial seismic sections acquired for hydrocarbon exploration and high resolution seismic sections acquired during the R/V Meteor Cruise M49/2 in 2001 and R/V Meteor Cruise M78/3a (May - June 2009) using different sources and streamer system. For the different data sets the BSR presents differences regarding its continuity and amplitude strength. In high resolution seismic, enhanced amplitudes and phase reversals are observed for several reflectors while deep penetration seismic shows only one single continuous reflector. This comparison may help to visualize the complexity of the free gas, gas hydrate and stratigraphic system behind the BSR, which is usually masked on low-frequency deep penetration seismic data

New hydroacoustic and core data reveal sediment transport patterns off Uruguay

Submarine landslides cause slope instabilities and might damage sea-floor infrastructure or even generate tsunami waves. Therefore it is of major importance to understand all processes related to gravity-driven mass wasting and slope stability at continental margins. New swath bathymetry and parametric echo-sounding data from the Uruguay shelf and slope north-east of the Rio de la Plata were collected during METEOR Cruise M78/3. These data are investigated in order to understand mass wasting and sedimentary transport processes at the margin off Uruguay. Large amounts of silty suspension freight are delivered from the Rio de la Plata estuary. These sediments are potentially unstable, leading to numerous mass transport units in the working area. Prominent features identified in the study include slide deposits, channels and several prominent escarpment structures. The situation is complicated by intensive slope parallel sediment transport due to strong contour currents. Our data indicate interaction between gravity-driven downslope transport and alongslope sediment transport. Contourite deposits in the headwall areas of mass wasting events suggest widespread weak layers at those deposits. The up to 70m-high headwalls, are focusing contour currents resulting in small alongslope channels. Future work will concentrate on the reconstruction of the geological/sedimentological history of the study area in order assess slope stability and sediment transport in greater detail

Submarine slope failure offshore Uruguay - first results

New geophysical acquired during cruise M78 with RV “Meteor” in 2009 reveal a large-scale slope failure complex. Positioned between 1800 and 3300 m water depth, the slope failure affected an area of at least 1200 km2. The failure is hosted in contouritic deposits. The morphology of the up 70 m high headwalls is underlain by a deeper reflector which we interpret as detachment. Listric faults positioned upslope these headwalls root in this detachment and are precursor of future failure at this location. The detachment correlates with a regional BSR mapped by Uruguayan colleagues. Cores recovered from 3 transects across the failure complex confirm that the acoustic transparent units are debrites. Sedimentological evidence in accordance with hydro-acoustic data indicate that debrites deposited downslope this failure complex are recent features on the slope

Sediment dynamics and geohazards offshore Uruguay and northern Argentina: first results from the multi-disciplinary Meteor-cruise M78-3

About 90% of the sediments generated by weathering and erosion on land get finally deposited at the ocean margins. The sediment distribution processes and landscape evolution on land are relatively well understood, but comparably little is known about the role and relative importance of marine sediment dynamics in controlling the architectural evolution of ocean margins. Important players include hemi-pelagic settling, down-slope and current-controlled along-slope sediment transport, depositional and post-depositional sedimentary processes (e.g. consolidation and diagenesis), as well as the destabilization of sediment bodies and their erosion. Submarine landslides in this context thus may represent an important sediment transport process, but also a major geo-hazard due to the increasing number of offshore constructions as well as their potential to instantaneously displace large water masses triggering waves in densely populated coastal areas. Here we present first results from a seagoing expedition that aimed at investigating the interaction processes of sediment redistribution, partitioning, deposition and diagenesis from the coast to the deep-sea along the western South-Atlantic passive continental margin. During RV Meteor Cruise M78/3 in May-July 2009 the shelf, slope and rise offshore Argentina and Uruguay have been investigated by means of hydroacoustic and seismic mapping as well as geological sampling with conventional coring tools as well as the new MARUM seafloor drill rig (MeBo) that revealed recovery of geological strata sampled from up to 50m below seafloor. The working area is characterized by a high amount of fluvial input by the Rio de la Plata river. The continental slope is relatively wide and shows average slope gradients between 1 and 2.5 but locally higher slope gradients may occur (>5). The transition for the continental rise with low slope gradients is found in ~3000 m water depth. The working area is located in a highly dynamic oceanographic regime. Cold Antarctic water masses of the northward flowing Malvina current meet warm water masses of the southward flowing Brazil current in the working area. Various types of sediment instabilities have been imaged in geophysical and core data, documenting particularly the continental slope offshore Uruguay to be locus of frequent submarine landslides. Apart from individual landslides, however, gravitational downslope sediment transport along the continental slope is restricted to the prominent Mar del Plata Canyon and possibly to smaller canyons indentified in the bathymetric data. The location of the canyons might be controlled by tectonics. In contrast, many morphological features (e.g. progradational terraces and slope parallel scarps with scour-geometries) reveal that sediment transport is predominantly influenced/controlled by strong contour bottom currents. This suggests a significant impact of the western boundary currents on the overall architectural evolution of the margin. Future studies using the acquired geophysical, sedimentological, physical property and geochemical data will (i) quantify the relative contribution of gravitational down-slope vs. along-slope processes through time in shaping this ocean margin and how it relates to the global ocean circulation pattern and sea-level change through time, (ii) investigate depositional and post-depositional processes and how they control submarine slope stability and submarine landslide initiation and (iii) explore the interaction and relative contribution of the various processes in controlling margin evolution, sediment dynamics and geohazard off Uruguay and Northern Argentina

Use of small angle neutron scattering to study the interaction of angiotensin II with model membranes

Understanding biological processes assumes a detailed understanding of the interaction of all involved molecules. Here the effect of the peptide hormone angiotensin II (Ang II), an agonist of the angiotensin receptors, on the structure of unilamellar and multilamellar dimyristoyl phosphatidylcholine vesicles was studied by small angle neutron scattering, dynamic light scattering and differential scanning calorimetry. The calorimetry data indicate a weak interaction of Ang II with the surface of the membrane bilayer, as the pretransition persists during all experiments, and the main transition is only slightly shifted towards higher temperatures. From the SANS data we were able to confirm the calorimetric data and verify the interaction of the hormone with the membrane surface. At low temperatures, when the lipid molecules are in the gel phase, more precisely in the ripple phase, the peptide penetrates in the head group core, but due to the close packing of the acyl chains, the hydrophobic region is not affected. In a temperature region below but close to the region of the phase transition, the hydrophibic core starts to be affected by the peptide, and the same is true for the fluid phase. Upon binding of the peptide, the thickness of the head group increases, and the scattering length density of the head group starts to rise with increasing peptide concentrations. This interaction and binding to the membrane surface may be relevant for the relocation, binding and reconstitution of the angiotensin receptors into the membrane. Second, the peptide adsorption to the membrane surface may contribute to the binding of Ang II in the active site of the recepto

High-resolution seismo-acoustic studies of alongslope and downslope sediment transport processes shaping depositional patterns at continental margins

Downslope and alongslope sediment transports represent important processes during the evolution of continental margins. This thesis reveals the impact of both transport processes on slope architecture in highly dynamic oceanographic settings and assesses their interaction using seismo- and hydroacoustic data. The study area covers the northern Argentine continental slope, where a contourite depositional system is located beneath the Brazil-Malvinas Confluence. The most prominent sedimentary features are represented by contourite terraces and the Mar del Plata canyon (MdP). Analysis of the slope architecture revealed the major influence of North Atlantic Deep Water production on the margin evolution since the Middle Miocene. The variability of morphosedimentary features with respect to the oceanographic regime indicates that contourite terraces are linked to water mass interfaces. The lack of sediments north of the MdP is the result of the disturbance of the current regime caused by the canyon. The importance of alongslope transport processes is shown in a novel study off Mozambique using hydroacoustic data imaging particles in water depth >200 m