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

In-situ borehole temperature measurements confirm dynamics of the gas hydrate stability zone at the upper Danube deep sea fan, Black Sea

Highlights • In-situ temperature measurements were conducted at the Danube deep sea fan. • Operations were performed with the MARUM-MeBo200 seafloor drill rig. • The BSR is located ∼20 m below the current gas hydrate stability zone. • Seismic data suggest presence of shallower BSR-like events. Abstract Coring, geophysical logging, and in-situ temperature measurements were performed with the MARUM-MeBo200 seafloor rig to characterize gas hydrate occurrences in sediments of the Danube deep sea fan, off Romania, Black Sea. The new drilling data showed no evidence for significant gas hydrate saturations within the sediments but the presence of free gas at the depth of the bottom-simulating reflector (BSR). In-situ temperature and core-derived geochemical data suggest that the current base of the gas hydrate stability zone (BGHSZ) is ∼20 m shallower than the BSR. Investigation of the seismic data around the drill sites shows several locations where free gas previously trapped at a former BGHSZ migrated upwards forming a new reflection above the BSR. This shows that the gas hydrate system in the Danube deep sea fan is still responding to climate changes initiated at the end of the last glacial maximum

Volcanic Flank Collapse, Secondary Sediment Failure and Flow‐Transition:Multi‐Stage Landslide Emplacement Offshore Montserrat, Lesser Antilles

Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse‐driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi‐phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late‐stage erosive density current that carved channel‐like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope‐acceleration of fine‐grained material that was suspended in the water column earlier during the slide. Late‐stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit

Contamination tracer testing with seabed drills: IODP Expedition 357

IODP Expedition 357 utilized seabed drills for the first time in the history of the ocean drilling program, with the aim of collecting intact sequences of shallow mantle core from the Atlantis Massif to examine serpentinization processes and the deep biosphere. This novel drilling approach required the development of a new remote seafloor system for delivering synthetic tracers during drilling to assess for possible sample contamination. Here, we describe this new tracer delivery system, assess the performance of the system during the expedition, provide an overview of the quality of the core samples collected for deep biosphere investigations based on tracer concentrations, and make recommendations for future applications of the system

First deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf: experiences from the MARUM-MeBo70 on Polarstern-Expedition PS104

The MARUM-MeBo (abbreviation for Meeresboden-Bohrgerät, the German expression for seafloor drill rig) is a robotic drilling system that is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen in close cooperation with Bauer Maschinen GmbH and other industry partners. The MARUM-MeBo drill rigs can be deployed from multipurpose research vessel like, RV MARIA S. MERIAN, RV METEOR, RV SONNE and RV POLARSTERN and are used for getting long cores both in soft sediments as well as hard rocks in the deep sea. The first generation drill rig, the MARUM-MeBo70 is dedicated for drilling depths of more than 70 m (Freudenthal and Wefer, 2013). Between 2005 and 2017 it was deployed on 18 research expeditions and drilled more than. 3 km into different types of lithologies including carbonate and crystalline rocks, gas hydrates, sands and gravel, glacial till and hemipelagic mud with an average recovery rate of 67 %. In February and March 2017 the MeBo70 was used on the West Antarctic continental shelf in the Amundsen Sea Embayment for the first time. The goal of the deployment on RV Polarstern expedition PS104 was to recover a series of sediment cores from different ages that will provide material for investigating the glaciation history of this area known as the most dynamic drainage area of the West Antarctic Ice Sheet. In this presentation we will focus on the operational experiences of this first deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf. References: Freudenthal, T and Wefer, G (2013) Drilling cores on the sea floor with the remote-controlled sea floor drilling rig MeBo. Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-201

First results of sedimentological investigations of MeBo drill cores recovered from the West Antarctic continental shelf in the Amundsen Sea

During expedition PS104 with RV Polarstern in February and March 2017 the MARUM MeBo 70 seabed drilling system was deployed at nine sites on the continental shelf of the Amundsen Sea Embayment, West Antarctica. A total of 57 meters of sediment core were recovered from 11 boreholes located in Pine Island Bay, Pine Island Trough, Bear Ridge and Cosgrove-Abbot Trough with recovery rates ranging from 7 to 76%. The main scientific objective of the drilling was to reconstruct the Late Mesozoic to Quaternary environmental history in this part of the Antarctic continental margin, with a special focus on the past dynamics of the marine based West Antarctic Ice Sheet (WAIS) from its inception to the last glacial cycle. Another main goal of the expedition was to test the suitability of the MeBo drill system for operating on the Antarctic continental shelf and recovering pre-glacial and glacially influenced sedimentary sequences. Here we will present the first results of sedimentological investigations carried out on the drill cores. These comprise (i) visual lithological descriptions, (ii) CT-scanning records of core stratigraphy, sedimentary structures, and possible artefacts induced by the drilling process, (iii) measurements of physical properties performed with a multi-sensor core logger, and (iv) characterisation of the geochemical composition of the drilled sedimentary strata using X-ray fluorescence (XRF) scanner data. Preliminary biostratigraphic investigations conducted on board ship indicated that the recovered sedimentary strata were deposited during various time slices spanning from the Late Cretaceous–Palaeocene to the Late Quaternary. We will provide an update of these initial chronological findings. Keywords: Drill cores, shelf sediments, West Antarctic Ice Sheet

Spectrum gamma ray borehole logging wire data of MeBo sediment core GeoB16601-7

Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string. The measurement was conducted as upcast by hooking up the probe inside the drill string with a wire. The trip out speed was about 3 cm/s and the logging frequency was 1 Hz. Data processing was conducted using the Antares software GeoBase5 including an environmental correction compensating for the attenuation of the gamma ray signal by the drill pipe

Spectrum gamma ray borehole logging of MeBo sediment core GeoB23731-2 (first run)

Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string. The measurement was conducted as upcast hooking up the logging string with a wire inside the drill string. This was the first of two subsequent runs. Wire speed was about 9 cm/s and the logging frequency was 0.5 Hz. Data Processing including the correction for bore hole diameter and signal attenuation by the drill string was conducted using the Antares software GeoBase 6.22.

Borehole temperature measurements at MeBo200 drill site GeoB23234-1, South China Sea

Borehole temperature measurements at site GeoB23234-1 were performed with the sea floor drill rig MARUM-MeBo200 during research expedition SO266 in November 2018 on Four Way Closure Ridge in the South China Sea. A platinum resistance sensor integrated in the 1343 Slimhole Memory Acoustic Tool developed by ANTARES Datasystems GmbH was used to measure the temperature of the fluid within the borehole with 103 mm diameter. The temperature range is –20 to +80 °C, the absolute accuracy within the limits of the measuring range is about 1 °C. The resolution of the temperature measurements is about 0.003 °C. Temperatures were logged with a frequency of 0.5 Hz by a memory adapter with an integrated clock that was synchronized with GPS-time. Borehole logging was conducted during trip out of the drill string. When the drilling operation was completed and the drill string was lifted by about 3.5 m the logging string was dropped into the drill string. After landing on the drill bit the logging string together with the drill string were tripped out of borehole. The depth control system of the drill rig was used to calculate the sensor depth with an accuracy of 0.1%