Annotated record of the detailed examination of ferromanganese concretions from the Bothnia Gulf, the Baltic Sea and the Barents sea collected by Boström, K. and Ingri, J. (Technical University of Lulea)

The collection of ferromanganese nodules at Naturhistoriska Riksmuseet, Stockholm, Sweden has been donated by Pr. Boström, K. and Ingri, J. from the Technical University of Lulea. They have been collected in the Bothnia Gulf, the Baltic Sea anfd the Barents sea from 1976 until 1985. In 1997 it is was put to the care custody of the Laboratory for Isotope Geology (LIG) of NRM. As part of the Access Project at LIG, Curt Boman has gone through the collection and established a database with detailed information about the samples it contains. Ferromanganese nodules typically display a rounded shape and are formed by redox processes at the interface between the seabed sediment and water. In addition to iron and manganese they also contain other metal elements. Nodules chemical composition reflects the substances found in the sediment to which they are associated. Since the nodules grow continuously, they reflect changes in the sedimentary environment chemistry on a yearly basis, which makes them very interesting as environmental archives. The nodules can be found locally in large quantities and due to their metal content they are also economically interesting as a source of raw materials.

A geomorphological seabed classification for the Weddell Sea, Antarctica, with links to ArcGIS project files

Sea floor morphology plays an important role in many scientific disciplines such as ecology, hydrology and sedimentology since geomorphic features can act as physical controls for e.g. species distribution, oceanographically flow-path estimations or sedimentation processes. In this study, we provide a terrain analysis of the Weddell Sea based on the 500 m × 500 m resolution bathymetry data provided by the mapping project IBCSO. Seventeen seabed classes are recognized at the sea floor based on a fine and broad scale Benthic Positioning Index calculation highlighting the diversity of the glacially carved shelf. Beside the morphology, slope, aspect, terrain rugosity and hillshade were calculated. Applying zonal statistics to the geomorphic features identified unambiguously the shelf edge of the Weddell Sea with a width of 45-70 km and a mean depth of about 1200 m ranging from 270 m to 4300 m. A complex morphology of troughs, flat ridges, pinnacles, steep slopes, seamounts, outcrops, and narrow ridges, structures with approx. 5-7 km width, build an approx. 40-70 km long swath along the shelf edge. The study shows where scarps and depressions control the connection between shelf and abyssal and where high and low declination within the scarps e.g. occur. For evaluation purpose, 428 grain size samples were added to the seabed class map. The mean values of mud, sand and gravel of those samples falling into a single seabed class was calculated, respectively, and assigned to a sediment texture class according to a common sediment classification scheme.

Profile of sediment echo sounding with links to ParaSound data files and swath sonar multibeam bathymetry during METEOR cruise M70/2b

Two highly active mud volcanoes located in 990-1,265 m water depths were mapped on the northern Egyptian continental slope during the BIONIL expedition of R/V Meteor in October 2006. High-resolution swath bathymetry and backscatter imagery were acquired with an autonomous underwater vehicle (AUV)-mounted multibeam echosounder, operating at a frequency of 200 kHz. Data allowed for the construction of ~1 m pixel bathymetry and backscatter maps. The newly produced maps provide details of the seabed morphology and texture, and insights into the formation of the two mud volcanoes. They also contain key indicators on the distribution of seepage and its tectonic control. The acquisition of high-resolution seafloor bathymetry and acoustic imagery maps with an AUV-mounted multibeam echosounder fills the gap in spatial scale between conventional multibeam data collected from a surface vessel and in situ video observations made from a manned submersible or a remotely operating vehicle.

Index properties, consolidation characteristics and sediment rebound of ODP Sites 167-1020 and 167-1021 sediments

Drilling during Leg 167 at the California margin was scheduled to recover continuous sedimentary sections. Multiple advanced piston core (APC) holes drilled at different depth offsets provided core overlap in successive APCs. Correlation of high-resolution laboratory physical properties data from adjacent APC holes was used to compile composite depth sections for each site. The composite depth sections were used to confirm continuous recovery and enable high-resolution sampling. The meters composite depth (mcd) scale differs from the shipboard meters below seafloor (mbsf) scale because of (1) core expansion following recovery (MacKillop et al., 1995, doi:10.2973/odp.proc.sr.138.118.1995), (2) coring gaps, and (3) stretching/compression of sediment during coring (Lyle, Koizumi, Richter, et al., 1997, doi:10.2973/odp.proc.ir.167.1997). Moran (1997, doi:10.2973/odp.proc.sr.154.132.1997) calculated that sediment expansion accounted for 90%-95% of the Leg 154 depth offset between shipboard mbsf and the mcd scales. Terzaghi's one-dimensional theory of consolidation (Terzaghi, 1943) describes the response of sediments to stress loading and release. Mechanical loading in marine environments is provided by the buoyant weight of the overlying sediments. The load increases with depth below seabed, resulting in sediment volume reduction as water is "squeezed" out of the voids in the sediment. Stress release during core recovery results in expansion of the sediment and volume increase as water returns to the sediment. The sediment expansion or rebound defines the elastic properties of the sediment. In this study we examine the elastic deformation properties of sediments recovered from Sites 1020 and 1021. These results are used to (1) correct the laboratory index properties measurements to in situ values and (2) determine the contribution of sediment rebound to the depth offset between the mbsf and mcd scales.

Phosphate d18O pore-water profiles of sediment core GeoB11807-2 and GeoB11804-4

Phosphorus cycling in the ocean is influenced by biological and geochemical processes that are reflected in the oxygen isotope signature of dissolved inorganic phosphate (Pi). Extending the Pi oxygen isotope record from the water column into the seabed is difficult due to low Pi concentrations and small amounts of marine porewaters available for analysis. We obtained porewater profiles of Pi oxygen isotopes using a refined protocol based on the original micro-extraction designed by Colman (2002). This refined and customized method allows the conversion of ultra-low quantities (0.5 - 1 µmol) of porewater Pi to silver phosphate (Ag3PO4) for routine analysis by mass spectrometry. A combination of magnesium hydroxide co-precipitation with ion exchange resin treatment steps is used to remove dissolved organic matter, anions, and cations from the sample before precipitating Ag3PO4. Samples as low as 200 µg were analyzed in a continuous flow isotope ratio mass spectrometer setup. Tests with external and laboratory internal standards validated the preservation of the original phosphate oxygen isotope signature (d18OP) during micro extraction. Porewater data on d18OP has been obtained from two sediment cores of the Moroccan margin. The d18OP values are in a range of +19.49 to +27.30 per mill. We apply a simple isotope mass balance model to disentangle processes contributing to benthic P cycling and find evidence for Pi regeneration outbalancing microbial demand in the upper sediment layers. This highlights the great potential of using d18OP to study microbial processes in the subseafloor and at the sediment water interface.