Geotechnical properties of marine sediments in the SW Iberia Margin – Implications to marine geohazards.

<p>Submarine mass-failures are recognized worldwide as a potential source of marine geo-hazards. They can compromise the safety and integrity of seafloor and subsurface infrastructures through destroying offshore installations or triggering potential tsunamis. This applies to the SW Iberia Margin, where the occurrence of damaging and tsunamigenic underwater landslides were evidenced in various research works.</p><p>This work assesses the geotechnical properties of the marine sediments forming the slopes of the SW Iberia Margin and provides implications to the marine geohazard in the region. Taking advantage of the availability of the cores from previous projects and expeditions (i.e. CONDRIBER, and IODP Expedition-339), we perform conventional Triaxial laboratory tests. These tests allow determining the in-situ shear strength and stress deformation properties, pre-and post-rupture of the undisturbed sediments.</p><p>Furthermore, we present, through a landslide case-study in the SW Iberia Margin, a sensitivity analysis of the marine geohazards (sliding mass drag forces and tsunamigenesis) to the geotechnical properties of the marine sediments. We demonstrate that the geotechnical analysis is crucial for an accurate modelling of the submarine mass movements, their impact on offshore installations, and their induced tsunamis.</p><p>This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project MAGICLAND – Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin (PTDC/ CTA-GEO/30381/2017).</p>

Holocene floodplain evolution in a central European loess landscape – geoarchaeological investigations of the lower Pleiße valley in NW Saxony

Undisturbed sediments are an important source for the reconstruction of the Holocene development of valleys. Wide floodplains with relatively small rivers in a region settled since 5500 BCE offer opportunities for investigations regarding climatic and anthropogenic landscape change. In the context of a motorway construction, excavations were carried out by the Saxonian Heritage Office in the year 2015. At one of the sites it was possible to get a view of the sediments of the Pleiße valley less than 100 m distance from large cross sections described by Neumeister (1964) in a former open cast mine. Archaeological finds and features, plant remains and radiocarbon dating as well as micromorphological and geochemical investigations helped to decipher the age and the characteristics of the Holocene sediments: above Weichselian loamy sands a sedge peat developed in small depressions during the Preboreal and Boreal. The sands and the sedge peat are covered by a “black clay”, which was still the topsoil during the Atlantic period. The sedimentation of 2.3 m thick overbank fines began after 4000 BCE. A depth of 1 m below the surface a medieval Slavic find layer was excavated. These results show that sedimentation processes in the lower Pleiße valley significantly changed after 4000 BCE. It is obvious that the increase in silty material in the floodplain is caused by the land clearance in the Neolithic period. More than half of the silty overbank fines were deposited before the Middle Ages began.

Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the south-east Pacific

Increasing industrial metal demands due to rapid technological developments may drive the prospection and exploitation of deep-sea mineral resources such as polymetallic nodules. To date, the potential environmental consequences of mining operations in the remote deep sea are poorly known. Experimental studies are scarce, especially with regard to the effect of sediment and nodule debris depositions as a consequence of seabed mining. To elucidate the potential effects of the deposition of crushed polymetallic nodule particles on abyssal meiobenthos communities, a short (11 d) in situ experiment at the seafloor of the Peru Basin in the south-east Pacific Ocean was conducted in 2015. We covered abyssal, soft sediment with approx. 2 cm of crushed nodule particles and sampled the sediment after 11 d of incubation at 4200 m water depth. Short-term ecological effects on the meiobenthos community were studied including changes in their composition and vertical distribution in the sediment as well as nematode genus composition. Additionally, copper burden in a few similar-sized but randomly selected nematodes was measured by means of micro X-ray fluorescence (µXRF). At the end of the experiment, 46±1 % of the total meiobenthos occurred in the added crushed nodule layer, while abundances decreased in the underlying 2 cm compared to the same depth interval in undisturbed sediments. Densities and community composition in the deeper 2–5 cm layers remained similar in covered and uncovered sediments. The migratory response into the added nodule material was particularly seen in polychaetes (73±14 %, relative abundance across all depth layers) copepods (71±6 %), nauplii (61±9 %) and nematodes (43±1 %). While the dominant nematode genera in the added nodule material did not differ from those in underlying layers or the undisturbed sediments, feeding type proportions in this layer were altered, with a 9 % decrease of non-selective deposit feeders and an 8 % increase in epistrate feeders. Nematode tissue copper burden did not show elevated copper toxicity resulting from burial with crushed nodule particles. Our results indicate that burial with a 2 cm layer of crushed nodule particles induces changes in the vertical structure of meiobenthos inside the sediment and an alteration of nematode feeding type proportions within a short time frame of 11 d, while nematode tissue copper burden remains unchanged. These findings considerably contribute to the understanding of the short-term responses of meiobenthos to physical disturbances in the deep sea.

Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the South-East Pacific

Increasing industrial metal demands due to rapid technological developments may drive the prospection and exploration of deep-sea mineral resources such as polymetallic nodules. To date, the potential environmental consequences of mining operations in the remote deep sea are poorly known. Experimental studies are scarce, especially with regard to the effect of sediment and nodule debris depositions as a consequence of seabed mining. To elucidate the potential effects of the deposition of crushed polymetallic nodule particles on abyssal meiobenthos communities, a short (11 days) in situ experiment at the Peru Basin in the South East Pacific Ocean was conducted. We covered abyssal, soft sediment with approx. 2 cm of crushed nodule particles and sampled the sediment after eleven days of incubation at 4200 m water depth. Short-term ecological effects on the meiobenthos community were studied including changes in their composition and vertical distribution in the sediment as well as nematode genus composition. Additionally, copper burden in a few similar-sized, but randomly selected nematodes was measured by means of µ-X-ray fluorescence. At the end of the experiment, 46 ± 1 % of the total meiobenthos occurred in the added crushed nodule layer while abundances decreased in the underlying 2 cm compared to the same depth-interval in original, undisturbed sediments. Densities and community composition in the deeper 2–5 cm layers remained similar in covered and undisturbed sediments. The migratory response into the added substrate was particularly seen in polychaetes (73 ± 14 %, relative abundance across all depth layers) copepods (71 ± 6 %), nauplii (61 ± 9 %) and nematodes (43 ± 1 %). While the dominant nematode genera in the added substrate did not differ from those in underlying layers or the undisturbed sediments, feeding type proportions in this layer were altered with a 9 % decrease of non-selective deposit feeders and an 8 % increase in epistrate feeders. Nematode tissue copper burden did not show elevated copper toxicity resulting from burial with crushed nodule particles. The results indicate that short-term substrate burial requires special attention with regard to ecological consequences of mineral extraction in the deep-sea.

Direct Disposal of Spent Fuel: Developing Solutions Tailored to Japan

With the past Government policy of 100% reprocessing in Japan now open to discussion, options for direct disposal of spent fuel (SF) are now being considered in Japan. The need to move rapidly ahead in developing spent fuel management concepts is closely related to the ongoing debate on the future of nuclear power in Japan and the desire to understand the true costs of the entire life cycle of different options. Different scenarios for future nuclear power — and associated decisions on extent of reprocessing — will give rise to quite different inventories of SF with different disposal challenges. Although much work has been carried out spent fuel disposal within other national programmes, the potential for mining the international knowledge base is limited by the boundary conditions for disposal in Japan. Indeed, with a volunteer approach to siting, no major salt deposits and few undisturbed sediments, high tectonic activity, relatively corrosive groundwater and no deserts, it is evident that a tailored solution is needed. Nevertheless, valuable lessons can be learned from projects carried out worldwide, if focus is placed on basic principles rather than implementation details.

Conjoin sets and stratigraphic integrity in a sandstone shelter: Kenniff Cave (Queensland, Australia)

It is a common assumption that archaeological deposits with well-defined bands of ‘undisturbed’ sediments possess absolute stratigraphic integrity and hence that discrete cultural events are sealed within them. This cautionary tale, based on the excavation of a sandstone shelter site in Queensland, shows that this precise stratigraphic and chronological resolution can no longer be taken for granted. Conjoin sets (stone flakes struck from the same core) demonstrate substantial vertical artefact migration between layers, with consequent implications for interpretation.

Lake Acidification Recovery can be Monitored using Chrysophycean Microfossils

Chrysophyte scales in a sediment core from Swan Lake, Sudbury, Ontario were studied to examine their sensitivity for inference of recent lakewater pH change. The study indicates that, corresponding to an increase in metal mining and smelting activity in the Sudbury basin, lake acidification commenced in 1940. However, as a result of reductions in SO2 emissions in the early 1970's, the lake's pH has recovered from its chronic low pH of 4.0 in 1977 to its high of 5.6 in 1987. The chrysophyte-inferred pH recovery mirrors the increase in measured lakewater pH. The study identifies the potential of chrysophytes to document recent pH recovery in soft-water lakes containing undisturbed sediments. The approach offers promise for understanding the response in lakes of poorly buffered regions to decreased atmospheric loadings of SO2 and in establishing and implementing SO2 mitigation standards.

Primary Production and Respiration in Pelagic and Benthic Communities at Two Intertidal Sites in the Upper Bay of Fundy

Primary production by microalgae on intertidal sediments during ebb tide at two sites in Cumberland and Minas Basin, Bay of Fundy, amounted to 47–83 g C∙m−2∙yr−1 Phytoplankton production measured during flood tide over intertidal sediments in Cumberland Basin varied from 4–10 g C∙m−2∙yr−1 with respiration in the water column between 6 and 12 g∙C∙m−2∙yr−1 depending on concentrations of suspended matter. Respiration by undisturbed sediments (47–62 g C∙m−2∙yr−1) was measured at both locations to estimate aerobic metabolic consumption of organic matter.Maximum rates of benthic primary production occurred during early and late summer at both locations but Values at the Cumberland Basin sites were two to three times greater than those observed in Minas Basin; Chlorophyll a in surface sediments was also lower at the stations in Minas Basin where coarser grained deposits reflect extensive sediment transport. Annual benthic respiration at the two stations in Cumberland Basin, however, was only slightly greater than that at four stations in Minas Basin. Spartina marshes, phytoplankton, and benthic microalgae may provide supplies of organic matter for aerobic consumption in these intertidal sediments which are more similar than are measures of benthic primary production.Key words: benthic microalgae, primary production, intertidal community metabolism, Bay of Fundy