ALBERT

Description: Highlights • The Fram Slide Complex has been active from late Miocene to late Pleistocene. • Local processes were critical for slope stability in the Fram Strait area. • Toe erosion caused by normal faulting may have led to retrogressive failure. • Low gradient contourite drifts might smooth and stabilize submarine slopes. • Low tsunami potential from the Fram Slide Complex could increase in the future. Abstract The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~ 120 km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.

Description: We used a new sedimentary record from a small kettle wetland to reconstruct the Late Glacial and Holocene vegetation and fire history of the Krutoberegovo-Ust Kamchatsk region in eastern Kamchatka Peninsula (Russia). Pollen and charcoal data suggest that the Late Glacial landscape was dominated by a relatively fire-prone Larix forest-tundra during the Greenland Interstadial complex (GI 1) and a subarctic steppe during the Younger Dryas (GS1). The onset of the Holocene is marked by the reappearance of trees (mainly Alnus incana) within a fern and shrub dominated landscape. The Holocene Thermal Maximum (HTM) features shifting vegetational communities dominated by Alnus shrubs, diverse forb species, and locally abundant aquatic plants. The HTM is further defined by the first appearance of stone birch forests (Betula ermanii) – Kamchatka's most abundant modern tree species. The Late Holocene is marked by shifts in forest dynamics and forest-graminoid ratio and the appearance of new non-arboreal taxa such as bayberry (Myrica) and meadow rue (Filipendula). Kamchatka is one of Earth's most active volcanic regions. During the Late Glacial and Holocene, Kamchatka's volcanoes spread large quantities of tephra over the study region. Thirty-four tephra falls have been identified at the site. The events represented by most of these tephra falls have not left evidence of major impacts on the vegetation although some of the thicker tephras caused expansion of grasses (Poaceae) and, at least in one case, forest die-out and increased fire activity.

Description: Highlights • Receiver functions from ocean-bottom seismometer stations reveal no significant crustal thickening in the surrounding of the Tristan da Cunha hot spot. • The mantle transition zone to the NW of Tristan da Cunha is thickened and cool. • The mantle transition zone is potentially thinned to the south/southwest of Tristan da Cunha. • A thickness of 60 to 75 km beneath Tristan da Cunha argues for a compositional control on the seismological lithosphere in the South Atlantic. Abstract The most prominent hotspot in the South Atlantic is Tristan da Cunha, which is widely considered to be underlain by a mantle plume. But the existence, location and size of this mantle plume have not been established due to the lack of regional geophysical observations. A passive seismic experiment using ocean bottom seismometers aims to investigate the lithosphere and upper mantle structure beneath the hotspot. Using the Ps receiver function method we calculate a thickness of 5 to 8 km for the oceanic crust at 17 ocean-bottom stations deployed around the islands. Within the errors of the method the thickness of the oceanic crust is very close to the global mean. The Tristan hotspot seems to have contributed little additional magmatic material or heat to the melting zone at the mid-oceanic ridge, which could be detected as thickened oceanic crust. Magmatic activity on the archipelago and surrounding seamounts seems to have only effected the crustal thickness locally. Furthermore, we imaged the mantle transition zone discontinuities by analysing receiver functions at the permanent seismological station TRIS and surrounding OBS stations. Our observations provide evidence for a thickened (cold) mantle transition zone west and northwest of the islands, which excludes the presence of a deep-reaching mantle plume. We have some indications of a thinned, hot mantle transition zone south of Tristan da Cunha inferred from sparse and noisy observations, which might indicate the location of a Tristan mantle plume at mid-mantle depths. Sp receiver functions image the base of lithosphere at about 60 to 75 km beneath the islands, which argues for a compositionally controlled seismological lithosphere-asthenosphere boundary beneath the study area.

Description: Highlights • Observations show that formation of sediment-laden sea ice occurs in coastal polynyas in winter. • Sea ice rafted sediments are a significant component of the Laptev Sea’s sediment budget. • No observational evidence for sediment entrainment into sea ice in mid-shelf polynyas at water depth greater than 20 m. Abstract Sea ice is an important vehicle for sediment transport in the Arctic Ocean. On the Laptev Sea shelf (Siberian Arctic) large volumes of sediment-laden sea ice are formed during freeze-up in autumn, then exported and transported across the Arctic Ocean into Fram Strait where it partly melts. The incorporated sediments are released, settle on the sea floor, and serve as a proxy for ice-transport in the Arctic Ocean on geological time scales. However, the formation process of sediment-laden ice in the source area has been scarcely observed. Sediment-laden ice was sampled during a helicopter-based expedition to the Laptev Sea in March/April 2012. Sedimentological, biogeochemical and biological studies on the ice core as well as in the water column give insights into the formation process and, in combination with oceanographic process studies, on matter fluxes beneath the sea ice. Based on satellite images and ice drift back-trajectories the sediments were likely incorporated into the sea ice during a mid-winter coastal polynya near one of the main outlets of the Lena River, which is supported by the presence of abundant freshwater diatoms typical for the Lena River phytoplankton, and subsequently transported about 80 km northwards onto the shelf. Assuming ice growth of 12 to 19 cm during this period and mean suspended matter content in the newly formed ice of 91.9 mg l-1 suggests that a minimum sediment load of 8.4x104 t might have been incorporated into sea ice. Extrapolating these sediment loads for the entire Lena Delta region suggests that at least 65% of the estimated sediment loads which are incorporated during freeze-up, and up to 10% of the annually exported sediment load may be incorporated during an event such as described in this paper.

Description: The recent volcanic eruptions of Eyjafjallajökull 2010 and Grímsvötn 2011 demonstrated the risks that mediumsized explosive Icelandic eruptions pose to the North Atlantic region. Using the Eyjafjallajökull 2010 eruption as a case study, we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive. During R/V Poseidon cruise 457, we recovered 13 box cores at 100–1600 m water depths and distances of 18–180 km southwest, south, and east of Iceland. Volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting. The predominantly basaltic particles are mostly derived from the Katla, Grímsvötn-Lakagígar, and Bárðarbunga-Veiðivötn volcanic systems. We also identified rhyolitic particles from the Askja 1875 and Öræfajökull 1362 eruptions. Only three out of almost 900 analyzed glass shards are derived from the recent Eyjafjallajökull 2010 eruption, suggesting that medium-sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of Iceland. We conclude that the frequency of past medium-sized eruptions is likely higher than detectable in this archive.

Description: Environmental histories that span the last full glacial cycle and are representative of regional change in Australia are scarce, hampering assessment of environmental change preceding and concurrent with human dispersal on the continent ca. 47,000 years ago. Here we present a continuous 150,000-year record offshore south-western Australia and identify the timing of two critical late Pleistocene events: wide-scale ecosystem change and regional megafaunal population collapse. We establish that substantial changes in vegetation and fire regime occurred B70,000 years ago under a climate much drier than today. We record high levels of the dung fungus Sporormiella, a proxy for herbivore biomass, from 150,000 to 45,000 years ago, then a marked decline indicating megafaunal population collapse, from 45,000 to 43,100 years ago, placing the extinctions within 4,000 years of human dispersal across Australia. These findings rule out climate change, and implicate humans, as the primary extinction cause.

Description: Slope failure like in the Hinlopen/Yermak Megaslide is one of the major geohazards in a changing Arctic environment. We analysed hydroacoustic and 2D high-resolution seismic data from the apparently intact continental slope immediately north of the Hinlopen/Yermak Megaslide for signs of past and future instabilities. Our new bathymetry and seismic data show clear evidence for incipient slope instability. Minor slide deposits and an internally-deformed sedimentary layer near the base of the gas hydrate stability zone imply an incomplete failure event, most probably about 30000 years ago, contemporaneous to or shortly after the Hinlopen/Yermak Megaslide. An active gas reservoir at the base of the gas hydrate stability zone demonstrate that over-pressured fluids might have played a key role in the initiation of slope failure at the studied slope, but more importantly also for the giant HYM slope failure. To date, it is not clear, if the studied slope is fully preconditioned to fail completely in future or if it might be slowly deforming and creeping at present. We detected widespread methane seepage on the adjacent shallow shelf areas not sealed by gas hydrates.

Description: Highlights: • Fungal infections represent an increasing threat to human health. • Fungal infections in plants are a worldwide problem to the agricultural industry. • Diverse antifungal compounds were isolated from different marine organisms. • The number of new antifungal marine natural products is rapidly developing. • Marine sponges and bacteria are the predominant sources for antifungal compounds. Abstract: Fungal diseases represent an increasing threat to human health worldwide which in some cases might be associated with substantial morbidity and mortality. However, only few antifungal drugs are currently available for the treatment of life-threatening fungal infections. Furthermore, plant diseases caused by fungal pathogens represent a worldwide economic problem for the agriculture industry. The marine environment continues to provide structurally diverse and biologically active secondary metabolites, several of which have inspired the development of new classes of therapeutic agents. Among these secondary metabolites, several compounds with noteworthy antifungal activities have been isolated from marine microorganisms, invertebrates, and algae. During the last fifteen years, around 65% of marine natural products possessing antifungal activities have been isolated from sponges and bacteria. This review gives an overview of natural products from diverse marine organisms that have shown in vitro and/or in vivo potential as antifungal agents, with their mechanism of action whenever applicable. The natural products literature is covered from January 2000 until June 2015, and we are reporting the chemical structures together with their biological activities, as well as the isolation source.

Description: Polymetallic nodule mining at abyssal depths in the Clarion Clipperton Fracture Zone (Eastern Central Pacific) will impact one of the most remote and least known environments on Earth. Since vast areas are being targeted by concession holders for future mining, large-scale effects of these activities are expected. Hence, insight into the fauna associated with nodules is crucial to support effective environmental management. In this study video surveys were used to compare the epifauna from sites with contrasting nodule coverage in four license areas. Results showed that epifaunal densities are more than two times higher at dense nodule coverage (〉25 versus ≤10 individuals per 100 m2), and that taxa such as alcyonacean and antipatharian corals are virtually absent from nodule-free areas. Furthermore, surveys conducted along tracks from trawling or experimental mining simulations up to 37 years old, suggest that the removal of epifauna is almost complete and that its full recovery is slow. By highlighting the importance of nodules for the epifaunal biodiversity of this abyssal area, we urge for cautious consideration of the criteria for determining future preservation zones.

Description: The Ontong Java and Manihiki oceanic plateaus are believed to have formed through high-degree melting of a mantle plume head. Boninite-like, low-Ti basement rocks at Manihiki, however, imply a more complex magma genesis compared with Ontong Java basement lavas that can be generated by ∼30% melting of a primitive mantle source. Here we show that the trace element and isotope compositions of low-Ti Manihiki rocks can best be explained by re-melting of an ultra-depleted source (possibly a common mantle component in the Ontong Java and Manihiki plume sources) re-enriched by ≤1% of an ocean-island-basalt-like melt component. Unlike boninites formed via hydrous flux melting of refractory mantle at subduction zones, these boninite-like intraplate rocks formed through adiabatic decompression melting of refractory plume material that has been metasomatized by ocean-island-basalt-like melts. Our results suggest that caution is required before assuming all Archaean boninites were formed in association with subduction processes.