Description: A seismological network was operated at the junction of the aseismic Walvis Ridge with the northwestern Namibian coast. We mapped crustal thickness and bulk Vp/Vs ratio by the H-k analysis of receiver functions. In the Damara Belt, the crustal thickness is ~35 km with a Vp/Vs ratio of 〈1.75. The crust is ~30 km thick at the coast in the Kaoko Belt. Strong variations in crustal thickness and Vp/Vs ratios are found at the landfall of the Walvis Ridge. Here and at ~150 km northeast of the coast, the crustal thickness increases dramatically reaching 44 km and the Vp/Vs ratios are extremely high (~1.89). These anomalies are interpreted as magmatic underplating produced by the mantle plume during the breakup of Gondwana. The area affected by the plume is smaller than 300 km in diameter, possibly ruling out the existence of a large plume head under the continent during the breakup.

Description: We will report on two drilling proposals within the International Ocean Discovery Program (IODP) to address open questions on Antarctic Ice-sheet (AIS) dynamics in a transect from the Weddell Sea to the Scotia Sea on the Atlantic side of the Southern Ocean. IODP proposal 848-pre (Ice-sheet and sea-level history of the Weddell Sea) shall drill three contourite drifts northeast of Riiser-Larson Ice Shelf on the slope of the southeastern Weddell Sea that contain high-resolution Mio-Pleistocene sections. As the southern extension of the Atlantic Ocean, the Weddell Sea is a key area to study Earth‘s past climate variability. It constitutes a major source of Antarctic Bottom Water formation, which influences the Atlantic Meridional Overturning Circulation. Moreover, the Weddell Gyre is an important cyclonic circulation system for water-mass communication between the Antarctic Ice Sheet and the Southern Ocean. One of the world's two largest ice shelves, the Filchner-Rønne Ice Shelf, drains into the Weddell Basin. Ice-sheet dynamics in the Weddell Sea sector of the East Antarctic Ice Sheet (EAIS) are highly susceptible to far-field changes in sea level. Practically all icebergs from the EAIS merge in the Weddell Sea before they exit Antarctica through the Scotia Sea, thereby providing a unique location to study AIS dynamics. Despite these paramount scientific issues that have, over the last two decades, identified the Weddell Sea as a key area to study past and present climate change, there has been no deep scientific drilling for high-resolution reconstruction of the Plio-Pleistocene. Our scientific objectives aim at achieving the first complete Late Neogene reconstruction for the Weddell Sea. We will address the overarching questions on changing ice-sheet dynamics, interhemispheric phasing of ice-sheet and climate events, ocean circulation, and bottom-water production. Specifically, we wish to unravel whether the formation of the contourite ridges north of Crary Fan were associated with a sea-level drop initiated through intensification of Northern Hemisphere glaciation during the Pliocene. Also, did the drainage pattern change during the Mid-Pleistocene Transition? Can we decipher ice-sheet dynamics on glacial-to-interglacial time scales and during the Last Glacial Maximum? Can we detect farfield sea-level effects and rates of sea-level rise from Iceberg Alley? Can we relate varve thickness variations obtained from counting and dating varved sediment on the contourite ridges to external (solar) or internal (ocean-atmosphere) variability on decadal-to-centennial time scales? IODP proposal 847-full revised (Plio-Pleistocene reconstruction of ice-sheet, atmosphere, and ocean dynamics in Iceberg Alley) shall drill two deep-ocean sites in the Scotia Sea farther north. We aim at delivering the first well-dated, high-resolution and spatially integrated record of variability in icebergs flux from Iceberg Alley, where a substantial number of Antarctic icebergs exit from the Weddell Sea into the warmer Antarctic Circumpolar Current (ACC). In particular, we will characterize the iceberg flux during the mid-Pliocene warm interval, the mid-Pleistocene transition, the warm interglacials of the last 800 kyr, and during glacial terminations. We will use the geochemical provenance of detrital material to determine regional sources of AIS mass loss; address inter-hemispheric phasing of ice-sheet and climate events, and the relation of AIS variability to sea level. We will also deliver critical information on changes in Drake Passage throughflow, meridional overturning in the Southern Ocean, CO2 transfer via wind-induced upwelling, sea-ice variability, bottom water outflow from the Weddell Sea, Antarctic weathering inputs, and changes in oceanic and atmospheric fronts in the vicinity of the ACC by comparing north-south variations across the Scotia Sea. Comparing changes in dust proxy records between the Scotia Sea and Antarctic ice cores will provide a detailed reconstruction of changes in the Southern Hemisphere westerlies on millennial and orbital time scales for the last 800 kyr. Extending this comparison beyond 800 kyr will help evaluating climate-dust couplings since the Pliocene, its potential role in iron fertilization and atmospheric CO2 drawdown during glacials, and whether dust and changes in Antarctic ice volume played a role in the mid-Pleistocene transition.

Description: Highlights • Crustal structure of Walvis Ridge reveals high seismic velocities in the lower crust intruding the African continent. • This modified crust is localized to approx. 100 × 100 km within the continent. • No indication for a large plume head observed The opening of the South Atlantic is a classical example for a plume related continental breakup. Flood basalts are present on both conjugate margins as well as aseismic ridges connecting them with the current plume location at Tristan da Cunha. To determine the effect of the proposed plume head on the continental crust, we acquired wide-angle seismic data at the junction of the Walvis Ridge with the African continent and modelled the P-wave velocity structure in a forward approach. The profile extends 430. km along the ridge and continues onshore to a length of 720. km. Crustal velocities beneath the Walvis Ridge vary between 5.5. km/s and 7.0. km/s, a typical range for oceanic crust. The crustal thickness of 22. km, however, is approximately three times larger than of normal oceanic crust. The continent-ocean transition is characterized by 30. km thick crust with strong lateral velocity variations in the upper crust and a high-velocity lower crust (HVLC), where velocities reach up to 7.5. km/s. The HVLC is 100 to 130. km wider at the Walvis Ridge than it is farther south, and impinges onto the continental crust of the Kaoko fold belt. Such high seismic velocities indicate Mg-rich igneous material intruded into the continental crust during the initial rifting stage. However, the remaining continental crust seems unaffected by intrusions and the root of the 40. km-thick crust of the Kaoko belt is not thermally abraded. We conclude that the plume head did not modify the continental crust on a large scale, but caused rather local effects. Thus, it seems unlikely that a plume drove or initiated the breakup process. We further propose that the plume already existed underneath the continent prior to the breakup, and ponded melt erupted at emerging rift structures providing the magma for continental flood basalts.

Description: The western Indian Ocean has been warming faster than any other tropical ocean during the 20th century, and is the largest contributor to the global mean sea surface temperature (SST) rise. However, the temporal pattern of Indian Ocean warming is poorly constrained and depends on the historical SST product. As all SST products are derived from the International Comprehensive Ocean-Atmosphere dataset (ICOADS), it is challenging to evaluate which product is superior. Here, we present a new, independent SST reconstruction from a set of Porites coral geochemical records from the western Indian Ocean. Our coral reconstruction shows that the World War II bias in the historical sea surface temperature record is the main reason for the differences between the SST products, and affects western Indian Ocean and global mean temperature trends. The 20th century Indian Ocean warming pattern portrayed by the corals is consistent with the SST product from the Hadley Centre (HadSST3), and suggests that the latter should be used in climate studies that include Indian Ocean SSTs. Our data shows that multi-core coral temperature reconstructions help to evaluate the SST products. Proxy records can provide estimates of 20th century SST that are truly independent from the ICOADS data base.

Description: Upwelling hot mantle plumes are thought to disintegrate continental lithosphere and are considered to be drivers of active continental breakup. The formation of the Walvis Ridge during the opening of the South Atlantic is related to a putative plume-induced breakup. We investigated the crustal structure of the Walvis Ridge (southeast Atlantic Ocean) at its intersection with the continental margin and searched for anomalies related to the possible plume head. The overall structure we identify suggests that no broad plume head existed during opening of the South Atlantic and anomalous mantle melting occurred only locally. We therefore question the importance of a plume head as a driver of continental breakup and further speculate that the hotspot was present before the rifting, leaving a track of kimberlites in the African craton.

Description: Studies of seismic tomography have been highly successful at imaging the deep structure of subduction zones. In a study complementary to these tomographic studies, we use array seismology and reflected waves to image a stagnant slab in the mantle transition zone. Using P and S (SH) waves we find a steeply dipping reflector centred at ca . 400 km depth and ca . 550 km west of the present Mariana subduction zone (at 20N, 140E). The discovery of this anomaly in tomography and independently in array seismology (this paper) helps in understanding the evolution of the Mariana margin. The reflector/stagnant slab may be the remains of the hypothetical North New Guinea Plate, which was theorized to have subducted ca . 50 Ma.

Description: Candida glabrata is the second most common pathogenic Candida species and has emerged as a leading cause of nosocomial fungal infections. Its reduced susceptibility to antifungal drugs and its close relationship to Saccharomyces cerevisiae make it an interesting research focus. Although its genome sequence was published in 2004, little is known about its transcriptional dynamics. Here, we provide a detailed RNA-Seq-based analysis of the transcriptomic landscape of C. glabrata in nutrient-rich media, as well as under nitrosative stress and during pH shift. Using RNA-Seq data together with state-of-the-art gene prediction tools, we refined the annotation of the C. glabrata genome and predicted 49 novel protein-coding genes. Of these novel genes, 14 have homologs in S. cerevisiae and six are shared with other Candida species. We experimentally validated four novel protein-coding genes of which two are differentially regulated during pH shift and interaction with human neutrophils, indicating a potential role in host–pathogen interaction. Furthermore, we identified 58 novel non-protein-coding genes, 38 new introns and condition-specific alternative splicing. Finally, our data suggest different patterns of adaptation to pH shift and nitrosative stress in C. glabrata, Candida albicans and S. cerevisiae and thus further underline a distinct evolution of virulence in yeast.

Description: Author(s): G. Weber, M. O. Herdrich, R. D. DuBois, P.-M. Hillenbrand, H. Beyer, L. Bozyk, T. Gassner, R. E. Grisenti, S. Hagmann, Yu. A. Litvinov, F. Nolden, N. Petridis, M. S. Sanjari, D. F. A. Winters, and Th. Stöhlker Beam lifetimes of stored U 28+ ions with kinetic energies of 30 and 50  MeV/u, respectively, were measured in the experimental storage ring of the GSI accelerator facility. By using the internal gas target station of the experimental storage ring, it was possible to obtain total projectile electron l... [Phys. Rev. ST Accel. Beams 18, 034403] Published Wed Mar 25, 2015