ALBERT

Beschreibung: Nature Geoscience 9, 56 (2016). doi:10.1038/ngeo2592 Authors: Caroline M. Eakin, Maureen D. Long, Alissa Scire, Susan L. Beck, Lara S. Wagner, George Zandt & Hernando Tavera Within oceanic lithosphere a fossilized fabric is often preserved originating from the time of plate formation. Such fabric is thought to form at the mid-ocean ridge when olivine crystals align with the direction of plate spreading. It is unclear, however, whether this fossil fabric is preserved within slabs during subduction or overprinted by subduction-induced deformation. The alignment of olivine crystals, such as within fossil fabrics, can generate anisotropy that is sensed by passing seismic waves. Seismic anisotropy is therefore a useful tool for investigating the dynamics of subduction zones, but it has so far proved difficult to observe the anisotropic properties of the subducted slab itself. Here we analyse seismic anisotropy in the subducted Nazca slab beneath Peru and find that the fast direction of seismic wave propagation aligns with the contours of the slab. We use numerical modelling to simulate the olivine fabric created at the mid-ocean ridge, but find it is inconsistent with our observations of seismic anisotropy in the subducted Nazca slab. Instead we find that an orientation of the olivine crystal fast axes aligned parallel to the strike of the slab provides the best fit, consistent with along-strike extension induced by flattening of the slab during subduction (A. Kumar et al., manuscript in preparation). We conclude that the fossil fabric has been overprinted during subduction and that the Nazca slab must therefore be sufficiently weak to undergo internal deformation.

Beschreibung: Groundwater arsenic concentrations in Vietnam controlled by sediment age Nature Geoscience 5, 656 (2012). doi:10.1038/ngeo1540 Authors: Dieke Postma, Flemming Larsen, Nguyen Thi Thai, Pham Thi Kim Trang, Rasmus Jakobsen, Pham Quy Nhan, Tran Vu Long, Pham Hung Viet & Andrew S. Murray

Beschreibung: Nature Geoscience 9, 884 (2016). doi:10.1038/ngeo2837 Authors: Daniel J. Repeta, Sara Ferrón, Oscar A. Sosa, Carl G. Johnson, Lucas D. Repeta, Marianne Acker, Edward F. DeLong & David M. Karl Biogenic methane is widely thought to be a product of archaeal methanogenesis, an anaerobic process that is inhibited or outcompeted by the presence of oxygen and sulfate. Yet a large fraction of marine methane delivered to the atmosphere is produced in high-sulfate, fully oxygenated surface waters that have methane concentrations above atmospheric equilibrium values, an unexplained phenomenon referred to as the marine methane paradox. Here we use nuclear magnetic resonance spectroscopy to show that polysaccharide esters of three phosphonic acids are important constituents of dissolved organic matter in seawater from the North Pacific. In seawater and pure culture incubations, bacterial degradation of these dissolved organic matter phosphonates in the presence of oxygen releases methane, ethylene and propylene gas. Moreover, we found that in mutants of a methane-producing marine bacterium, Pseudomonas stutzeri, disrupted in the C–P lyase phosphonate degradation pathway, methanogenesis was also disabled, indicating that the C–P lyase pathway can catalyse methane production from marine dissolved organic matter. Finally, the carbon stable isotope ratio of methane emitted during our incubations agrees well with anomalous isotopic characteristics of seawater methane. We estimate that daily cycling of only about 0.25% of the organic matter phosphonate inventory would support the entire atmospheric methane flux at our study site. We conclude that aerobic bacterial degradation of phosphonate esters in dissolved organic matter may explain the marine methane paradox.

Beschreibung: Nature Geoscience 10, 376 (2017). doi:10.1038/ngeo2938 Authors: Flemming Larsen, Long Vu Tran, Hoan Van Hoang, Luu Thi Tran, Anders Vest Christiansen & Nhan Quy Pham

Beschreibung: Nature Geoscience 10, 376 (2017). doi:10.1038/ngeo2938 Authors: Flemming Larsen, Long Vu Tran, Hoan Van Hoang, Luu Thi Tran, Anders Vest Christiansen & Nhan Quy Pham

Beschreibung: Nature Geoscience 7, 391 (2014). doi:10.1038/ngeo2175 Author: Long Xiao As well as being a milestone in technology, the Chang'e lunar exploration programme establishes China as a contributor to space science. With much still to learn about the Moon, fieldwork beyond Earth's orbit must be an international effort.

Beschreibung: Although most data suggest that the India-Eurasia continental collision began 45-55 Myr ago, the architecture of the Himalayan-Tibetan orogen is dominated by deformational structures developed in the Neogene period (〈23 Myr ago). The stratigraphic record and thermochronometric data indicate that erosion of the Himalaya intensified as this constructional phase began and reached a peak around 15 Myr ago. It remained high until 10.5 Myr ago and subsequently slowed gradually to 3.5 Myr ago, but then began to increase once again in the Late Pliocene and Pleistocene epochs. Here we present weathering records from the South China Sea, Bay of Bengal and Arabian Sea that permit Asian monsoon climate to be reconstructed back to the earliest Neogene. These indicate a correlation between the rate of Himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 Myr. We interpret this correlation as indicating dynamic coupling between Neogene climate and both erosion and deformation in the Himalaya. © 2008 Macmillan Publishers Limited. All rights reserved.

Beschreibung: Within oceanic lithosphere a fossilized fabric is often preserved originating from the time of plate formation. Such fabric is thought to form at the mid-ocean ridge when olivine crystals align with the direction of plate spreading. It is unclear, however, whether this fossil fabric is preserved within slabs during subduction or overprinted by subduction-induced deformation. The alignment of olivine crystals, such as within fossil fabrics, can generate anisotropy that is sensed by passing seismic waves. Seismic anisotropy is therefore a useful tool for investigating the dynamics of subduction zones, but it has so far proved difficult to observe the anisotropic properties of the subducted slab itself. Here we analyse seismic anisotropy in the subducted Nazca slab beneath Peru and find that the fast direction of seismic wave propagation aligns with the contours of the slab. We use numerical modelling to simulate the olivine fabric created at the mid-ocean ridge, but find it is inconsistent with our observations of seismic anisotropy in the subducted Nazca slab. Instead we find that an orientation of the olivine crystal fast axes aligned parallel to the strike of the slab provides the best fit, consistent with along-strike extension induced by flattening of the slab during subduction (A. Kumar et al., manuscript in preparation). We conclude that the fossil fabric has been overprinted during subduction and that the Nazca slab must therefore be sufficiently weak to undergo internal deformation. © 2015 Macmillan Publishers Limited. All rights reserved.