Paired Sr isotope (⁸⁷Sr/⁸⁶Sr, δ^88/86Sr) systematic of pore water profiles: A new perspective in marine weathering and seepage studies

The simultaneous and independent determination of the radiogenic (87Sr/86Sr) and the fractionation reflecting stable (!88/86Sr) Sr isotope ratio on pore waters, sediments and precipitates (e.g. carbonates and sulfates) opens a new perspective in the field of submarine weathering and Sr contribution to the ocean chemistry. Four initial case studies covering (1.) CO2 seeps of the Okinawa Trough (OT), (2.) mud volcanoes (MV) and mounds in the Gulf of Cadiz (GoC) and the (3.) Central American Fore Arc as well as first results from the (4.) Black Sea are conducted and reflect a stable Sr perspective on seeps from a broad range of geological settings. Referred to NIST-SRM-987, in this study the IAPSO seawater (SW) standard has a !88/86Sr of 0.39 ‰ (±0.03, 2SD). As a prominent systematic deviation the OT pore water (PW) data from a site with CO2 hydrate and liquid CO2 occurence show values ranging from 0.27 to 0.59 ‰ (286 to 64 cm sediment depth), accompanied by a weak inversely correlated trend from 0.2 to 0.15 ‰ for the corresponding bulk sediment (286 to 36 cm). In contradiction to a simple fluid/SW-mixing approach as driving mechanism for the PW stable Sr trend the 87Sr/86Sr signature stays within analytical uncertainty constant with depth (0.70980 (1)) and differs significantly from SW (0.70917 (1)) and the more radiogenic, slightly heterogeneous sediment (0.71892-0.71731). Potential explanation for the observed !88/86Sr trend and PW signatures heavier than SW are (a) strong fractionation processes enriching light isotopes in secondary precipitates and remineralisation products and heavier signatures in the remaining fluid and/or (b) preferential dissolution of heavier mineral phases. Examples for the latter kind of sediment component are determined in a detailed study of the Mercator MV (GoC) by high !88/86Sr ratios of 0.72 for authigenic and 0.92 ‰ for potentially extruded gypsum crystals. Combined with PW data from the other seep settings (0.2 to 0.52 ‰) a broad range of Sr contribution and fractionation processes becomes evident

Data sets for author name disambiguation: an empirical analysis and a new resource

Data sets of publication meta data with manually disambiguated author names play an important role in current author name disambiguation (AND) research. We review the most important data sets used so far, and compare their respective advantages and shortcomings. From the results of this review, we derive a set of general requirements to future AND data sets. These include both trivial requirements, like absence of errors and preservation of author order, and more substantial ones, like full disambiguation and adequate representation of publications with a small number of authors and highly variable author names. On the basis of these requirements, we create and make publicly available a new AND data set, SCAD-zbMATH. Both the quantitative analysis of this data set and the results of our initial AND experiments with a naive baseline algorithm show the SCAD-zbMATH data set to be considerably different from existing ones. We consider it a useful new resource that will challenge the state of the art in AND and benefit the AND research community

Lithium isotope geochemistry of marine pore waters: Insights from cold seep fluids

Lithium concentration and isotope data (δ7Li) are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments, a sediment-hosted hydrothermal system and two Mediterranean brine basins. The new reference data and literature data of hydrothermal fluids and pore fluids from the Ocean Drilling Program follow an empirical relationship between Li concentration and δ7Li (δ7Li = −6.0(±0.3) · ln[Li] + 51(±1.2)) reflecting Li release from sediment or rocks and/or uptake of Li during mineral authigenesis. Cold seep fluids display δ7Li values between +7.5‰ and +45.7‰, mostly in agreement with this general relationship. Ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite–illite is the major sink for light pore water Li in deeply buried continental margin sediments. Deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport-related fractionation trends. Pore fluids on passive margins receive disproportionally high amounts of Li from intensely weathered and transported terrigenous matter. By contrast, on convergent margins and in other settings with strong volcanogenic input, Li concentrations in pore water are lower because of intense Li uptake by alteration minerals and, most notably, adsorption of Li onto smectite. The latter process is not accompanied by isotope fractionation, as revealed from a separate study on shallow sediments. A numerical transport-reaction model was applied to simulate Li isotope fractionation during upwelling of pore fluids. It is demonstrated that slow pore water advection (order of mm a−1) suffices to convey much of the deep-seated diagenetic Li signal into shallow sediments. If carefully applied, Li isotope systematics may, thus, provide a valuable record of fluid/mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure

Origin of light volatile hydrocarbon gases in mud volcano fluids, Gulf of Cadiz - evidence for multiple sources and transport mechanisms in active sedimentary wedges

Widespread mud volcanism across the thick (<= 14 km) seismically active sedimentary prism of the Gulf of Cadiz is driven by tectonic activity along extensive strike-slip faults and thrusts associated with the accommodation of the Africa-Eurasia convergence and building of the Arc of Gibraltar, respectively. An investigation of eleven active sites located on the Moroccan Margin and in deeper waters across the wedge showed that light volatile hydrocarbon gases vented at the mud volcanoes (MVs) have distinct, mainly thermogenic, origins. Gases of higher and lower thermal maturities are mixed at Ginsburg and Mercator MVs on the Moroccan Margin, probably because high maturity gases that are trapped beneath evaporite deposits are transported upwards at the MVs and mixed with shallower, less mature, thermogenic gases during migration. At all other sites except for the westernmost Porto MV, delta C-13-CH4 and delta H-2-CH4 values of similar to -50 parts per thousand and -200 parts per thousand, respectively, suggest a common origin for methane; however, the ratio of CH4/(C2H6 + C3H8) varies from similar to 10 to > 7000 between sites. Mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply-buried sediments, possibly associated with biodegradation of C2+ homologues and secondary methane production at Captain Arutyunov and Carlos Ribeiro MVs. At the deep-water Bonjardim, Olenin and Carlos Ribeiro MVs, generation of C2+-enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge. At Porto MV, gases are highly enriched in CH4 having delta C-13-CH4 similar to -50 parts per thousand, as at most sites, but markedly lower delta H-2-CH4 Values < -250 parts per thousand, suggesting that it is not generated by thermal cracking of n-alkanes but rather that it has a deep Archaeal origin. The presence of petroleum-type hydrocarbons is consistent with a thermogenic origin, and at sites where CH4 is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments similar to 2-4 km deep. These fluids then migrate into shallower, thermally immature muds, driving their mobilization and extrusion at the seafloor. At Porto MV, the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of CH4. (C) 2009 Elsevier B.V. All rights reserved

Cysteine oxidation and disulfide formation in the ribosomal exit tunnel.

Funder: DFG graduate college: CLiC State of Hesse HMWK: BMRZUnderstanding the conformational sampling of translation-arrested ribosome nascent chain complexes is key to understand co-translational folding. Up to now, coupling of cysteine oxidation, disulfide bond formation and structure formation in nascent chains has remained elusive. Here, we investigate the eye-lens protein γB-crystallin in the ribosomal exit tunnel. Using mass spectrometry, theoretical simulations, dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance and cryo-electron microscopy, we show that thiol groups of cysteine residues undergo S-glutathionylation and S-nitrosylation and form non-native disulfide bonds. Thus, covalent modification chemistry occurs already prior to nascent chain release as the ribosome exit tunnel provides sufficient space even for disulfide bond formation which can guide protein folding