A new global gas hydrate budget based on numerical reaction-transport modeling and a novel parameterization of Holocene and Quaternary sedimentation

This study provides new estimates for the global methane hydrate inventory based on reaction-transport modeling [1]. A multi-1D model for POC degradation, gas hydrate formation and dissolution is presented. The model contains an open three-phase system of two solid (organic carbon, gas hydrates), three dissolved (methane, sulfates, inorganic carbon) and one gaseous (free methane) compounds. The reaction module builds upon the kinetic model of POC degradation [2] which considers a down-core decrease in reactivity of organic matter and the inhibition of methane production via accumulation of metabolites in sediment pore fluids. Global input grids have been compiled from a variety of oceanographic, geological and geophysical data sets including a parameterization of sedimentation rates in terms of water depth (Holocene) and distance to continents (Quaternary).The world's total gas hydrate inventory is estimated at 1.74 x 1013 m3 – ~2 x 1015 m3 CH4 (STP) or, equivalently, 8.3 – ~900 Gt of methane carbon. The first value refers to the present day conditions using the relatively low Holocene sedimentation rates; the second value corresponds to a scenario of higher Quaternary sedimentation rates along continental margins. This increase in the POC input could be explained by re-deposition process at the continental rise and slope due to erosion of continental shelf sediments during glacial times. Our results show that in-situ POC degradation is at present not an efficient hydrate forming process. Significant hydrate deposits are more likely to have formed at times of higher sedimentation during the Quaternary or/and as a consequence of active upward fluid transport

GH-3PAD – a new numerical solver for multiphase transport in porous media - new insights on gas hydrate and free gas co-existence

Gas Hydrate-3 Phase Advanced Dynamics (GH-3PAD) code has been developed to study the geophysical and biochemical processes associated with gas hydrate as well as free methane gas formation and dissolution in marine sediments. Biochemical processes influencing in-situ organic carbon decay and, therefore, gas hydrate formation, such as Anaerobic Oxidation of Methane (AOM), sulfate reduction, and methanogenesis have been considered. The new model assumes a Lagrangian reference frame that is attached to the deposited sedimentary layers, which compact according to their individual lithological properties. Differential motion of the pore fluids and free gas is modeled as Darcy flow. Gas hydrate and free gas formation is either controlled by 1) instant gas hydrate crystallization assuming local thermodynamical equilibrium or by a 2) kinetically controlled rate of gas hydrate growth. The thermal evolution is computed from an energy equation that includes contributions from all phases present in the model (sediment grains, saline pore fluids, gas hydrate, and free gas). A first application of the GH-3PAD model has been the Blake Ridge Site, offshore South Carolina. Here seismic and well data points to the out-of-equilibrium co-existence of gas hydrate and free gas. It has been reported that these two distinct phases appear within sediment column with a gaseous phase tending to migrate upwards throughout the Gas Hydrate Stability Zone (GHSZ) until it reaches the seafloor despite relatively low gas hydrate content (4 – 7 vol. % after Paull et al., 1996). With the GH-3PAD model we quantify the complex transport- reaction processes that control three phase (gas hydrate, free gas, and dissolved CH4) out-of-equilibrium state. References: Paull C. K., Matsumoto R., Wallace P. J., 1996. 9. Site 997, Shipboard Scientific Party. Proceeding of the Ocean Drilling Program, Initial Reports, Vol. 164

Implications of subduction rehydration for earth's deep water cycle

The “standard model” for the genesis of the oceans is that they are exhalations from Earth’s deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et al. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et al. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consis-tent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components

Transport- reaction modeling of marine gas hydrate deposits- global results

We have developed a multi-1D numerical model of gas hydrate formation and dissolution processes in anoxic marine sediments and, by this model, we have estimated the new global gas hydrate inventory (BURWICZ E. B. et al., 2011). The reaction-transport model contains various chemical compounds (solid organic carbon, dissolved methane, inorganic carbon, and sulfates, gas hydrates, and free methane gas). The rates of POC degradation, anaerobic methane oxidation, sulfate reduction, and methanogenesis are kinetically controlled. Gas hydrate stability zone (GHSZ) is defined as a combination of pressure, temperature, and (to a smaller degree) salinity conditions. The lower boundary of the GHSZ is defined as the intersection of gas hydrate and methane gas solubilities. The diffusion equations are solved using a fully-implicit finite-differences method, while all transport processes are resolved by a Semi-Lagrangian scheme. Global input data sets (1°x1° resolution) were compiled from various oceanographic, geological and geophysical sources. The entire model was implemented in Matlab

Estableciendo relaciones entre el mundo y el yo en las prácticas socio-religiosas. Una mirada hacia la comunicación religiosa romana

Starting from the notion of religion as communication and resonance, this article analyses the details and varieties of religious communication in ancient Rome. Decentring the traditional focus on “sacrifice” by admitting that sacra facere was far more than “sacrifice”, allows us to use the rich evidence for the many facets, pragmatic relationships and cognitive associations of such rituals for an analysis focused on the self-world relations that were established in such performances. The article will model religious ritual as a triangular relationship between human agents (in active as well as passive roles), their “special” or “divine” addressees and animals or objects not just casually employed but constitutive for such communication. It will further argue that such religious practices have a specific relational quality which makes them particularly important for establishing relationships, foregrounding the reflexive, self-observing character of such “intensified” practices. Against this background, the body of this article follows the many conceptual and material associations and implications of Roman religious ritual, thus arguing for the individual and cultural malleability of ritual relations. It is construing a heuristic grid and on that basis plausibilizes the claim that self-world relations are established and habitualized in practices that are characterized by their inclusion of not unquestionably plausible addressees and hence more intensively mediatized and more self-reflexive than many other social practices.Partiendo de la noción de religión como comunicación y resonancia, este artículo analiza los detalles y las variedades de la comunicación religiosa en la antigua Roma. Ampliar el foco de atención tradicional en el “sacrificio” admitiendo que sacra facere era mucho más que “sacrificar” nos permite utilizar la abundante documentación que atestigua las múltiples facetas, relaciones pragmáticas y asociaciones cognitivas de los rituales para analizar las relaciones entre el mundo y el yo individual que se establecen en la ejecución de tales ceremonias. El artículo aborda el ritual religioso como una relación triangular entre los agentes humanos (tanto en papeles activos como pasivos), sus receptores “especiales” o “divinos” y los animales u objetos empleados en dicha comunicación no simplemente de manera casual, sino como elementos constitutivos de la misma. Sostiene, además, que las prácticas religiosas tienen una cualidad relacional específica que las hace particularmente importantes para establecer relaciones, poniendo en primer plano el carácter reflexivo y auto-observante de estas prácticas “intensificadas”. Con este telón de fondo, el cuerpo del estudio investiga las numerosas asociaciones e implicaciones conceptuales y materiales del ritual religioso romano, defendiendo así la maleabilidad individual y cultural de las relaciones rituales. Se construye un marco heurístico dentro del cual es posible afirmar que las relaciones entre el mundo y el yo se establecen y se vuelven habituales en prácticas que se caracterizan por incluir destinatarios no incuestionablemente plausibles y, en consecuencia, por ser más intensamente mediatizadas y más autorreflexivas que muchas otras prácticas sociales

Une méthodologie pour l’historiographie de la religion ancienne

Starting from a discussion about the usefulness of a historical approach to ancient religion, I propose basing the historiography of ancient religion on a set of three concepts, replacing three others that have been widely used. First, I contend that we need to shift our focus from questions of identity to questions of agency, not least in the face of earlier traditions of historiography of regions outside the imperial capitals. The application of an agentic perspective entails a further unavoidable consequence. The concept of “religions” must be replaced by that of “lived religion”, even for the past, once again shifting the focus to the local and the entire range of social agents and their cultural production. This agentic and material focus is further supplemented by a spatial one. Thus, I propose moving away from the widespread focus on civic religion in cities to embrace the perspective of urban religion. Lastly, I briefly touch upon the problem of the selection of forms of contemporary historiography of religion.Partant d’une discussion sur l’utilité d’une aproche historique de la religion ancienne, l’article propose de fonder une étude historique de la religion ancienne sur un ensemble de trois concepts, qui en remplacent trois autres qui ont été abondamment utilisés. Tout d’abord, il propose de déplacer l’accent des questions d’identité vers les questions d’agentivité, notamment face aux traditions précédentes de l’historiographie des régions situées en dehors des capitales impériales. Dans cette perspective d’agentivité, une conséquence s’impose. Le concept de «religions» doit être remplacé par celui de «religion vécue», même pour le passé, en mettant à nouveau l’accent sur le local et sur l’ensemble des agents sociaux et leur production culturelle. L’accent mis sur l’agentivité et le matériel est enfin complété par un facteur spatial. L’article propose de remplacer l’accent largement répandu sur la religion civique des villes par une perspective axée sur la «religion urbaine». Enfin, il aborde brièvement le problème de la sélection des formes d’historiographie actuelles de la religion

The experience of pilgrimage in the Roman Empire: communitas, paideiā, and piety-signaling

Pilgrimage of various types is well attested in the pre-Christian religions of the Roman Empire, but there is comparatively little evidence for the personal experiences of pilgrims. Some recent studies have argued that typical pilgrims of this period were members of the intellectual elite highly versed in literary culture (paideia) who saw sacred places as museums of Greek culture. In this paper, I try to reconstruct what we can about the experience of pilgrimage in early Roman Empire, looking at three cases studies: a. Philo’s somewhat idealized account of Jewish pilgrimage to Jerusalem, which stresses intense common feeling (or communitas, to use Victor Turner’s term) between participants; b. Pilgrimage to the oracle of Apollo at Claros, to which cities of Asia Minor and elsewhere sent sacred delegations, largely made up choirs of children who performed hymns at the sanctuary. It may be suggested that the experience of the pilgrimage was in large part an educative one - learning about Greek culture and learning how to behave in public; itmight even be seen as a sort of rite of passage. c. The healing-pilgrimages of Aelius Aristides to Pergamum and elsewhere. Aristides’ experience at Pergamum is full of paideia, though that was not the primary motivation, and it sometimes approaches communitas, though in the end the presence of other people tends to serve the purpose of an audience and foil for his own brilliance. Key aspects of his experience seem to be: a) suffering and b) a feeling of closeness to the god, sometimes bordering on identification with him

Melt-induced buoyancy may explain the elevated rift-rapid sag paradox during breakup of continental plates

The division of the earth’s surface into continents and oceans is a consequence of plate tectonics but a geological paradox exists at continent-ocean boundaries. Continental plate is thicker and lighter than oceanic plate, floating higher on the mantle asthenosphere, but it can rift apart by thinning and heating to form new oceans. In theory, continental plate subsides in proportion to the amount it is thinned and subsequently by the rate it cools down. However, seismic and borehole data from continental margins like the Atlantic show that the upper surface of many plates remains close to sea-level during rifting, inconsistent with its thickness, and subsides after breakup more rapidly than cooling predicts. Here we use numerical models to investigate the origin and nature of this puzzling behaviour with data from the Kwanza Basin, offshore Angola. We explore an idea where the continental plate is made increasingly buoyant during rifting by melt produced and trapped in the asthenosphere. Using finite element simulation, we demonstrate that partially molten asthenosphere combined with other mantle processes can counteract the subsidence effect of thinning plate, keeping it elevated by 2-3 km until breakup. Rapid subsidence occurs after breakup when melt is lost to the embryonic ocean ridge