ALBERT

Description: Mud Volcanism and fluid seepage are widespread phenomena in the Gulf of Cadiz (SW Iberian Margin). In this seismically active region located at the boundary between the African and Eurasian plates, fluid flow is typically focused on deeply rooted active strike-slip faults. The geochemical signature of emanating fluids from various mud volcanoes (MVs) has been interpreted as being largely affected by clay mineral dehydration and recrystallization of Upper Jurassic carbonates. Here we present the results of a novel, fully-coupled 1D basin-scale reactive-transport model capable of simulating major fluid forming processes and related geochemical signatures by considering the growth of the sediment column over time, compaction of sediments, diffusion and advection of fluids, as well as convective and conductive heat flow. The outcome of the model is a realistic approximation to the development of the sediment pore water system over geological time scales in the Gulf of Cadiz. Combined with a geochemical reaction transport model for clay mineral dehydration and calcium carbonate recrystallization, we were able to reproduce measured concentrations of Cl, strontium and 87Sr/86Sr of emanating mud volcano fluids. These results support previously made qualitative interpretations and add further constraints on fluid forming processes, reaction rates and source depths. The geochemical signature at Porto MV posed a specific problem, because of insufficient constraints on non-radiogenic 87Sr/86Sr sources at this location. We favour a scenario of basement-derived fluid injection into basal Upper Jurassic carbonate deposits (Hensen et al., 2015). Although the mechanism behind such basement-derived flow, e.g. along permeable faults, remains speculative at this stage, it provides an additional source of low 87Sr/86Sr fluids and offers an idea on how formation water from the deepest sedimentary strata above the basement can be mobilized and eventually initiate the advection of fluids feeding MVs at the seafloor. The dynamic reactive-transport model presented in this study provides a new tool addressing the combined simulation of complex physical-geochemical processes in sedimentary systems. The model can easily be extended and applied to similar geological settings, and thus help us to provide a fundamental understanding of fluid dynamics and element recycling in sedimentary basins.

Description: Reliable data are the base of all scientific analyses, interpretations and conclusions. Evaluating data in a smart way speeds up the process of interpretation and conclusion and highlights where, when and how additionally acquired data in the field will support knowledge gain. An extended SMART monitoring concept is introduced which includes SMART sensors, DataFlows, MetaData and Sampling approaches and tools. In the course of the Digital Earth project, the meaning of SMART monitoring has significantly evolved. It stands for a combination of hard- and software tools enhancing the traditional monitoring approach where a SMART monitoring DataFlow is processed and analyzed sequentially on the way from the sensor to a repository into an integrated analysis approach. The measured values itself, its metadata, and the status of the sensor, and additional auxiliary data can be made available in real time and analyzed to enhance the sensor output concerning accuracy and precision. Although several parts of the four tools are known, technically feasible and sometimes applied in Earth science studies, there is a large discrepancy between knowledge and our derived ambitions and what is feasible and commonly done in the reality and in the field.

Description: Gas hydrates are one of the largest marine carbon reservoirs on Earth. The conventional understanding of hydrate dynamics assumes that the system converges to a steady-state over geological time-scales, achieving fixed concentrations of gas hydrate and free gas phase. However, using a high-fidelity numerical model and consistently resolving phase states across multiple fluid-fluid and fluid-solid phase boundaries, we have identified well-defined periodic states embedded within hydrate system dynamics. These states lead to cyclic formation and dissolution of massive hydrate layers that is self-sustaining even in the absence of external triggers. This previously unresolved characteristic could manifest as spontaneous gas discharge and pressure release in, supposedly, unperturbed systems. Our findings challenge the foundational principle that the gas hydrate systems have unique steady-state solutions. Instead, existence of periodic states introduces an irreducible uncertainty in gas hydrate dynamics which puts significant error bars on previous hydrate estimates.

Description: Highlights • Sedimentation-driven gas hydrate recycling is cyclic in nature with time scales set by reactive multi-phase transport. • Each cycle can be divided into three distinct phases: 1) gas accumulation phase, 2) gas breakthrough phase and 3) uninhibited hydrate build-up phase. • In the presence of sufficient accumulated gas, convex deposition of hydrate acts like a mechanical nozzle for the ascending gas flow. Gas hydrate recycling is an important process in natural hydrate systems worldwide and frequently leads to the high gas hydrate saturations found close to the base of the gas hydrate stability zone (GHSZ). However, to date it remains enigmatic how, and under which conditions, free gas invades back into the GHSZ. Here we use a 1D compositional multi-phase flow model that accounts for sedimentation to investigate the dominant mechanisms that control free gas flow into the GHSZ using a wide-range of parameters i.e. hydrate formation kinetics, sediment permeability, and capillary pressure. In the first part of this study, we investigate free gas invasion into the GHSZ without any sedimentation, and analyse the dynamics of hydrate formation in the vicinity of the base of GHSZ. This helps establish plausible initial conditions for the main part of the study, namely, hydrate recycling due to rapid and continuous sedimentation. For the case study, we apply our numerical model to the Green Canyon Site 955 in the Gulf of Mexico, where the reported high hydrate saturations are likely a result of hydrate recycling driven by rapid sedimentation. In the model, an initial hydrate layer forms due to the invasion of a specified volume of rising free gas. This hydrate layer is consistent with the local pressure, temperature and salinity state. This hydrate layer is then thermally de-stabilised by sedimentation resulting in free gas formation and hydrate recycling. A key finding of our study is that gas hydrate recycling is a cyclic process which can be divided into three phases of 1) gas hydrate melting and free gas nozzling through the hydrate layer, 2) formation of a new gas hydrate layer as the old layer vanishes, and 3) fast uninhibited grow of a new hydrate layer. High hydrate saturations of about 80% can be attained purely through physical, burial-driven recycling of gas hydrates, without any additional gas input from other sources. Hydrate recycling is, therefore, highly dynamic with its own inherent cyclicity rather than a gradual process paced by the rate of sediment deposition.

Description: Highlights • Well-defined periodic states are embedded within the steady-state hydrate dynamics. • Periodic states lead to cyclic formation and dissociation of massive hydrate layers. • Periodic states are fully self-sustaining even in the absence of external triggers. • Spontaneous gas migration & pressure release occur in supposedly unperturbed systems. • Existence of periodic states implies an irreducible uncertainty in hydrate dynamics. Abstract Gas hydrates are one of the largest marine carbon reservoirs on Earth. The conventional understanding of hydrate dynamics assumes that the system, in the absence of external triggers, converges to a steady-state over geological time-scales, achieving fixed concentrations of gas hydrate and free gas phase. However, using a high-fidelity numerical model and consistently resolving phase states across multiple fluid-fluid and fluid-solid phase boundaries, we have identified well-defined periodic states embedded within hydrate system dynamics. These states lead to cyclic formation and dissolution of massive hydrate layers that is self-sustaining for the majority of natural marine settings. This previously unresolved characteristic could manifest as spontaneous gas migration and pressure release in, supposedly, unperturbed systems. Our findings show that the gas hydrate systems are not bound to have unique steady-state solutions. Instead, existence of periodic states introduces an irreducible, but, quantifiable uncertainty in gas hydrate dynamics which adds significant error bars to global gas hydrate inventory estimates.

Description: Highlights • This study simulates the sedimentation-driven development of multiple stacked BSRs in the Danube paleo-delta, Black Sea. • Formation of multiple BSRs in the Black Sea is controlled by the sequence of sedimentation events of the levees induced by sea-level changes. • Kinetics of phase transitions plays a key role in the coexistence, location, and timing of the multiple BSRs. • Development of multiple stacked BSRs is possible only under a narrow range of parameters, unique for the Danube delta setting. Abstract The gas hydrate stability zone (GHSZ) is defined by pressure-temperature-salinity (pTS) constraints of natural gas hydrate (GH) system. It refers to a depth interval which usually extends several hundred meters into the sediment column at sufficient water depths. The lower boundary of the GHSZ often coincides in seismic reflection data with a bottom simulating reflector (BSR), which indicates the transition between the underlying free gas and the overlying no-free gas zone at the thermodynamic stability boundary. The GHSZ in geological systems is dynamic and can shift in response to sedimentation processes and/or changes in environmental conditions such as bottom water temperatures, hydrostatic pressure, and water salinity. The appearance of multiple BSRs has been interpreted as remnants of former GHSZ shifts which have persisted over geological timescales. In this study, we numerically simulate the sedimentation-driven development of multiple stacked BSRs in the Danube deep-sea fan in the Black Sea. We show that in this dynamic sediment depositional regime sufficient amounts of residual gas remain trapped in the former GHSZ, given sufficiently high initial gas hydrate saturations, so that paleo-BSRs could persist over long time scales (similar to 300 kyr). In particular, the formation and persistence of multiple BSRs in the Danube Delta is controlled by the sequence of sedimentation events of the levees induced by sea-level change. The kinetics of methane phase transitions between gas hydrate, dissolved methane, and free gas plays a key role in the coexistence, location and timing of the multiple BSRs. Thus, For a given permeability, distinct multiple BSRs appear only for a narrow range of GH formation (10(-14) 〈 k(f) [mol/m(2) Pa s] 〈= 10(-12)) and dissociation rates (10(-16) 〈 k(d) [mol/m(2) Pa s] 〈 10(-14)).

Description: This open access book presents the results of three years collaboration between earth scientists and data scientists, in developing and applying data science methods for scientific discovery. The book will be highly beneficial for other researchers at senior and graduate level, interested in applying visual data exploration, computational approaches and scientifc workflows.