Numerical and diagnostic techniques for modelling stratified coastal seas

The thesis provides numerical and diagnostic techniques for studying processes in stratified coastal seas with numerical models. A method for quantifying processes of stratification and mixing in shallow seas is introduced. Furthermore, the thesis analyses discretisation errors in models of larger seas. The new numerical technique of adaptive grids is presented, which reduces discretisation errors in permanently stratified seas effectively.Die Arbeit untersucht numerische und diagnostische Techniken, um Prozesse in geschichteten Küstenmeeren mit Hilfe numerischer Modelle zu studieren. Es wird einerseits eine Methode vorgestellt, mit der die Prozesse der Schichtung und Durchmischung in flachen Gewässern quantifiziert werden können. Andererseits werden in der Arbeit Diskretisierungsfehler bei der numerischen Modellierung größerer Meeresgebiete analysiert und die neue numerische Technik der adaptiven Modellgitter vorgestellt, mit der Diskretisierungsfehler in permanent geschichteten Meeren effektiv reduziert werden können

Modular System for Shelves and Coasts (MOSSCO v1.0) - a flexible and multi-component framework for coupled coastal ocean ecosystem modelling

Shelf and coastal sea processes extend from the atmosphere through the water column and into the sea bed. These processes are driven by physical, chemical, and biological interactions at local scales, and they are influenced by transport and cross strong spatial gradients. The linkages between domains and many different processes are not adequately described in current model systems. Their limited integration level in part reflects lacking modularity and flexibility; this shortcoming hinders the exchange of data and model components and has historically imposed supremacy of specific physical driver models. We here present the Modular System for Shelves and Coasts (MOSSCO, http://www.mossco.de), a novel domain and process coupling system tailored---but not limited--- to the coupling challenges of and applications in the coastal ocean. MOSSCO builds on the existing coupling technology Earth System Modeling Framework and on the Framework for Aquatic Biogeochemical Models, thereby creating a unique level of modularity in both domain and process coupling; the new framework adds rich metadata, flexible scheduling, configurations that allow several tens of models to be coupled, and tested setups for coastal coupled applications. That way, MOSSCO addresses the technology needs of a growing marine coastal Earth System community that encompasses very different disciplines, numerical tools, and research questions.Comment: 30 pages, 6 figures, submitted to Geoscientific Model Development Discussion

First Results of Modelling Benthos Influence on Sediment Entrainment Using a Generic Approach within the MOSSCO Framework

Sediment Transport and Morphodynamic

The Predominant Processes Controlling Vertical Nutrient and Suspended Matter Fluxes across Domains - Using the New MOSSCO System from Coastal Sea Sediments up to the Atmosphere

Integrated Modeling of Hydro-System

Closed-Loop Process Control for Electron Beam Freeform Fabrication and Deposition Processes

A closed-loop control method for an electron beam freeform fabrication (EBF(sup 3)) process includes detecting a feature of interest during the process using a sensor(s), continuously evaluating the feature of interest to determine, in real time, a change occurring therein, and automatically modifying control parameters to control the EBF(sup 3) process. An apparatus provides closed-loop control method of the process, and includes an electron gun for generating an electron beam, a wire feeder for feeding a wire toward a substrate, wherein the wire is melted and progressively deposited in layers onto the substrate, a sensor(s), and a host machine. The sensor(s) measure the feature of interest during the process, and the host machine continuously evaluates the feature of interest to determine, in real time, a change occurring therein. The host machine automatically modifies control parameters to the EBF(sup 3) apparatus to control the EBF(sup 3) process in a closed-loop manner

Maximum sinking velocities of suspended particulate matter in a coastal transition zone

Marine coastal ecosystem functioning is crucially linked to the transport and fate of suspended particulate matter (SPM). Transport of SPM is controlled by, amongst other factors, sinking velocity ws. Since the ws of cohesive SPM aggregates varies significantly with size and composition of the mineral and organic origin, ws exhibits large spatial variability along gradients of turbulence, SPM concentration (SPMC) and SPM composition. In this study, we retrieved ws for the German Bight, North Sea, by combining measured vertical turbidity profiles with simulation results for turbulent eddy diffusivity. We analyzed ws with respect to modeled prevailing dissipation rates ϵ and found that mean ws were significantly enhanced around log10(ϵ (m2 s−3)) ≈ −5.5. This ϵ region is typically found at water depths of approximately 15 to 20 m along cross-shore transects. Across this zone, SPMC declines towards the offshore waters and a change in particle composition occurs. This characterizes a transition zone with potentially enhanced vertical fluxes. Our findings contribute to the conceptual understanding of nutrient cycling in the coastal region which is as follows. Previous studies identified an estuarine circulation. Its residual landward-oriented bottom currents are loaded with SPM, particularly within the transition zone. This retains and traps fine sediments and particulate-bound nutrients in coastal waters where organic components of SPM become remineralized. Residual surface currents transport dissolved nutrients offshore, where they are again consumed by phytoplankton. Algae excrete extracellular polymeric substances which are known to mediate mineral aggregation and thus sedimentation. This probably takes place particularly in the transition zone and completes the coastal nutrient cycle. The efficiency of the transition zone for retention is thus suggested as an important mechanism that underlies the often observed nutrient gradients towards the coast.BMBF/PACEBMBF/FKZ 030634ABMBF/FKZ 03F0667AHelmholtz Society/PACESNiedersächsisches Ministerium für Wissenschaft und Kultur (MWK)Niedersächsisches Ministerium für Umwelt und Klimaschutz (MUK)Coastal Observing System for Northern and Arctic Seas (COSYNA

On the separation between inorganic and organic fractions of suspended matter in a marine coastal environment

A central aspect of coastal biogeochemistry is to determine how nutrients, lithogenic- and organic matter are distributed and transformed within coastal and estuarine environments. Analyses of the spatio-temporal changes of total suspended matter (TSM) concentration indicate strong and variable linkages between intertidal fringes and pelagic regions. In particular, knowledge about the organic fraction of TSM provides insight to how biogenic and lithogenic particulate matter are distributed in suspension. In our study we take advantage of a set of over 3000 in situ Loss on Ignition (LoI) data from the Southern North Sea that represent fractions of particulate organic matter (POM) relative to TSM (LoI $\equiv$ POM:TSM). We introduce a parameterization (POM-TSM model) that distinguishes between two POM fractions incorporated in TSM. One fraction is described in association with mineral particles. The other represents a seasonally varying fresh pool of POM. The performance of the POM-TSM model is tested against data derived from MERIS/ENVISAT-TSM products of the German Bight. Our analysis of remote sensing data exhibits specific qualitative features of TSM that can be attributed to distinct coastal zones. Most interestingly, a transition zone between the Wadden Sea and seasonally stratified regions of the Southern North Sea is identified where mineral associated POM appears in concentrations comparable to those of freshly produced POM. We will discuss how this transition is indicative for a zone of effective particle interaction and sedimentation.The dimension of this transition zone varies between seasons and with location. Our proposed POM-TSM model is generic and can be calibrated against in situ data of other coastal regions

How is climate change affecting marine life in the Arctic?

Rising temperature is melting the ice that covers the Arctic Ocean, allowing sunlight into waters that have been dark for thousands of years. Previously barren ice-covered regions are being transformed into productive seas. Here we explain how computer modelling can be used to predict how this transformation will affect the food web that connects plankton to fish and top-predators like whales and polar bears. Images of starving polar bears have become symbolic of the effects of warming climate. Melting of the sea-ice is expected to reduce the bears’ ability to hunt for seals. However, at the same time, the food web upon which they depend is becoming more productive, so it is not completely clear what the eventual outcome will be for the bears. Computer models help us to understand these systems and inform policy decisions on the management of newly available Arctic resources

The Benthic Geoecology Model Within The Modular System For Shelves And Coasts (MOSSCO)

The Modular System for Shelves and Coasts (MOSSCO) integrates physical, biological, chemical and geological models of shelves and coasts for the North Sea and Baltic Sea in an exchangeable way. The MOSSCO software forms a coupling framework for exchanging data and models, which distinguishes between physical domains (Earth System compartments such as the benthic and pelagic zone) and processes (such as benthic geochemistry, physical erosion and biological stabilization). Information exchange across physical domains with different grids and time steps are managed using the ESMF (Earth System Modelling Framework), whereas coupling of processes within individual modules is achieved using FABM (Framework for Aquatic Biogeochemical Models). This paper reports coupling of a newly developed benthic geoecology model to the MOSSCO framework. This new model incorporates the biological effects of macrofauna (the bivalve Tellina fabula is taken as an example) and microphytobenthos on erodibility and critical bed shear stress. The model is implemented in an object-oriented generic modular way so that it can be extended to any number of biological effects on the sediment transport for an arbitrary number of species. Finally, the application of the coupled model is demonstrated in simulation of a1D setup

Stability and Evolution of Supernova Fallback Disks

We show that thin accretion disks made of Carbon or Oxygen are subject to the same thermal ionization instability as Hydrogen and Helium disks. We argue that the instability applies to disks of any metal content. The relevance of the instability to supernova fallback disks probably means that their power-law evolution breaks down when they first become neutral. We construct simple analytical models for the viscous evolution of fallback disks to show that it is possible for these disks to become neutral when they are still young (ages of a few 10^3 to 10^4 years), compact in size (a few 10^9 cm to 10^11 cm) and generally accreting at sub-Eddington rates (Mdot ~ a few 10^14 - 10^18 g/s). Based on recent results on the nature of viscosity in the disks of close binaries, we argue that this time may also correspond to the end of the disk activity period. Indeed, in the absence of a significant source of viscosity in the neutral phase, the entire disk will likely turn to dust and become passive. We discuss various applications of the evolutionary model, including anomalous X-ray pulsars and young radio pulsars. Our analysis indicates that metal-rich fallback disks around newly-born neutron stars and black holes become neutral generally inside the tidal truncation radius (Roche limit) for planets, at \~10^11 cm. Consequently, the efficiency of the planetary formation process in this context will mostly depend on the ability of the resulting disk of rocks to spread via collisions beyond the Roche limit. It appears easier for the merger product of a doubly degenerate binary, whether it is a massive white dwarf or a neutron star, to harbor planets because it can spread beyond the Roche limit before becoming neutral.[Abridged]Comment: 34 pages, 2 figures, accepted for publication in Ap