Development of an adaptive disturbance rejection system for the rapidly deployable stable platform—Part 2: Controller design and closed loop response

Currently, both military and civilian operations that require at-sea cargo transfers are severely limited by environmental conditions and loading forces that induce vessel motions. To increase the robustness of at-sea cargo transfer to these environmental conditions and loading forces, efforts have recently been made toward an actively controlled, rapidly deployable stable platform (RDSP). The purpose of the research presented here is to implement an output feedback adaptive controller and adaptive disturbance rejection scheme that will mitigate the effect of environmental conditions and reject disturbances caused by various loading situations. Because of the controller's distinct ability to adapt to various operating conditions, anticipate and reject load disturbances of unknown magnitude, and adjust to stay within input saturation constraints, the framework is a good fit for the RDSP. Three missions are considered using a previously developed 3 degree of freedom simulation of a 1/10th scale RDSP prototype. Results show successful mitigation of load disturbances and a significant reduction in pitch motions using a control command that remains within the given amplitude and rate constraints. In the case of cargo transfer operations, the adaptive control system is able to significantly increase the cargo throughput by rejecting the disturbances before they are able to cause large pitching dynamics.     

Developing a sustainable indicator system based on the pressure–state–response framework for local fisheries: A case study of Gungliau,Taiwan

To sustain fishery development and ensure the supply of fish, the role that a sustainable development indicator system plays in the evaluation of fishery management performance is becoming increasingly important. A sustainable indicator system based on the Pressure–State–Response (PSR) framework was developed for local fisheries in Gungliau, Taiwan, between 1995 and 2003. Factor analysis and canonical correlation analysis were also applied to aggregate indicators and analyse the linkage of indicators. The most serious problem facing fishery system in Gungliau is conflicting local and higher levels of enforcement that result in the problems of effort, harvest and fleet age composition related to the pressure component. Fishery resources and the state of ecosystem were also affected by marine environmental change, especially by El Ñino. Consequently, fishermen adjusted their effort and investment to the variation of Fishery resources, leading Gungliau fisheries to unsustainability.     

Fluid expulsion from overpressured basins: Implications for Pb–Zn mineralisation and dolomitisation of the East Midlands platform,northern England

Our understanding of burial diagenesis within carbonates is often limited by poor constraints on available fluid volumes and geochemistry. However, regional stratigraphic and burial history data are often readily available. Using these data to develop numerical models which couple sedimentological and hydrological basin evolution, we estimate the volumes and geochemistry of fluids that were available to drive dolomitisation and Pb-ore genesis within the Carboniferous, Derbyshire Platform of northern England. Current conceptual models of these processes invoke tectonic release of burial-induced overpressure developed within adjacent Dinantian basins as a drive for reactive fluid flow to the platform. Our simulations show that compaction-driven flow may lead to a supply of fluids that is more complex in its temporal evolution than may be expected. Spatial variations in the rate of fluid expulsion from different sediments lead to a staggered delivery of fluids from different sources. Rapid fluid expulsion within deeper sediments leads to a downwards-decreasing pressure gradient that subsequently draws down fluid from within overlying sediments. Thus, early fluid supply to the platform is sourced from the deep basins while later fluid supply descends from above the platform as well as from the sides. We suggest that such a flow development may have important implications for the relative timing and distribution of a sequence of diagenetic products within the platform. This hypothesis is tested using volume estimates from our simulations. We conclude that although this staggered fluid supply model may be applicable generically, it appears that it is only valid for explaining mineralisation in the Derbyshire Platform. Fluid volumes supplied to the platform are insufficient to explain dolomitisation. Our simulations are supported by a sensitivity analysis that identifies that compaction-driven flow in this system is strongly controlled by the rate of burial and sediment permeabilities within the compacting basins.     

Mathematical modeling of competition for ammonium among Bacteria, Archaea and cyanobacteria within cyanobacterial mats: Can ammonia-oxidizers force nitrogen fixation?

Molecular analysis of cyanobacterial mat communities indicated that cyanobacteria, ammonia-oxidizing Archaea (AOA), and ammonia-oxidizing bacteria (AOB) coexist in those systems, competing for ammonium; this situation would imply competitive exclusion. We attempted to model how ammonia utilization niche partitioning occurs, and how ammonium levels can influence the interaction between those groups in a one-dimensional diffusionlimited system using Michaelis-Menten kinetics to describe ammonium consumption by each of those three groups. In our model, AOAs were able to dominate ammonium uptake by the community under most circumstances, except for unrealistically high (millimolar) levels of ammonium, where AOBs gained advantage. Cyanobacteria were unable to effectively compete for ammonium with either AOBs or AOAs throughout the mat at all ammonium concentrations and cell counts, suggesting that the presence of AOAs or AOBs forces cyanobacteria into nitrogen fixation mode. Such interaction can make cyanobacterial mats a net nitrogen source, as well as provide a carbon-independent energy transfer pathway from primary producers to the rest of the ecosystem.     

Development and Extension of An Aggregated Scale Model: Part 1–Background to ASMITA

Whilst much attention has been given to models that describe wave, tide and sediment transport processes in sufficient detail to determine the local changes in bed level over a relatively detailed representation of the bathymetry, far less attention has been given to models that consider the problem at a much larger scale(e.g. that of geomorphological elements such as a tidal flat and tidal channel). Such aggregated or lumped models tend not to represent the processes in detail but rather capture the behaviour at the scale of interest. One such model developed using the concept of an equilibrium concentration is the Aggregated Scale Morphological Interaction between Tidal basin and Adjacent coast(ASMITA). In this paper we provide some new insights into the concepts of equilibrium, and horizontal and vertical exchange that are key components of this modelling approach. In a companion paper, we summarise a range of developments that have been undertaken to extend the original model concept, to illustrate the flexibility and power of the conceptual framework. However, adding detail progressively moves the model in the direction of the more detailed process-based models and we give some consideration to the boundary between the two.Highlights ? The concept of aggregating model scales is explored and the basis of the ASMITA model is outlined in detail; ? The relationship between dispersion as used in fast-scale process-based models and the horizontal exchange used in aggregated models is explored; ? The basis for formulating suitable equilibrium relationships is explained; ? Alternative ways to include advection and dispersion are examined.     

Development of the Mesoscale Cyclone of September 1–3, 2015, according to Satellite and Numerical Simulation Data

Izvestiya, Atmospheric and Oceanic Physics - A mesoscale cyclone, which developed in early September 2015 over the ice-free Laptev Sea and then, gradually intensifying, moved towards the East...     

Facies and seismic analysis of the Late Carboniferous–Early Permian Finnmark carbonate platform (southern Norwegian Barents Sea): An assessment of the carbonate factories and depositional geometries

The late Palaeozoic buried Finnmark platform, in the Norwegian Barents Sea, is a depositional system which developed under major modifications of palaeoclimatic and palaeoceanographic conditions, given by the northward drifting of the Arctic depositional domain beyond the tropical belt, the activity of the Gondwanan icecaps, and the gradual closure of the Eastern European seaway. In this study, detailed core/microfacies analysis from the explorations wells 7128/4-1 and 7128/6-1, combined with new 2D seismic sections and available dataset from previous studies in the eastern Finnmark area, have allowed a re-evaluation of the depositional scenarios associated with the Ørn and Isbjørn/Polarrev Formations. The late Asselian–early Sakmarian depositional record of the Ørn Formation, followed by the middle Sakmarian transition to the Isbjørn/Polarrev Formations, shows depth-related variations in sedimentation modes and a change of the platform morphology.In particular, a shift from Chloroforam to Bryonoderm sedimentation mode took place through a stratified water column during the deposition of the Ørn Formation, over what we suggest was a distally steepened ramp. In the late Sakmarian, the deposition of the Isbjørn/Polarrev Formations, characterised by a full Bryonoderm sedimentation mode, took place through a cooler non stratified water column, leading to the gradual instauration of a homoclinal ramp profile.Among the other results, our integrated study suggests the development of subtidal heterozoan mounds associated with the Ørn Formation, predating the formation of the larger, stacked and well-known heterozoan distal complexes of the Polarrev Formation. Given the good potential of the Ørn Formation within the Finnmark depositional domain, our results may help to improve the assessment of future evaluations of reservoir properties in the area, which are closely associated with the depositional style and their post-depositional modifications.     

A global wave parameter database for geophysical applications. Part 1: Wave-current–turbulence interaction parameters for the open ocean based on traditional parameterizations

Ocean surface mixing and drift are influenced by the mixed layer depth, buoyancy fluxes and currents below the mixed layer. Drift and mixing are also functions of the surface Stokes drift U_ss, volume Stokes transport T_S, a wave breaking height scale H_swg, and the flux of energy from waves to ocean turbulence Φ_oc. Here we describe a global database of these parameters, estimated from a well-validated numerical wave model, that uses traditional forms of the wave generation and dissipation parameterizations, and covers the years 2003–2007. Compared to previous studies, the present work has the advantage of being consistent with the known physical processes that regulate the wave field and the air–sea fluxes, and also consistent with a very large number of in situ and satellite observations of wave parameters. Consequently, some of our estimates differ significantly from previous estimates. In particular, we find that the mean global integral of Φ_oc is 68 TW, and the yearly mean value of T_S is typically 10–30% of the Ekman transport, except in well-defined regions where it can reach 60%. We also have refined our previous estimates of U_ss by using a better treatment of the high frequency part of the wave spectrum. In the open ocean, U_ss ≃ 0.013U₁₀, where U₁₀ is the wind speed at 10 m height.     

The depth-varying response of coastal circulation and water levels to 2D radiation stress when applied in a coupled wave–tide–surge modelling system during an extreme storm

During storm events wave setup in shallow regions can contribute significantly to the total water elevation, and radiation stress can also generate alongshore drift influencing sediment transport. In low lying coastal regions this generates the potential for flood inundation and morphological change. A coupled tide–surge–wave modelling system is therefore required for accurate forecasting. Liverpool Bay, UK, is taken as a case study because it has a resource of observations and incorporates three estuaries, thus providing conditions to assess the model performance both at the open coast and within estuarine environments. The model covers a region encompassing depths from about 50 m below the mean tidal level to shallow wetting and drying regions, and has previously given good wave and surge hindcasts both for individual storm events and multi-year studies.The present study builds on an already accepted model, to include and assess the spatial influence of 2D radiation stress when implemented in a 3D circulation model. The results show that the method is computationally efficient, so relevant for operational use, and also provides a plausible solution. The varied influence of radiation stress across a coastal domain is demonstrated, with larger impact at an estuary mouth and along the open coast, while having lesser impact within an estuary and further offshore.     

Authigenic carbonates from the eastern Black Sea as an archive for shallow gas hydrate dynamics – Results from the combination of CT imaging with mineralogical and stable isotope analyses

Authigenic carbonates associated with cold seeps provide valuable archives of changes in the long-term seepage activity. To investigate the role of shallow-buried hydrates on the seepage strength and fluid composition we analysed methane-derived carbonate precipitates from a high-flux hydrocarbon seepage area (“Batumi seep area”) located on the south-eastern Black Sea slope in ca. 850 m. In a novel approach, we combined computerized X-ray tomography (CT) with mineralogical and isotope geochemical methods to get additional insights into the three-dimensional internal structure of the carbonate build-ups.     

A method for the calculation of anaerobic oxidation of methane rates across regional scales: an example from the Belt Seas and The Sound (North Sea–Baltic Sea transition)

Estimating the amount of methane in the seafloor globally as well as the flux of methane from sediments toward the ocean–atmosphere system are important considerations in both geological and climate sciences. Nevertheless, global estimates of methane inventories and rates of methane production and consumption through anaerobic oxidation in marine sediments are very poorly constrained. Tools for regionally assessing methane formation and consumption rates would greatly increase our understanding of the spatial heterogeneity of the methane cycle as well as help constrain the global methane budget. In this article, an algorithm for calculating methane consumption rates in the inner shelf is applied to the gas-rich sediments of the Belt Seas and The Sound (North Sea–Baltic Sea transition). It is based on the depth of free gas determined by hydroacoustic techniques and the local methane solubility concentration. Due to the continuous nature of shipboard hydroacoustic measurements, this algorithm captures spatial heterogeneities in methane fluxes better than geochemical analyses of point sources such as observational/sampling stations. The sensibility of the algorithm with respect to the resolution of the free gas depth measurements (2 m vs. 50 cm) is proven of minor importance (a discrepancy of <10%) for a small part of the study area. The algorithm-derived anaerobic methane oxidation rates compare well with previous measured and modeling studies. Finally, regional results reveal that contemporary anaerobic methane oxidation in worldwide inner-shelf sediments may be an order of magnitude lower (ca. 0.24 Tmol year^–1) than previous estimates (4.6 Tmol year^–1). These algorithms ultimately help improve regional estimates of anaerobic oxidation of methane rates.     

Palynology and geochemistry of channel-margin sediments across the tidal–fluvial transition,lower Fraser River,Canada: Implications for the rock record

In the tidally influenced Fraser River, Canada, palynological and carbon isotope (δ¹³C_org) signatures of channel-margin sediments are compared to environmental parameters (e.g., grain size, water salinity) to establish how the signatures vary across the tidal–fluvial transition. Palynological assemblages in the Fraser River are dominated by tree pollen, which constitutes between 85% and 95% of all assemblages. Dinocyst abundances do not exceed 2% of the total palynological assemblage, and the number and diversity of dinocysts gradually decreases landward. The calculated landward limit for dinocysts is at approximately 83 river km, which is relatively close to the upstream limit of the tidal backwater (at ∼100 km). δ¹³C_org values show minimal variability across the tidal–fluvial transition, and the average value is approximately −26‰. The δ¹³C_org signature of river sediments indicates a dominance of terrestrially sourced organic matter regardless of brackish-water and tidal influence on sediment deposition.Six palynological and geochemical trends are identified as relevant to the rock record. 1) In deltaic environments, palynological and geochemical characteristics are less useful than sedimentological and ichnological characteristics for establishing depositional conditions. 2) In marginal-marine settings, low abundances and low species diversities of dinocysts, coupled with a “terrestrial” geochemical signature (δ¹³C_org < −25‰) do not necessarily indicate deposition in a terrestrial environment. 3) Dinocyst abundances above 1% of the total palynomorph population can indicate a significant marine influence on sediment deposition. 4) Mud beds, preferably bioturbated, should be preferentially sampled in order to maximize palynomorph recovery. 5) Marine palynomorphs can occur, albeit in very low concentrations, to the landward limit of the tidal–backwater zone. 6) Palynological and geochemical data should be compared across the paleo-depositional environment in order to establish general trends and remove local variations caused by biases such as grain size.     

Linear and non-linear T–S models for the eastern North Atlantic from Argo data: Role of surface salinity observations

Linear and non-linear empirical models for salinity (S) are estimated from the Argo temperature (T) and salinity (delayed) data. This study focuses on the reconstruction of salinity in the upper 1200 m of the eastern North Atlantic Ocean, a region characterized by the presence of many different water masses. While previous studies have found it necessary to split this region by boxes to fit different polynomial models in each box, a unique model valid for the entire region is fitted here. Argo profiles are randomly distributed on two sets: one for fitting the models and one for testing them. Non-linear regressions are built using neural networks with a single hidden layer and the fitting data set is further divided into two subsets: one for adjusting the coefficients (training data) and one for early stopping of the fitting (validation data). Our results indicate that linear regressions perform better than the climatologic T–S relationship, but that non-linear regressions perform better than the linear ones. Non-linear training using a three-data subsets strategy successfully prevents overfitting even when networks with 90 neurons in the hidden layer are being trained. While the presence of local minima may complicate the generalization of non-linear models to new data, network committees (created by training the same network from different random initial weights) are shown to better reproduce the test data. Several predictors are tested, and the results show that geographical, or surface, information does provide significant information. These results highlight the potential applications of future satellite missions measuring sea-surface salinity to reconstruct, when combined with temperature profiles, vertical salinity profiles.     

Simulating present climate of the global ocean–ice system using the Meteorological Research Institute Community Ocean Model (MRI.COM): simulation characteristics and variability in the Pacific sector

A long-term spin-up and a subsequent interannual simulation are conducted for the ocean–ice component of the climate model intercomparison project (CMIP)-class earth system model of the Japan Meteorological Agency/Meteorological Research Institute. This experiment has three purposes: first is to assess the ability of our model with the Coordinated Ocean–ice Reference Experiments (COREs) forcing in reproducing the present ocean-climate; second is to understand the ocean-climate variability for the past 60 years; third is to present an example of evaluating an ocean–ice interannual variability simulation. The Pacific Ocean is focused on for the last two purposes. After integrating for about 1500 years with repeated use of a detrended CORE interannual forcing, the model reaches a quasi-steady state where the present climate is reproduced satisfactorily. Then, the interannual variability simulation is conducted with the retrieved forcing trend and the result is analyzed. The simulation is successful at reproducing the long-term variability in the Pacific and surrounding oceans. Brief analyses of the tropical and mid-latitude upper layer, deep circulation, and the Arctic sea ice are presented. A caveat in treating other parts of the globe is due to the recent intense convection in the Southern Ocean caused by a remarkably increasing trend of the Southern Hemisphere westerly. Overall, the current simulation with our CMIP-class ocean–ice model is shown to be useful for studying the present ocean-climate variability, specifically in the Pacific sector. It could also be used as a benchmark control experiment that facilitates further research, model development, and intercomparison.     

Making sense of censuses and dealing with missing data: trends in pup counts of Cape fur seal Arctocephalus pusillus pusillus for the period 1972–2004

Trends in the population of Cape fur seals Arctocephalus pusillus pusillus were estimated from counts of pups on aerial photographs of colonies taken between 1972 and 2004 to determine trends in the overall population and subpopulations. Incomplete coverage resulted in missing data in some years. Various methods of determining proxy values for missing data were assessed, and it was concluded that different methods were applicable to Namibian and South African colonies. This reflected variation in trends of pup counts between the countries, which was associated with differences in productivity between the southern and northern Benguela ecosystems. In Namibia, temporal changes in pup numbers were non-linear in some years and there was correspondence in fluctuations at most colonies. This appeared to be on account of an effect of periodic, wide-scale prey shortages that reduced birth rates. There was a northward shift in the distribution of seals in the northern Benguela system. In South Africa, pup counts were much less variable between years, probably on account of a relative stability of food supply. A linear approach was therefore suitable for determining proxy values for missing data at South African colonies. Pup counts suggest that there has been little change in the overall population of the Cape fur seals since 1993, when it was estimated at about two million animals.     

Wave–ice interactions in the marginal ice zone. Part 2: Numerical implementation and sensitivity studies along 1D transects of the ocean surface

The theoretical foundation of a wave–ice interaction model is reported in Part 1 of this study. The model incorporates attenuation of ocean surface waves by sea ice floes and the concomitant breaking of the floes by waves that determines the structure of the marginal ice zone (MIZ). A numerical implementation of the method is presented here. Convergence of the numerical method is demonstrated, as temporal and spatial grids are refined. A semi-analytical method, which does not require time-stepping, is also developed to validate the numerical results, when dispersion is neglected. The wave energy lost during ice breakage is parameterized, as part of the numerical method. Sensitivity studies are conducted in relation to the energy loss and also dispersive effects, the choice of the attenuation model, the properties of the wave field, and sea ice properties such as concentration, thickness and breaking strain. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and ice model data, are shown to conclude the results section. These are compared to estimates of MIZ widths based on a concentration criteria, and obtained from remotely-sensed passive microwave images.