Simulating the temporal and spatial dynamics of the North Sea using the new model GETM (general estuarine transport model)

Here we present results of a 1-year realistic North Sea simulation from the new model GETM (general estuarine transport model) and assess the capabilities of this model by comparing them to model results from the well-known HAMSOM (Hamburg shelf sea and ocean model) model, in situ data from the North Sea project and satellite-derived sea-surface temperature data. The annual cycle and the spatial variability of stratification and mixing in the North Sea is simulated. It is shown that the new model is successful in reproducing the general temporal and spatial dynamics of the North Sea. The major advantages of GETM for achieving improved results in this simulation are the implementation of general vertical coordinates, of a state-of-the-art turbulence model and of higher-order advection schemes. By exploiting the full capabilities of these features a more realistic simulation could be achieved. We found that the greatest differences in the model results are produced by applying advection schemes of different complexity. Here we are able to demonstrate that better advection schemes lead to stronger horizontal gradients and stronger vertical stratification during summer. When comparing these results to measurements from the North Sea project and to satellite data, we find that these stronger gradients are more realistic. Therefore, we consider it as essential to use such high-order advection schemes if the spatial variability of estuarine or shelf seas like the North Sea is to be resolved adequately. The advanced turbulence closure scheme also contributed to more realistic simulation of the vertical stratification. Finally, general vertical coordinates better resolve the shallow regions, but are also useful for the deeper regions, as they allow a better estimation of sea-surface temperature compared to traditional coordinates.Responsible Editor: Phil Dyke     

Three-dimensional modelling of estuarine turbidity maxima in a tidal estuary

A new numerical model for simulating estuarine dynamics is introduced here. This model, called General Estuarine Transport Model (GETM), has been specifically designed for reproducing baroclinic, bathymetry-guided flows where the tidal range may exceed the mean water depth in large parts of the domain such that drying and flooding processes are relevant. Several physical and numerical features of the model support exact and stable results for such domains. For the physics, high-order turbulence closure schemes guarantee proper reproduction of vertical exchange processes. Among the specific numerical features, generalised vertical coordinates, orthogonal curvilinear horizontal coordinates, high-order TVD advection schemes and stable drying and flooding algorithms have been implemented into GETM. The model is applied here to simulate the dynamics of estuarine turbidity maxima (ETMs), a complex feature present in most tidal estuaries. First, idealised simulations for a two-dimensional domain in the xz space will be shown to reproduce the basic generation mechanisms for ETMs. Then, a realistic three-dimensional simulation of the Elbe estuary in Northern Germany will be carried out. It is demonstrated that for a given forcing situation the model reproduces a stable ETM at the correct location.Responsible Editor: Phil Dyke     

Dynamics of medium-intensity dense water plumes in the Arkona Basin, Western Baltic Sea

In this study, the dynamics of medium-intensity inflow events over Drogden Sill into the Arkona Sea are investigated. Idealised model simulations carried out with the General Estuarine Transport Model suggest that most of the salt transport during such inflow events occur north of Kriegers Flak, a shoal with less than 20 m water depth surrounded by water depths of more than 40 m. This assumption about the pathway is supported by recent ship-based observations in the Arkona Sea during a medium-intensity inflow event. The propagation of a saline bottom plume could be observed during several days after having passed Drogden Sill. In the area north of Kriegers Flak the plume was about 10 m thick, and propagated with more than 0.5 m s⁻¹ and a salinity of up to 20 psu (with ambient water salinity being 8 psu) eastwards. Although the model simulations were idealised, the structural agreement between the observation and model result was good. The structure and pathways of these medium-intensity inflow events are of specific interest due to the plans for erecting extensive offshore wind farms in the Arkona Sea which may under certain circumstances lead to increased entrainment of ambient water into the bottom plumes.     

Acid-gas injection at West Stoddart, British Columbia: An analogue for the detailed hydrogeological characterization of a CO2 sequestration site

Geological sequestration of CO₂ is an option for significantly reducing emissions into the atmosphere. Various hydrocarbon companies in western Canada are currently injecting acid-gas (CO₂ and H₂S) into deep subsurface formations. At West Stoddart, in northeast British Columbia, acid-gas has been injected since 1998 at 1600 m depth into sandstones of the Triassic Halfway Formation, which forms a regional aquifer. A comprehensive subsurface characterization was conducted of the regional and local-scale geology, reservoir characteristics, mineralogy, in situ fluid properties, and hydrogeology. Preliminary results from geochemical and numerical multi-phase flow modelling suggest that the majority of the injected acid-gas will dissolve in the formation water and remain within a radius of a few kilometres of the injection well. The experience with the acid-gas injection at West Stoddart and other operations in the Alberta Basin has shown that the process of large-scale CO₂-injection into deep aquifers is technically feasible.     

Assessing climate change impacts on the Iberian power system using a coupled water-power model

Climate change is expected to have a negative impact on the power system of the Iberian Peninsula; changes in river runoff are expected to reduce hydropower generation, while higher temperatures are expected to increase summer electricity demand, when water resources are already limited. However, these impacts have not yet been evaluated at the peninsular level. We coupled a hydrological model with a power market model to study three impacts of climate change on the current Iberian power system: changes in hydropower production caused by changes in precipitation and temperature, changes in temporal patterns of electricity demand caused by temperature changes, and changes in irrigation water use caused by temperature and precipitation changes. A stochastic dynamic programming approach was used to develop operating rules for the integrated system given hydrological uncertainty. We found that changes in precipitation will reduce runoff, decrease hydropower production (with accompanying increases in thermal generation), and increase irrigation water use, while higher temperatures will shift power demand from winter to summer months. The combined impact of these effects will generally make it more challenging to balance agricultural, power, and environmental objectives in the operation of Iberian reservoirs, though some impacts could be mitigated by better alignment between temporal patterns of irrigation and power demands.     

Modelling a real-world buried valley system with vertical non-stationarity using multiple-point statistics

Stationarity has traditionally been a requirement of geostatistical simulations. A common way to deal with non-stationarity is to divide the system into stationary sub-regions and subsequently merge the realizations for each region. Recently, the so-called partition approach that has the flexibility to model non-stationary systems directly was developed for multiple-point statistics simulation (MPS). The objective of this study is to apply the MPS partition method with conventional borehole logs and high-resolution airborne electromagnetic (AEM) data, for simulation of a real-world non-stationary geological system characterized by a network of connected buried valleys that incise deeply into layered Miocene sediments (case study in Denmark). The results show that, based on fragmented information of the formation boundaries, the MPS partition method is able to simulate a non-stationary system including valley structures embedded in a layered Miocene sequence in a single run. Besides, statistical information retrieved from the AEM data improved the simulation of the geology significantly, especially for the deep-seated buried valley sediments where borehole information is sparse.     

Mussel fishery affects diet and reduces body condition of Eiders Somateria mollissima in the Wadden Sea

Although the Danish Wadden Sea is of international importance for several bird species, large-scale blue mussel Mytilus edulis fishing took place from 1984–1987, ceasing thereafter due to low mussel stocks. Mussel fishing removes much of the blue mussel biomass, especially larger individuals. Hence we predict that intensive mussel fishing will affect their predators, such as the Eider Somateria mollissima, which is predominantly a blue mussel feeder by, 1) reducing the amount of blue mussels in their diet relative to alternative prey items, 2) exploitation of smaller blue mussel shell classes, 3) loss of body condition, 4) changing feeding distribution to aggregate to the remaining mussel stocks, and 5) decreasing numbers. Before winter 1986/87 blue mussel biomass was estimated at 40,600 tons, decreasing to 15,400 tons in 1987/88 due to mussel fishery. We collected Eiders in both periods to monitor their diet and body mass and used aerial surveys to determine changes in numbers and distribution. Between the two periods, blue mussels declined in the Eiders diet, numbers of Eiders with empty stomachs increased and the mean length of blue mussel taken by Eiders decreased. Eider body condition declined from 1986/87 to 1987/88, mostly the result of the reduction in numbers of individuals with blue mussel remains in their gizzards and in better body condition compared to those taking alternative food items or having empty gizzards. Eiders shifted their distribution from the southern part of the Danish Wadden Sea to the northern part, where the remaining blue mussel stocks were situated. Eider numbers were lowest in 1987/88, the year of lowest blue mussel stocks. We conclude that intensive mussel fishery affected the Eider's diet, reduced their body condition and affected distribution and abundance. The results also showed that availability of blue mussels may have a key role in building up and maintaining body condition in Eiders during winter.     

Preliminary Mapping and Characterisation of Soils in the Pirin Mountains (Bulgaria)

Soft types, humus types and vegetation as well as their hypsometric variation were analysed in terms of sequences in the northern part of the high mountains of the Pirin National Park at altitudes between 1000 and 2400 m a.s.l. The study area is characterised by a large variety of natural parameters like petrology (mainly marble and granite), morphology (different slope deposits, exposition) and the orographic climate gradient. Statistical analyses using these parameters provided a basis for the soil group classification of the sites. Based on a Digital Terrain Model (DTM) and a geological map of the Pirin National Park, the results of these statistical analyses were used to generate a "map of potential soft groups" (regionalisation using GIS). Six potential soil groups could be determined. The resulting map exhibits a confidence level of 68% on 74.4% of the covered area. Rendzic Leptosols, in combination with Folio Histosols and Histi-lithic Leptosols occur in the alpine and subalpine regions on calcareous substrates. With decreasing altitude they are replaced by a mosaic of Rendzic Leptosols, Phaeozems and an increasing occurrence of Cambic Umbrisols. Umbrisols found on silicatic substrates in the alpine region are replaced by Cambic Umbrisols with decreasing altitude as well. Hence, pedogenesis is characterised by increasing browning and depth of the soil profiles with decreasing altitude. The pH-level is slightly acidic to neutral in lower zones and on calcareous rocky bases. Acidification increases in the subalpine zone. Soft pH decreases down to 4 on silicate subtrates. Typical humic values in mineral topsoils are 10 to 12%, and in organic layers of the softs above 2000 m a.s.l, they are even more. The C:N ratio closely ranges around 20 (median).