ALBERT

Description: Representation of the shelf areas in the global ocean model: key study, questions and perspectives The East Siberian Arctic Shelf (ESAS), consisting of the Laptev, East Siberian and Chukchi Seas, represents the shallowest and broadest shelf region of the entire World Ocean. It occupies a little more than 20% of the total area covered by the Arctic Ocean (AO) and represents a critical physical and biochemical gateway for exchange between AO and terrestrial zone with complex oceanographic and biogeochemical regime influenced by both seawaterof Pacific and Atlantic origins. The is a growing need for better quality estimations of circulation and dynamics on the shelf to answer major present and future scientific, ecosystem and societal issues, because of changing climate. It is a complex task as soon as the ESAS represents wide area with variety of regimes and there is still substantial uncertainty in their role and feedbacks with the wider climate system. Making progress on this is largely dependent on the accurate reproducing of the physical environment in the coupled coastal-open ocean system. We would like to propose modeling system that will help to answer questions on the ESAS observed and future trends and dynamics features across time and space scales tracing the signal through the system Estuaries-ESAS-AO in both upscaling and downscaling directions. To reach mentioned goals, we built a coastal branch of the finite volume version of the global sea ice-ocean model FESOM (Danilov et al., 2004; Danilov, 2012; Wang et al., 2014). FESOM is the first model worldwide that provides multi-resolution functionality to large-scale ocean modeling, allowing to bridge the gap between scales. This unique feature is crucial for high efficient coupling, as soon as the exchange zone can be resolved similarly (with the same resolution) by the global and local solutions. Additional strong side of the elaboration of the coastal branch for the existing global model is a possibility to organize flux treatment in a same manner, increasing efficiency of coupling. Danilov, S., Kivman, G., Schröter, J. (2004). A finite-element ocean model: principles and evaluation, Ocean Model., 6, 125–150. Danilov, S. (2012). Two finite-volume unstructured mesh models for large-scale ocean modeling. Ocean Modell., 47, 14–25. Wang, Q., Danilov, S., Sidorenko, D., Timmermann, R., Wekerle, C., Wang, X., Jung, T., and Schröter, J. (2014). The Finite Element Sea Ice-Ocean Model (FESOM) v.1.4: formulation of an ocean general circulation model, Geosci. Model Dev., 7, 663–693.

Description: Rapid frontline retreat and melting of tidewater glaciers along the Antarctic Peninsula cause surface erosion resulting in a washout of suspended particulate matter (SPM) into coastal surface waters. In Potter Cove, a fjord of ~8.5 km2 surface area, meltwater streams transport 23000-39000 tons of eroded sediments per year that disperse into a five meter thick surface layer varying in spatial expansion depending on wind direction and tidal circulation. We addressed the spatial dynamics of the sediment plume in Potter Cove by modelling SPM circulation under different hydrographic scenarios. We applied numerical implementation of the three-dimensional unstructured-mesh model FESOM-C intended for coastal simulations (1). This model is equipped with the high order horizontal advection schemes and rich variety of the vertical turbulence closures based on implemented GOTM turbulence module (2). The model is based on a finite-volume cell-vertex discretization and works on hybrid unstructured meshes composed of triangles and quads. Model performance was validated by available observations. Our results reveal that water transportation due to lower velocity values close to the glacier front; retain the SPM inside the cove, so that this inner-cove area is more strongly impacted by sedimentation.

Description: Species in the brackish and estuarine ecosystems will experience multiple changes in hydrographic variables due to ongoing climate change and nutrient loads. Here, we investigate how a glacial relict species (Saduria entomon), having relatively cold, low salinity biogeographic origin, could be affected by the combined scenarios of climate change and eutrophication. It is an important prey for higher trophic-level species such as cod, and a predator of other benthic animals. We constructed habitat distribution models based occurrence and density of this species across the entire Baltic and estimated the relative importance of different driving variables. We then used two regional coupled ocean-biogeochemical models to investigate the combined impacts of two future climate change and nutrient loads scenarios on its spatial distribution in 2070-2100. According to the scenarios, the Baltic Sea will become warmer and fresher. Our results show that expected changes in salinity and temperature outrank those due to two nutrient-load scenarios (Baltic Sea Action Plan and business as usual) in their effect on S. entomon distribution. The results are relatively similar when using different models with the same scenarios, thereby increasing the confidence of projections. Overall, our models predict a net increase (and local declines) of suitable habitat area, total abundance and biomass for this species, which is probably facilitated by strong osmoregulation ability and tolerance to temperature changes. We emphasize the necessity of considering multiple hydrographic variables when estimating climate change impacts on species living in brackish and estuarine systems.

Description: The long-wave dynamics of the Lombok Strait, which is the most important link of the West Indonesian throughflow connecting the Pacific and Indian Ocean waters, was simulated and analyzed. A feature of the strait is its extremely complex relief, on which water transport creates a field of pronounced vertical velocities, which requires consideration of the nonhydrostatic component of pressure. The work presents a 3-D nonhydrostatic model in curvilinear coordinates, which is verified on a test problem. Particular attention is paid to the method of solving the 3-D elliptical solver for a nonhydrostatic problem in boundary-matched coordinates and a vertical σ level. The difference in transport through the Lombok Strait is determined by the difference in atmospheric pressure over the Pacific and Indian Oceans. Based on the results of the global simulation, the role of these factors in terms of their variability is analyzed, and the value of nonhydrostatic pressure in the dynamics of the Lombok Strait is revealed and evaluated. The vertical dynamics of the Lombok Strait are considered in detail based on hydrostatic and nonhydrostatic approaches.

Description: Shelf areas represent a critical transition zone between the terrestrial area and the deep ocean. These marine areas attract particulate attention due to high human activity there and its vulnerability to natural hazards. The coastal zones and deep ocean evolve in time as one entity. However, there is still substantial gap in understanding of the deep signal fate in the coastal areas. Making progress on this largely depends on the accurate representation of the physical environment in a coupled coastal-open ocean system. In current work, we present newly developed FESOM-C numerical solution and its application to the North Sea hydrodynamics under climate change pressure. FESOM-C is a coastal branch of the global Finite Element (VolumE) Sea-ice Ocean Model FESOM. It was developed to focus on smaller scales than FESOM and on physical and dynamical processes commonly not accounted in largescale models. FESOM-C numerical core is created in a way to provide most efficient exchange of fluxes between coastal and global solutions. The model performance was evaluated based on hydrodynamics simulations for the southeastern part of the North Sea. The simulation results cover the period from January 2010 to December 2014 and show good agreement with data from autonomous observation stations, ferries and glider expeditions. We also made an analysis of the river tracers, which determines the temporal and spatial dynamics of zones affected by the different freshwater sources. The continuing sea level rise suggests significant changes in shelf hydrodynamics. Based on numerical simulations we present the sensitivity study of the North Sea dynamics to the changes of the sea level at the open boundary. The particular attention was paid to the changes in the tidal residual circulation, which largely defines the biogeochemical transport in the coastal zones.

Description: There is a growing need in the high quality estimations of long-term dynamics and circulation features in the coastal areas to answer major present and future societal, ecosystem and other questions, because of changing climate. On long time scales, the coastal dynamics change not only because of variable forcing, but also due to exchanges with the evolving global ocean. Over recent years, considerable efforts have been invested into developing regional models and applying them to the coastal areas. These models are used by different institutions to study currents, sediment transport and ecosystem dynamics. They are well-established tools equipped with necessary parameterizations and modules that may be required in shelf or coastal modeling. However, they are regional models with open boundaries. When it comes to applying them to study long-term trends and variability in the regional sea, they have to be coupled to a large-scale modeling system. However, numerical algorithms used by global models can be insufficient to simulate coastal dynamics. There are issues related to vertical advection and mixing, stability in case of very thin sigma layers, absence of wetting/drying option etc. One more point is the choice of time step in case of highly varying resolution. Coastal refinement can be added to the global models, but at the same time they will lose efficiency. Unstructured-mesh coastal models are too dissipative and expensive to simulate global circulation at present. A way out of this situation is coupling global and coastal models (one or two ways nesting). To reach this goal we present a coastal branch of the global model FESOM (Danilov et al. 2004, Wang et al. 2014). FESOM is a well-established large-scale ocean circulation model which is tested in numerous applications and participates in ocean model intercomparison project (see CORE-II virtual special issue of Ocean Modelling). It is the first model worldwide which provides multi-resolution functionality to large-scale ocean modeling, allowing one to bridge the gap between the scales and has the finite volume version at the current stage. FESOM_coastal treats the input/output characteristics in the same manner and share partly physical core with the global solution. It supports full coastal functionality, has cell-vortex finite volume discretization and works on any configurations of triangular, quadrangular or hybrid meshes.