The research in this sub-project focuses on modelling of the regional circulation in the geometrically complex Caribbean bays and lagoons, which are dominated by multi-scale flows. In a sense it explicitly aims to link our interdisciplinary research; from large scale climate change to the small scale biogeomorphology of the coastal bays and lagoons under study. To achieve this we use proven technology; but uniquely couple the effect of long term climate change trends including short term extreme events on calcifying macro algae. We go from the global scales of Sub-Project A to the scale of the Caribbean reefs and lagoons of Sub-Project C. The modelling systems applied in this sub-project will simulate tidal, wind and wave driven flows, wind waves from ocean basin to inlets scales using one integrated model domain and mesh, and a local biogeomorphology model. In particular, hydrodynamic features such as eddies, high flow gradients and wave transformation zones that form within and outside the bay and lagoon systems will be dynamically resolved at very high levels of localized mesh resolution. Parallel scalable model design will ensure that very high resolution grids can be efficiently simulated on high performance computers. We will use the coupled, unstructured mesh, parallel,SWAN+ADCIRC wave-current model developed by Delft University of Technology, the University of Notre Dame, the University of Texas at Austin, and the University of North Carolina at Chapel Hill and Delft3D for the biogeomorphology. The IMAU-Delft-NIOZ-RUN teams will downscale from climate models, to regional models, to bays and lagoons.

The project aim is to gain a deeper insight in the flow dynamics of Canadian Arctic and Baffin Bay. The Canadian Arctic Archipelago (CAA) is a complex area formed by narrow straits and islands in the Arctic. It is an important pathway for tidal energy exchange, freshwater, and sea-ice transport from the Arctic Ocean to the Labrador Sea and ultimately to the Atlantic Ocean. The flux of freshwater through the CAA plays an important role in the local freshwater budget of the Arctic and North Atlantic and may play an important role in convective processes in the Labrador Sea. Changes in the circulation of freshened seawater and ice can significantly affect the distribution of sea-ice in the Arctic, recirculation of the surface waters and freshwater fluxes around Greenland as well as the strength of ocean circulation in the Atlantic and, therefore, have the potential to influence both regional and global climate. Yet, the ocean circulation in this region is poorly understood. Tides may contribute to sea ice deformation, they produce mixing and heat anomalies required for polynya formation. These periodic openings of the pack ice influence heat exchange and enhance the rate of ice production. On the other hand ice conditions and stratification cause seasonal variations in the tidal constituents. It is known that ocean waves can fracture ice and hence stimulate melting. On the other hand, decreased ice coverage can give larger fetch for wave generation. The contribution of sea ice on freshwater fluxes is not clearly understood. Our ultimate goal is to develop high resolution regional coupled ice-ocean-wave model which accurately simulate mass, heat and salt transports, correctly reproduces tidal wave dynamics, capture the complex tidal structure,resolve residual currents and tide-induced water transports along the coast and in the narrow straights. Since winds modulate the state of the sea ice cover, determining variability in multi-year and first-year ice distribution, regions of net growth and melt of sea ice, and the amount of total freshwater content, the meteorological forcing should also be included.The first step is to setup a high-resolution tidal model of the domain. We start with a model two-dimensional (depth integrated) model run, to simulate the water surface elevation and barotropic tidal velocities. The model will be calibrated and validated against available water level and current data. Specific results of interest include predictions of tidal datums, such as mean high water, tidal range, etc., at all points in the model domain. Additionally, calculations of root-mean-square tidal speed will be made to indicate regions of strong tidal mixing.

In this research the numerical modelling of alongshore currents in a surf zone will be investigated. The focus will be on alongshore currents induced by waves, tide and wind. The transformation of surface gravity waves in the near shore results in alongshore currents. Besides, wind and the tidal wave propagating along the coast induce currents. The main question will be on the interaction between these different forcing terms on the resulting alongshore. Knowledge on alongshore currents is of importance for, e.g. swimmer safety, beach erosion and nourishment stabilities. In this research we will use SWASH, a non-hydrostatic wave model recently developed at the Delft University of Technology, to model this wave and current phenomena. The proposed research require simulations that have a substantial demand on computational resources.

The project “Tracing the sinking of dense ocean waters in the North Atlantic Ocean” aims at investigating the role of eddies in deep water formation (strong and deep mixing of surface and ocean waters that sets the density properties of deep ocean waters in the region) and water mass exchange in the North Atlantic with regard to climate change scenarios. Caused by global warming, an increased freshwater flux in the North Atlantic is expected, mainly originating from the melting glaciers on Greenland. These fresh and therefore light water masses are likely to interfere with the deep-water formation and water mass exchange. Unfortunately, the high eddy activity in this region makes it difficult to predict the consequences of the increased freshwater flux. Most studies so far concentrate on model simulations with a too coarse resolution (usually 1 Degree) to properly resolve the North Atlantic eddy activity. Therefore, it is questionable whether these coarse simulations correctly represent the effect of an increased freshwater flux in this region and its consequences on the global circulation. In the underlying study, we aim to use high-resolution (0.1 Degree) model data to investigate the deep-water formation and water mass exchange. For the latter, we will use Lagrangian particles to inquire the pathways of water masses leaving the North Atlantic. We will compare the sinking of these water masses with theoretical considerations that suggest a direct connection of the sinking locations with the density balance of the boundary current. These diagnostics will be performed in three different scenarios. In a control simulation (CTRL) the freshwater flux will be as estimated for present day climate. The influence of climate change will be considered in two other scenarios. In the first scenario an enhanced freshwater flux will be applied over a broad swath in the North Atlantic (between 50N and 60N) (HOSING). In the second scenario, the an enhanced freshwater flux will be applied around Greenland (GREENLAND)). Details of the described scenarios are described in Weijer et al. (2012). The above-mentioned diagnostics should be applied for all three scenarios in order to estimate the impact of ocean eddies in these different scenarios. It is thus necessary to use high-resolution (temporal and spatial) model data to perform the Lagrangian and density budget analysis to answer the underlying research questions of this project.

North Atlantic CLUEDO: Controls on Light Upper ocean waters Entering the Deep Ocean The ocean circulation in the subpolar North Atlantic, characterized by warm northward surface currents and cold southward deep currents, is crucial for climate. Ground-breaking new observations have revealed that it is poorly represented in climate models. This casts doubts on the reliability of circulation changes and associated sea-level rise these models simulate for a warming climate. By creatively combining realistic and idealized simulations, fundamental understanding of the physics governing this North Atlantic circulation is improved. This guides improvement of climate model skills and interpretation of observations.