Shelf and coastal sea processes extend from the atmosphere through the water column and into the seabed. These processes reflect intimate interactions between physical, chemical, and biological states on multiple scales. As a consequence, coastal system modelling requires a high and flexible degree of process and domain integration; this has so far hardly been achieved by current model systems. The lack of modularity and flexibility in integrated models hinders the exchange of data and model components and has historically imposed the supremacy of specific physical driver models. We 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 Earth System Modeling Framework (ESMF) and on the Framework for Aquatic Biogeochemical Models (FABM). It goes beyond existing technologies by creating a unique level of modularity in both domain and process coupling, including a clear separation of component and basic model interfaces, flexible scheduling of several tens of models, and facilitation of iterative development at the lab and the station and on the coastal ocean scale. MOSSCO is rich in metadata and its concepts are also applicable outside the coastal domain. For coastal modelling, it contains dozens of example coupling configurations and tested set-ups for coupled applications. Thus, MOSSCO addresses the technology needs of a growing marine coastal Earth system community that encompasses very different disciplines, numerical tools, and research questions.

The Weser estuary has been subject to profound changes in topography in the past 100 years through natural variations and river engineering measures, leading to strong changes in hydrodynamics. These changes are also expected to have affected the dynamics of saltwater intrusion. Using numerical modelling, we examined saltwater intrusion in the Weser estuary in four different system states (1966, 1972, 1981, 2012). Models of each system state were set up with the respective topography and boundary values. We calibrated and validated each model individually to account for differences in sediments, bedforms, and the resolution of underlying bathymetric data between historical and recent system states. In simulations of 1 hydrological year, each with realistic forcing (hindcasting study), the influence of topography is overshadowed by the effects of other factors, particularly river discharge. At times of identical discharge, results indicate a landward shift of the salinity front between 1966 and 2012. Subsequent simulations with different topographies but identical boundary conditions (scenario study) confirm that topography changes in the Weser estuary affected saltwater intrusion. Solely through the topography changes, at a discharge of 300 m³ s⁻¹, the position of the tidally averaged and depth-averaged salinity front shifted landwards by about 2.5 km between 1972 and 1981 and by another 1 km between 1981 and 2012. These changes are significant but comparatively small, since due to seasonal variations in run-off, the tidally averaged saltwater intrusion can vary by more than 20 km. An analysis of the salt flux through a characteristic cross section showed that saltwater intrusion in the Weser estuary is primarily driven by tidal pumping and only to a lesser degree due to estuarine circulation. However, results indicate that the contribution of individual processes has changed in response to anthropogenic measures.

The world’s coasts and deltas are progressively threatened by climate change and human activities. The degree at which coastlines can adapt to these changes strongly depends on the sediment availability. The availability of muddy sediments is however poorly known. This study aims at developing a mud budget for the world’s largest system of uninterrupted tidal flats: the Wadden Sea. The resulting mud budget is nearly closed: ~ 12 million ton/year enters the system on its western end, ~ 1.5 million ton/year is added by local rivers, while ~ 12 million ton annually deposits or is extracted by anthropogenic activities. A mud deficit already exists in the downdrift areas, which will only become more pronounced with increased sea level rise rates. Mud is thus a finite resource similar to sand, and should be treated as such in sediment management strategies. Resolving future challenges will therefore require a cross-border perspective on sediment management.

Marine spatial planning requires reliable data for, e.g., the design of coastal structures, research, or sea level rise adaptation. This task is particularly ambiguous in the German Bight (North Sea, Europe) because a compromise must be found between economic interests and biodiversity since the environmental status is monitored closely by the European Union. For this reason, we have set up an open-access, integrated marine data collection for the period from 1996 to 2015. It provides bathymetry, surface sediments, tidal dynamics, salinity, and waves for the German Bight and is of interest to stakeholders in science, government, and the economy. This part of a two-part publication presents data from numerical hindcast simulations for sea surface elevation, depth-averaged current velocity, bottom shear stress, depth-averaged salinity, wave parameters, and wave spectra. As an improvement to existing data collections, our data represent the variability in the bathymetry by using annually updated model topographies. Moreover, we provide data at a high temporal and spatial resolution (Hagen et al., 2020b); i.e., numerical model results are gridded to 1000 m at 20 min intervals (https://doi.org/10.48437/02.2020.K2.7000.0004). Tidal characteristic values (Hagen et al., 2020a), such as tidal range or ebb current velocity, are computed based on numerical modeling results (https://doi.org/10.48437/02.2020.K2.7000.0003). Therefore, this integrated marine data collection supports the work of coastal stakeholders and scientists, which ranges from developing detailed coastal models to handling complex natural-habitat problems or designing coastal structures.