Ocean currents transport an enormous mass of heat. Consequently, the ocean circulation plays an important role in the Earth's climate system. Horizontal pressure gradients and the Coriolis force are in geostrophic balance in the ocean for horizontal distances greater than a few tenths of kilometers and for times exceeding a few days and beyond the Equator. The surface geostrophic currents can be obtained by the ocean's dynamic topography -- the difference between the sea surface and the geoid. These currents are proportional to the surface slope. Therefore, observing the dynamic topography provides valuable information for improving or evaluating ocean circulation models. The sea surface is directly observed by satellite radar altimetry while the geoid cannot be observed directly. The satellite-based gravity field determination requires different measurement principles (satellite-to-satellite tracking (e.g. GRACE), satellite-gravity-gradiometry (GOCE)). In addition, hydrographic measurements (salinity, temperature and pressure; near-surface velocities) provide information on the dynamic topography. The observation types have different representations and spatial as well as temporal resolutions. Therefore, the determination of the dynamic topography is not straightforward. The main goal of the project COSIMO is the model design and development to provide estimates of the time variable dynamic topography based on a consistent combination of all observation groups. Special attention is paid to the complete error description of the observations and its rigorous propagation. The study area is the North Atlantic Ocean. The knowledge of the heat transport related to the Gulf Stream is of major interest regarding the climate of Europe. The time variability of the surface geostrophic currents especially along the Gulf Stream are determined and studied. Normal equations of the dynamic topography at different points in time can be provided for the assimilation into ocean circulation models for further oceanographic studies.