Modeling sound propagation is an essential tool to assess the risk of air-gun shots on marine mammals. Based on a 2.5D finite-difference code a new full waveform modeling approach will be presented, which determines both SELs of single shots and cumulative SELs of multiple shots fired along a seismic line. Point source approximations of air-gun clusters typically deployed by R/V Polarstern in polar regions are used as sound sources. Marine mammals are simulated as static receivers. Applications to deep and shallow water models including constant and depth-dependent sound velocity profiles show dipole-like directivities in case of single shots and tubular cumulative SEL fields beneath the seismic line in case of multiple shots. Compared to a semi-infinite model the incorporation of sea floor reflections enhances the seismically induced noise close to the sea surface. Refraction due to sound velocity gradients and sound channeling in near-surface ducts are evident, but affect only low to moderate levels. Hence, exposure zone radii derived for different critical hearing thresholds are almost independent of the sound velocity structure. With decreasing thresholds radii increase according to a spherical spreading law in case of single shots and according to a cylindrical spreading law in case of multiple shots.