The former, interfacial waves, are partly visible at the surface, but the latter, abyssal waves, remain elusive. Depending on the local rate with which density increases with depth, they propagate either horizontally or obliquely into theĪbyss. Due to slight differences in density, these waves easily displace fluid parcels vertically over hundreds of metres. This stable stratification supports underwater waves. The ocean’s salt and heat content, which determines its density, vary with depth. These may possibly impact natural and man-made structures, and may transport heat and material vertically. In uniformly stratified seas, these waves differ from surface waves in nearly every conceivable aspect, creating underwater ‘storms’ at certain hotspots. This paper introduces various underwater waves that appear on interfaces or in continuous density stratification.

These underwater waves (internal waves) are generated by the same forces, but owe their existence to the ocean’s non-uniform density distribution. In addition to surface waves generated by wind, tidal forces or, in case of tsunamis, seismic events, there exists a less well-known class of bigger waves under water.

Download waves under the sea