Measurements of low‐frequency ambient noise in the Greenland Sea

Abstract

Sonobuoy measurements of omnidirectional ambient noise spectra have been made at several positions between the Denmark Strait and the Fram Strait off the east coast of Greenland. Results from lines of buoys placed normal to the ice edge indicate that, below 200 Hz, the noise level is essentially uniform across the edge, with no peak observed in the level at the interface between the ice cover and the open water. Noise levels tend to be insensitive to wind speed/sea state, showing a typical level of 83 dB re: 1 μPa2/Hz at 100 Hz. Usually, the buoy nearest the coast shows the highest spectral level, suggesting that coastal processes are perhaps the principal source of low‐frequency ambient noise in the Nordic Seas. Several mechanisms could be responsible for the noise, one hypothesis being the movement of glaciers from the Greenland ice cap, at an elevation of ≈ 2000 m, down towards the sea. Each glacier contains on the order of a billion tonnes of ice or more which grinds its way over rough, rocky terrain. This movement generates seismic waves in the ground which could couple into the ocean through the seabed: An interface (Scholte) wave may propagate along the sea bottom and radiate acoustic energy into the water column.