We would like to highlight another vital measurement that we take at each site, the sound velocity and temperature with depth profile. We use a special device that measures pressure, temperature and sound velocity as it is lowered down by a winch. We can literally reach the bottom of the ocean with a pretty long winch cable which is about 6.9 km long! The graph below shows the sound velocity and the temperature with depth down to 2000 metres. It is interesting to see how the temperature decreases rapidly to about 5 degrees Celsius at 700 metres depth and then decreases gradually to about 3 degrees Celsius at 2 km depth. The sound velocity also decreases rapidly from about 1540 metres per second at the surface down to about 1480 m/s at about 700 metres depth, however it starts to increase gradually with depth below 700 metres depth. The main reason for its increase is due to increase in pressure and density. The sound velocity profile is an important measure when imaging the topography of the ocean floor…. more on that in an upcoming post.