Ocean cold as water at greater depths. Below the thermocline, water is very cold, ranging from −1 °C to 3 °C. Because this deep and cold layer contains the bulk of ocean water, the average temperature of the world ocean is 3.9 °C. If a zone undergoes dramatic changes in salinity with depth, it contains a halocline. If a zone undergoes a strong, vertical chemistry gradient with depth, it contains a chemocline. The halocline often coincides with the thermocline, and the combination produces a pronounced pycnocline. The deepest point in the ocean is the Mariana Trench, located in the Pacific Ocean
Atlantic Ocean Tunnel Atlantic Ocean Tunnel The Atlantic Ocean Tunnel () is an undersea tunnel that is part of Norwegian County Road 64 which connects Kristiansund Municipality to Averøy Municipality in Møre og Romsdal county, Norway. The eastern end of the tunnel is on Kirkelandet island in the town of Kristiansund and the western end of the tunnel is on the island of Averøya, just west of the village of Sveggen. The long tunnel runs beneath the Bremsnesfjorden, reaching a depth of , making it one of the deepest undersea tunnels in the world. Construction began in 2006, and the tunnel opened on