A lot of interesting things can be said about the seabed. Sunlight penetrates the water very weakly and complete darkness reigns already at a depth of 200 meters. With depth, external pressure increases sharply - every 10 meters per atmosphere; at a 10-kilometer depth it is equal to 1000 atmospheres! Ordinary thermometers at a depth of 3-5 kilometers flatten, turning into glass dust. But thermometers protected from pressure show that at great depths in the sea all year round the same temperature is one or two degrees of heat.