Physics and Chemistry of the Oceans

Abstract

Pressure in a liquid increases rapidly with depth. Hence in the sea, a surface swimmer using a snorkel cannot breathe at depths greater than about 50 cm because the pressure difference between the surface and 50 cm depth is too great (c. 0.05 atm or about 4 cm Hg). The atmospheric pressure at sea level is called one atmosphere and is caused by the weight of air above. This weight is on average 1.033 kg cm ^{- 2} or 14. 7lb in ^{- 2}, and is equivalent to the weight of a column of mercury 760 mm high. Atmospheric pressure is also measured in bars.