What are major ocean biogeochemical properties and how do they change?
The average depth of the oceans is about 3800 m. Circulation and biological processes largely govern the vertical variations (profiles) of dissolved substances in the oceans. While the mixing or circulation in the upper layers of the ocean is forced by wind that in the deep ocean is density driven. A layer in which a sharp decrease in temperature occurs immediately below the surface mixed layer is known as thermocline , below which also the temperature continues to decrease but slowly (Figure 3). Therefore, observing a vertical profile (or behaviour) of a property would enable us infer the processes controlling that property in the water column. The dissolved oxygen concentration (Figure 3) in the surface layers of the ocean is very high but decreases sharply across the pycnocline (a boundary where a strong gradient in density occurs – more or less in the region of thermocline). Higher concentrations of oxygen are maintained in the surface mixed layer because of its continuous exchange
