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  • Print publication year: 2009
  • Online publication date: June 2012

5 - Thermohaline circulation

from Part II - Wind-driven and thermohaline circulation

Summary

Water mass formation/erosion

The balance of water masses in the world's oceans consists of two major processes: water mass formation and erosion. Most water masses are formed near the upper surface and sink. Furthermore, through either transformation or erosion, water mass properties are continually transformed, so that a water mass gradually loses its identity. Therefore, some types of water mass are formed below the surface layers through the mixing of water masses originated from the sea surface; however, in this chapter, we primarily focus on formation/erosion of water masses in connection with surface processes.

According to the penetration depth, water-mass formation is generally separated into two major categories, those of deep water and mode water. The second category of water mass normally sinks to a relatively shallow part of the world's oceans. In this chapter, we first discuss deepwater formation and then mode water formation.

Sources of deep water in the world's oceans

In a broad sense, the balance of deep water in the world's oceans consists of two major opposing processes: the supply of newly formed water masses through deepwater formation and the removal of deep water through mixing and erosion. Deepwater formation is closely related to the downward branch of the vertical circulation, which continuously supplies the water masses, while deepwater erosion is closely related to the upward branch of the vertical circulation, which continuously removes the water masses. Both processes are essential for water mass balance and thermohaline circulation in the world's oceans.