Finally, the deep sea trenches. They occupy only a minute fraction of the sea floor, and because they do not have a big impact on the ocean circulation they are more a curosity than a matter of great importance in physical oceanography

Note that most trenches are so narrow that on the scale of this map regions much deeper than 7000 m rarely show up - they are mostly hidden underneath the thick red 7000 m depth contour. The only trench of significant width is the Puerto Rico trench (1) in the Atlantic Ocean north of the Carribean Sea. The other trench of the Atlantic ocean is the Sandwich trench (2) east of the South Sandwich Islands and the Scotia Sea.

The only trench in the Indian Ocean is the Sunda trench (3). Barely deeper than 7000 m, it does not show up much on this map; it stretches along the entire coast of Sumatra and Java with depths often not quite reaching 7000 m.

The extensive trench system of the Pacific Ocean includes the Kermadec trench (4) and the Tonga trench (5) in the southwest and the Peru and Atacama (Chile) trench (6) in the southeast. A very deep and long trench system is found in the northern hemisphere. Its main components are the Mariana trench (7), which contains the greatest known ocean depth at 11022 m (known as the Vitiaz Deep after the research vessel that discovered it), the Japan trench (8), the Kuril trench (9) and the Aleutian trench (10). The Philippine trench (11) is furthest to the west.

Although the geography of the deep sea trenches is interesting, it is of course not necessary to remember all these details for a successful completion of this exercise. Of more interest in the present context is the connection between trenches and crustal plate movement.