Deep Ocean Trench A trench is any long, narrow, steep-sided depression in the ocean bottom. The deepest known depression of this kind is the Mariana Trench, which lies east of the Mariana Islands in the western North Pacific Ocean . Of the Earth's 20 major trenches, 17 are found in the Pacific. The only Atlantic trenches are the Puerto Rico Trench north of the Caribbean islands and the South Sandwich Trench east of Drake Passage between South America and Antarctica. The single major Indian Ocean trench is the Java Trench south of Indonesia. The cross sections of trenches generally are V-shaped with steeper landward sides. Geophysical data provide important clues concern