Beyond these three uses, there is much disagreement over when to capitalize. Every major publication and publisher has its own standards, and many writers have their own preferences (which are generally overridden by in-house rules during publication).
Deep-sea trench. Deep-sea trench, also called oceanic trench , any long, narrow, steep-sided depression in the ocean bottom in which occur the maximum oceanic depths, approximately 7,300 to more than 11,000 metres (24,000 to 36,000 feet). They typically form in locations where one tectonic plate subducts under another.
Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor. Oceanic trenches are a distinctive morphological feature of convergent plate boundaries, along which lithospheric plates move towards each other at rates that vary from a few mm to over ten cm per year.