Water absorbs oxygen. Water absorbs less oxygen at higher temperature, so oceans have less oxygen at surface and more at lower depths, which are cooler. At ocean bottoms, hydrogen sulfide comes from thermal vents. It rises and prevents further oxygen absorption at ocean depth {chemocline}. Below chemocline is high hydrogen sulfide, and above chemocline is high oxygen. Green sulfur bacteria and purple sulfur bacteria use hydrogen sulfide and are near ocean bottom. Photosynthetic organisms use dissolved carbon dioxide and sunlight so they stay near surface. Zooplankton use oxygen and so stay above chemocline.
Physical Sciences>Earth Science>Planet>Temperature History
5-Earth Science-Planet-Temperature History
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Date Modified: 2022.0224