Final answer:
Oxygen decreases as you move deeper into the sediments due to oxygen depletion caused by organic matter decay.
Step-by-step explanation:
Oxygen goes decreases as you move deeper into the sediments. This is because oxygen availability decreases with depth. The process of oxygen decreasing with depth is known as oxygen depletion. As organic matter decays in deeper sediments, bacteria consume oxygen during the decomposition process, leading to less oxygen being available.