Answer:
Phytoplankton.
Step-by-step explanation:
Phytoplankton, which is Greek for "drifting plants" are microscopic, one-celled organisms that drift in the sunlit areas in the oceans and they are key to bringing carbon down into the ocean biological pump from the atmosphere via the process of photosynthesis.
Phytoplankton are super important! They generate about 50% of the atmosphere's oxygen, which is the same amount as all land plants combined. They also form the base of virtually every ocean food web. In short, phytoplankton makes other ocean (and land) life possible.