Question

What will happen if phytoplankton disappeared will density of oceans decrease

Answer 1

Plankton are the base of the marine food web, without them all larger organisms will probably die. No plankton=no fish= no food for millions of people. Without ocean life millions (if not billions) of people will start to starve. Such desperation can only lead to more problems (think wars fought over food, etc

Answer 2

Phytoplankton, in turn, convert that CO2 into oxygen or die and bury it at the bottom of the ocean. If the phytoplankton are disappearing, Richardson says, "the ocean as a carbon sink is declining, and what that means is ultimately more CO2 will stay in the atmosphere instead of being dissolved in the ocean."