How Might a Decline in Phytoplankton Affect the Climate of Earth

How might a decline in phytoplankton affect the climate of Earth?

A) A decline in phytoplankton could alter the carbon cycle by moving less carbon dioxide from the atmosphere into phytoplankton tissues.Since carbon dioxide is a greenhouse gas,more of it in the atmosphere could contribute to global warming.
B) A decline in phytoplankton could alter the phosphorous cycle by moving less phosphorous from the atmosphere into phytoplankton tissues.Since phosphorous is a greenhouse gas,more of it in the atmosphere could contribute to global warming.
C) A decline in phytoplankton could alter the hydrologic cycle by moving less water from the atmosphere into phytoplankton tissues.Since water is a greenhouse gas,more of it in the atmosphere could contribute to global warming.
D) A decline in phytoplankton could alter the oxygen cycle by moving less oxygen from the atmosphere into phytoplankton tissues.Since oxygen is a greenhouse gas,more of it in the atmosphere could contribute to global warming.