Explanation:

• Coccolithophores are single-celled algae living in the upper layers of the world's oceans. They have been playing a key role in marine ecosystems and the global carbon cycle for millions of years. 
• Coccolithophores calcify marine phytoplankton that produce up to 40% of open ocean calcium carbonate and are responsible for 20% of the global net marine primary productivity.
• At equilibrium, coccolithophores absorb more carbon dioxide than they produce, which is beneficial for the ocean ecosystem.
• The scientists analyzed the maximum coccolithophore diversity during mid-summer in the Subtropical Zone (STZ - located roughly between tropics) and Sub-Antarctic Zone (SAZ - roughly between 46 - 60 south of equator), which is controlled by elevated silicate, low temperature, and low salinity conditions. Hence only statement 1&2 are correct.