Ocean acidification is a problem.
 In addition, ocean warming, along with increased productivity of phytoplankton from higher CO2 levels exacerbates ocean deoxygenation
The most notable example of ocean acidification is the Paleocene-Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago when massive amounts of carbon entered the ocean and atmosphere, and led to the dissolution of carbonate sediments across many ocean basins

