Editing Paleoclimatology (section)

=== Foraminifera and Isotopic Signatures ===
The most critical proxies found in ocean sediment are the fossilized microscopic shells of marine organisms called '''foraminifera''' (or "forams"). These single-celled organisms extract calcium carbonate (CaCO3) from the seawater to build their shells.

The ratio of Oxygen-18 to Oxygen-16 incorporated into the calcite of a foram shell depends heavily on the temperature and isotopic composition of the ocean water at the time it lived.
* '''Benthic Foraminifera:''' Living on the deep ocean floor, the shells of benthic forams provide a record of deep-ocean temperatures and global ice volume. When massive continental ice sheets grow during ice ages, they lock up vast amounts of the lighter Oxygen-16 on land, leaving the global oceans enriched with heavy Oxygen-18. Benthic forams incorporate this heavy oxygen into their shells, providing a direct proxy for past sea levels and glaciation.
* '''Planktonic Foraminifera:''' Living in the sunlit surface waters, planktonic forams provide records of past sea surface temperatures (SSTs) and regional ocean circulation patterns.