In geochemistry, paleoclimatology and paleoceanography δ18O or delta-O-18 is a measure of the deviation in ratio of stable isotopes oxygen-18 (18O) and oxygen-16 (16O). It is commonly used as a measure of the temperature of precipitation, as a measure of groundwater/mineral interactions, and as an indicator of processes that show isotopic fractionation, like methanogenesis. In paleosciences, 18O:16O data from corals, foraminifera and ice cores are used as a proxy for temperature.

Maureen E. "Mo" Raymo is an American paleoclimatologist and marine geologist. She is the Co-Founding Dean Emerita of the Columbia Climate School and the G. Unger Vetlesen Professor of Earth & Environmental Sciences at Columbia University. From 2011 to 2022 she was also the Director of the LDEO Core Repository and until 2024 was the Founding Director of the LDEO Hudson River Field Station. From 2020 to 2023 she was first Interim Director then Director of Lamont-Doherty Earth Observatory, the first climate scientist and first female scientist to head the institution.