The timing of sea-level change provides important constraints on the mechanisms driving Earth's climate between glacial and interglacial states. Fossil corals constrain the timing of past sea level by their suitability for dating and their growth position close to sea level. The coral-derived age for the last deglaciation is consistent with climate change forced by Northern Hemisphere summer insolation (NHI), but the timing of the penultimate deglaciation is more controversial. We found, by means of uranium/thorium dating of fossil corals, that sea level during the penultimate deglaciation had risen to ~85 meters below the present sea level by 137,000 years ago, and that it fluctuated on a millennial time scale during deglaciation. This indicates that the penultimate deglaciation occurred earlier with respect to NHI than the last deglacial, beginning when NHI was at a minimum.

Features indicating the coral is in growth position are: co, the orientation of the coral; cap, the positioning of an algal crust on the upper surface of the coral; gp, the orientation of partially filled geopetals within the coral; and cf, whether the coral forms part of a continuous framework.

Supplement to: Thomas, Alexander L; Henderson, Gideon M; Deschamps, Pierre; Yokoyama, Yusuke; Mason, Andrew J; Bard, Edouard; Hamelin, Bruno; Durand, Nicolas; Camoin, Gilbert (2009): Penultimate deglacial sea-level timing from Uranium/Thorium dating of Tahitian corals. Science, 324(5931), 1186-1189