Penultimate Deglacial Sea-Level Timing from Uranium/Thorium Dating of Tahitian Corals

Abstract

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.

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…Consequently, no site currently has both LGM and PGM coral sea-level estimates. Drill cores from Tahiti, however, have corals from the PGM (Thomas et al, 2009) as well as corals 'bracketing' the LGM (Bard et al, 1996(Bard et al, , 2010Thomas et al, 2009;Deschamps et al, 2012). Tahiti is also unusual in that it has independently constrained subsidence rates (based on radiometrically dated lava flows; Bard et al, 1996;Le Roy, 1994), which e when assumed to be constant through time e help in obtaining good tectonically corrected elevations.…”

“…Tahiti is also unusual in that it has independently constrained subsidence rates (based on radiometrically dated lava flows; Bard et al, 1996;Le Roy, 1994), which e when assumed to be constant through time e help in obtaining good tectonically corrected elevations. A drill core from Tiarei (Tahiti; Thomas et al, 2009) has in-growthposition corals of the same genus (Porites sp.) for the PGM and the end of Marine Isotope Stage 3 (end of MIS 3;~29 ka).…”

Late Pleistocene gray whales (Eschrichtius robustus) offshore Georgia, U.S.A., and the antiquity of gray whale migration in the North Atlantic Ocean

“…With Pleistocene eustatic sea-level changes, the physical locality of JY Reef has experienced multiple submergence and subaerial exposure over the past 1 Ma (Miller et al, 2005;Rohling et al, 2009;Thomas et al, 2009), and these changes also altered the depositional setting at JY Reef. The two gray whale specimens reported here, radiometrically aged to 41 ka and 48 ka, provide two separate indications that the general area of JY Reef was submerged at this time.…”

Sensitivity of Red Sea circulation to sea level and insolation forcing during the last interglacial

“…However, to maintain our records comparable with other studies from the Red Sea, the Gulf of Aden, and the latest sea-level study on the last interglacial (Kopp et al, 2009), we have used the age model of Rohling et al (2008b). Since there is no scientific concordance about the exact stratigraphic location of the MIS 5e boundaries (Shackleton et al, 2003) or their ages (e.g., Imbrie et al, 1984;Winograd et al, 1992;Henderson and Slowey, 2000;Thompson and Goldstein, 2005;Thomas et al, 2009), the boundaries are not used for developing the age model, but are indicated only for visual orientation in the graphics. Following Lisiecki and Raymo (2005) and Rohling et al (2008b), sea-level maximum was set at 123 ka BP and other control points were defined by visual correlation of the benthic foraminiferal δ 18 O record of Lisiecki and Raymo (2005) and the SPECMAP δ 18 O record (Imbrie et al, 1984, Table 1, Fig.…”