Rapid sea-level fall and deep-ocean temperature change since the last interglacial period

Abstract

We have dated Huon Peninsula, Papua New Guinea and Barbados corals that formed at times since the Last Interglacial Period, applying both ^(230)Th and ^(231)Pa dating techniques as a test of age accuracy. We show that Marine Isotope Stage (MIS) 5e ended prior to 113.1 ± 0.7 kyr, when sea level was −19 m. During MIS 5b sea level was −57 m at 92.6 ± 0.5 kyr, having dropped about 40 m in approximately 10 kyr during the MIS 5c–5b transition. Sea level then rose more than 40 m during the MIS 5b–5a transition, also in about 10 kyr. MIS 5a lasted until at least 76.2 ± 0.4 kyr, at a level of −24 m at that time. Combined with earlier data that places MIS 4 sea level at −81 m at 70.8 kyr, our late MIS 5a data indicate that sea level fell almost 60 m in less than 6 kyr (10.6 m/kyr) during the MIS 5–4 transition. The magnitude of the drop is half that of the glacial–interglacial amplitude and approximately equivalent to the volume of the present-day Antarctic Ice Sheet. During this interval the minimum average rate of net continental ice accumulation was 18 cm/yr, likely facilitated by efficient moisture transport from lower latitudes. At three specific times (60.6 ± 0.3, 50.8 ± 0.3, and 36.8 + 0.2 kyr) during MIS 3, sea level was between −85 and −74 m. Sea level then dropped to −107 m at 23.7 ± 0.1 kyr early in MIS 2, before dropping further to Last Glacial Maximum (LGM) values and then rising to present values during the last deglaciation. Times of rapid sea-level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation, supporting the idea that these factors may have resulted in high water-vapor pressure in moisture sources and efficient moisture transport to high-latitude glaciers, thereby contributing to glacial buildup. We combined our sea-level results with deep-sea δ^(18)O records as a means of estimating the temperature and ice-volume components in the marine δ^(18)O record. This analysis confirms large deep-ocean temperature shifts following MIS 5e and during Termination I. Deep-ocean temperatures changed by much smaller amounts between MIS 5c and 2. Maximum temperature shift in the deep Pacific is about 2°, whereas the shift at a site in the Atlantic is 4°. Under glacial conditions temperatures at both sites are near the freezing point. The shift in the Atlantic is likely caused by a combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form.

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