The coral record of last interglacial sea levels and sea surface temperatures

The rise and fall of the Last Interglacial (LI) sea levels and sea surface temperatures (SSTs) are evaluated using U-series dating combined with Sr/Ca ratios in corals from both stable and tectonically uplifted sites. Along t he stable coastal margin of Western Australia, an extensive series of LI co ral reefs occur at heights of 2-3 m above present-day sea level. These cora ls have a very tight cluster of U-234-Th-230 ages ranging from 129 +/- 1 to 119 +/- 1 ka, as well as a narrow range of initial delta(234)U values of 1 50 +/- 5, similar to modem seawater. Bahamas, which is also a stable site, has an essentially identical pattern of U-series ages from 130 +/- 1 to 120 +/- 1 ka. Barbados and Huon Peninsula are tectonically active sites where the LI terraces are found at elevations of > 50 and > 200 m, respectively. U-series ages from corals exposed in the lower footwall of these uplifted r eefs, allow better constraints to be placed on the rate of sea level rise w hich initiated the LI. Corals from the Huon Peninsula constrain sea level a t - 80 +/- 10 m at 131 +/- 2 ka, and from Barbados, at - 30 +/- 5 m at 129 +/- 1 ka. Combined with constraints from stable sites, these observations r equire an exceedingly rapid rise in sea level of 30-50 m per 1000 years at 130 +/- 1 ka. This indicates that large-scale catastrophic melting of the o nce massive continental ice sheets occurred in phase with the rapidly incre asing northern hemisphere (NH) summer insolation, consistent with the orbit al forcing being the main driver of glacial-interglacial climate change. Th ere is also some evidence from Huon Peninsula, although still not conclusiv e, for a precursor oscillation in sea level during the penultimate deglacia tion, that may have been within similar to - 20 m of present-day levels at similar to 135 ka. SSTs for the LI Porites corals from the Huon Peninsula and Western Australi a have mean annual temperatures and seasonal ranges that are remarkably sim ilar to present-day patterns. The tropical site of Huon Peninsula has SSTs of 29 +/- 1 degrees C, which is indistinguishable from the SSTs given by mo dem corals. At Ningaloo Reef in Western Australia, similar mean annual (sim ilar to 24 degrees C) and summer maximum SSTs of 27-29 degrees C are found in both LI and modem corals. The only significant difference is the similar to 1 degrees C cooler winter minimum SSTs of similar to 21 degrees C for t he LI compared to present-day minimums of similar to 22 degrees C. LI SSTs from these southern hemisphere (SH) sites were thus very similar, or at mos t, only slightly cooler than today, despite sea levels being up to 4 m high er. This maybe indicative of asymmetric warming of the Earth, with the incr eased NH insolation during the LI period being responsible for the extensiv e melting of the mainly NH-based ice sheets, and hence, higher global sea l evels. The observation of relatively high sea levels in the LI, together wi th the rapid pulses of sea level rise, indicates that the potential now exi sts for greenhouse warming to initiate increases in sea level of at least s everal metres on relatively short time-scales (10(2) years). (C) 2000 Elsev ier Science B.V. All rights reserved.