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| Top two lines show sea levels during the last interglacial were about 9 meters higher than the present [bottom 4 lines] |
Michael J. O’Leary, Paul J. Hearty, William G. Thompson, Maureen E. Raymo, Jerry X. Mitrovica
& Jody M. Webster
& Jody M. Webster
Nature Geoscience (2013) doi:10.1038/ngeo1890
Published online 28 July 2013
Abstract: During the last interglacial period, 127–116 kyr ago, global mean sea level reached a peak of 5–9 m above present-day sea level. However, the exact timing and magnitude of ice sheet collapse that contributed to the sea-level highstand is unclear. Here we explore this timing using stratigraphic and geomorphic mapping and uranium-series geochronology of fossil coral reefs and geophysical modelling of sea-level records from Western Australia. We show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118.1±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. Accounting for glacial isostatic adjustment and localized tectonics, we conclude that eustatic sea level rose to about 9 m above present at the end of the last interglacial. We suggest that in the last few thousand years of the interglacial, a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets and substantial sea-level rise.
Abstract: During the last interglacial period, 127–116 kyr ago, global mean sea level reached a peak of 5–9 m above present-day sea level. However, the exact timing and magnitude of ice sheet collapse that contributed to the sea-level highstand is unclear. Here we explore this timing using stratigraphic and geomorphic mapping and uranium-series geochronology of fossil coral reefs and geophysical modelling of sea-level records from Western Australia. We show that between 127 and 119 kyr ago, eustatic sea level remained relatively stable at about 3–4 m above present sea level. However, stratigraphically younger fossil corals with U-series ages of 118.1±1.4 kyr are observed at elevations of up to 9.5 m above present mean sea level. Accounting for glacial isostatic adjustment and localized tectonics, we conclude that eustatic sea level rose to about 9 m above present at the end of the last interglacial. We suggest that in the last few thousand years of the interglacial, a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets and substantial sea-level rise.
I investigated this subject for my M.S. degree in Earth science (Emporia State University Kansas, 2005).
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On the east coast of Penang Island off Malaysia, I found a wide terrace at about 12 meters, which I presumed was wave-cut during an previous interglacial.
(Penang Island is separated from Sumatra by the Strait of Malacca which is less than 120 meters deep. The island is entirely granite lacking sedimentary platforms. I found another terrace at 2 meters, which marked the Holocene Climate Optimum about 5000 years before the present when sea level was about 2 meters (6 feet) higher than now. There are higher terraces from earlier interglacials. The west coast has less pronounced terraces probably eroded because the prevailing winds are from the west.)
Penang island is rising at about 2 meters per 100,000 years. That means the wave-cut terrace at 12 meters would have been 10 meters above sea level if the land had not risen. That indicates sea-level was 10 meters above the present 100,000 years ago, during the Eemian inter-glacial MIS3.
Ten meters is about 33 feet. Given that my only tools were a map, a satellite image and a GPS unit with altimeter, an error of 4 feet on my part seems right for experimental error.
I find the research reported by O'Leary and others to be convincing. In 2006 Overpeck and others reported sea level as high as 20 feet (6 meters) but the results of O'Leary's team is closer to what I found in my own field work.
http://judithcurry.com/2013/08/30/ice-sheet-collapse/
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