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The Ka'ena Highstand of O'ahu, Hawai'i: Further Evidence of Antarctic Ice Collapse during the Middle Pleistocene

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Title: The Ka'ena Highstand of O'ahu, Hawai'i: Further Evidence of Antarctic Ice Collapse during the Middle Pleistocene
Authors: Hearty, Paul J.
Issue Date: Jan 2002
Publisher: University of Hawai'i Press
Citation: Hearty PJ. 2002. The Ka'ena Highstand of O'ahu, Hawai'i: further evidence of Antarctic ice collapse during the middle Pleistocene. Pac Sci 56(1): 65-81.
Abstract: Marine isotope stage (MIS) 11 may well represent one of the most
significant interglacial highstand events of the past million years. Ocean volume
changes charted from coastal exposures imply partial or complete melting of
some of the world's major ice caps during a middle Pleistocene interglacial. The
coastal geology of both Bermuda and the Bahamas yields evidence of an MIS 11
highstand 20 m higher than present. Further support for this catastrophic episode
in sea-level history is revealed in subtidal and intertidal deposits at +28 ± 2
m in O'ahu, Hawai'i. The stratigraphy, petrology, and uplift history of the Hawaiian
deposits strongly suggest a correlation with MIS 11, and a compilation of
amino acid racemization, uranium/thorium (alpha and mass spectrometry), and
electron spin resonance ages shows a scatter between 300 and 550 kyr. When
corrected for uplift, the Ka'ena Highstand succession at Wai'anae Health Center
(OWH1) reveals a "stepping up" of sea level through the interglaciation,
similar to that described in the Bahamas. Previous studies on O'ahu attributed
all 28 m elevation of the Ka'ena Highstand to uplift since 0.5 Ma, but now it
appears that only 8 m of that was caused by uplift, and the remaining 20 m by
eustatic sea-level rise. These findings from O'ahu strengthen evidence for the
complete disintegration of the Greenland and West Antarctic ice sheets and
partial melting of the East Antarctic ice sheet during the middle Pleistocene. If
the instability of polar ice sheets can be linked to prolonged warm interglaciations
as the data suggest, then existing conservative predictions for the magnitude
of sea-level change by future "greenhouse" warming are seriously underestimated.
ISSN: 0030-8870
Appears in Collections:Pacific Science Volume 56, Number 1, 2002

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