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Oxygen isotopes, sea level changes and the temperature history of a coral reef environment in New Guinea over the last 105years

Palaeogeography Palaeoclimatology Palaeoecology
Publication Date
DOI: 10.1016/0031-0182(86)90101-x
  • Earth Science


Abstract Coral reef terraces consisting of an upward succession of fringing and barrier reef types are preserved on land along the raising coast of Huon Peninsula, New Guinea. Seven coral reef units, I–VII from the coast landwards spaced at about 20-kyr interval, provide a rather complete record of sea levels, oxygen isotopes and temperature of teh surface tropical ocean over the duration of the high sea level events of the last glacial cycle. The systematic sampling of the coral reefs was restricted to the massive Tridacna gigas species (the giant clam) which are about 0.7%0 enriched in 18O relative to calcite equilibrium value and the presence of symbionts seems to have no effect on the δ 18O of their aragonitic skeleton. Sea levels rose rapidly to 5–6.5 m above present during the last interglacial which on stratigraphic grounds and δ 18O compositions can be separated into an early phase whose δ 18O is similar to modern (reef VIIa dated at 138 kyr) and a late phase that is 0.6%0 heavier (reef VIIb dated at 118 kyr). Fringing reefs VI, V, IV, III and II record short-lived high sea levels stands at 107, 85, 60, 45 to 40 and 31 kyr respectively that stopped short of the present sea level (−12, −19, −28, −32 to −42 m). The general decline of the high sea level stands corresponds to an average 18O enrichment of 1.7%0 measured between the early interstadials of isotope stage 5 (VI and V) and the late interstadials of isotope stage 3 (IV, IIIa, IIIb, and II). The maximum 18O enrichment of 1.7%0 relative to present was registered during a regressive phase of reef IIIa. Stratigraphic evidence indicates that sea level lows in the range of −37 to −55 m below present have occurred in between the high sea level stands but those are unlikely to represent the lowest sea levels of the last glacial cycle. Sea levels and δ 18O ddta pair offer important clues regarding the partitioning of ice volume and temperature in δ 18O records. The results suggest that the ice volume effect accounts for the observed δ 18O changes during the early interstadial culminations but only for 29–46% during the late interstadial culminations. Sea water cooling beyond the threshold limit of coral reef growth (∼ 18°C) did not occur during the last glacial cycle. The temperature of the surface tropical ocean was similar to present during the early interstadials of isotope stage 5 and cooler by 3°C below present during the later interstadials of isotope stage 3.

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