Holocene sea level instability in the southern Great Barrier Reef, Australia: high-precision U–Th dating of fossil microatolls
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Three emergent subfossil reef flats from the inshore Keppel Islands, Great Barrier Reef (GBR), Australia, were used to reconstruct relative sea level (RSL). Forty-two high-precision uranium–thorium (U–Th) dates obtained from coral microatolls and coral colonies (2σ age errors from ±8 to 37 yr) in conjunction with elevation surveys provide evidence in support of a nonlinear RSL regression throughout the Holocene. RSL was as least 0.75 m above present from ~6500 to 5500 yr before present (yr BP; where “present” is 1950). Following this highstand, two sites indicated a coeval lowering of RSL of at least 0.4 m from 5500 to 5300 yr BP which was maintained for ~200 yr. After the lowstand, RSL returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yr BP at all three sites. A second possible RSL lowering event of ~0.3 m from ~2800 to 1600 yr BP was detected before RSL stabilised ~0.2 m above present levels by 900 yr BP. While the mechanism of the RSL instability is still uncertain, the alignment with previously reported RSL oscillations, rapid global climate changes and mid-Holocene reef “turn-off” on the GBR are discussed.
KeywordsSea level Holocene Great Barrier Reef Microatoll Uranium–thorium Reef hiatus
We thank C. Murray-Wallace and one anonymous reviewer for their comments which improved this manuscript. Also Hannah Markham, Mauro Lepore, Martina Prazeres, Ian Butler and others involved in fieldwork, the crew of MV Adori, and A.D. Nguyen. This study was funded by the National Environmental Research Programme Tropical Ecosystems Hub Project 1.3 to J-xZ, JMP, SGS, TRC, Y-xF and others, Australian Research Council Linkage, Infrastructure, Equipment and Facilities (LIEF) grant (LE0989067 for the MC-ICP-MS) to J-xZ, JMP, Y-xF and others, and an Australian Postgraduate Award to NDL. Samples were collected under permit G12/34,979.1.
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