Mid-Holocene sea-level and coral reef demise: U-Th dating of subfossil corals in Moreton Bay, Australia

Abstract

It is increasingly apparent that sea-level data (e.g. microfossil transfer functions, dated coral microatolls and direct observations from satellite and tidal gauges) vary temporally and spatially at regional to local scales, thus limiting our ability to model future sea-level rise for many regions. Understanding sealevel response at 'far-field' locations at regional scales is fundamental for formulating more relevant sea-level rise susceptibility models within these regions under future global change projections. Fossil corals and reefs in particular are valuable tools for reconstructing past sea levels and possible environmental phase shifts beyond the temporal constraints of instrumental records. This study used abundant surface geochronological data based on in situ subfossil corals and precise elevation surveys to determine previous sea level in Moreton Bay, eastern Australia, a far-field site. A total of 64 U-Th dates show that relative sea level was at least 1.1 m above modern lowest astronomical tide (LAT) from at least ˜6 600 cal. yr BP. Furthermore, a rapid synchronous demise in coral reef growth occurred in Moreton Bay ˜5 800 cal. yr BP, coinciding with reported reef hiatus periods in other areas around the Indo-Pacific region. Evaluating past reef growth patterns and phases allows for a better interpretation of anthropogenic forcing versus natural environmental/climatic cycles that effect reef formation and demise at all scales and may allow better prediction of reef response to future global change.

Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes

“…Corals currently grow primarily around islands in the southern part of the bay, but true reef development to sea level is absent (Lybolt et al, 2011). However, Holocene reef growth was much more widespread and major fringing reefs occupied the western shores of the bay between Wellington Point and Cleveland (Leonard et al, 2013). The locations of corals used in this study are shown in Fig.…”

“…2. They were recovered from various points along the western margin of the bay from Wellington Point to Cleveland and from Peel, Goat, Coochiemudlo, and Macleay islands, which extend the distribution across the bay (Lybolt et al, 2011;Leonard et al, 2013). Griffin (1993, 1999) measured 14 C content in biannual coral samples from Heron Island (23 • S, 152 • E) and Abraham Reef (22 • 06 S, 153 • 00 E) in the southern GBR.…”

Temporal overlap of humans and giant lizards (Varanidae; Squamata) in Pleistocene Australia

“…UeTh dating (also known as U-series dating or 238 Ue 234 Ue 230 Th disequilibrium dating) is an isotopic dating technique commonly used to determine the age of carbonate materials, such as speleothem and coral (Price et al, 2009a;Yu et al, 2012;Leonard et al, 2013). The dating method is based on the decay of 238 U to stable 206 Pb via intermediate daughter isotopes, such as 234 U (with a half-life of 245,250 ± 490 years, see Cheng et al, 2000) and 230 Th (with a half-life of 75,690 ± 230 years).…”

Discarding the evidence: The place of natural resources stewardship in the creation of the Peel Island Lazaret Midden, Moreton Bay, southeast Queensland

“…The large barrier islands of Moreton Bay are sand islands, formed as a result of sand mobilisation and accretion as sea-level rose and fell throughout the Pleistocene (Leonard et al, 2013). Peel Island, however, is a rocky land mass, and would have been a high point on the Moreton plain at times of low sea-level, just as it is a prominent island at times of high sea-level.…”