Investigating spatio-temporal variability of initial 230Th/232Th in intertidal corals

Hong-Wei Chiang; Belle E. Philibosian; Aron J. Meltzner; Chung-Che Wu; Chuan-Chou Shen; R. Lawrence Edwards; Chih-Kai Chuang; Bambang W. Suwargadi; Danny H. Natawidjaja

doi:10.1016/j.quascirev.2023.108005

USGS · 70242042

Investigating spatio-temporal variability of initial 230Th/232Th in intertidal corals

Hong-Wei Chiang·Belle E. Philibosian·Aron J. Meltzner·Chung-Che Wu·Chuan-Chou Shen·R. Lawrence Edwards·Chih-Kai Chuang·Bambang W. Suwargadi·Danny H. Natawidjaja

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Abstract

One of the key factors in obtaining precise and accurate 230 Th ages of corals, especially for corals with ages less than a few thousand years, is the correction for non-radiogenic 230 Th based on an initial 230 Th/ 232 Th value ( 230 Th/ 232 Th 0 ). Studies that consider coral 230 Th/ 232 Th 0 values in intertidal environments are limited, and it is in these environments that corals have Th concentrations 100–1000 times greater than open-ocean corals. Here we present 66 reconstructed U–Th isochrons of modern and Holocene Porites lutea and lobata corals from throughout the Sumatran forearc islands (SFI). Mean square of weighted deviates ( MSWD ) is used to evaluate the variabilities of 28 location-specific 230 Th/ 232 Th0 values before the regional mean. Results show no significant spatial difference between the means of 3.1 ± 3.2 × 10 −6 for the northern SFI and 4.7 ± 1.3 × 10 −6 for the southern SFI. Using the weighted mean of 4.3 ± 2.5 × 10 −6 for all islands has the advantage that no data need be subjectively excluded in the calculation of reliable 230 Th ages, where a local initial value is unknown. There were no clear centennial to millennial time-scale changes in 230 Th/ 232 Th 0 in the past 2500 years. This study, therefore, suggests a reliable value of initial 230 Th/ 232 Th ratio in intertidal environments.

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Hong-Wei Chiang, Belle E. Philibosian, Aron J. Meltzner, Chung-Che Wu, Chuan-Chou Shen, R. Lawrence Edwards, Chih-Kai Chuang, Bambang W. Suwargadi, Danny H. Natawidjaja. 2023. Investigating spatio-temporal variability of initial 230Th/232Th in intertidal corals. https://doi.org/10.1016/j.quascirev.2023.108005

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