Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals

One hundred eighty U–Th data, including 23 isochrons on 24 pristine modern and Holocene corals and 33 seawater samples, were analyzed using sector-field mass spectrometry to understand the variability of initial 230Th/232Th (230Th/232Th0). This dataset allows us to further assess the accuracy and pr...

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Main Authors: Shen, Chuan-Chou, Li, Kuei-Shu, Sieh, Kerry, Natawidjaja, Danny H., Cheng, Hai, Wang, Xianfeng, Edwards, R. Lawrence, Lam, Doan Dinh, Hsieh, Yu-Te, Fan, Tung-Yung, Meltzner, Aron J., Taylor, Fred W., Quinn, Terrence M., Chiang, Hong-Wei, Kilbourne, K. Halimeda
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Language:English
Published: 2012
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Online Access:https://hdl.handle.net/10356/95399
http://hdl.handle.net/10220/8665
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spelling sg-ntu-dr.10356-953992020-03-07T12:45:25Z Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals Shen, Chuan-Chou Li, Kuei-Shu Sieh, Kerry Natawidjaja, Danny H. Cheng, Hai Wang, Xianfeng Edwards, R. Lawrence Lam, Doan Dinh Hsieh, Yu-Te Fan, Tung-Yung Meltzner, Aron J. Taylor, Fred W. Quinn, Terrence M. Chiang, Hong-Wei Kilbourne, K. Halimeda DRNTU::Science::Geology::Volcanoes and earthquakes One hundred eighty U–Th data, including 23 isochrons on 24 pristine modern and Holocene corals and 33 seawater samples, were analyzed using sector-field mass spectrometry to understand the variability of initial 230Th/232Th (230Th/232Th0). This dataset allows us to further assess the accuracy and precision of coral 230Th dating method. By applying quality control, including careful sampling and subsampling protocols and the use of contamination-free storage and workbench spaces, the resulting low procedural blanks give an equivalent uncertainty in age of only ±0.2–0.3 yr for 1–2 g of coral sample. Using site-specific 230Th/232Th0 values or isochron techniques, our study demonstrates that corals with an age less than 100 yrs can be 230Th-dated with precisions of ±1 yr. Six living subtidal coral samples were collected from two continental shelf sites, Nanwan off southern Taiwan in the western Pacific and Son Tra off central Vietnam in the South China Sea; one coral core was drilled from an open-ocean site, Santo Island, Vanuatu, in the western tropical Pacific; and modern and fossil intertidal coral slabs, 17 in total, were cut from six sites around the islands of Simeulue, Lago, North Pagai and South Pagai of Sumatra in the eastern Indian Ocean. The results indicate that the main source of thorium is the dissolved phase of seawater, with variation of 230Th/232Th0 depending on local hydrology. With intense input of terrestrial material, low 230Th/232Th0 atomic ratios of 4.9 × 10−6 and 3.2 × 10−6 with a 10% variation are observed in Nanwan and Son Tra, respectively. At the Santo site, we find a value of 5.6 × 10−6 at 4 horizons and one high value of 24 × 10−6 in a sample from AD 1974.6 ± 0.5, likely due to the upwelling of cold water during a La Niña event between AD 1973 and 1976. The natural dynamics of 230Th/232Th0 recorded in the intertidal corals at sites in the Sumatran islands are complicated so that this value varies significantly from 3.0 to 9.4 × 10−6. Three of the 141 modern coral 230Th ages differ from their true ages by −23 to +4, indicating the presence of detrital material with anomalous 230Th/232Th values. Duplicate measurement of coeval subsamples is therefore recommended to verify the age accuracy. This improved high precision coral 230Th dating method raises the prospects of refining the age models for band-counted and tracer-tuned chronologies and of advancing coral paleoclimate research. 2012-09-28T04:35:57Z 2019-12-06T19:14:04Z 2012-09-28T04:35:57Z 2019-12-06T19:14:04Z 2008 2008 Journal Article Shen, C. C., Li, K. S., Sieh, K., Natawidjaja, D., Cheng, H., Wang, X., et al. (2008). Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals. Geochimica et Cosmochimica Acta, 72(17), 4201-4223. 00167037 https://hdl.handle.net/10356/95399 http://hdl.handle.net/10220/8665 10.1016/j.gca.2008.06.011 en Geochimica et cosmochimica acta © 2008 Elsevier Ltd.
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic DRNTU::Science::Geology::Volcanoes and earthquakes
spellingShingle DRNTU::Science::Geology::Volcanoes and earthquakes
Shen, Chuan-Chou
Li, Kuei-Shu
Sieh, Kerry
Natawidjaja, Danny H.
Cheng, Hai
Wang, Xianfeng
Edwards, R. Lawrence
Lam, Doan Dinh
Hsieh, Yu-Te
Fan, Tung-Yung
Meltzner, Aron J.
Taylor, Fred W.
Quinn, Terrence M.
Chiang, Hong-Wei
Kilbourne, K. Halimeda
Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
description One hundred eighty U–Th data, including 23 isochrons on 24 pristine modern and Holocene corals and 33 seawater samples, were analyzed using sector-field mass spectrometry to understand the variability of initial 230Th/232Th (230Th/232Th0). This dataset allows us to further assess the accuracy and precision of coral 230Th dating method. By applying quality control, including careful sampling and subsampling protocols and the use of contamination-free storage and workbench spaces, the resulting low procedural blanks give an equivalent uncertainty in age of only ±0.2–0.3 yr for 1–2 g of coral sample. Using site-specific 230Th/232Th0 values or isochron techniques, our study demonstrates that corals with an age less than 100 yrs can be 230Th-dated with precisions of ±1 yr. Six living subtidal coral samples were collected from two continental shelf sites, Nanwan off southern Taiwan in the western Pacific and Son Tra off central Vietnam in the South China Sea; one coral core was drilled from an open-ocean site, Santo Island, Vanuatu, in the western tropical Pacific; and modern and fossil intertidal coral slabs, 17 in total, were cut from six sites around the islands of Simeulue, Lago, North Pagai and South Pagai of Sumatra in the eastern Indian Ocean. The results indicate that the main source of thorium is the dissolved phase of seawater, with variation of 230Th/232Th0 depending on local hydrology. With intense input of terrestrial material, low 230Th/232Th0 atomic ratios of 4.9 × 10−6 and 3.2 × 10−6 with a 10% variation are observed in Nanwan and Son Tra, respectively. At the Santo site, we find a value of 5.6 × 10−6 at 4 horizons and one high value of 24 × 10−6 in a sample from AD 1974.6 ± 0.5, likely due to the upwelling of cold water during a La Niña event between AD 1973 and 1976. The natural dynamics of 230Th/232Th0 recorded in the intertidal corals at sites in the Sumatran islands are complicated so that this value varies significantly from 3.0 to 9.4 × 10−6. Three of the 141 modern coral 230Th ages differ from their true ages by −23 to +4, indicating the presence of detrital material with anomalous 230Th/232Th values. Duplicate measurement of coeval subsamples is therefore recommended to verify the age accuracy. This improved high precision coral 230Th dating method raises the prospects of refining the age models for band-counted and tracer-tuned chronologies and of advancing coral paleoclimate research.
format Article
author Shen, Chuan-Chou
Li, Kuei-Shu
Sieh, Kerry
Natawidjaja, Danny H.
Cheng, Hai
Wang, Xianfeng
Edwards, R. Lawrence
Lam, Doan Dinh
Hsieh, Yu-Te
Fan, Tung-Yung
Meltzner, Aron J.
Taylor, Fred W.
Quinn, Terrence M.
Chiang, Hong-Wei
Kilbourne, K. Halimeda
author_facet Shen, Chuan-Chou
Li, Kuei-Shu
Sieh, Kerry
Natawidjaja, Danny H.
Cheng, Hai
Wang, Xianfeng
Edwards, R. Lawrence
Lam, Doan Dinh
Hsieh, Yu-Te
Fan, Tung-Yung
Meltzner, Aron J.
Taylor, Fred W.
Quinn, Terrence M.
Chiang, Hong-Wei
Kilbourne, K. Halimeda
author_sort Shen, Chuan-Chou
title Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
title_short Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
title_full Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
title_fullStr Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
title_full_unstemmed Variation of initial 230Th/232Th and limits of high precision U–Th dating of shallow-water corals
title_sort variation of initial 230th/232th and limits of high precision u–th dating of shallow-water corals
publishDate 2012
url https://hdl.handle.net/10356/95399
http://hdl.handle.net/10220/8665
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