Variability in the Holocene marine radiocarbon reservoir effect for the Tropical West Pacific
Dr Quan Hua1, Prof Sean Ulm2, Prof Kefu Yu3,4, Dr Tara Clark5,6, Dr Luke Nothdurft7, Dr Nicole Leonard6, Prof John Pandolfi8, Dr Geraldine Jacobsen1, Prof Jian-xin Zhao6
1Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia, 2ARC Centre of Excellence for Australian Biodiversity and Heritage, College of Arts, Society and Education, James Cook University, Cairns, Australia, 3Guangxi Laboratory on the Study of Coral Reefs in the South China Sea and Coral Reef Research Centre of China, Guangxi University, Nanning, China, 4Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), , China, 5School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, Australia, 6School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia, 7School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane, Australia, 8ARC Centre of Excellence for Coral Reef Studies, School of Biological Sciences, The University of Queensland, Brisbane, Australia
Reliable determination of the marine radiocarbon reservoir effect (e.g., marine radiocarbon reservoir correction (ΔR)) is important for the construction of robust radiocarbon chronologies for marine archives for various research areas including archaeology, palaeoecology, paleoceanography, Quaternary research and climate change studies. In this study, we examined temporal ΔR variability for the South China Sea (SCS) and the Great Barrier Reef (GBR) during the past ~8.1 ka based on ¹⁴C analysis of ²³⁰Th-dated corals.
Coral samples, including Acropora sp., Cyphastrea sp., Favia sp. and Porites sp., were collected from Xisha (or Paracel) Islands and Yongshu Reef, Nansha (or Pratly) Islands in the SCS; Clerke Island, Gore Island, Haggerstone Island, Alexandra Reef and High Island in the northern GBR; and Great Keppel Island in the southern GBR. A total of 44 unaltered coral samples (based on SEM screening, δ²³⁴U and initial ²³⁰Th/²³²Th ratios) were analysed for ²³⁰Th and ¹⁴C. ²³⁰Th dates were determined using a VG Sector-54 thermal ionization mass spectrometer (TIMS) or a Nu Plasma MC-ICP-MS in the Radiogenic Isotope Facility, The University of Queensland, with a precision better than 0.5% (2σ). Subsamples of these dated corals were then taken for radiocarbon analysis using the STAR AMS facility at ANSTO with a typical precision of ~0.3-0.4% (1σ).
Results show large ΔR variations of ~410 yr and ~490 yr for the SCS and the northern GBR at ~5.5-8.1 ka and ~5.5-7 ka, respectively, and a smaller ΔR variability of ~200 yr for the SCS at ~2-3.5 ka. Changes in the sources (or ¹⁴C level) of upwelled waters in the Tropical East Pacific, and variations in Pacific-wide and regional/local ocean circulation associated with climate change might be responsible for these observed ΔR variations . The results of our study also indicate the need for regional marine radiocarbon calibration curves for improved radiocarbon dating of marine samples as the observed Holocene ΔR values for the Tropical Pacific are not fully reproduced by recent modelling work using a 3D ocean model , which takes into account climate change effects. Ocean circulation changes were included in the model for the period 11.5-50 ka but possibly not considered or not well represented for the Holocene, which might explain the differences between the observed and modelled ΔR values.
 Q. Hua, S. Ulm, S., K. Yu, T.R. Clark, L.D. Nothdurft, N.D. Leonard, J.M. Pandolfi, G.E. Jacobsen, J.-x. Zhao, Quat. Sci. Rev. 249 (2020) 106613.
 M. Butzin, P. Köhler, G. Lohmann, Geophys. Res. Lett. 44 (2017) 8473.
Dr. Quan Hua is a Principal Research Scientist within the Environmental Research Theme at the Australian Nuclear Science and Technology Organisation (ANSTO). He has long working experience in radiocarbon dating and its applications in Quaternary and climate change studies. His current research focuses on radiocarbon calibration, and high-resolution proxy records of climate series from coral, speleothems, tree rings and sediments.