Evaluation of ocean acidification rate in the South China Sea using B isotopic compositions in corals over the past 300 years and development of B macro-sublimation technique

  • 王 子豪

Student thesis: Master's Thesis


Ocean acidification (OA) caused by the uptake of elevated atmospheric CO2 can impact profoundly on the physiology of marine calcifiers and entire ocean ecosystem Due to the spatial and temporal limitation on currently available seawater pH records the actual variability and ocean acidification rate are poorly known Especially only a few centennial-scale seawater pH record studies were conducted in the South China Sea (SCS) and western Pacific Ocean region Here we provide a 300-year Porites sp coralline δ11B record from Xisha Islands northern SCS The collection selection and storage of coral samples were performed carefully to avoid potential contamination Based on the X-ray photographs and U-Th dating technique the coral samples spanning from 1680 AD to 1960 AD were sub-sampled manually in 5-year time resolution Boron isotopic determination methodology was systematically evaluated with δ11B-known referential materials including in-house standard Alfa-B and coral standard JCp-1 i e cleaning protocols instrumental stability and accuracy purifying technique and reproducibility of coralline δ11B records The results of above assessment suggest that our δ11B data are reliable and applicable and the analytical uncertainties of δ11B in JCp-1 (24 3±0 4?) were equal to an uncertainty of ~0 05 pH unit (2SD) in pH reconstruction The δ11B values of corals ranged from 21 4? to 26 0? corresponding to seawater pH range between 7 74 and 8 38 The seawater pH variation could be divided into three stages i e (1) 1680-1855 AD at a OA rate of -0 00005 pH unit/yr; (2) 1860-1877 AD with OA rate -0 0228 pH unit/yr; (3) 1882-1960 AD at a OA rate of -0 0014 pH unit/yr Our δ11B data covaried with other western Pacific coral δ11B record at most of the time reflecting the global ocean-air interaction of increasing atmospheric CO2 During 1850 AD to 1960 AD the OA rates in the SCS area (-0 0004~-0 0021 pH unit/yr) were higher than that in the Great Barrier Reef(GBR) region (+0 0003~+0 0006 pH unit/yr) The OA rate was the highest one in Xisha Islands at a value of -0 0021 pH unit/yr The preliminary results suggest that ocean acidification occurred heterogeneously in the time period 1850 AD to 1960 AD soon after the Industrial Revolution The northern SCS region tended to be a sink of atmospheric CO2 whereas the GBR region tended to be a source of CO2 Regional ocean-air interaction or other controlling factors are possible explanations of the differences mentioned above and require further assessments Regarding to the small volume (~50μL) limitation on currently applicable micro-sublimation protocol here we developed a novel macro-sublimation technique with two new-designed devices The preliminary results show that a ten-fold improvement on sample volume is achievable and provided the settings of optimal performance for two devices By applying the novel technique additional dilutions after sublimation are not required and the boron isotopic determination can be done on samples with lower boron concentration Further investigations and experiments are still necessary for a systematic evaluation of the technique
Date of Award2016 Aug 31
Original languageEnglish
SupervisorChen-Feng You (Supervisor)

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