We used positive thermal ionization mass spectrometry (PTIMS) to generate high precision 11B records in Porites corals of the mid-late Holocene from the South China Sea (SCS). The 11B values of the Holocene corals vary significantly, ranging from 22.2 to 25.5‰. The paleo-pH records of the SCS, reconstructed from the 11B data, were not stable as previously thought but show a gradual increase from the Holocene thermal optimal and a sharp decrease to modern values. The latter is likely caused by the large amount of anthropogenic CO2 emissions since the Industrial Revolution but variations of atmospheric pCO2 cannot explain the pH change of the SCS before the Industrial Revolution. We suggest that variations of monsoon intensity during the mid-late Holocene may have driven the sea surface pH increase from the mid to late Holocene. Results of this study indicate that the impact of anthropogenic atmospheric CO2 emissions may have reversed the natural pH trend in the SCS since the mid-Holocene. Such ocean pH records in the current interglacial period can help us better understand the physical and biological controls on ocean pH and possibly predict the long-term impact of climate change on future ocean acidification.
Liu Yi, Weiguo Liu, Zicheng Peng, Yingkai Xiao, Gangjian Wei, Weidong Sun, Jianfeng He, Guijian Liu, and Chen-Lin Chou, in press. Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals. Geochimica et Cosmochimica Acta. Article (subscription required).
