Tropical Geography

   

Growth Rate of Porites Corals from Tanmen, Hainan Island: Climatic Significance during Mid-Holocene

Yue'er Lia,b,c(), Kefu Yua,b,c,2(), Tingli Yana,b,c, Leilei Jianga,b,c   

  1. 1.a School of Marine Sciences, Guangxi University
    b.Guangxi Laboratory on the Study of Coral Reefs in the South China Sea
    c.Coral Reef Research Center of China, Nanning 530004, China
    2.Southern Marine Sciences and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China
  • Received:2023-04-07 Revised:2023-08-13 Online:2023-09-21
  • Contact: Kefu Yu E-mail:yueeeeeer@126.com;kefuyu@ scsio.ac.cn

Abstract:

Coral growth rate is a physical index that is particularly closely associated with climatic factors such as Sea Surface Temperature (SST). The growth rate is minimally affected by environmental changes and serves as a high-resolution indicator in the study of climatic and environmental variation, making it a useful tool in paleoclimatic coral research. However, previous research on coral growth rate has primarily focused on the modern period, with limited investigation of the Mid-Holocene, which shares similar climatic characteristics with the current warm period. It is especially important to understand the climate and environmental conditions during the Mid-Holocene to gain insight into contemporary climate change processes and mechanisms. To address this gap, we first collected a modern Porites coral core and 23 Mid-Holocene subfossil coral cores from Tanmen, located on the eastern coast of Hainan Island. Using X-ray radiography and image processing methods, we measured and analyzed the coral growth rates of all cores, resulting in the identification of growth rate patterns during the Mid-Holocene. Additionally, by analyzing the environmental factors that impact modern coral (2005-2021 AD), we established a linear relationship between coral growth rate (L) and SST in Tanmen, expressed as SST=2.945±0.237×L+22.481±0.301(1?s.e.). By applying this equation, we reconstructed an annual average SST sequence of 406 years during the Mid-Holocene (6,143-4,356 a BP). The results indicate that the average coral growth rate during the Mid-Holocene was 1.079 cm/a, ranging from 0.607 to 1.670 cm/a, with noticeable fluctuations. The coral growth rate sequence also revealed three consecutive periods of low growth rate, accompanied by a significant increase in interannual variability after 4,515 a BP, resulting in more complex fluctuations. Moreover, the reconstructed SST sequence based on coral growth rate data shows that the mean SST of the Mid-Holocene was 25.7±0.54 ℃, which is comparable to the modern SST in the context of global warming. The average annual SST varied from 24.7 to 26.8℃ in the Mid-Holocene, exhibiting considerable fluctuations between warm and cold periods, and with three distinct periods of low SST at 5,860, 5,660, and 5,160 a BP. This provides detailed insights into the temperature variations during the Mid-Holocene. In addition, a comparison of the spectral cycles of coral growth rates between the modern and Mid-Holocene periods (5,427-5,394, 5,243-5,209, 4,515-4,456, and 4,404-4,356 a BP) revealed significant ENSO cycles of three to seven years, observed in both modern and Mid-Holocene corals. During the Mid-Holocene, the primary ENSO cycle changed: its frequency decreased considerably, indicating that ENSO activity was weaker than that observed in the modern period. However, further statistical analysis utilizing the probability density function (PDF) demonstrated a gradual increase in ENSO variability during this period. The results of this study offer novel insights into tropical climate characteristics of the Mid-Holocene.

Key words: Sea Surface Temperature, ENSO, Mid-Holocene, Coral Growth Rate, Northern South China Sea

CLC Number: 

  • P736.4