Geochemical Journal, Vol. 51 (No. 4), pp. e9-e14, 2017
Hiroto Kajita,1 Atsuko Yamazaki,1,2 Takaaki Watanabe,1 Chung-Che Wu,3 Chuan-Chou Shen3 and Tsuyoshi Watanabe1,2*
1Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
2KIKAI Institute for Coral Reef Sciences, Kikai Town, Kagoshima 891-6151, Japan
3High-Precision Mass Spectrometry and Environment Change Laboratory, Department of Geosciences, National Taiwan University, Taipei 106, Taiwan, R.O.C.
(Received December 31, 2016; Accepted April 26, 2017; Online published June 7, 2017)
Understanding seasonal to interannual characteristics of the climate during the transition from the "Holocene Optimum" (7.0–5.0 kyr BP) to mid-Holocene cold and dry period (4.6–4.0 kyr BP) is important since it is related to the evolution and collapse of human civilization in East Asia. To investigate those characteristics, we reconstructed a seasonal scale sea surface temperature (SST) and measured oxygen isotope ratios (δ18O) in seawater (δ18Oseawater) using modern and fossil (4.9 kyr) corals from Kikai Island. Larger seasonal amplitudes observed among the reconstructed SST values and δ18Oseawater change at 4.9 kyr suggest that the East Asian Monsoon (EAM) circulation might be stronger than the present-day. Our compiled coral records, along with the previous studies from Kikai Island, also suggest that the largest SST amplitude during the Holocene Optimum was recorded at 4.9 kyr and an abrupt cold climate shift occurred during the Holocene Optimum and the Pulleniatina Minimum Event (PME) in the north-western Pacific.
Key words: Mid-Holocene, coral record, paleo-SST, paleo-SSS, Kikai Island