Earth Science Frontiers ›› 2018, Vol. 25 ›› Issue (4): 285-298.DOI: 10.13745/j.esf.sf.2018.5.28

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Application of longchain diol and its index as environmental indicators of coastal upwelling regions along eastern Guangdong in the northern South China Sea.

MAO Shengyi,ZHU Xiaowei,JIA Guodong,WU Nengyou   

  1. 1. Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
    2. Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
    3. School of Ocean and Earth Sciences, Tongji University, Shanghai 200092, China
    4. Key Laboratory of Gas Hydrate(Ministry of Land and Resources), Qingdao Institute of Marine Geology, Qingdao 266071, China
  • Received:2017-03-22 Revised:2017-06-05 Online:2018-07-15 Published:2018-07-15

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Abstract:  This study examined three short columnar sediment cores from the summer upwelling region along the east coast of Guangdong, in the northern South China Sea (SCS). Through analyses of diol distribution and quantitative reconstruction of diol environmental parameters, we conducted a preliminary exploration on the sea surface temperature (SST), upwelling activity and evolution of the sedimentary environment, and their mutual interactions, over the last 80 years. The results show that the longchain diol index (LDI) was a good indicator of the annual average SST in the coastal area of eastern Guangdong, where the distribution characteristics from three sediment cores showed an overall SST increase and a similar multiyear timescale trend. In addition, LDISST and diol parameter 2 showed an excellent linear relationship (R2=0.85, n=49), with consistent overall distribution, mean multiyear variations, and El NioSouthern Oscillation (ENSO) cycles. And the majority of high/low values correlated well with ENSO warm/cold cycles or strong/weak years of the SCS summer monsoon. These results indicate that diol parameter 2 can be regarded as a representative indicator of the upwelling strength in eastern Guangdong (multiyear/singleyear timescale). 1,14diol content and ENSO index showed similar fluctuation characteristics on a multiyear timescale, indicating 1,14diol content alone can not reflect information on the multiyear variations of upwelling. Therefore, diol parameter 2 was used for the preliminary reconstruction of upwelling evolution over the last 80 years in eastern Guangdong. The upwelling strength showed an overall increasing distribution trend, with a ~2 to 5year variation cycle; the overall/multiyear distribution characteristics of the 1,15C30 (diol/diol+acyloin) ratio, on the other hand, showed opposing trend with diol parameter 2, possibly a result of resuspension and reoxidation of 1,15C30 diol source due to upwelling activities. Higher 1,15C30 ratio (≥0.82) generally reflects a strong reducing environment, which has a poor correlation with oxygen content in the water body of the upwelling region.

Key words:  northern South China Sea, coastal upwelling regions, longchain diols

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