The biogenic silica variation and paleoproductivity evolution in the eastern Indian Ocean during the past 20 000 a Yonghang Xu 1 *, Liang Wang 1 , Zhikun Lai 1 , Xiaohui Xu 1 , Feng Wang 1 , Shengfa Liu 2, 3 , Xuefa Shi 2, 3 , Rainer Arief Troa 4 , Rina Zuraida 5 , Eko Triarso 4 , Marfasran Hendrizan 6 1 Laboratory of Ocean and Coast Geology, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen 361005, China 2 Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China 3 Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China 4 Marine Research Center, Agency of Research and Human Resources for Marine and Fisheries, Jakarta 14420, Indonesia 5 Marine Geological Institute, Agency for Research and Development for Energy and Mineral Resources, Bandung 40174, Indonesia 6 Research Center for Geotechnology, Indonesia Institute of Sciences, Bandung 40135, Indonesia Received 27 October 2017; accepted 6 February 2018 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract The biogenic silica of sediment samples from Core CJ01-185 which is collected from the eastern India Ocean off the Sunda Strait is analyzed to evaluate the impact of the opening of the Sunda Strait on a paleoproductivity evolution. The new results indicate that the biogenic silica mass values of Core CJ01-185 show the lowest 0.86% in the last glacial period, and reach its maxima of 1.89% in the late Holocene. Furthermore, the biogenic silica mass accumulation rate (MAR BSi ) values also vary with much higher during the late Holocene than during the last glaciation. The input of additional terrigenous materials from the Java Sea has enhanced the paleoproductivity and increased the biogenic silica mass and MAR BSi values after the opening of the Sunda Strait. It is suggested that the paleoproductivity in the study area is mainly influenced by the southeast monsoon and upwelling before the opening of the Sunda Strait. However, the paleoproductivity is dominated by the terrigenous materials input other than by the southeast monsoon or upwelling in the Holocene. Key words: biogenic silica, paleoproductivity, Sunda Strait, eastern India Ocean Citation: Xu Yonghang, Wang Liang, Lai Zhikun, Xu Xiaohui, Wang Feng, Liu Shengfa, Shi Xuefa, Troa Rainer Arief, Zuraida Rina, Triarso Eko, Hendrizan Marfasran. 2019. The biogenic silica variation and paleoproductivity evolution in the eastern Indian Ocean during the past 20 000 a. Acta Oceanologica Sinica, 38(1): 78–84, doi: 10.1007/s13131-019-1372-z 1  Introduction Biogenic silica (BSi) which is mostly composed of siliceous plankton (such as diatom, radiolarian and sponge spicule re- mains), is a major biogenic component of marine sediments. Of these groups of siliceous plankton, diatoms account for the most BSi production. Diatoms are particularly in high-latitude areas and along some continental margins, especially in upwelling areas (De Wever et al., 2002; Karleskint et al., 2012). More than 40% of the global primary production is attributable to diatoms, suggesting a close coupling of the ocean’s silica and carbon cycles (Nelson et al., 1995). Therefore, changes in a BSi abund- ance in sedimentary record is a potentially important paleopro- ductivity proxy (DeMaster, 1991; Ragueneau et al., 1996; Rague- neau et al., 2000). The eastern Indian Ocean (EIO) is the important pathway of heat transfer from the Western Pacific Warm Pool to the Indian Ocean (Qu et al., 2005; Sprintall et al., 2014). The upwelling sys- tem along the Sumatra-Java coast is associated with the mon- soon climate (Fig.1). The upwelling-related high primary pro- ductivity was a major control factor for the observed high carbon and nitrogen contents of surface sediments off southeast Java (Susanto et al., 2001) (Figs 2a and b). In this study, we present a continuous, high-resolution re- cord from Core CJ01-185 collected from eastern India Ocean off the Sunda Strait, and now carried out the biogenic silica and the biogenic silica flux over the past ca. 19 500 a. We attempt to seek a correlation that may inherently exist between biogenic silica and a paleoenvironment condition and the influence of the pa- leoproductivity evolution before and after the opening of the Sunda Strait. 2  Background of the study area The Sunda Shelf between the Indonesian Archipelago and Viet Nam, is one of the largest shelves and has a water depth of   Foundation item: The National Programme on Global Change and Air-sea Interaction under contract Nos GASI-GEOGE-06-03 and GASI-02-IND-CJ01; the China-Indonesia Joint Project under contract No. “BENTHIC”; the Third Institute of Oceanography, Ministry of Natural Resources Research Grant under contract No. 2015015. *Corresponding author, E-mail: xuyonghang@tio.org.cn   Acta Oceanol. Sin., 2019, Vol. 38, No. 1, P. 78–84 https://doi.org/10.1007/s13131-019-1372-z http://www.hyxb.org.cn E-mail: hyxbe@263.net