Upwelling and anthropogenic forcing on phytoplankton productivity and community structure changes in the Zhejiang coasta
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Upwelling and anthropogenic forcing on phytoplankton productivity and community structure changes in the Zhejiang coastal area over the last 100 years DUAN Shanshan1,2, XING Lei1,2, ZHANG Hailong1,2, FENG Xuwen3, YANG Haili3, ZHAO Meixun1,2* 1
Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education, Qingdao 266100, China 2 Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China 3 Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China Received 24 October 2013; accepted 24 March 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores (#34: 28.5°N, 122.272°E; CJ12-1269: 28.861 9°N, 122.515 3°E) from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970s and increased rapidly after the late 1990s at Site #34; and it started to increase gradually from the middle 1960s and increased rapidly after the late 1980s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B (dinosterol/brassicasterol) ratio of Core #34 since the 1960s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios. Key words: biomarkers, phytoplankton community structure, Min-Zhe coastal mud area, Changjiang Diluted Water, upwelling Citation: Duan Shanshan, Xing Lei, Zhang Hailong, Feng Xuwen, Yang Haili, Zhao Meixun. 2014. Upwelling and anthropogenic forcing on phytoplankton productivity and community structure changes in the Zhejiang coastal area over the last 100 years. Acta Oceanologica Sinica, 33(10): 1–9, doi: 10.1007/s13131-014-0535-1
1 Introduction Due to enhanced human activity, the Changjiang River (CR) drainage basin has experienced significant changes during the past century, and these changes have affected both the environments and ecosystem of the Changjiang River Estuary (CRE) (Liu
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