Extreme flood and main stream swings have exerted significant influences on the sediment records of the Yangtze River delta. However, studies about the influence by the main stream swings to flood sediments remain limited. Based on chronological, sedimentological, and geochemical analysis of a sediment core CJK from outside of the south channel mouth in the Yangtze subaqueous delta, this work establishes the historical records of floods and main stream swings. The results show that the main stream swing periods mainly occurred in 1840-1860 CE (south channel), 1860-1890 CE (north channel), 1900-1927 CE (shift from north to the south channel), 1927-1940 CE (south channel), and 1940-1980 CE (north channel). 4 flood periods (1842-1852, 1922-1938, 1954-1962, and 1970-1983 CE) and 5 extreme floods (1860, 1870, 1890, 1945, and 1950 CE) were identified. Comparing the historical documents with above identified floods indicates that flood events are more easily identified when the main stream shift to the south channel, but not when the main stream shifted to the north channel (except high-magnitude and high-frequency floods). In addition, human activities (e.g. dam constructions) have significantly changed grain size compositions in the Yangtze subaqueous delta after 1980s, which possibly complicated the extraction of flood event signals.
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