This study investigates Holocene sedimentary evolution and hypoxia development using borehole cores CJK06 and CJK09, in combination with other published core data. Based on lithology and microfossil (benthic foraminifera) characteristics, seven types of sedimentary facies were identified from the base upward: river, tidal flat, tide-influenced river, transgressive lag, estuary, inner-shelf, and prodelta. Isochronous correlation among the cores was established relying on accelerator mass spectrometry ¹⁴C dates. Facies succession indicates that a weak progradation occurred in coastal environments (12–10 ka BP) due to the Younger Dryas-induced deceleration of sea-level rise; rapid deposition locally occurred in the southern marginal area of tide-dominated estuary environments (10–8 ka BP), likely due to the junction of the Yangtze and Qiantangjiang River currents; and marine current-induced fluid mudflows prevailed in the shallow marine environments (8–1 ka BP), with the cooling climates of 5–1 ka BP. Furthermore, prodelta and shallow marine environments co-occurred with an uneven progradation of the delta within the last 1 ka, while deposition occurred just inside the more southern, delta-influenced area. The occurrence of euryhaline benthic foraminifera suggests that an enhanced freshwater discharge of the mid-Holocene (8–5 ka BP) was followed by a sharp decline in the late Holocene (5–1 ka BP) with climate change. The occurrence of cold-water benthic foraminifera indicates a severe cold-water condition during the mid-Holocene due to the intrusion of upwelling currents triggered by the propelling force of warm currents and summer monsoon winds. In addition, the occurrence of low-oxygen foraminiferal assemblages reveals that hypoxia has developed since 10 ka BP in stages consistent with the sedimentary evolution: localized hypoxia formation coincident with the southern depocenter during the early Holocene (10–8 ka BP); severe hypoxia with enhanced freshwater discharge and upwelling current intrusion during the mid-Holocene; and weakened hypoxia of the late Holocene, mainly due to the sharp decline in freshwater discharge. Within 1 ka BP, freshwater discharge from the approaching river mouth and increased nutrient inputs from enhanced human activities on land have contributed to the prevalence of hypoxia, especially in the southern deltaic area. Overall, it was revealed that the freshwater discharge modulated with climate variations and delta progradation plays a primary role in controlling the sedimentary evolution and hypoxia development during the mid-late Holocene.

这项研究使用钻孔岩心CJK06和CJK09，结合其他已发布的岩心数据，研究了全新世沉积演化和低氧发育。根据岩性和微化石（底栖有孔虫）特征，从底部向上确定了七种沉积相：河流，潮滩，受潮汐影响的河流，海侵滞后，河口，内陆架和三角洲。依靠加速器质谱建立核之间的等时相关¹⁴C日期。相演替表明，由于年轻的得里亚树引起的海平面上升减速，沿海环境（12－10 ka BP）发生了较弱的发育。潮汐为主的河口环境（10-8 ka BP）的南部边缘地区发生了局部快速沉积，这可能是由于长江流与钱塘江流的交汇处所致；在浅海环境（8–1 ka BP）中，海流引起的流体泥浆流普遍存在，冷却气候为5–1 ka BP。此外，前三角洲和浅海环境同时出现在最后1 ka内，三角洲的分布不均匀，而沉积仅发生在受三角洲影响较南部的区域内。欧亚底栖有孔虫的发生表明，全新世中期（8-5 ka BP）的淡水排放量增加，随后的全新世（5-1 ka BP）则随着气候变化而急剧下降。冷水底栖有孔虫的发生表明全新世期间中部出现了严重的冷水状况，这是由于暖流和夏季风的推动推动了上升流的侵入。此外，低氧有孔虫组合的发生表明，从10 ka BP开始，低氧与沉积演化的阶段相一致：全新世早期（10-8 ka BP）与南部沉积中心相吻合的局部低氧形成。全新世中期严重缺氧，淡水排放增加，涌流上升；以及全新世晚期的缺氧减弱，这主要是由于淡水排放量的急剧下降。在1 ka BP内，接近的河口的淡水排放以及陆地上人类活动的增强增加了养分投入，这导致了低氧的流行，特别是在南部三角洲地区。总的来说，揭示了受全新世中期气候变化和三角洲增长调节的淡水排放在控制沉积演化和缺氧发展中起着主要作用。