缺氧水域
地质学
全新世
海湾
海洋学
沉积岩
河口
总有机碳
沉积物
盐度
海平面
河流
沉积作用
地球化学
古生物学
环境化学
构造盆地
化学
作者
Jaesoo Lim,Sangheon Yi,Youngeun Kim
摘要
Abstract Coastal evolution is influenced by past sea-level changes and resultant shifts from fluvial- to marine-dominant environments and the accompanying significant geochemical and isotopic changes in the water mass and sediments. We investigated the elemental and isotopic features of coastal sedimentary cores (27 m in length) from a small paleo-bay located on the southern coast of Korea to determine such geochemical variability and specify past changes in the bay environment and anoxic conditions and possible links to past climate changes. We analyzed total organic carbon (TOC), total sulfur (TS), their isotopes (δ 13 C TOC and δ 34 S TS ), and pyrite. The δ 13 C TOC values ranging from −25 to −19‰ (a proxy for terrestrial influence) were lower than average (−22.5‰) before 8300 cal yr BP and since 500 cal yr BP, while the intervening Early to Late Holocene showed higher δ 13 C TOC values, indicating a shallow coastal environment. The δ 34 S TS values fluctuating between −35 and +5‰ resembled sedimentation rate change. Based on the changes in the ratios of TOC to TS (C/S ratios), sedimentation rate, and δ 34 S TS , we found five possible periods with higher salinity and intensified anoxic conditions at millennial timescales: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP. These intensified anoxic conditions seem to have been influenced by increased air temperature and sea-surface temperature conditions, which could have intensified the intensity of thermal stratification (less ventilation and mixing) between surface and bottom waters and resultant anoxic conditions.
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