日本海末次冰期以来沉积作用和环境演化及其控制要素

Sedimentation and environment evolution of the Sea of Japan since the Last Glaciation and its driving forces

  • 摘要: 基于对日本海南部、中部和西部3个沉积岩芯的综合研究,探讨了末次冰期以来日本海不同区域的沉积作用、环境演化特征及其控制因素。结果发现:在距今8ka以前,日本海南部、中部和西部陆源碎屑物质分别由河流物质、西风携带的风尘物质和海冰输运的物质组成;8ka以来日本海西部沉积物中存在连续分布的火山物质,推测与利曼寒流形成有关,标志着现代日本海表层环流格局的形成。在末次冰期,日本海中部和南部因为水体层化较强,导致底层水通风较弱,而日本海西部则由于盐析作用,通风较强。在冰消期早期,随着海平面上升,东海北部高盐水团再次入侵日本海,改善了日本海深层水体通风条件,但在日本海西部因受到常年海冰覆盖的影响,沉积物氧含量显著减小;在冰消期晚期和早全新世,日本海南部深层水体通风减弱,而在日本海中部和西部通风较好;但8ka以来日本海通风普遍增强。日本海的沉积作用和环境演化受海平面、东亚季风(西风环流)和对马暖流控制,但不同海域对上述3个因子的响应程度存在差异。海平面变化是控制日本海环境变化的首要因子,它直接制约着日本海与周围水体的交换程度;东亚夏季风影响日本海表层水体层化,而东亚冬季风则控制着日本海西部海冰的形成和深层水体垂向对流;8ka以来对马暖流成为控制日本海环境演化的重要因子,它的入侵增强了表层和底层水体交换,提高了日本海深层水体和沉积物溶解氧的更新速率。

     

    Abstract: Sedimentation processes, environmental variations and driving mechanisms of the Sea of Japan since the Last Glaciation are discussed in this paper on the basis of a comprehensive study of three sediment cores retrieved from the southern, central and western parts of the Sea of Japan. The main findings are as follows. (1) Before 8 ka, terrigenous materials in the southern, central and western parts of the Sea of Japan were mainly coming from rivers, westerly wind and sea ice, respectively. The continuous distribution of volcanic materials in the sediments of the western Sea of Japan since 8 ka is probably related to the formation of the Liman Cold Current, which marks the formation of modern surface circulation pattern of the Sea of Japan. (2) The variations in ventilation characterized by oxygen-depletion in the south and central owe its origin to the strong surface stratification, while well-ventilated condition in the western Sea of Japan related to the active winter sea ice formation. With the eustatic sea level rising after the Last Glacial Maximum, cold and salty waters from the northern East China Sea intruded into the Sea of Japan through the Tsushima Strait during the Heinrich Stadial 1, that facilitate the deep ventilation in the south and central Sea of Japan. However, due to the perennial sea ice cover at the western part of the Sea of Japan, the sedimentary oxygenation declined significantly. During the Late Deglaciation and earlier Holocene, the deep ventilation of the Sea of Japan was dampened in the south but well maintained in the central and west. Generally, the deep ventilation in the entire Sea of Japan has been ameliorated since 8 ka due to the invasion of the high-salinity Tsushima Warm Current. Main driving factors controlling the sedimentary processes and environmental changes in the Sea of Japan are sea level changes, East Asian monsoon (and the westerly wind) and the Tsushima Warm Current, but the responses to the three factors are distinct from place to place. Sea level is the first-order factor that constraints the water exchange between the Sea of Japan and surrounding sea waters. The East Asian summer monsoon brings large amounts of freshwater to the Sea of Japan, while the East Asian winter monsoon controls the sea ice formation and thus the deep water convection. Since 8ka, the Tsushima Warm Current, a more important determinant factor, intruded into the Sea of Japan, which enhanced the exchange between surface and deep waters and thus the renewal rate of oxygen in the deep water and sediments.

     

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