Deep‐Water Formation in the North Pacific During the Late Miocene Global Cooling
Deep‐Water Formation in the North Pacific During the Late Miocene Global Cooling
复制标题
晚中新世全球变冷期间北太平洋深水的形成
DOI：
10.1029/2020pa003946
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发表时间：
2021-02
影响因子：
3.5
通讯作者：
Lina Zhai;S. Wan;C. Colin;Debo Zhao;Y. Ye;Zhao-jun Song;Xuebo Yin;Xuefa Shi;Anchun Li
中科院分区：
文献类型：
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作者：
Lina Zhai;S. Wan;C. Colin;Debo Zhao;Y. Ye;Zhao-jun Song;Xuebo Yin;Xuefa Shi;Anchun Li
为了追踪日本海和北太平洋晚中新世以来的深水演化，对日本海综合大洋钻探计划（IODP）站点U1425和U1430的沉积物进行了多代理研究，包括有机碳和氮同位素沿着以及主要和微量元素浓度。高的总有机碳（TOC）通量，以及其他已发表的地球化学和沉积证据，表明在日本海缺氧深水的发生在1.74Ma之前。低氮同位素值可能表明几乎完全反硝化。与此相反，生物生产的急剧增加，但减少了埋藏的有机质在20.7.4 -4 Ma，如高富集系数的Ba（BaEF）值，以及低TOC通量，突出了增强的深水充氧在日本海在这段时间。我们认为，在上新世早期日本海半封闭之前，北太平洋的深水地层通过北方深水航道向日本海深处通风。晚中新世全球变冷导致赤道-极地温度梯度同步增加，可能导致中纬度风暴路径南移，加上东亚夏季风减弱和水汽输送减弱，导致中纬度地区降水减少。北太平洋表面盐度的潜在增加可能打破了海洋分层，有利于深水形成，并进一步导致日本海的深水通风。
A multiproxy study including organic carbon and bulk nitrogen isotopes along with major and trace element concentrations in sediments from Integrated Ocean Drilling Program (IODP) Sites U1425 and U1430 in the Japan Sea have been conducted in order to trace deep‐water evolution in the Japan Sea and the North Pacific since the late Miocene. The high total organic carbon (TOC) flux, as well as other published geochemical and sedimentary evidence, indicates the occurrence of anoxic deep‐water in the Japan Sea before ∼7.4 Ma. The low‐nitrogen isotope values probably suggest nearly complete denitrification. In contrast, the sharply enhanced biological production but decreased burial of organic matter during ∼7.4–4 Ma, as shown by high enrichment factor of Ba (BaEF) values, together with low TOC flux, highlights enhanced deep‐water oxygenation in the Japan Sea during that time. We suggest that deep‐water formation in the North Pacific ventilated the deep Japan Sea via northern deep seaways before the sea became semi‐closed in the early Pliocene. The synchronously increased equator‐to‐pole temperature gradients driven by late Miocene global cooling may have caused southward shift of mid‐latitude storm tracks, coupled with the weakened East Asian summer monsoon and moisture transport, leading to decreased precipitation in mid‐latitude regions. The potential increases in surface salinity in the North Pacific may have broken the ocean stratification and favored deep‐water formation, and further caused deep‐water ventilation in the Japan Sea.