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首页> 外文期刊>Journal of quaternary science: JQS >Sea level at the last glacial maximum, constrained by oxygen isotopic curves of planktonic foraminifera in the Japan Sea
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Sea level at the last glacial maximum, constrained by oxygen isotopic curves of planktonic foraminifera in the Japan Sea

机译：受日本海中浮游有孔虫的氧同位素曲线限制，最后一次冰川期的海平面

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The Japan Sea is connected with the Okhotsk Sea and Northwest Pacific through three straits, viz. Mamiya (Tartarskiy), Soya and Tsugaru, and with the East China Sea through Tsushima Strait, all having sill depths of <140m. Therefore, the Japan Sea was almost isolated from the surrounding seas during the Last Glacial Maximum (LGM; ca. 20ka). As a result of nearly broken communication with the surrounding seas and strengthened surface stratification due to locked fresh water in the basin during the LGM, it became an anoxic basin. This major shift in the surface water properties of the basin left its imprint in the oxygen isotopic composition (δ~(18)O_(PF)) of the planktonic foraminifera. The δ~(18)O_(PF) exhibits extremely low values (～0.5‰ vs. Belemnite from Pedee formation, South Carolina: PDB) during the last two glacial maxima, ca. 20ka (Marine Isotope Stage (MIS) 2.2) and ca. 140ka (MIS 6.2). These decreases are in contrast to the expected generally high glacial values of >3‰ recorded in the MIS 3-4 sections of the studied cores. This observation indicates nearly similar surface water conditions in the Japan Sea during both the previous glacial maxima, and hence suggests negligible effect of strait tectonics on the sea level since the last 140ka. Low δ~(18)O_(PF) values with small amplitude are also observed at the cold stage MIS 6.4, but not observed at another cold stage MIS 4.2. This observation suggests that the low-salinity surface water in the Japan Sea started to develop at the sea level between MIS 4.2 and 6.4. Judging from the cross-section of the Tsushima Strait and the sea floor topography of the East China Sea, the sea level between MIS 4.2 and 6.4 must have been between 90m and 100m below the present. From a proportional relationship between the standard δ18O curve (LR04) in deep-sea cores and globally averaged sea-level change, the eustatic sea level obtained for the LGM is 120±7m below the present. Thus the Japan Sea, in a far-field location from the continental ice sheets, provides an important clue for estimation of the eustatic sea level at the LGM.
机译：日本海通过三个海峡与鄂霍次克海和西北太平洋相连。 Mamiya（Tartarskiy），Soya和Tsugaru，以及通过对马海峡的东中国海，门槛深度均小于140m。因此，在最后一次冰河期（LGM）期间，日本海几乎与周围的海隔绝了。由于在LGM期间流域内的淡水被锁定，与周围海洋的连通几乎中断，地表分层增加，因此成为缺氧流域。流域地表水性质的这一主要变化使它在浮游有孔虫的氧同位素组成（δ〜（18）O_（PF））中留下了印记。在最后两个冰期最大值期间，δ〜（18）O_（PF）表现出极低的值（相对于南卡罗来纳州Pedee形成的贝伦石：PDB）约为0.5‰。 20ka（海洋同位素阶段（MIS）2.2）和140ka（MIS 6.2）。这些减少与所研究岩心的MIS 3-4部分中记录的通常较高的冰川值> 3‰相反。这项观测结果表明，在先前的两次冰期最大值期间，日本海的地表水状况几乎相似，因此表明自从最后一个140ka以来，海峡构造对海平面的影响可忽略不计。在冷态MIS 6.4处也观察到低的δ〜（18）O_（PF）值，幅度较小，而在另一个冷态MIS 4.2处没有观察到。该观察结果表明，日本海的低盐度地表水开始在MIS 4.2和6.4之间的海平面上发展。从对马海峡的横截面和东海的海底地形来看，MIS 4.2和6.4之间的海平面必须比现在低90m至100m。从深海核心区的标准δ18O曲线（LR04）与全球平均海平面变化之间的比例关系来看，LGM所获得的近海平面比目前低120±7m。因此，在远离大陆冰盖的远场位置的日本海，为估算LGM的欣喜海平面提供了重要线索。

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