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Development of Paleoceanographic Proxy for Sea Ice and Analysis of Historical Variation in Okhotsk Sea Ice.

海冰古海洋学代理的开发和鄂霍茨克海冰历史变化分析。

基本信息

批准号：
12440151
负责人：
NAKATSUKA Takeshi
金额：
$ 9.6万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

Sea ice influences climate system on Earth through several ways such as increasing the surface albedo, interfering air-sea heat exchanges and driving thermo-haline circulations in ocean. The purpose of this study is to investigate historical variation in the sea ice of the Sea of Okhotsk, which is now located at lowest latitude in the world. Firstly, we had developed paleoceanographic proxies for Okhotsk sea ice, and applied them to sediment cores. We attempted to utilize two kinds of proxies. One was a group of characteristic biomarkers in diatom (main species of ice algae), Highly Branched Isoprenoids (HBI), and the other was terrigenous clastic materials transported by sea ice, Ice Rafted Debris (IRD). Unfortunately, we could not apply HBI for the reconstruction of Okhotsk sea ice because HBI was not found in sediments of the Sea of Okhotsk. However, comparison between time-series data of sinking particles collected by sediment traps and satellite observations of seasonal sea ice distribution could demonstrate that the IRD actually drops only during the period of sea ice melting, and IRD could be applied to reconstruct past changes in production and distribution of sea ice in the Sea of Okhotsk. We applied the IRD and many other proxies for paleoceanographic environments to sediment cores in the Sea of Okhotsk, and have obtained following results. 1) In glacial periods, sea ice expanded frequently according to global cooling events known as Heinrich Events. 2) During a warm period of early and middle Holocene (9000-6000 yrs BP), sea ice was more abundant rather than today. Micropaleontological and geochemical data clarified that during early and middle Holocene Coccolithopholid dominated diatom under the warm and less saline circumstance at that time. These facts suggest a possibility that in Holocene the Okhotsk sea ice has expanded not by cooling but due to freshening of seawater.

海冰通过增加地表反照率、干扰海气热交换和驱动海洋热盐环流等方式影响地球气候系统。本研究的目的是调查鄂霍次克海海冰的历史变化，鄂霍次克海现在位于世界上最低的纬度。首先，建立了鄂霍次克海冰古海洋学代用指标，并将其应用于沉积物岩心。我们尝试使用两种代理。一类是硅藻（冰藻的主要种类）中的一类特化生物标志物——高支异戊二烯类（HBI），另一类是海冰运输的陆源碎屑物质——冰筏碎屑（IRD）。不幸的是，由于在鄂霍次克海的沉积物中没有发现HBI，我们无法将HBI用于鄂霍次克海冰的重建。然而，将沉积物捕集器收集的沉降颗粒时间序列数据与海冰季节性分布的卫星观测数据进行比较，可以发现IRD实际上只在海冰融化期间下降，并且可以应用IRD重建鄂霍次克海海冰的产生和分布的过去变化。将IRD和其他古海洋环境指标应用于鄂霍次克海沉积物岩心，得到了以下结果：2)在全新世早期和中期（距今9000-6000年）的温暖期，海冰比现在更丰富。微古生物学和地球化学资料表明，在早、中全新世时期，在温暖、低盐环境下，硅藻以球石藻为主。这些事实表明，全新世鄂霍次克海冰的扩大可能不是由于冷却，而是由于海水变新鲜。