Environmental changes of the Okhotsk Sea in the western Pacific since 1.8 Ma
Date Issued
2006
Date
2006
Author(s)
Liu, Ya-Jiun
DOI
zh-TW
Abstract
The Okhotsk Sea located in the northwestern Pacific and also the northeastern Asia is the largest marginal sea in the world and is characterized by seasonal sea-ice. Core MD012414 is collected in the central of the Okhotsk Sea and is the longest sedimentary core in the area. According to the paleomagnetic stratigraphy, the core recorded the environmental changes in the past 1.77 Myrs. The proxies including mineral assemblages, major elements, sea-ice rafted materials and grain size analyses of the core sediments were utilized to discuss the environmental changes. Three mineral assemblages of core sediments can be distinguished and described as followed; the first, terrigenous minerals including quartz and plagioclase; the second, minerals of biogenous shells containing calcite and opal; and the last, the dolomite peaked out in early of interglacial periods of late Quaternary and related to the oxic-reduced condition. Based on the variations of biogenous minerals, the whole core records can be distinguished into four periods. The first period, from 1.77 Ma to 1.25 Ma, the Okhotsk Sea was in a circumstance of high siliceous productivity. The second period, from 1.25 Ma to 0.8 Ma, showed low biogenous mineral contents and represented a severe environment. The third period, from 0.8 Ma to 0.48 Ma, calcite was the major biogenous minerals instead of opal. It implied a different nutrient condition. The fourth period characterized by five 100 kyrs cycling were corresponded to the late Quarternary glacial-interglacial cycles. As the results of major elements, the variations of SiO2/Al2O3 and CaO/Al2O3 were related to opal and calcite, respectively; the ratios of TiO2/Al2O3、Al2O3/Al2O3、Fe2O3/Al2O3 and K2O/Al2O3 were associated with detridus materials, and the ratios of P2O5/Al2O3 and MnO/Al2O3, increased suddenly in the early of deglacial periods of late Quaternary were sensitive to the oxic-reduced conditions. The record of sea-ice rafted materials suggests a change of the sedimentation environment occurred in 0.8 Ma. It may be correlated to the extensive mountain glaciers of Kamchatka when the global atmospheric circulation was in a different condition. The results of grain size analyses of the core sediments showed no close relationships with the variations of mineral and major elements. It infers that the sea-ice rafted materials disturbed the grain size distributions.
Subjects
鄂霍次克海
礦物
環境變遷
Okhotsk sea
minerals
environment changes
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-95-R91224102-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):957e272347b1943fcdf630fb60e43ac6