Millennial-scale variations of late Pleistocene radiolarian assemblages in the Bering Sea related to environments in shallow and deep waters
- 標題
- Millennial-scale variations of late Pleistocene radiolarian assemblages in the Bering Sea related to environments in shallow and deep waters
- 作者
- Takuya Itaki, Sunghan Kim, Stephan F. Rella, Masao Uchida, Ryuji Tada, Boo-Keun Khim
- 文件屬性
- 國外期刊
- 知識分類
- 基礎研究
- 出版年
- 2012
- 刊名
- Deep Sea Research Part II
- 關鍵字
- Paleoceanography; Micropaleontology; Dansgaard–Oeschger cycles; Melt-water discharge; Ventilation; Productivity; Radiolaria; Bering Sea
- 點閱數
- 2312
摘要
A high-resolution record of the radiolarian assemblage from 60 to 10 ka was investigated using a piston core (PC-23A) obtained from the northern slope of the Bering Sea. Faunal changes based on the 29 major radiolarian taxa demonstrated that the surface and deep water conditions in the Bering Sea were related to the orbital and millennial-scale climatic variations known as glacial–interglacial and Dansgaard–Oeschger (D–O) cycles, respectively. During interstadial periods of the D–O cycles, the assemblage was characterized by increases in the high-latitude coastal species Rhizoplegma boreale and the upper-intermediate water species Cycladophora davisiana, while the sea-ice related species Actinomma borealeand A. leptodermum and many deep-water species such as Dictyophimus crisiae and D. hirundo tended to be reduced. This trend was more apparent in two laminated intervals at 15–13.5 and 11.5–11 ka, which were correlated with well-known ice-sheet collapse events that occurred during the last deglaciation: melt-water pulse (MWP)-1A and MWP-1B, respectively. The radiolarian faunal composition in these periods suggests that oceanic conditions were different from today: (1) surface water was affected by increased melt-water discharge from continental ice-sheet, occurring at the same time as an abrupt increase in atmospheric temperature, (2) upper-intermediate water (ca. 200–500 m) was well-ventilated and organic-rich, and (3) lower-intermediate water (ca. 500–1000 m) was oxygen-poor. Conversely, the sea-ice season might have been longer during stadial periods of the D–O cycles and the last glacial maximum (LGM) compared to the interstadial periods and the earliest Holocene. In these colder periods, deep-water species were very abundant, and this corresponded to increases in the oxygen isotope value of benthic foraminifera. Our findings suggest that the oxygen-rich water was present in the lower-intermediate layer resulting from intensified ventilation.