Diatom, silicoflagellate and ebridian biostratigraphy and paleoceanography in IODP 323 Hole U1343E at the Bering slope site

作者：Teraishi A^*; Suto I; Onodera J; Takahashi K

来源：Deep Sea Research Part II: Topical Studies in Oceanography , 2016, 125: 18-28.

DOI：10.1016/j.dsr2.2013.03.026

• IODP Expedition 323 Hole U1343E
• Bering Sea
• Pleistocene-Pliocene
• Diatoms
• Silicoflagellate
• Ebridian
• Paleoceanography
• Biostratigraphy

Integrated Ocean Drilling Program (IODP) Expedition 323 was dedicated to reconstruct the details of the Pliocene-Pleistocene paleoenvironmental conditions of the Bering Sea. In this study, fossil diatom assemblages from Hole U1343E were investigated to define diatom biostratigraphy and reveal paleoceanography of the Bering slope region throughout Pleistocene. As the results, four diatom zones with Neogene North Pacific Diatom zone codes (NPD) were determined from the Neodenticula seminae Zone (NPD 12) to the N. koizumii Zone (NPD 9). Diatom biohorizons defined in this study closely correspond with onboard data, but the distinct difference is recognized at the top of the N. koizumii. Additional four biostratigraphic zones estimated by three silicoflagellate and one ebridian datums suggest the core sediment age younger than 2.5 Ma. The fluctuations of several paleoenvironmental diatom indicators show that cold conditions with sea-ice existed throughout the duration of the interval studied as well as sea ice expansion occurred at ca. 1.9 Ma and ca. 0.9 Ma. Moreover, increases of neritic diatom species reveal a drop in sea level. Neodenticula seminae is the diatom tracer of the Aleutian Current and hence the decrease of this taxon suggests decrease in inflow of the North Pacific water mass. Although the sea levels must have been dropped during the cold time interval, the consistent occurrences of N. seminae indicate that the surface water circulation in the Bering Sea was significantly influenced by the Alaskan Stream at ca. 1.9 Ma. On the other hand, during the other cooling event at ca. 0.9 Ma, which corresponds to the mid-Pleistocene transition (MPT) event, an increase of neritic diatom species and decrease of N. seminae were observed. This suggests that coastal environmental conditions accompanied the sea level drop and that the inflow from the North Pacific was weakened. The increases of sea-ice and neritic diatom species suggest that the sea ice and coastal conditions were developed after the cooling at 0.9 Ma. The ages at remarkable changes of silicoflagellate assemblages correspond to the ages of global climate shifts at ca. 1.4 Ma, 1.25 Ma, and 0.8-0.9 Ma. The unusual alternate dominances of Distephanus medianoctisol in glacial and Dictyocha species in interglacial periods during the 1.25-0.8 Ma interval suggest the north-south migration of water masses between the Bering Sea and the Subarctic North Pacific.

• 出版日期2016-4