Migration of the Antarctic Circumpolar Current in the late Neogene; reconstruction from sediment wave on the Conrad Rise, Indian Sector of the Southern Ocean

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Author(s): Oiwane, H.; Ikehara, M.; Suganuma, Y.; Nakamura, Y.; Nogi, Y.; Miura, H.; Sato, T.
Author Affiliation(s): Primary:
National Institute of Polar Research, Tokyo, Japan
Kochi University, Japan
Japan Agency for Marine-Earth Science and Technology, Japan
National Institute of Advanced Industrial Science and Technology, Japan
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: ACC is the largest and strongest ocean current in the world. It is important for the interoceanic exchange of water, exchange of gases to the atmosphere, and thermal isolation of the Antarctic continent. Fluctuation of the ACC has been reconstructed from several methods such as microfossils, anisotropy of magnetic susceptibilities, and statistical analysis of Ice-Rafted Debris. On the other hand, sediment waves are investigated and interpreted to reconstruct the fluctuation of the bottom- and contour currents. In this study, we tried reconstructing the ACC using sediment waves based on multidisciplinary survey on the Conrad Rise in the Indian sector of the Southern Ocean. The Conrad Rise is a topographic high that is elevated ca. 3000 m from the ocean floor. We conducted multibeam bathymetry, seismic reflection, and sediment coring on the southwestern slope of the rise. Seismic units on the Conrad Rise are divided into three units, A, B, and C in descending order. Unit A shows transparent to low amplitude with sediment wave structure. Sediment waves don't show systematic changes of its dimension and thickness. Sedimentary core showed that the surface sediment is composed of diatom ooze. Unit B shows higher amplitude than that of unit A, and shows planar, parallel configuration. Unit C has high-amplitude reflectors at its top and shows chaotic facies below. Based on morphological characteristics of the sediment waves, oceanographic setting of the Conrad Rise, and components of the surface sediment, it is most likely that the sedimentary structure and component of the Unit A is significantly constrained by the ACC. On the other hand, the Unit B shows planar configuration suggesting deposition without current effect. Additionally, higher amplitude suggests different component form that of the Unit A. These a series of evidence represent difference of sedimentary environment between units A and B, especially on the point of the influence of the ACC. Accordingly, onset of the Unit A deposition is probably accompanied by the placement of the ACC on the Conrad Rise. Extrapolating the surface sedimentary rate of 41.5 cm/kyr (Katsuki et al., 2011) to the bottom of the unit, obtaining ca. 1 Ma as the estimated bottom age. Component of the Unit B is estimated as calcareous ooze deposited in the north of the ACC, based on the correlation with the ODP Site 1093. All these discussions into consideration, we concluded that the ACC have migrated northward to be placed in the present position at ca. 1 Ma, and then diatom ooze of the Unit A started depositing, and also sediment waves are started forming.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Antarctic Circumpolar Current; Atlantic Ocean; Cenozoic; Conrad Rise; Currents; Indian Ocean; Leg 177; Marine sediments; Neogene; ODP Site 1093; Ocean Drilling Program; Ocean currents; Sediments; South Atlantic; Tertiary; Upper Neogene
Coordinates: S495835 S495835 E0055156 E0055156
Record ID: 2014044769
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