Influence of relative sea level on a marginal sea environment and its implication for reconstructing ice volume changes using IODP Expedition 346, Site U1427

Thursday, 18 December 2014
Takuya Sagawa, Kyushu Univ, Fukuoka, Japan, Ryuji Tada, University of Tokyo, Bunkyo-ku, Japan, Richard W Murray, Boston Univ, Boston, MA, United States and Carlos A Alvarez Zarikian, Texas A&M University, College Station, TX, United States
Pleistocene climate is characterized by glacial-interglacial changes in the ice volume. Reconstruction of ice volume is essential for understanding past climate change and is usually based on variations in the oxygen isotope composition of benthic foraminifera shells, which in turn are influenced by bottom water temperature. Another approach is to use the oxygen isotope composition of planktonic foraminifer in semi-enclosed seas, where the surface environments are sensitive to sea level change. The oceanographic condition at the sea north of Japanese islands is also largely influenced by the eustatic change. The Japanese islands and inter island shallow straits (sill depth less than 130 m) limit seawater exchange between the North Pacific and the marginal seas. The oxygen isotope record in this area show a unique feature and is a candidate for reconstructing global sea level history.

During the Integrated Ocean Drilling Program (IODP) Expedition 346 “Asian Monsoon” (29 July–27 September 2013), a shallow marine sediment sequence was recovered from the slope of north coast of western Japan, Site U1427. The shipboard data highlight the sediment contains well-preserved foraminifer and has high sedimentation rate of ~40 cm/kyr. A complete splice down to ~400 m provides the potential for a continuous record for the last ~1.4 Ma. Preliminary isotope results show isotopic variations correspond to lithological change and therefore show similar variation to physical properties of the sediment, such as bulk density, natural gamma ray, and so on. The result suggests that the oxygen isotope of foraminifer in this area may provide key information on past global ice volume changes.