[M-IS02] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS02-06] Occurrence of IOD-like long-term transition in the NE tropical Indian Ocean during the mid-Brunhes dissolution interval

*高田 裕行¹、Boo-Keun Khim²、Kiseong Hyeong³、Inha Seo⁴、Youngsook Huh⁵、朝日 博史⁶、Jongmin Lee⁷、瀬戸 浩二⁸ (1.Institute of Geologic Hazard and Industrial Resources、2.Department of Oceanography, Pusan National University、3.Global Ocean Research Center, Korean Institute of Ocean Science and Technology、4.Department of Earth and Environmental Sciences, Jeonbuk National University、5.School of Earth and Environmental Sciences, Seoul National University、6.Center for Advanced Marine Core Research, Kochi University、7.Deep-sea Mineral Resources Research Center, Korea Institute of Ocean Science and Technology、8.Estuary Research Center, Shimane University)

キーワード：benthic foraminifera、faunal analysis、food supply、upwelling

We investigated Quaternary benthic foraminifera in cores GPC04 and GPC03 (2991 m and 3650 m water depth, respectively; ~5ºN and ~90ºE) in the northeast tropical Indian Ocean (TIO) to elucidate the relationship between the surface and deep oceans during the mid-Brunhes dissolution interval, concerning on the occurrence of the Indian Ocean Dipole mode (IOD)-like long-term transition since ~520 ka. Several studies noted various impacts of the IOD in the TIO to global climates (Yamagata et al., 2004). Recently, Abram et al. (2020) reported IOD-like phenomena during the late Holocene in the TIO, mainly based on oxygen isotope of corals, emphasizing the importance of the IOD-like variations even in the geological past.

Benthic Foraminifera Accumulation Rate (BFAR) at our two study sites increases gradually during late MIS 9 to early MIS 7. This timing is roughly in synchronous to the intensified upwelling at ODP Site 758 (close to core GPC04 site) that is inferred by %Globigerina bulloides (Chen and Farrell, 1991). Gupta et al. (2010) reported that %G. bulloides at ODP Sites 723 and 728 (western Arabian Sea) generally increased since ~300 ka, in contrast to its decrease at ODP Site 758. These opposite changes in %G. bulloides between the Southern Bay of Bengal (northeast TIO) and the western Arabian Sea (northwest TIO) across ~300 ka would represent the dipole pattern of the upwelling in the TIO, i.e., the shift of the modern IOD mode.

BFAR with food supply from the surface ocean is strongly influenced by the intensity variations of the equatorial westerly in the Indian Ocean, as proposed in the central TIO (Gupta et al., 2010). The IOD-like long-term transition during the mid-Brunhes dissolution interval (~533–191 ka) would aid to understand various paleoceanographic/paleoclimatic events in the remote areas, similar to the ENSO-like long-term changes in the equatorial Pacific Ocean.

References:
1. Yamagata et. al., 2004, Earth's Climate, pp. 1–23
2. Abram et al., 2020, QSR, 237, 106302.
3. Chen & Farrell, 1991, Proc. ODP, Sci. Results, 121, pp. 125–140.
4. Gupta et al., 2010, GRL, 37, doi:10.1029/2009GL042225.