[U-03] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia

[U03-P12] Early Pleistocene Fauna Assemblage Analysis in High Latitude South Pacific

*YIHSUAN WU^1,2, Li Lo^1,2,3, Frank Lamy^4,5, Gisela Winckler⁶, Carlos Alvarez Zarikian⁷, Helge Arz⁸, Chandranath Basak⁹, Anieke Brombacher¹⁰, Oliver Esper⁴, Jesse Farmer¹¹, Julia Gottschalk¹², Lisa Herbert¹³, Shinya Iwasaki¹⁴, Vera Lawson¹⁵, Lester Lembke-Jene⁴, Elisa Malinverno¹⁶, Elisabeth Michel¹⁷, Jennifer Middleton⁶, Simone Moretti¹⁸, Christopher Moy¹⁹, Ana Christina Ravelo²⁰, Christina Riesselman¹⁹, Mariem Saavedra-Pellitero²¹, Inah Seo²², Raj Singh²³, Rebecca Smith²⁴, Alexandre Souza²⁵, Joseph Stoner²⁶, Igor Venancio P. de Oliveira²⁷, Sui Wan²⁸, Xiangyu Zhao²⁹ (1.NTU, 2.Paleoceanography Laboratory, NTU, 3.RCFE, 4.AWI, 5.MARUM, 6.Lamont–Doherty Earth Observatory, Columbia Univ, 7.IODP, 8.IOW, 9.University of Delaware, 10.Yale Univ., 11.UMass Boston, 12.Kiel Univ., 13.Stony Brook Univ., 14.JAMSTEC, 15.Rutgers Univ., 16. University of Milano-Bicocca, 17.IPSL, 18.MPIC, 19.University of Otago, 20.UCSC, 21.University of Portsmouth, 22.KIOST, 23.Indian Institute of Technology Bhubaneswar, 24.UMass Amherst, 25.Federal University of Rio de Janeiro, 26.Oregon State Univ., 27.INPE-Brazil, 28.CAS, 29.National Institute of Polar Research)

Keywords:South Pacific, Foraminifera assemblage, Subantarctic Mode Water

The warm pool in the western Pacific developed during the early Pleistocene. The main reason for the developing period of the warm pool is that the cooling signal from the subtropical gyre in the South Pacific was transported to the low latitude, but the records in the high latitude in the South Pacific are still missing. To solve this question, we use the foraminifera assemblage from the IODP Site U1541 sediment core during the early Pleistocene to test the hypothesis and to find the warm pool developing period. The fauna assemblage analyses of planktonic foraminifera revealed 7 genera and species with abundances >3%. Neogloboquadrina pachyderma (39.6% – 96.9%) dominated most of this period, Globorotalia spp. (0.6 – 55.3%) had peaks sometimes; Globigerina bulloides (0% – 22.4%) varied with the glacial/interglacial period. The morphic variation of N. pachyderma was also shown in this site. We found that N. pachyderma has 4 or 4.5 – 5 chambers (type a; prefer cool environment) variation in the final whorl. The relative abundance of type a decreased during 2.4 – 2.1 Ma, stayed in a low percentage during 2.1 – 1.8 Ma, and gently increased after ~1.8 Ma. On the contrary, the relative abundance of 4.5 – 5 chambers N. pachyderma (type b; prefer warm environment) increased, stayed in a high percentage during 2.1 – 1.8 Ma, and decreased in the same period. These results implied that the sea surface temperature became warm during 2.1 – 1.8 Ma. We also examined the phase relationships between planktonic foraminifera amount and obliquity, and the coherency rose after ~2.1 Ma. The foraminifera assemblage and the phase relationship changes in the Southern Ocean might imply the positive Southern Annular Mode-like scenario during 2.1 – 1.8 Ma. In modern positive Southern Annular Mode phase, the stronger westerlies contract and move poleward, and the sea surface temperature may increase at Site U1541 location duo to the southward Subtropical Front. The Subantarctic Mode Water production would be higher during the positive Southern Annular Mode phase in the present time, and more cool water is transported from high latitudes through subtropical gyres and tropical Pacific. This scenario might also have happened during 2.1 – 1.8 Ma, and the cooling water was transported to a low latitude and formed the warm pool.