[M-IS06] Evolution and variability of the Tropical Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS06-P03] Upper ocean temperature change in the tropical-subtropical western North Pacific during the last 700 kyr

Takayuki Uchida², *Takuya Sagawa¹, Keiji Horikawa³, Masafumi MURAYAMA⁴, Yoshimi Kubota⁵, Mahsa Saeidi Ortakand⁵ (1.Institute of Science and Engineering, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University, 3.Toyama University, 4.Kochi University, 5.National Museum of Nature and Science)

Keywords:Glacial-interglacial cycle, Sea surface temperature, Themocline temperature, Planktonic foraminifera

The subtropical North Pacific is one of the largest waters that provide heat and vapor to atmosphere, and therefore, has influences on the global climate. Understanding past temperature variations in the subtropical North Pacific is essential for understanding long-term global climate change. However, paleotemperature record in the subtropical North Pacific region is scarce because most of the area has great water depth that prevent carbonate preservation in seafloor sediments.
This study aims to provide a glacial-interglacial scale paleotemperature record in the western subtropical North Pacific over the past 700kyr. The sediment core used in this study was retrieved on the West Mariana Ridge in the subtropical gyre at water depth of 2677 m, which allows carbonate microfossils to be well preserved. Sea surface temperature (SST) and thermocline temperature (TT) were reconstructed using Mg/Ca ratios of the planktonic foraminifera Globigerinoides ruber and Pulleniatina obliquiloculata, respectively. Although the SST and TT show glacial-interglacial cycle, the warming at the glacial terminations were more gradual than records in the western tropical region, and thus the temperature records do not show a clear saw-tooth pattern that is a general characteristic of glacial-interglacial cycles. This is partly due to the earlier onset of warming during glacial periods, especially in the TT record.
These findings may indicate that as polar ice sheets expanded, the meridional pressure gradient increased, strengthening the trade winds and the subtropical gyre. Consequently, the western Pacific warm pool expanded latitudinally in the western tropical Pacific, while NPTW formation and westward transport increased in the eastern tropical Pacific. The results of this study imply that surface water temperature structure within the subtropical gyre was closely related to the global ice sheet expansion and the large-scale atmospheric circulation.