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

[MIS02-P06] Impact of obliquity variation on structure of thermocline water mass in the western tropical Pacific over the last 180 kyr

*Uchida Takayuki¹, Takuya Sagawa², Yoshimi Kubota³ (1.Graduate School of Natural Science and Technology. Kanazawa University, 2.Institute of Science & Engineering. Kanazawa University, 3.National Museum of Nature & Science)

Keywords:Western Pacific warm pool, Planktonic foraminifera, Reconstruction of paleotemperature

The western Pacific warm pool (WPWP) is an important heat and vapor source for the atmospheric circulation and influences climate conditions worldwide. One important feature of tropical weather is Intertropical convergence zone (ITCZ). The latent heat released by convective activity of ITCZ drives the atmospheric circulation, and ITCZ also influences oceanic structures. We call the upwelling zone related to ITCZ “thermocline ridge” because the isotherm is raised on the north-south section of the vertical water temperature. As just described, ITCZ have a significant impact on the atmosphere and ocean. However, it is not well understood how long-term variations of ITCZ affect the ocean interior. Here, this study examines how the ITCZ affected the ocean interior by clarifying the behavior of thermocline ridge during glacial – interglacial cycles. The sample used in this study is a piston core KH92-1 3aPC collected on the West Caroline Basin located in the WPWP. This site is located beneath the current thermocline ridge. Surface and thermocline temperatures were reconstructed by Mg/Ca of planktonic foraminifera, Globigerinoides ruber and Pulleniatina obliquiloculata, respectively, for the last 180 kyr. Water temperature and δ¹⁸O_local(proxy of salinity) of thermocline depth showed smaller values corresponding to smaller obliquity. Thermocline in this site consists of two water masses: a warm, high-salinity North Pacific tropical water (NPTW) and a cold, low-salinity upwelling water. It is likely that the variation of obliquity was driving the thermocline water mass structure of this site, and suggested that NPTW contributed more when high obliquity, and upwelling water contributed more when small obliquity. Therefore, the variation of obliquity probably changes [1] the amount of NPTW transported [2] intensity of upwelling [3] north-south Shift of thermocline ridge along with ITCZ. These may be related to changes in the width of the ITCZ and the north-south transport of heat due to variations in the obliquity.