[M-IS03] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS03-P01] Changes in Central Northwest Pacific Oceanography Over the Last 10 Million Years: Insights into the Late Miocene Cooling Event

*Kenji Matsuzaki¹ (1.Atmosphere and Ocean Research Institute, The university of Tokyo)

Keywords:Central Northwest Pacific, Sea Surface Temperature, Winter Monsoon, Deep-Sea Circulation

Since the middle Miocene, the planet has experienced a gradual decline in temperature, highlighted by two significant episodes: the Late Miocene Global Cooling (LMGC) and the Northern Hemisphere Glaciation (NHG). In this research, I investigated these periods by analyzing the variation in radiolarian microfossils at Ocean Drilling Program site 1208, revealing oceanographic shifts over the past 10 million years. I focused on the reconstruction of sea surface temperatures (SSTs) using data from radiolarian species that lived between 0 and 10 million years ago. These reconstructed SSTs were then juxtaposed with alkenone-based SST estimates from the same site. My results confirm a generally accurate SST record over the studied period, derived from extant radiolarian species. However, notable variances between the SSTs indicated by radiolaria and those indicated by alkenones were detected during the LMGC and NHG phases. The differences are thought to stem from the impact of the subsurface waters, at depths of approximately 50 to 100 meters, on the radiolarian community during intense cooling intervals. Additionally, other radiolarian groups' relative abundances suggested a reconfiguration of regional water circulation during the LMGC, potentially leading to a weakened Pacific meridional overturning circulation, an intensified north-south temperature disparity, and a southward shift of the subtropical front. During the NHG phase, it is likely that the North Pacific intermediate waters extended southeastward.

From: Matsuzaki, K. M. "Evolution of oceanography of the central Northwest Pacific over the past 10 million years with focus on late Miocene global cooling." Paleoceanography and Paleoclimatology 38 (2023): e2023PA004789.