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

[MIS02-07] Radiolarians based Sea Surface Temperature estimates in the Northwest Pacific: suitability and potential limits

*Kenji Matsuzaki¹, Takuya Itaki², Kyung Eun Lee³, Yoshimi Kubota⁴, Takuya Sagawa⁵, Keiji Horikawa⁶, Masafumi Murayama⁷ (1.Atmosphere and Ocean Research Institute, The university of Tokyo, 2.AIST, Geological Survey of Japan, 3.Division of Marine Environment and Bioscience, Korea Maritime University, 4.Geology and Paleontology, National Museum of Nature and Science, 5.Faculty of Geosciences and Civil Engineering, Institute of Science and Engineering, Kanazawa University, 6.Faculty of Science, Academic Assembly, University of Toyama, 7.Faculty of Agriculture and Marine Science, Department of Marine Resource Science, Kochi University)

Keywords:North Pacific, Sea Surface Temperature, Radiolarians, Alkenone, Mg/Ca SST

Sea surface temperature (SST) estimates based on radiolarian microfossils based on statistics such as a Imbrie and Kipp transfer function were developed in the early 1970s and showed promising results. Since, micropaleontologists tried to increase the accuracy of their reconstruction relying on more advanced statistics such as the Modern Analogue Technique or Partial Least Square method, which is an improved transfer function. In 2017, a new radiolarian assemblage dataset was proposed for estimates summer SSTs in the Northwest Pacific, however, it has the disadvantage that most of the samples were collected near Japanese coast and its application may be restricted to regional studies.
Since then, several Japanese domestic cruises have been conducted in the East China Sea and the open Northwest Pacific (e.g., KH-21-3; KS-22-4; KH-22-7) and 30 new core top sediments have been collected. In this study, we propose to analyze changes in radiolarian assemblages in these new 30 core top sediments and to compile it with previously obtained assemblage data for clarifying the entire radiolarian species distribution in the Northwest pacific and try to estimate properly and suitably SST based on radiolarians species.
In this context, direct comparison between radiolarian-based SSTs and geochemically estimated SST (Mg/Ca, Alkenone) are not often conducted. This is because sediments rich in radiolarians have a low preservation in calcareous matter such as foraminifera and vice-versa. However, this is obvious that such a comparison would be a great step forward in promoting the suitability of radiolarian-based SST.
The East China Sea (ECS), an area directly under the influence of the East Asian Monsoon, is a marginal sea of the northwest Pacific where calcareous and siliceous preservation state are both good and. thus direct comparison is possible between radiolarian and foraminiferal Mg/Ca and alkenone SSTs. Therefore, we re-estimate radiolarian SST based on the new dataset obtained in this study at IODP Site U1249 drilled at water depths of about 700 m in the ECS, and discuss similarities and disparities between the radiolarian/ Mg/Ca and alkenone SST with a particular focus of the sensitivity of each SST proxy to the East Asian Monsoon dynamic.