[MIS23-P25] Estimation of past intermediate water temperatures in the northwestern Pacific based on radiolarians: it’s suitability and constrains
Keywords:Northwest Pacific, Intermediate water temperature, Radiolarians
In this context, we analyzed 87 surface sediment samples covering the northwestern Pacific Ocean from 1° to 50°N and 120° to 167°E. Among, 77 samples were collected by the Geological Survey of Japan and 10 samples were collected by the Japan Agency for Marine-Earth Science. Changes in radiolarian assemblages have been analyzed on these samples. When we try to reconstruct temperature of the intermediate water based on microfossil assemblages, two major issues constrain the reconstruction. Because intermediate water species represent a much lower portion of the total assemblage, the variation of their relative abundances are less significant than those recorded in the surface and would cause some biases in the reconstruction. The second issue is that the intermediate water temperature changes greatly between 200 and 1000 m. This also create biases. For try to minimize the effect of such biases, we proposed a normalization of the data-set and tied our normalized assemblage to the temperature at water depth of ca. 500 m. This water depth has been chosen because of the relative stability of temperatures between 500-1000m, and most of our selected species cover the water depth of ca. 500 m. This enable us to estimate past intermediate water temperature at ca. 500 m within an error margin of 1.2 ℃ (R2=0.84), which is promising. However, some concerns remain, particularly for temperature higher than 9℃, but for temperature lower than 9℃, it seem that our method is relatively suitable (R2=0.89).