Testing the presence of the climate mode warmer than present based on the paleoenvironmental analysis

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In the last year of this project, we conducted alkenone and major element analysis of MD-2408 core off Akita covering the last 160 kys (upper 27m), and high-resolution grain size analysis of PC-5 core further off Akita covering the MIS (Marine Isotope Stage) 5 and 6. By combining the data from Old Ridge and off Akita that we obtained in the second year, we reconstructed temporal variations of the north-south gradients of alkenone SST (Sea Surface Temperature) and eolian dust grain size during the last 160 kys. The results are as follows.1) The eolian dust grain size variation during the last 100 kys recorded in PC-5 core off Akita shows distinct millennial-scale variability that faithfully follows the millennial-scale variability of d^<18>O record of Greenland ice (GRIP) core known as Dansgaard-Oeschger Cycles (DOC). In addition, eolian dust grain size variation in PC-5 core shows similar millennial-scale variation during the MIS 5e similar to d^<18>O record of GRIP. GRIP d^<18>O recor … More d during the MIS 5e has been controversial because of its possible disturbance. However, our new eolian dust grain size record strongly support the reliability of the GRIP record during the MIS 5e and suggest the presence of abrupt climatic changes during interglacial periods.2) N-S comparison of the eolian dust grain size during the last 130 kys also suggests intensification of the summer monsoon during the periods of higher northern summer insolation. Superimposed on this are millennial-scale changes with intensified summer monsoon during the interstadials of DOC, suggesting millennial-scale climatic jump is associated with N-S jump of the summer monsoon front.3) Alkenone SST of the Japan Sea during MIS 5e was approximately 5 C higher than the present Millennial-scale variability of the SST is not distinct at Oki Ridge where influence of the Tsushima Warm Current was continuous, whereas the SST shows distinct millennial-scale variation in association with DOC due to the intermitted influence of the Tsushima Warm Current. Less