Paleoenvironment Evolution Of The Kuroshio Drainage Area During The Last Glacial Maximum

34.2 meter-long MD05-2908 sedimentation core has been obtained in the Southern of Okinawa Trough by Calypso piston core, when a China-France international cooperation program IMAGES XII-MD147 Micro Polo1 cruise in the western Pacific has been executed on July, 2005. The author constructed age model of this core by AMS14C data, analyzed characters of planktonic foraminifera groups through FP-12E planktonic foraminifera transfunction and Q-mode analysis methods, and discussed the evolvement the Kuroshio and paleoenvironment records during the mid-late Holocene. Results show that there are 5 big flood events occurred in Holocene linked with warm and wet climate, and influenced by high sea levels during the time.During the period from 7000a B.P. to 4400a B.P., strength of the Kuroshio has the trend to reinforce steadily, the mainstream of which located in the Okinawa Trough all the time. During the period from 4000a B.P. to 3000a B.P., the strength of the Kuroshio has become weakened or the mainstream of it has moved eastwardly, and the impact of dilute water has reinforced. After 3000a B.P., the strength of the Kuroshio has intensified step by step, and period when the Kuroshio was the most active was from 1650a BP to nowadays, however, in the year of 600 and 140a B.P., the strength of the Kuroshio has weakened transitorily. Pulleniatina Minimum Event reflected in MD05-2908 core very well, which occurred from 3900a to 2800a B.P. and lasted about 1100a. When such an Event occurred, both monsoons in winter and in summer could have been strengthened.Climate change trend during mid-late Holocene in the Okinawa Trough can be divided into four stages: the first low temperature stage was from 7.0 to 4.8 cal ka B.P., the relatively high temperature stage was from 4.8 to 4.1 cal ka B.P., the stage with lowest temperature was from 4.1 to 2.4 cal ka B.P. and after 2.4 ka B.P., the temperature stand with a high level. The Holocene events (6.3～5.8,5.5,4.6～4.2,3.6～3.0,2.9～2.4,1.3～1.1,0.5～0.1 cal ka B.P.) in the southern Okinawa Trough can be identified by contrast to the records from China and other regions in the world, the youngest one(AD 950 to 1350) corresponding in time to the Medieval Warm Period. Result of spectral analysis of core MD05-2908 showed that there were several millennial scale periods such as 3008a and 1061 a and other periods as 215a, 123a, 103～107a, 81～78a and 71～73a etc, which linked with the strength of solar activity.Since the mid-late Holocene, strength of the Kuroshio in the Okinawa Trough has been reinforced step by step, which attached the largest about 4.0 ka B.P., and then, the strength of the Kuroshio has been weakened or the axis of the Kuroshio has moved eastwardly from 4.0 to 3.0 ka B.P.. After 3.0ka B.P., the strength of the Kuroshio has been reinforced again continuously, and has a fluctuation during 1.0ka BP.By anglicizing the oxygen isotope and abundant of Pulleniatina obliquiloculata of 14 sedimentation cores in the Okinawa Trough, results showed that main axis of the Kuroshio has been activating in the Okinawa Trough during the Last Glacial Maximum (LGM), however, the strength of which has been weakened and the move path of which has been changed largely.