동위원소 단계 6, 2에서의 알케논 온도: 온도변화에 대한 서로 다른 기작

Abstract

Stratigraphy and paleoenvironmental changes since the last Marine Isotope Stage (MIS) 9 were reconstructed based on the oxygen isotope compositions of forminifera and alkenons data from the deep-sea sediments piston core (M04-PC1A) taken from the Korea Plateau in the East Sea. Oxygen isotopic records of the planktonic foraminifera, that were estimated to be ca. 320 ka in age, show the MIS from 1 to 9. Comparing this result with previously reported stable isotope data in the East Sea as well as the global oxygen isotope trend, it is suggested that paleoceanographic and paleoclimatic changes in the East Sea has been quite different from those of open oceans: it reserves freshwater input signals and steep drop of paleotemperature (about 2 per mil heavier) at the MIS 2.1 and 6.2, respectively. Especially, paleotemperature variations of the surface water in the East Sea were reconstructed using unsaturated longchain alkenones (ULA) along with oxygen isotope data. The result shows that paleotemperature was about 10oC lower than today’s surface temperature during the MIS 6.2. However, paleotemperature during the MIS 2.2 was characterized by relatively small temperature drop of about 3 oC. Both oxygen isotope and ULA data show the systematic coeval trend throughout the late Quaternary. The relatively big SST differences between MIS 6 and MIS 2 may closely relate with paleoceanographic environments such as deep water circulation, local river runoff during each glacial periods. Physiographic situation due to the lowered sea-level is a plausible explanation of the big SST differences. These data suggesting local oceanographic conditions were more distinctive feature and have prevailed since the MIS 6 in the East Sea.