Terrestrial n-alkane signatures and alkenone SSTs in southwestern part of the East Sea (Japan Sea) since the last glacial period: paleoclimatological implication

Abstract

This study provides reconstruction of paleoclimate and paleoproductivity in southwestern part of the East Sea. The occurrence of long chain n-alkanes(C25-C35)and unsaturated ketones, TOC, and CaCO3 were analyzed to measure terrestrial organic matter inputs and the past sea surface temperatures in this area. Since this site is shallow in depth (187m) and is expected to be influenced by terrestrial organic matter inputs due to its proximity to the continent, we also examined applicability of alkenone SSTs in this region. The concentration of total C37 (alkenone) and total long chain n-alkanes were fluctuating accordingly, however during LGM, carbon preference index (CPI27-31) recorded the highest value (10.1) suggesting freshening of terrestrial n-alkanes during this period. This increased CPI value at 18 ka B.P. was accompanied by decreased alkenone SSTs, which rose again from 92-106 ka B.P with diminished CPI values at the same period. A predominance of odd carbon-numbered compounds is indicated by the CPI27-31 varying between 4.9 and 10.1, with a mean value of 7.0. CPI27-31 shows higher values from 17-55ka and 73-83 ka B.P., and lower values during Holocene, 60-70 ka, and 92-121 ka B.P. The results revealed changes in terrestrial organic matter inputs in East Sea in relation to paleoclimate therefore this research will be helpful in understanding paleoeclimatological changes in East Sea associated with terrestrial ic matter inputs and the past sea surface temperatures in this area. Since this site is shallow in depth (187m) and is expected to be influenced by terrestrial organic matter inputs due to its proximity to the continent, we also examined applicability of alkenone SSTs in this region. The concentration of total C37 (alkenone) and total long chain n-alkanes were fluctuating accordingly, however during LGM, carbon preference index (CPI27-31) recorded the highest value (10.1) suggesting freshening of terrestrial n-alkanes during this period. This increased CPI value at 18 ka B.P. was accompanied by decreased alkenone SSTs, which rose again from 92-106 ka B.P with diminished CPI values at the same period. A predominance of odd carbon-numbered compounds is indicated by the CPI27-31 varying between 4.9 and 10.1, with a mean value of 7.0. CPI27-31 shows higher values from 17-55ka and 73-83 ka B.P., and lower values during Holocene, 60-70 ka, and 92-121 ka B.P. The results revealed changes in terrestrial organic matter inputs in East Sea in relation to paleoclimate therefore this research will be helpful in understanding paleoeclimatological changes in East Sea associated with terrestrial