5:15 PM - 6:45 PM
[MIS03-P07] Paleoclimate changes in the northern East Asia reconstructed by terrestrial plant biomarker analysis of the ocean drilling core from the northern Japan Sea over the last 700 kyr
Keywords:Terrestrial plant biomarker, IODP, terpenoid, the Japan Sea, Paleovegetation proxy
The Japan Sea is a marginal sea that is connected to the open ocean through four straits, and the surface is characterized by the Tsushima Warm Current (TWC) and Liman Current, and the deep water is occupied by Japan Sea Proper Water. In glacial-interglacial cycles in the Quaternary, the sea surface environment in the Japan Sea has repeatedly changed by sea level fluctuation. It is reported that the land bridge was formed between the continent and Hokkaido, in the northern part of the Japan Sea, during the last glacial maximum (LGM) as a result of sea level fall. Moreover, the northern regions have been significantly affected by the East Asian Winter Monsoon (EAWM) (Ikehara and Itaki, 2007). In the present study, we analyzed terrestrial plant biomarkers of a sediment core from the northern Japan Sea (IODP Exp. 346, site U1422) for the last 700 kyr to reconstruct the variations in paleovegatation and the related terrestrial paleoclimate.
The sediment cores in this study were drilled at Site U1422 in the northern part of the Japan Basin (the Japan Sea off the western coast of Hokkaido) at 43°45.99’N, 138°49.99’E during Integrated Ocean Discovery Program (IODP) Exp. 346. We focused on the duration from the present to the MIS 16 (- ca. 700 ka). Lipids were extracted with organic solvents, and separated to aliphatic, aromatic and polar fractions. Lipids were identified and quantified by GC-MS and GC-FID.
The cycle of sedimentary dark/light color layers observed in the U1422 core was not correlated with the glacial/interglacial cycle, but some of dark layers correspond to increasing spikes of concentrations of terrestrial plant biomarkers such as dehydroabietic acid (DAA; coniferous diterpenoid) and friedelin (angiospermous triterpenoid). These biomarkers are thought to be derived from forest vegetation. The dark layers are known to be deposited under reduced bottom water condition, which was associated with surface water stratification. From these insights, we interpret the paleoclimatic regime during the timings of the deposition of dark layers and higher DAA and friedelin concentrations as the following scenario; 1) river waters were efficiently supplied to the Japan Sea and added to the TWC under humid climate related to summer monsoon, 2) subsequently, the expansion of fresh waters in the sea surface and subsurface layers of the Japan Sea. 3)Water stratification was developed and bottom water condition became reduced, resulting in formation of the dark layers.
The sediment cores in this study were drilled at Site U1422 in the northern part of the Japan Basin (the Japan Sea off the western coast of Hokkaido) at 43°45.99’N, 138°49.99’E during Integrated Ocean Discovery Program (IODP) Exp. 346. We focused on the duration from the present to the MIS 16 (- ca. 700 ka). Lipids were extracted with organic solvents, and separated to aliphatic, aromatic and polar fractions. Lipids were identified and quantified by GC-MS and GC-FID.
The cycle of sedimentary dark/light color layers observed in the U1422 core was not correlated with the glacial/interglacial cycle, but some of dark layers correspond to increasing spikes of concentrations of terrestrial plant biomarkers such as dehydroabietic acid (DAA; coniferous diterpenoid) and friedelin (angiospermous triterpenoid). These biomarkers are thought to be derived from forest vegetation. The dark layers are known to be deposited under reduced bottom water condition, which was associated with surface water stratification. From these insights, we interpret the paleoclimatic regime during the timings of the deposition of dark layers and higher DAA and friedelin concentrations as the following scenario; 1) river waters were efficiently supplied to the Japan Sea and added to the TWC under humid climate related to summer monsoon, 2) subsequently, the expansion of fresh waters in the sea surface and subsurface layers of the Japan Sea. 3)Water stratification was developed and bottom water condition became reduced, resulting in formation of the dark layers.