11:15 〜 11:30
[MIS06-08] Variations in paleovegetation recorded by plant-derived terpenoids in the sediments from Lake Dabusu, northeastern China, over the past 7.2 ka
キーワード：バイオマーカー、植物テルペノイド、古植生、完新世最温暖期、大陸湖、ダブス湖
Lacustrine sediments are important archives to understand paleoclimatic changes in inland areas. Recently, plant-derived biomarkers including terpenoids can be used to reconstruct paleovegetation in inland areas (Lin et al., 2022; Z^atková et al., 2023). The authors have reported the vegetation changes using plant terpenoids in the inland lake in Japan (Fukuchi et al., 2024). In the present study, we analyze plant terpenoids compositions of lacustrine sediments from continental inland lake in China to reconstruct paleovegetational changes and to examine the applicability of terpenoid biomarker proxies to the reconstruction in inland lake sediment.
We used a sediment core (DBB core) collected from the southern part of Lake Dabusu during January 2004. Lake Dabusu is a continental lake located in northeastern China. The present climate around the lake is temperate and affected by the East Asia Monsoon (EAM). In winter, northwesterly wind brings cool and dry air, whereas in the short summer, warm and moist air is transported from the ocean. The core depth was 15.92 m. The ages were determined by AMS 14C dating of the dried humic samples, and the lowermost horizon was estimated to be about 7,200 cal yrs BP (Sawada et al., 2020). The sediments (2 cm thick) were extracted by solvents and then separated into fractions by silicagel column. The apolar and polar fractions were analyzed by GC-MS.
In the DBB core sediment samples, terrestrial plant-derived diterpenoids (DTs; gymnosperm origin) and triterpenoids (TTs; angiosperm origin) were identified. Dehydroabietic acid (DAA) was the only identified DT and the concentration of DAA was significantly lower than those of TTs through the core. This implies the contribution of conifer trees was relatively lower around the lake, consistent with pollen data from the peat deposits in Lake Dabusu (Niu et al., 2022). Also by the pollen data, the source vegetations of DAA might be Pinaceae species. Alkenone paleothermometrical data implies that the temperatures were highest from 5.5 to 5.3 kyr BP, when were the Holocene Thermal Maximum (HTM) in the region, with some decreasing spikes corresponded to the cooling events (Sawada et al., 2020). The ratios of DAA to the total triterpenoids (DAA/TTs) were relatively higher from 7 to 6.5 kyr BP, corresponding to the timing of lower alkenone-based temperatures, but decreased after 5.2 kyr BP with the increase in the temperatures. Before the HTM, conifer trees might little contribute, while it decreased by the warming of the inland area. During the Holocene Optimum, there were several increasing spikes at 6.1, 5.5, and 5.1 kyr BP. These spikes correspond to decreases of alkenone-based temperature and aquatic plant index (Paq) of n-alkane as reported previously (Sawada et al., 2020). These results suggest the contribution of Pinaceae increased by the short-time cooler and drier climates. The spikes at 6.1 and 5.5 kyr BP might be affected by weakening of EASM caused by Asian monsoon events 1 and Bond event 4.
We used a sediment core (DBB core) collected from the southern part of Lake Dabusu during January 2004. Lake Dabusu is a continental lake located in northeastern China. The present climate around the lake is temperate and affected by the East Asia Monsoon (EAM). In winter, northwesterly wind brings cool and dry air, whereas in the short summer, warm and moist air is transported from the ocean. The core depth was 15.92 m. The ages were determined by AMS 14C dating of the dried humic samples, and the lowermost horizon was estimated to be about 7,200 cal yrs BP (Sawada et al., 2020). The sediments (2 cm thick) were extracted by solvents and then separated into fractions by silicagel column. The apolar and polar fractions were analyzed by GC-MS.
In the DBB core sediment samples, terrestrial plant-derived diterpenoids (DTs; gymnosperm origin) and triterpenoids (TTs; angiosperm origin) were identified. Dehydroabietic acid (DAA) was the only identified DT and the concentration of DAA was significantly lower than those of TTs through the core. This implies the contribution of conifer trees was relatively lower around the lake, consistent with pollen data from the peat deposits in Lake Dabusu (Niu et al., 2022). Also by the pollen data, the source vegetations of DAA might be Pinaceae species. Alkenone paleothermometrical data implies that the temperatures were highest from 5.5 to 5.3 kyr BP, when were the Holocene Thermal Maximum (HTM) in the region, with some decreasing spikes corresponded to the cooling events (Sawada et al., 2020). The ratios of DAA to the total triterpenoids (DAA/TTs) were relatively higher from 7 to 6.5 kyr BP, corresponding to the timing of lower alkenone-based temperatures, but decreased after 5.2 kyr BP with the increase in the temperatures. Before the HTM, conifer trees might little contribute, while it decreased by the warming of the inland area. During the Holocene Optimum, there were several increasing spikes at 6.1, 5.5, and 5.1 kyr BP. These spikes correspond to decreases of alkenone-based temperature and aquatic plant index (Paq) of n-alkane as reported previously (Sawada et al., 2020). These results suggest the contribution of Pinaceae increased by the short-time cooler and drier climates. The spikes at 6.1 and 5.5 kyr BP might be affected by weakening of EASM caused by Asian monsoon events 1 and Bond event 4.