25th International Meeting on Organic Geochemistry IMOG 2011

P-463
Holocene paleoclimatic variations recorded by biomarkers in
sediment cores from the Dabusu Lake, northeastern China
Ken Sawada 1 , Makiko Ono 1 , Yuroyuki Kitagawa 2 , Hu Ke 3
1 Faculty of Science, Hokkaido University, Sapporo, Japan, 2 Nagoya University, Nagoya, Japan, 3 Jilin
University, Chanchun, China (corresponding author:sawadak@mail.sci.hokudai.ac.jp)
The Dabusu Lake (44°49‘N, 123°40‘E) is a
continental saline lake in the northeastern China. The
climate around this lake is affected by East Asian
monsoon. Biomarker found in such lacustrine
sediment can be useful as powerful proxy for
reconstructing paleoclimatic and paleoenvironmental
variations in intercontinental area. In this study, we
analyzed biomarkers such as long-chain n-alkanes
and alkenones to reconstruct paleotemperature and
lake water level, respectively. From these biomarker
records, we suggest the millennial-scale variations of
Holocene paleoclimate in northeastern China.
Two cores (DB-A and DB-B) were collected during
January, 2004 in the Dabusu Lake. The DB-A and
DB-B core sites are located near the shore, where
lake water is completely dried in winter at present,
and central area of the lake, respectively. Humic
substance was separated from the DB-B sediments
by HF and HCl acidification. Radiocarbon ( 14 C) ages
of the humin were determined by using AMS of the
Paleolabo Co. Japan. Extraction and separation of
lipids were performed as reported previously [1].
Long-chain n-alkanes and alkenones were analyzed
by GC and GC/ MS. Alkenone unsaturation indices
(U K 37 and U K‘ 37) and carbon preferential index (CPI) of
n-alkanes were individually calculated by using
conventional equations [2,3]. The n-alkane proxy for
submerged and floating aquatic macrophyte (Paq=
(C23+C25)/(C23+C25+C29 + C31)) [4] was also calculated.
The C37-C40 di- to tetra-unsaturated alkenones were
identified in all samples of DB-A and DB-B cores. The
U K 37 and U K‘ 37 values varied by depths in both DB-B
and DB-A cores, especially with some higher spikes
of U K‘ 37 values. Annual and summer temperatures
from the U K‘ 37 were calculated by using the equations
which previously established in lacustrine sediments
of Chinese lakes [5,6]. Annual and summer
temperatures of DB-A and DB-B cores were
estimated to be -0.46 to 6.29°C and -4.65 to 9.61°C,
respectively. The larger variability of paleotemperature
observed in DB-A may be caused by
local effects such as seasonality of alkenonesynthesizing
algal production. Interestingly, highest
spikes (6.29°C) of temperatures were found at 333-
335 cm depth in DB-B. Calendar ages converted from
AMS 14 C ages are 4230±27 yrBP in 100 cm depth and
5551±28 yrBP in 370 cm depth of DB-B. The age of
the layer of warmer spike (333-335 cm depth) is
estimated to be ca. 5350 yrBP by interpolation.
Previous pollen study suggested that the Holocene
Optimum was observed in north-central China region
during 7900-4450 yrBP [7], which includes the timing
of the warmer spikes in the Dabusu Lake.
The CPIs tended to increase, while Paq decreased
from bottom to top (over the past about 6500 years) of
DB-A and DB-B, especially DB-A. The trend of CPI
variation indicates increase of input of terrestrial
higher plant wax to lacustrine sediments. The Paq
trend indicates that aquatic plant community decline
within this lake. These findings suggest that the lake
water level was lower, resulting from change to arid
condition around the lake from bottom to top. These
aridity variations recorded by the n-alkane proxies
were concordant with those of alkenone-based
temperatures.
References
[1] Sawada, K., Handa, N., Shiraiwa, Y., Danbara, A.,
Montani, S. (1996) Org. Geochem. 24, 751-764.
[2] Prahl, F.G., Muehlhausen, L.A. and Zahnle, D.
(1988)Geochim. Cosmochim. Acta. 52, 2303-2310.
[3] Bray, E.E. and Evans, E.D. (1961) Geochim.
Cosmochim. Acta. 27, 1113-1127.
[4] Ficken, K.J., Li, B., Swain, D.L. and Eglinton, G.
(2000) Org. Geochem. 31, 745-749.
[5] Sun, Q., Chu, G., Li, S., Lu, C. and Zheng, M.
(2004) Chinese Sci. Bull. 49, 2082-2086.
[6] Chu, G., Sun, Q., Li, S., Zheng, M., Jia, X., Lu, C.,
Liu, J. and Liu, T. (2005) Geochim. Cosmochim.
Acta 69, 4985-5003.
[7] Xiao, J.L.J., Xu, Q., Nakamura, T., Yang, X., Liang,
W. and Inouchi, Y. (2004) Quat. Sci. Rev. 23,
1669-1679.
588