Program University

Chinese Science Bulletin

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Springer

Changes in sea surface temperature in western South

China Sea over the past 450 ka

LI Li, WANG Hui, LI JianRu, ZHAO MeiXun & WANG PinXian

State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China

Sea surface temperature over the past 450 ka was obtained by the unsaturation of molecular fossil-long

chain alkenone with a resolution of about 1 ka from the western South China Sea. This is the longest

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temperature profile in the South China Sea at such high resolution. The U3 7-SST results revealed similar

glacial-interglacial cycles as the 18O profile of planktonic foraminifera, with SST variability of 23

25.5 for glacial and 25 28 for interglacial periods. The highest SST (28.4 ) was recorded at

MIS5.5 and lowest SST (22.6 ) during MIS2. The SST record preceded the planktonic foraminiferal 18O

on five glacial-interglacial transitions. Comparison of temperature records from the Southern and

Northern Hemispheres indicated a more Southern Hemisphere-like pattern for the temperature variation

in the SCS. Strong precession and semiprecession signals in the spectra of our SST record manifest

the tropical phenomena.

sea surface temperature, unsaturation of long chain alkenone, South China Sea, paleoclimate, late Quaternary

OCEANOLOGY

in the western Pacific, has recently become an interna-

In the late 1970s, the CLIMAP program projected no

tional focal point in paleoceanographical studies. Many

remarkable change in sea surface temperature (SST) in

researchers had tried to reconstruct SST variations in the

middle and low latitudes during the last glacial maxi-

mum (LGM) by using foraminifera transfer function[1], SCS using different kinds of methods. Results from Mg/

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a-SST[11 14] and U3 7-SST[15 21] techniques appear to be

making a misimpression that the tropic region was in-

more reliable than those from other methods in recon-

sensitive to climate change during the glacial/interglacial

cycle. Only a decade ago, Thunell et al.[2] considered structing SST, although methods based on planktonic

foraminiferal assemblages are still being used[8 10].

that SST in the tropic Pacific did not change much in the

However, the time span for most SST records generated

last glacial-interglacial cycle using the modern analog

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by U3 7 and Mg/Ca techniques in the SCS is relatively

technique on foraminifera. Because not all the plank-

short, with the longest being only for the last 260 ka[11].

tonic foraminifera used in these estimates lived in the

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In this study, we used U3 7 method to reconstruct SST

sea surface and their assemblages were affected by

variability in the western SCS off Vietnam for an ex-

many different environmental factors, it is always diffi-

tended sequence over the past 450 ka. We will also dis-

cult to get the precise temperature information no matter

cuss the differences between various SST methods and

which paleoecological method is used. With the devel-

between the lower and higher latitudes, as well as the

opment of analytical techniques over the years, recon-

struction of the SST has extended from paleoecology Received March 28, 2008; accepted December 11, 2008; published online April 5, 2009

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into geochemistry methods, among which the U3 7-SST doi: 10.1007/s11434-009-0083-9

Corresponding author (email: *******@******.***.**)

and the Mg/Ca-SST methods have been widely used for Supported by the National Natural Science Foundation of China (Grant Nos.

40403012 and 40621063), Program for Young Excellent Talents in Tongji University

paleotemperature reconstructions. (Grant No. 2006KJ055), National Basic Research Program of China (Grant No.

The South China Sea (SCS), the largest marginal sea 2007CB815904) and Shanghai Rising-Star Program (A) (Grant No. 08QA14065)

Citation: Li L, Wang H, Li J R, et al. Changes in sea surface temperature in western South China Sea over the past 450 ka. Chinese Sci Bull, 2009, 54, 3335 3343,

doi: 10.1007/s11434-009-0083-9

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U3 7-SST measurement. About 2 3 g freeze-dried

SST characterization of the tropic region in glacial- in-

terglacial cycles. samples were extracted ultrasonically four times by di-

chloromethane/methanol (3:1, V/V), after adding an in-

1 Materials and methods ternal standard. The extracts were concentrated (3000

r/min, 5 min) and then saponified with 3 mL of 6%

Core MD05-2901(14 22.50 N, 110 44.60 E, w.d. 1454

KOH/methanol overnight. Neutral components were

m, core length 3649 cm) was retrieved during IMAGE

recovered by extraction with n-hexane four times, then

XII cruise through a Chinese-French cooperation ven-

separated into alkanes and alcohols by silica gel column.

ture in 2005 (Figure 1). Samples were taken at 8-cm

Alkenones within the alcohol subfraction were analyzed

intervals except between 1365 cm and 1435 cm where

by gas chromatography after derivitization by N, O-bis

no sample was collected because of severe disturbance

(trimethylsily)-trifluoroacetamide (BSTFA) (70, 2 h).

of the ship during coring.

Gas chromatography (GC) measurement. GC was

performed on a Trace GC 2000 chromatography (Finni-

gan, Thermo Electron) equipped with HP-1 capillary

column (50 m 0.32 mm 0.17 m, J&W) and flame

ionization detector. Both the injector and detector were

set at 300 . Helium was used as the carrier gas with a

flow rate of 1.2 mL/min by splitless injecting. The oven

was kept initially at 60 for 1 min, then was pro-

grammed from 60 to 200 at 20 /min, followed by

5 /min to 270, then 1.3 /min to 300 (maintained

for 18 min), 5 /min to 310 (maintained for 5 min).

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The standard deviation for U3 7 method is 0.006, corre-

sponding SD for SST estimation in this study is

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