South China Sea hydrological changes and Pacific Walker
Circulation variations over the last millennium
Hong Yan, Liguang Sun, Delia W. Oppo, Yuhong Wang, Zhonghui Liu, Zhouqing Xie,
Xiaodong Liu, Wenhan Cheng
Supplementary Information
Supplementary Figures
W1
W2, W3
E3
M1
W4
E2E1
100E 180 60W140W140E60E 100W
0
15N
30N
15S
30S
-0.35 0.35-0.15-0.55 0.15 0.55
Supplementary Figure S1. Modern precipitation pattern of tropical Pacific. Correlations of
monthly mean anomalies of precipitation30
with the NINO3 index31
from November 1981 to November
2010. Locations of hydrology records in the tropical Pacific are also indicated: W1-our South China
Sea records, W2-Indonesia 6,7
, W3-Indonesia8, W4-Vietnam
20, M1-Washington Island
17,
E1-Galapagos13
, E2-Ecuador12
and E3-Peru10,11
. Locations that were drier/wetter during the Little Ice
Age than during the Medieval Climate Anomaly Period are marked in blue/red.
Supplementary Figure S2. Study area. Maps showing the geographical location of the study area (a),
the Xisha Islands (b), the Dongdao Island (c), and the distribution of morphological zones of the
Dongdao Island. The bottom diagram is the section drawing of topography, vegetations, soils and
parent materials along the section line from old beacon to Cattle Pond, which is indicated in the top
right figure (c).
No
v
0
5
10
15
20
a
0
0.5
1
1.5
2
2.5
0
100
200
300
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Ja
n
Ma
r
Se
p
Ju
l
Ma
y
Ave
rag
e la
titu
de
of
50
0h
Pa
IT
CZ
Pre
cip
ita
tio
n (
mm
)
Cyclo
ne
fre
qu
en
cy
Latitude of study site
b
c
Supplementary Figure S3. Modern seasonal climatic characteristics in South China Sea. Monthly
mean latitude of ITCZ in South China Sea from 1991 to 2001 (a)14
. The red line indicates the latitude of
our study site. Monthly mean cyclone frequency (b) and precipitation (c) in Dongdao Island from 1991
to 200114
.
AD
Galapagos, Eastern Pacific
Dongdao Island, Western Pacific
An
nu
al p
recip
ita
tio
n (
mm
)A
nn
ua
l p
recip
ita
tio
n (
mm
)
SO
I
a
b
c
100
1000
10000
1965 1975 1985 1995
-5
-3
-1
1
3
5
0
500
1000
1500
2000
2500
1965 1975 1985 1995
Supplementary Figure S4. Correlations between annual Southern Oscillation index and rainfall
in Dongdao Island and Gálapagos. Comparisons of Gálapagos annual rainfall (a)13
, the SOI index
(b)16
and the annual rainfall on the Dongdao Island (c) during the period of 1965 to 2000. Gray bars
represent El Niño events during this period. Precipitation changes in the western and eastern tropical
Pacific exhibit a “seesaw effect” in response to the Pacific walker circulation variation, and the
Gálapagos (Dongdao) annual rainfall from 1951 to 1997 (from 1958 to 2005) is negatively (positively)
correlated with the SOI index, with r=-0.43, p<0.005, n=47 (r=0.4, p<0.005, n=48).
DY2
South China Sea
Sand barriers
Cattle Pond
DY4
50 m
Tropical tree
Shrub
Grass
Overland flows
Overland flows
Drinking site for Cattle
DY6
North
Supplementary Figure S5. Sampling site description. The geographical features of the “Cattle
Pond”. There are several dozens of cattle, which were brought to island in recent years, living in the
centre woodland of the island. One might think this would disturb lake sediment. However, according
to the investigation in the field, as well as in the laboratory, no disturbance is evident. First, the cattle
on Dongdao Island are a variety of the Chinese yellow cattle that rarely wallow in water and mud.
Second, we investigated their lifestyle over a month and found that the cattle lived in the centre island
and never went out of the woodland. They drink water in only one small region of Cattle Pond where
water trickles out into the woodland and is not barricaded by coral rocks. Third, our sampling sites are
far away from the drinking corner and surrounded by coral rock. Combined with the progressive
sedimentary lithology, similar sediment grain size variation of two cores and the results of 14
C dating,
the disturbance from cattle does not seem to occur or is insignificant in the Cattle Pond.
Supplementary Figure S6. Lithological characteristics of the lake sediment cores. Legend (left
corner): 1. Middle to fine grained coral sandy mud with brown-red color, containing some plant
remains and seabird droppings. 2. Well-sorted coral sand. 3. Grey-white coral, shell, and sandy gravel.
A more detailed description of the lithological characteristics of DY2 and DY4 was given by Liu et al
(2008)18
. The similar fluctuations of sediment mean grain size (MGS)-versus-depth profiles (Original
data and 3-point sliding standardized means) of DY2 core (d), DY6 (e) and DY4 (f) suggest that the
sediments in the Cattle Pond have not been disturbed during or after deposition. This is further
supported by the radiocarbon dating results, which show no age inversions with increasing depth. The
radiocarbon dating of terrestrial plant remains in lake water body is not subjected to reservoir effects.
Based upon the similar fluctuations of grain size profiles, the dating results of DY2, DY4 and DY6
correspond with each other and the age model of DY6 can be built from those of DY2 and DY4. The
age for the surface sediment was assumed AD 2003, and the age between two adjacent dating results
was obtained by linear interpolation. The age models are given in panels g, h, and i.
0
50
1000 1500 2000
DY
4-M
GS
(mm
*10-3
)
f
40
45
50
55
60
65
70
0102030405060708090100
100
200
300
400
500
600
0102030405060708090
0
20
40
60
1000 1500 2000
cal yr AD
De
pth
(cm
)
0
50
100
150
200
250
e
AD 1024±30
58cm69cm
84cm88cm
Depth (cm)
DY
2-M
GS
(mm
*10-3
)
aDY2
DY4
d
b
c
1 2 3
DY
6-M
GS
(mm
*10
-3)
112cm
DY6
0
50
100
150
1000 1500 2000
cal yr AD
De
pth
(cm
)
cal yr AD
De
pth
(cm
)
g
h
i
Depth (cm)
0
50
100
150
200
250
1860 1880 1900 1920 1940 1960 1980 2000
-2
-1
0
1
SO
I In
de
x
-2
-1
0
1
40 80 120 160 200
DY6-MGS-(mm*10-3
)
r=0.58, p<0.01
AD
DY
6-M
GS
-(m
m*1
0-3)
SO
I In
de
x
Supplementary Figure S7. Correlation between sediment grain size and SOI. Correlation between
the DY6 sediment mean grain size and 10 year-smoothing instrumental Southern Oscillation Index
(SOI)15,16
over the last 140 years, time series comparison and scatter plot (r=0.58, p<0.01, n=26). SOI
data come from http://www.cgd.ucar.edu/cas/catalog/climind/SOI.signal.annstd.ascii.
Supplementary Figure S8. Comparison with other Asia-western Pacific hydrological records. (a)
δ18
O data from a Wanxiang Cave speleothem (raw data in gray and 6 point moving average in red)5; (b)
δ18
O data from a Heshang Cave speleothem (raw data in gray and 6 point moving average in pink)4; (c)
sediment grain size-versus-age profiles (DY6) of Cattle Pond (raw data in gray and 6 point moving
average in blue, this study); (d) δ18
Osw data from Indonesia marine sediment (raw data in gray and 2
point moving average in black)7; (e) Normalized δDwax data from Indonesia marine sediment for the
C30 n-acids (raw data in gray and 2 point moving average in purple)8; Gray bars represent the time
periods of MCA (~ AD 800-1300) and LIA (~ AD 1400-1850).
-3
-2
-1
0
1
2
3
1000 1200 1400 1600 1800 2000
-0.7
-0.5
-0.3
-0.1
0.1
LIA
-8.5
-8
-7.5
1000 1200 1400 1600 1800 2000
-9.5
-9
-8.5
-8
-7.5
-7
0
50
100
150
200
250
300
Wa
nxia
ng
Ca
ve
(3
3°N
)
δ18O
(‰
vs.V
PD
B)
He
sh
an
g C
ave
(3
0°N
)
δ18O
(‰
vs.V
PD
B)
Do
ng
da
o Isla
nd
(1
6.7
°N)
lake
se
dim
en
t M
GS
(m
m*1
0-3)
Ind
on
esia
(3
°S) δ
D (
C30 n
-acid
s)
(‰ v
s.V
SM
OW
, n
orm
alize
d)
Ind
on
esia
(3
°S)
δ18O
sw
(‰
vs.V
SM
OW
)
a
b
c
e
d
Year (AD)
Wet
Dry
MCA
Supplementary Tables
Calibrated age (cal yr BP) Laboratory
number
Sample
number
Dated material Depth (cm)
14C Conventional
age (yr BP) Intercept 2 sigma
BA05842 DY4-21 Plant caryopsis 20-21 305±40 417, 314, 411 474-289
BA05843 DY4-36 Plant caryopsis 35-36 765±35 675 735-656
BA05844 DY4-45 Plant caryopsis 44-45 900±35 790 924-730
BA051074 DY4-58(1) Plant caryopsis 57-58 1020±30 932 970-804
BA051075 DY4-58(2) Plant caryopsis 57-58 985±30 926 953-794
BA051076 DY4-58(3) Plant caryopsis 57-58 980±30 925 951-793
BA051077 DY4-71(1) Plant caryopsis 70-71 1025±30 933 971-917
BA051078 DY4-71(2) Plant caryopsis 70-71 960±30 916 945-790
BA051079 DY4-71(3) Plant caryopsis 70-71 1010±40 930 972-795
BA051080 DY4-71(4) Plant caryopsis 70-71 965±30 919 947-790
BA05846 DY4-71(5) Plant caryopsis 70-71 995±35 928 966-794
BA05849 DY4-87 Plant caryopsis 86-87 1340±35 1284 1306-1181
BA03236 DY2-20 Bulk organic carbon 19-20 250±70 298 475-1
BA03237 DY2-54 Bulk organic carbon 53-54 850±60 738 923-667
BA03239 DY2-95 Bulk organic carbon 94.5 1440±65 1327 1510-1262
BA03240 DY2-C1 Plant caryopsis 94.5 1360±40 1288 1331-1184
Supplementary Table S1. AMS 14
C dating results. AMS 14
C dates and calibrated ages of the
sediment cores from the Cattle Pond on the Dongdao Island
Supplementary Table S2. 210
Pb dating results. 210
Pb activity (unsupported), cumulative dry mass and
modeled ages of DY6. The 210
Pb chronology was constructed by assuming constant rate of supply (CRS)
and relating the exponential 210
Pb decay profiles with the cumulative dry mass – depth profiles as
determined using bulk density measurements (DY6) and using a CRS computer model. dpm/g = decays
per minute per gram dry sediment17
.
Depth
(cm)
210Pb activity
(dpm/g)(±4)
Cum.dry mass
(g/cm2)
Modeled age
(yr AD)
0.25 197.754 0.38 2003
0.75 210.832 0.715 2001
1.25 174.692 1.095 1999
1.75 192.015 1.575 1997
2.25 164.671 2.085 1994
2.75 193.251 2.605 1991
3.25 170.714 3.125 1987
3.75 182.171 3.655 1983
4.25 174.539 4.215 1978
4.75 165.618 4.705 1972
5.25 129.575 5.225 1966
5.75 94.653 5.725 1960
6.25 90.397 6.255 1955
6.75 38.544 6.795 1949
7.25 51.885 7.275 1946
7.75 44.001 7.775 1942
8.25 45.197 8.205 1938
8.75 34.337 8.705 1934
9.25 32.268 9.175 1930
9.75 32.344 9.685 1926
10.25 35.541 10.225 1921
10.75 35.056 10.775 1914
11.25 32.592 11.265 1905
11.75 20.916 11.825 1895
12.25 18.541 12.365 1885
12.75 13.273 12.885 1873
13.25 26.407 13.465 1861
Supplementary References
30 Janowiak, J. E. & Xie, P. P. CAMS-OPI: A global satellite-rain gauge merged product for real-time precipitation
monitoring applications. Journal of Climate 12, 3335-3342 (1999). 31
Reynolds, R. W., Rayner, N. A., Smith, T. M., Stokes, D. C. & Wang, W. Q. An improved in situ and satellite SST
analysis for climate. Journal of Climate 15, 1609-1625 (2002).