Supplementary Information for 1
Dynamics of the intertropical convergence zone over the western 2
Pacific during the Little Ice Age 3
Hong Yan, Wei Wei, Willie Soon, Zhisheng An, Weijian Zhou, Zhonghui Liu, Yuhong 4
Wang, Robert M. Carter 5
6
7
This file includes: 8
Supplementary discussion 9
Supplementary Figure s1 to s10 10
Supplementary Table s1 11
References 12
13
14
15
16
17
18
19
20
21
Dynamics of the intertropical convergence zone over the western Pacific during the Little Ice Age
SUPPLEMENTARY INFORMATIONDOI: 10.1038/NGEO2375
NATURE GEOSCIENCE | www.nature.com/naturegeoscience 1
© 2015 Macmillan Publishers Limited. All rights reserved
Supplementary discussion: 22
Supporting evidence from decadal-multidecadal-centennial scale oscillations 23
In addition to the MCA-LIA-recent 150 years transition, other multidecadal-scale 24
oscillations in solar output have also occurred over the last millennium1,2
. If solar 25
output is a significant factor for tropical hydrologic variation over the last millennium, 26
then the paleo-hydrology records should have recorded the signals of these 27
oscillations. Although most proxy-hydrology records are low resolution, and not 28
accurately dated enough to capture decadal-centennial-scale variations, such 29
oscillations have been detected in several high resolution precipitation records from 30
the Asian-Australian monsoon area. These multi-decadal hydrologic variations are 31
consistent with our proposal of a contracted monsoon/ITCZ during solar irradiance 32
minimum. For example, some decadal changes in a speleothem record from north 33
China3 and a coral record from northeast Australia
4 are correlated with decadal 34
variations of the solar irradiance, with increased rainfall during the peaks of the solar 35
activity (D4 and D8 records in Fig. s10). Meanwhile, and conversely, hydrological 36
records from the western Pacific region5 reveal increased rainfall during the troughs 37
of the solar output (W2 record in Fig. s10). An increased rainfall in the tropical 38
western Pacific during the solar minimum was also supported by a recent study which 39
found that the precipitation in Indonesia increased abruptly at the time of the solar 40
minimum around 2800 yr BP6. 41
On the other hand, power spectrum analysis indicates that the periodicities of the 42
speleothem δ18
O series from monsoonal China3,7-9
are similar to and consistent with 43
the presence of solar cycles - such as the well known 80-120 yr and ~20 yr 44
periodicities. 45
It is important to note, however, that not all the variations in rainfall records from 46
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the Asian-Australian monsoon area exhibit good correspondence with solar output. 47
For example, no multi-decadal oscillations were observed in fluvial sedimentary 48
records from the Magela Creek Flood Plain10
. However, good reasons exist that could 49
explain disagreements between decadal variation in a proxy record and the solar 50
activity record. Those reasons include time delays for hydrologic changes in response 51
to solar activity forcing, spatial differences of the local and regional rainfalls in 52
response to the solar forcing (e.g., wet, dry and no changes in different regions in 53
response to the same solar minima) and a lack of quality in particular proxy 54
records (e.g. time resolution, error of age model). 55
Finally, it is noteworthy that the impacts of decadal to centennial scale cycles in 56
solar activity on tropical hydrology have long been known to occur in speleothem, 57
lake and marine sediment records from tropical Latin America, central Africa and 58
elsewhere11-17
. 59
60
The contraction of ITCZ and the strengthening of Pacific Walker Circulation 61
during LIA 62
The extended clear dry conditions that obtained in mid-northern part of the mainland 63
China and northern Australia during the LIA are consistent with the disappearance or 64
weakening of the ITCZ/monsoonal rainfall in these regions, and point to a contraction 65
of the ITCZ’s sphere of influence (see the summary presented in Fig. s6 and s7). At 66
the same time, the precipitation zones converged more narrowly within the tropics and 67
resulted in more rainfall in the Indo-Pacific warm-fresh pool region. However, the 68
contracted ITCZ/monsoon was probably not the only cause of dilution of the warm 69
pool. As well, concurrent changes of ENSO/Walker circulation, which today has a big 70
impact on modern western Pacific hydrology, probably contributed to the changes in 71
© 2015 Macmillan Publishers Limited. All rights reserved
multi-decadal to centennial- scale precipitation in this region5,18,19
. 72
Indeed, a number of papers have addressed the ENSO/Walker circulation 73
variations in the tropical Pacific during the past millennium. Overall, the results 74
remain unclear, controversy stemming from a perceived contradiction between the 75
reduced east-west tropical Pacific SST gradient (El Niño-like) and the enhanced 76
Pacific Walker circulation (La Niña-like)20
. The best available SST reconstructions in 77
the western19,21
, eastern22,23
and mid24
tropical Pacific suggest25,26
an LIA marked by 78
relative warming in the eastern and central tropical Pacific, accompanied by 79
substantial cooling in the western equatorial ocean and a more El Niño-like state 80
(when compared and contrasted with conditions during the MCA). In contrast, nearly 81
all hydrological reconstructions from the tropical Pacific suggested a more La 82
Niña-like mean state during the LIA than during the MCA. These include records 83
from the Indo-Pacific5,18,19,21,27
, the central tropical Pacific 28
and the eastern 84
equatorial Pacific29,30
that indicate wetter, drier and drier conditions, respectively, 85
during the LIA than during the MCA. Meanwhile, theoretical models and computer 86
simulations also project contradictory results for the mean climatic state during the 87
LIA and the MCA. For example, the “ocean dynamical thermostat” mechanism31-33
88
predicts a more El Niño-like state in the LIA than in the MCA, while the coupled 89
general circulation models (CGCM) project a possible strengthening of the Walker 90
circulation (La Niña-like state) during the LIA34,35
(see ref20
for detailed discussion). 91
Several co-working factors could contribute to explain the conflict between the SST 92
records and the hydrological records, such as the inappropriate interpretation of the 93
current SST/hydrological records (e.g. the primary mode of the SST or hydrological 94
records in tropical Pacific on centennial scale perhaps might not be ENSO variation, 95
but instead represent the meridional temperature gradient or ITCZ changes). A 96
decoupling between the atmospheric and oceanic response to forcing on centennial 97
© 2015 Macmillan Publishers Limited. All rights reserved
timescales is another possibility. More high-resolution proxy records and climate 98
models are thus needed in the future research that seeks to clarify this unresolved 99
puzzle. 100
In summary, although the temperature-based reconstructions indicate an El 101
Nino-like SST pattern existed in the tropical Pacific during the LIA24,25
, the 102
hydrological studies, based upon either proxy records5,18,19,29
or model simulations34
, 103
present a clear strengthening of the Pacific Walker circulation during the LIA, which 104
in turn would cause increased precipitation in the Indo-Pacific warm-fresh pool region. 105
Moreover, the model results in this study also implied an increased zonal precipitation 106
contrast between east and west tropical Pacific during the LIA (Fig. s9 and ref36
), 107
which would probably also manifest itself as an enhanced Pacific Walker circulation. 108
That is to say, the contracted western Pacific monsoon/ITCZ and enhanced Pacific 109
Walker circulation probably co-existed during the LIA interval, with both mechanisms 110
contributing extra precipitation to the wet and warm pool region of the western 111
Pacific. 112
This co-existence of a contracted ITCZ/monsoon and strengthened Pacific 113
Walker circulation during the LIA raises some issues that need to be addressed in 114
future studies. For example, both ITCZ contraction and Walker circulation 115
strengthening could increase convection in the western Pacific warm pool, but which 116
factor is the dominant cause? Also, what interaction, if any, occurs between ITCZ 117
behavior and Walker circulation on multi-decadal to centennial scales (e.g., the 118
contraction of the western Pacific marine-continental ITCZ could increase convection 119
activity in the western Pacific, and therefore enhance Pacific Walker Circulation)? 120
121
122
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A brief description of the ECHO-G and MPI-ESM models: Ability to simulate 123
global monsoon and monsoon-related climate variations 124
ECHO-G model: the ECHO-G model has very reasonable performance on simulating 125
the monsoonal precipitation. In Liu et al. (2009)36
, the authors have compared the 126
simulated annual mean precipitation and global monsoon mode with those from the 127
observation and reanalysis data (Figure 1 in their paper). They show quite consistent 128
patterns and confirm the reliability of the model performance. In this paper, the 129
authors have conducted two ECHO-G experiments, one with fixed external forcing 130
used as a control experiment and the other with three external forcings, i.e. solar 131
variability, greenhouse gas concentration and volcanic forcing36
. 132
MPI-ESM model: the basic model simulation and capability of MPI-ESM for the last 133
millennium has been described by Jungclaus et al. (2010)37
. Although there is no 134
special focus on the performance of the model on monsoonal precipitation in that 135
paper, a follow-up paper by Man et al. (2012)38
studied theEast Asian summer 136
monsoon during the last millennium. Man et al. (2012) compared the simulated 137
summer precipitation over the East Asian monsoon region with that observed, using 138
reanalysis data. Figure 2 in their paper reports good agreement among datasets 139
regarding the precipitation and the 850-hpa wind patterns. After the validation of the 140
simulation results, the authors also demonstrated that the model can capture the East 141
Asian summer monsoon change during the MCA and LIA periods via model-data 142
comparison. Hence, the works by Man et al. (2012) add confidence to our use of 143
MPI-ESM model for studying the TSI-induced ITCZ contraction hypothesis around 144
the Indo-Pacific warm-fresh pool region during the Little Ice Age interval. 145
146
147
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Supplementary Figures 148
149
Figure s1: Hydrologic proxy records D139
, D240
, D38, D4
3 and D5
7 from the EASM 150
area showing dry condition during the LIA relative to MCA/recent 150 years. The 151
locations of these records are shown in Fig.1. Please see the Methods section for the 152
definitions of the Relative Wet Index (RWI) and the wet/dry condition during the LIA 153
relative to the MCA/recent 150 years. 154
155
80
85
90
-8.5
-8
-7.5
-0.6
-0.3
0
0.3
0.6
-0.5
0
0.5
1
-9.5
-9
-8.5
-8
-7.5
1000 1200 1400 1600 1800 2000
AD
LIA
Hes
han
g c
ave
(30
.5°N
)
δ1
8O
(‰,V
PD
B)
Go
ngh
ai lak
e (3
8.9
°N)
S-3
00
mT
(%
)
MCA
RWI= -85%Wet
Wan
xia
ng
cav
e (3
3.3
°N)
δ1
8O
(‰,V
PD
B)
Hu
ang
ye
cav
e (3
3.5
°N)
δ1
8O
(‰,V
PD
B)
Lo
ngx
i (3
5°N
)
Dro
ugh
t/F
loo
d in
dex
Dry
D1
D2
D3
D4
D5
RWI= -153%
RWI= -110%
RWI= -74%
RWI= -112% RWI= -102%
RWI= -145% RWI= -144%
RWI= -96% RWI= -90%
Dry LIA
Dry LIA
Dry LIA
Dry LIA
Dry LIA
© 2015 Macmillan Publishers Limited. All rights reserved
156
Figure s2: Hydrologic proxy records N19, N2
41, W1
42,43 and W2
5,27 from the EASM 157
area indicate no apparent change of rainfall and wet conditions during the LIA relative 158
to the MCA. The locations of these records are shown in Fig.1. Please see the 159
Methods section for the definitions of the Relative Wet Index (RWI) and the wet/dry 160
condition during the LIA relative to the MCA/recent 150 years. 161
162
163
164
-8.0
-7.5
-7.0
Wet
Dry
20
30
40
50
60
-2
-1
0
1
2
1000 1200 1400 1600 1800 2000AD
-9.0
-8.0
-7.0
Do
ngg
e ca
ve
(25
.3°N
)
δ1
8O
(‰,V
PD
B)
Lo
ngq
uan
cav
e (2
5.5
°N)
δ1
8O
(‰,V
PD
B)
Do
ngd
ao,
SC
S (
16
.7°N
)
MG
S (
µm
)
Hu
guan
g M
arr
(21
.9°N
)
No
n-r
esid
ual
Sr
(µg
/g)
LIAMCAN1
N2
W1
W2
RWI= -24%
RWI= -153%
RWI= 29%RWI=-24%
RWI= 121%
RWI= 189%
RWI= 156% RWI= 163%
No apparent change
No apparent change
LIA relative to MCA
Wet LIA
Wet LIA
© 2015 Macmillan Publishers Limited. All rights reserved
165
Figure s3: Hydrologic proxy records D1044,45
, D1210
, D1346
from the northern 166
Australia monsoon area showing dry condition during the LIA relative to the 167
MCA/recent 150 years. The locations of these records are shown in Fig. 2. Please see 168
the Method section for the definitions of the Relative Wet Index (RWI) and the 169
wet/dry condition during the LIA relative to the MCA/recent 150 years. 170
171
0
2
4
6
8
10
12
14
16
-8.5
-8.0
-7.5
-7.0
-6.5
-6.0
-5.5
-5.0
-2.5
-1.5
-0.5
0.5
1.5
1000 1200 1400 1600 1800 2000
AD
Mag
ela
Cre
ek P
lain
(12°S
)
Sed
imen
t fl
ux (
10-3
*g/c
m2/y
ear)
RWI= -155%
LIAMCAD12
D10
Bro
mfi
eld S
wam
p (
17.3
°S)
Hum
ific
atio
n r
esid
ual
s
Wet
Dry
KN
I-51 c
ave
(15.3
°S)
δ1
8O
(‰,V
PD
B)
D13
RWI= -178%
RWI= -105%RWI= -142%
RWI= -92%RWI= -80%
Dry LIA
Dry LIA
Dry LIA
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172
Figure s4: Coral records D647-49
, D750
, D84 and D9
51 from northeast Australia showing 173
dry conditions during the LIA relative to the last 150 years (i.e., D6, D7 and D8: 174
seawater δ18
O record calculated from the coral δ18
O and Sr/Ca; D9: rainfall 175
reconstruction in Great Barrier Reef derived from coral luminescence). The locations 176
of these records are shown in Fig. 2. Please see the Methods section for the definitions 177
of the Relative Wet Index (RWI) and the wet/dry condition during the LIA relative to 178
the most recent 150 years. 179
180
181
Wet
Dry
-100
0
100
200
-0.4
-0.2
0
0.2
0.4
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
AD
LIAN
ew C
aled
onia
(2
2°S
)
Sea
wat
er δ
18O
(‰
,VP
DB
)
Dry LIA
Recent
150 years
RWI= -71%
Tro
pic
al Q
uee
nsl
and
(~
17
°N)
Rai
nfa
ll (
mm
)Gre
at B
arri
er R
eef
(~1
8.5
°S)
Sea
wat
er δ
18O
(‰,V
PD
B)
D6
D8
D9
1400
Dry LIARWI= -143%
Dry LIARWI= -92%
1500 1600 1700 1800 1900 2000
-0.4
-0.2
0
0.2
0.4
D7
Dry LIARWI= -62%
Flin
der
s R
eef
(1
7.5
°S)
Sea
wat
er δ
18O
(‰
,VP
DB
)
© 2015 Macmillan Publishers Limited. All rights reserved
182
Figure s5: Proxy hydrology records N352
, N453
, W354
, W418
and W519,21
from the ASM 183
area indicate no apparent change of rainfall and wet conditions during the LIA relative 184
to the MCA. The locations of these records are shown in Fig. 2. Please see the Method 185
section for the definitions of the Relative Wet Index (RWI) and the wet/dry condition 186
during the LIA relative to the MCA/recent 150 years. 187
188
-160
-140
-120
-31
-29
-27
-25
-23
-0.7
-0.5
-0.3
-0.1
1000 1200 1400 1600 1800 2000
-2
-1
0
1
2
3
AD
-6.9
-6.7
-6.5
-6.3
-6.1
-5.9
-5.7
Lak
e L
adin
g (
8°S
)
Lea
f w
ax δ
D (
‰,V
PD
B)
Lia
ng
Lu
ar c
ave
(8.5
°S)
δ1
8O
(‰,V
PD
B)
Lo
gun
g L
ake
(8°S
)
δ1
3C
(‰,V
PD
B)
LIAMCA
N4
N3
W3
W5
W4
Mak
assa
r S
trai
t (5
°S)
δ1
8O
(‰,V
PD
B)
Mak
assa
r S
trai
t (4
°S)
Lea
f w
ax δ
D (
‰,V
PD
B)
Wet
Dry
RWI= 87%RWI= 41%
RWI= 124%RWI= 176%
RWI= 152% RWI= 142%
RWI= 152%
RWI= 86%
RWI= 78%
RWI= -138%
No apparent change
Wet LIA
Wet LIA
Wet LIA
Wet LIA relative to
MCA
© 2015 Macmillan Publishers Limited. All rights reserved
189
Figure s6: Near synchronous retreat of the EASM and the ASM during the LIA. 190
Hydrological records from the front areas of the EASM (top panel) and the ASM 191
(middle panel). The composite hydrological changes (30 years smoothing) of the 192
EASM (the average of records D1, D2, D3 and D4) and the ASM (the average of 193
records D10, D12 and D13) are shown in the bottom panel. All proxy records are 194
normalized to standard Z-scores. Standard Z-scores are calculated according to 195
Z=(X-V)/SD; where X is original value, V is the averaged of each time series, and SD 196
is the standard deviation of each time series. 197
198
-3
-2
-1
0
1
2
3
4
1000 1200 1400 1600 1800 2000
D1
D2
D3
D4
-3
-2
-1
0
1
2
3
D12
D13
D10
Year (AD)
Z-s
core
s
Z-s
core
s
Z-s
core
s
-2
-1
0
1
2
1000 1200 1400 1600 1800 2000
EASM
ASMLIA
Wet
Dry
EASM
ASM
© 2015 Macmillan Publishers Limited. All rights reserved
199
Figure s7: Schematic map depicting the current extent of the monsoon/ITCZ in the 200
East Asia-Australia area, and the hypothesized contraction of the monsoon/ITCZ zone 201
during the LIA. The hydrologic records in Figure 1 and 2 are also marked here. The 202
pink lines indicate the northern and southern limits of modern EASM and ASM. The 203
red shaded areas indicate the areas with possibly lower precipitation during the LIA 204
than during the MCA. The blue shaded area indicates the area with possibly more 205
precipitation during the LIA than occurred during the MCA. The monsoon/ITCZ 206
rainbelt would spend more time in the blue shaded area during the LIA than it did 207
during the previous MCA, while the rainbelt would spend less time in, or even 208
disappear from, the red shaded areas during the LIA. 209
210
D1D2D3
D4 D5
N1N2
W1
W2
60E 80E 100E 120E 140E 160E
45N
30N
15N
EQ
15S
30S
D6D7
D8
D9D12 D10
N3
W3
W4W5
D13
Dry LIA area?
Modern southern monsoon limit
Modern northern monsoon limit
Dry LIA area?
Wet LIA area?
D11N4
© 2015 Macmillan Publishers Limited. All rights reserved
-1
-0.5
0
0.5
1
1000 1200 1400 1600 1800 2000
-1
-0.5
0
0.5
1
1000 1200 1400 1600 1800 2000
AD
W/M
2W
/M2
-2.5
-1.5
-0.5
0.5
1.5
2.5
1000 1200 1400 1600 1800 2000
-2.5
-1.5
-0.5
0.5
1.5
2.5
1000 1200 1400 1600 1800 2000
AD
W/M
2
W/M
2
TSI (%MM decrease: -0.25%) TSI (%MM decrease: -0.65%)
TSI (%MM decrease: -0.25%) TSI (%MM decrease: -0.65%)
-0.5
-0.25
0
0.25
0.5
1000 1200 1400 1600 1800 2000
-0.6
-0.3
0.0
0.3
0.6
1000 1200 1400 1600 1800 2000
AD
W/M
2W
/M2
TSI (%MM decrease: -0.1%)
TSI (%MM decrease: -0.1%)
LIA LIA LIA
LIA LIA LIA
211
Figure s8: Top panels show the solar forcing variations over the last millennium 212
caused by the changes of the total solar irradiance (TSI, red line)1 and orbital 213
parameters (green is the July insolation at 23.5ºN and blue is the January insolation at 214
23.5ºS)55
. The TSI curve in the left, middle and right panel has been calculated by 215
assuming a TSI reduction by -0.1%, -0.25 % and -0.65% during the Maunder 216
Minimum1,56,57
. Please note the drastically different amplitude of solar forcing as 217
indicated by the changing vertical scales for each TSI scenario and that the January 218
and July dates may have been be shifted by about 17 days from AD 1000 to 2000 219
owing to apsidal precession58
of the Earth-Sun orbits. The bottom panel shows the 220
total solar forcing of the Northern Hemisphere at 23.5ºN (green) and the Southern 221
Hemisphere at 23.5ºS (blue), calculated by adding up the solar forcing that results 222
from changes in the intrinsic solar output and orbital parameters. The total solar 223
forcing for the last 1000 years shows the dominance of the symmetric solar forcing 224
rooted in the intrinsic solar magnetic activity variations rather than the anti-symmetric 225
solar insolation forcing caused by the Sun-Earth orbital precession parameters. 226
It should be noted that the range of the TSI amplitude change of about 0.2% to 227
0.6% shown in Bard et al (2000)1 is fully consistent with the empirical results shown 228
in Zhang et al. (1994)59
, and that the independent estimates for TSI variations from 229
© 2015 Macmillan Publishers Limited. All rights reserved
the study of solar-type stars by Zhang et al. (1994) has not yet been objectively ruled 230
out. We also wish to emphasize that our adopted choice of TSI amplitude of variations 231
follow empirically constrained results based on observations rather than theoretical 232
modeling works. That fact explains why the TSI in our climate simulation 233
experiments (-0.25%) and Liu et al (2009) (-0.3%) are still relatively larger than the 234
-0.1% recommended by Schmidt et al. (2011) for TSI change between the Maunder 235
Minimum and present57
. The 0.1% value is roughly rooted in the measured TSI 236
peak-to-peak amplitude for the 11-yr solar cycle variations (see e.g., Willson and 237
Hudson 1991)60
, whereas a drastically smaller TSI amplitude value of 0.04% listed in 238
Schmidt et al (2011) is specifically related to the theoretical assumption of no (or only 239
very small) TSI change in the published work of Wang et al. (2005)61
. Because the 240
small TSI amplitude variation is largely a theoretical assumption rather than any 241
confirmed, measured reality, we have chosen to adopt -0.25% as the optimal TSI 242
amplitude value for our climate simulation experiments shown in Figure 3d and 243
Figure s9. 244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
© 2015 Macmillan Publishers Limited. All rights reserved
260
-0.1
5-0
.05
00
.05
0.1
5
13
63
13
65
13
67
800 1000 1200 1400 1600 1800
Year (AD)
GM
I a
no
ma
lie
s [m
m/d
ay]
TS
I [w
/m^2
]
(c)(b)
(d)
(a)
261
Figure s9: (a) Low-pass (> 90-year timescales) filtered global monsoon index (GMI; 262
black) based on MIP-ESM last millennium simulation with only TSI (red) as external 263
forcing37
. In this simulation, 0.25% TSI change from the Maunder Minimum to 264
present has been applied (see Fig. s8 for our choice of the TSI data and amplitude). 265
Here the GMI is defined as the sum of local summer precipitation over the monsoon 266
domains in both hemispheres, where the annual range (MJJAS precipitation minus 267
NDJFM precipitation in the NH and NDJFM minus MJJAS precipitation in the SH) 268
of precipitation exceeds 2 mm/day and the local summer precipitation exceeds 55% of 269
annual rainfall36
. (b) Summer precipitation pattern under low solar activity conditions 270
© 2015 Macmillan Publishers Limited. All rights reserved
over the last millennium. The anomalies have been calculated by regression analysis 271
of the GMI with the local summer (June to August in the Northern Hemisphere and 272
December to February in the Southern Hemisphere) precipitation during AD 273
850-1850. A low-pass filter has been applied to both the GMI and precipitation filed 274
prior to the analysis in order to concentrate on precipitation pattern associated with the 275
solar variability on multidecadal-to-centennial timescales. The high correlation 276
(r=0.45 when GMI lags TSI by 10 years) between the two indices suggests that the 277
centennial precipitation pattern here is primarily forced by the solar variability. The 278
zonal mean precipitation pattern, which revealed decreased monsoon precipitation in 279
both northern and southern tropical-subtropical monsoon area, and increased rainfall 280
in equatorial area, is also given (c). (d) The simulated annual mean precipitation 281
anomaly during the late Maunder minimum62
of the LIA (AD 1690-1740) with 282
reference to the long-term (AD 1000-1800) mean (i.e., similar to Fig. 3d, but Fig. 3d 283
focuses on western Pacific region while here a circum-global view over the tropics is 284
presented). Here the interval for LIA has been chosen according to the simulated GMI 285
in (a), when the model has better performance on simulating the monsoonal 286
precipitation associated with the solar irradiance during the Maunder Minimum. 287
288
© 2015 Macmillan Publishers Limited. All rights reserved
289
Figure s10: Comparison between solar irradiance2 (in the original net radiative 290
forcing units defined in Ref. 2) and hydrological records D43, D8
4 and W2
5 from the 291
Asian-Australian monsoon area. The vertical shaded bars indicate time intervals of 292
decadal-scale solar irradiance minima. Significant correlations were observed between 293
solar irradiance and hydrological records D8 (r = 0.54, p<0.05) and W2 (r = 0.68, 294
p<0.05). We adopted the composite solar irradiance record from Ref. 2, which is the 295
splice of the 0.25% TSI series from Ref. 1 for 1000-1610 AD (hence similar to results 296
shown in the top panels of Fig. s8); another higher temporal resolution TSI taken from 297
Ref. 2 was used for the 1610-1998 AD interval. It is worth noting that the calculated 298
- 0. 3
- 0. 2
- 0. 1
0
0. 1
0. 2
0. 3
- 3
- 2. 5
- 2
- 1. 5
- 1
- 0. 5
0
0. 5
1
1. 5
2
1000 1500 2000
- 0. 6
- 0. 4
- 0. 2
0
0. 2
0. 4
0. 6
- 8. 8
- 8. 6
- 8. 4
- 8. 2
- 8
- 7. 8
- 7. 6
- 7. 4
- 2
- 1. 5
- 1
- 0. 5
0
0. 5
1
1. 5
2
- 0. 70
- 0. 60
- 0. 50
- 0. 40
- 0. 30
- 0. 20
- 0. 10
0. 00
-8.8
-8.6
-8.4
-8.2
-8
-7.8
-7.6-0.3
-0.2
-0.1
0
0.1
0.2
0.3-2
-1
0
1
2
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
1000 1200 1400 1600 1800 2000
Gre
at B
arri
er R
eef
(~18
.5°S
)
Sea
wat
er δ
18O
(‰,V
PD
B)
Wan
xia
ng
cav
e (3
3.3
°N)
δ1
8O
(‰,V
PD
B)
D4
Do
ngd
ao,
SC
S (
16
.7°N
)
MG
S (
µm
)
W2
D8
So
lar
irra
dia
nce
(W/m
2)
Wet
Dry
Wet
Dry
Wet
Dry
AD
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correlations between proxy records and solar activity record are dominated by the 299
low-frequency (i.e., centennial and bicentennial) variability, not the decadal variability. 300
Moreover, only parts of (not all) decadal variability in proxy records are correlated 301
with the solar activity record. Some reasons exist that could explain the disagreement 302
between the decadal variation of proxy records and solar activity records, including 303
time delays for hydrologic changes in response to solar activity forcing, spatial 304
differences of the local and regional rainfalls in response to solar variations (e.g., wet, 305
dry and no changes in different regions in response to the same solar minima) and the 306
quality of the proxy records (e.g., time resolution, error of age model). 307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
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Supplementary Table 329
Table s1: RWI values and t-test statistics calculated for the difference of two means 330
(LIA vs. MCA or Recent 150 years) for the EASM-ASM hydrologic records in Fig. 1 331
and Fig.2. In addition, we have also performed sensitivity tests to confirm the robustness of our 332
adopted RWI results but choosing slightly different start and end intervals for MCA, LIA and 333
current warm period (e.g., LIA covering AD 1400-1850 instead of the main choice of AD 334
1400-1700 adopted or MCA to be from AD 1000-1400 compared to the chosen MCA interval of 335
AD 1000-1300). We did not find any drastic change to our RWI and t-test results under such 336
perturbations. Only some slight changes were observed in the records from transition area, such as 337
N1, N3 et al. 338
339
Region Record
Number Reference
RWI, p value of the t-test (two tails), Hydrological condition
Hydrological condition between LIA
and MCA
Hydrological condition between
LIA and recent 150 years
EASM D1 39 -85%, p<0.01, Dry -153%, p<0.01, Dry
EASM D2 40 -110%, p<0.01, Dry -74%, p<0.01, Dry
EASM D3 8 -112%, p<0.01, Dry -102%, p<0.01, Dry
EASM D4 3 -145%, p<0.01, Dry -144%, p<0.01, Dry
EASM D5 7 -96%, p<0.01, Dry -90%, p<0.01, Dry
EASM N1 9 -24%, p>0.05, No apparent change -153%, p<0.01, Dry
EASM N2 41 29%, p>0.05, No apparent change 24%, p>0.05*, No apparent
change
EASM W1 42,43 121%, p<0.01, Wet 189%, p<0.01, Wet
EASM W2 5,27 156%, p<0.01, Wet 163%, p<0.01, Wet
ASM D6 47-49 -71%, p<0.01, Dry
ASM D7 50 -62%, p<0.05 (0.021), Dry
ASM D8 4 -143%, p<0.01, Dry
ASM D9 51 -92%, p<0.01, Dry
ASM D10 44,45 -92%, p<0.01, Dry -80%, p<0.01, Dry
ASM D12 10 -155%, p<0.01, Dry -178%, p<0.01, Dry
ASM D13 46 -105%, p<0.01, Dry -142%, p<0.01, Dry
ASM N3 52 87%, p>0.05, No apparent change 41%, p>0.05, No apparent
change
ASM N4 53 78%, p<0.01, Wet -138%, p<0.01, Dry
ASM W3 54 124%, p<0.01, Wet 176%, p<0.01, Wet
ASM W4 18 152%, p<0.01, Wet 142%, p<0.05 (=0.023), Wet
ASM W5 19,21 173%, p<0.01, Wet 86%, p<0.01, Wet
340
341
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