Supplementary information
Supplementary Figure 1
Figure S1. The Riwasa basin lies in the Bhiwani District of Haryana State, India
(Saini et al., 2005). The sampled exposed well section (red circle) is located at
N28°47’21. 6’’ E075°57’24.6’’. Overlain on the photograph are the
geomorphological units in the Riwasa area, inselbergs (black with white outlines),
lacustrine deposits (blue areas), aeolian sand dunes and sheets (unshaded regions).
Also shown on the picture is the location of Riwasa village and Dhani Mahu village
(black). (Source: Google. (2013) Google Earth (Version 6.1) [Computer program].
Available at http://www.google.com/earth/download/ge/agree.html (Accessed 24
1
March 2013)
Supplementary Figure 2
Figure S2. Adult calcite carapace of the ostracod species Cyprideis torosa that was
used for oxygen isotopic measurement. This species thrives in NaCl-rich waters and is
abundant in Riwasa paleolake sediments.
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Supplementary Figure 3:
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Figure S3: (A) Example of a well-preserved specimen of M. tuberculata used for
isotopic analysis and radiocarbon dating from paleolake Riwasa sediments. (B) X-ray
diffractogram of the M. tuberculata shell with expected positions of peaks for
aragonite (red lines).
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Supplementary Figure 4
5
6
Figure S4. (A&B) Shell fragments from 247-278cm used for AMS 14C dating of the
base of the Riwasa well section. (C) XRD indicates the shell fragments are composed
of both calcite (red peaks) and aragonite (blue peaks) with calcite as the dominant
mineral. This contrasts with whole shells of M. tuberculata, which are pure aragonite
(Fig. S2). The radiocarbon age obtained on the shell fragments was younger than
expected (8665±40 14C yr B.P.) because of diagenetic alteration of aragonite to
calcite. We reject this date on the basis of poor preservation.
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Supplementary Figure 5
8
Figure S5. Photographs of the hardground (A) Gastropod beachrock showing lithified
gastropod shells embedded in calcite cement forming the hardground. (B) Samples of
hardground showing fossil root casts filled by darker sediment.
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Supplementary Figure 6
Figure S6. Scanning electron photomicrograph of the hardground showing (A) a
smooth, well-preserved gastropod in calcite cement; (B) calcite crystals cementing the
shells.
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Supplementary Figure S7
Figure S7. Mineralogy of the hardground as determined by X-ray diffraction. XRD
results of hardground cement show 2-theta peak of calcite in red (C), traces of halite,
NaCl in green (H) and quartz in blue (Q).
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Supplementary Figure 8
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Figure S8: (A) Massive calcareous deposits (Unit III) in the Riwasa well section
sediments capped by 12-cm hardground (Unit II). (B) Photograph of the Riwasa well
section with lithostratigraphy (left) and environmental interpretation (right). From top
to bottom; Unit I- Silty sand; Unit II- Argillaceous hardground; Unit III- Massive
calcareous shelly deposit with gastropod and ostracods; Unit IVa- Greenish silt with
ostracod and gastropod shells, Unit IVb- Gray silt with ostracods; Unit V- yellow
aeolian sand. Overlain on the photograph is the 18O of C. torosa (black), M.
tuberculata (green) and bulk carbonate (blue). The hardground exposure surface
forms a hard bench marking the transition between Units I and II.
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Supplementary Figure 9
Figure S9: Bulk carbonate 18O and 13C isotopes in paleolake Riwasa sediments.
The lithology and faunal assemblage indicate a lacustrine environment beginning at
11 kyr B.P. The 18O shows two periods of high values: one associated with the hard
ground between ~8.3-7.9 kyr B.P. and the other at ~9.6 kyr B.P., preceding the shift
to lower 18O at 9.4 kyr B.P., which marks the onset of the deep-water phase. The
bulk oxygen isotopes are low and carbon isotopes are highest during the deep-water
phase reflecting high primary productivity between 9.4 to 8.3 kyr B.P. The lack of
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covariance between the bulk carbonate 18O and 13C before and after the deep water
phase suggests presence of secondary carbonates (Talbot, 1990).
Supplementary Figure 10
Figure S10. The nearest International Atomic Energy Association (IAEA) GNIP
station to Riwasa, from which water isotope data are available, is at New Delhi.
Seasonal variations in monthly precipitation (yellow bars), surface air temperatures
(red) and 18O of precipitation (purple) from New Delhi. The rainfall at New Delhi
(representative of north Indian plains) is mainly caused by the northwesterly moving
monsoon depressions from the head of Bay of Bengal and the rainout efficiency is
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about 56% (Bhattacharya et al., 2003; Sengupta and Sarkar, 2006). The low18O
values associated with maximum summer rainfall in July-Aug-Sept extend into
October and November before increasing after December (Rozanski et al., 1993). The
seasonal range in 18O is large, averaging -7.5‰ during the summer monsoon season
and 0.3‰ during the dry season.
AGE ESTIMATION OF THE HARDGROUND
Onset of hardground formation:
We have estimated what effect a small hard water error might have on the estimated
age of the onset and end of hardground formation (Table S1, S2, S3).
Depth
Age (14C
yr)
2
error
HW error
(14C yr)
Corrected
age (14C yr)
Cal. age
2 error
(yr B.P.)
121
7505
±45
100
7405
8205
145
121
7505
±45
200
7305
8100
90
Table S1: Hard water lake error correction of 100-200 14C yr B.P. of the estimated
age of the onset of hardground formation at 121 cm.
End of hardground formation:
As the sediment lithology is same following the hardground to top of the section, the
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end of the hardground formation at 108cm was estimated by extrapolation by the
sedimentation rate obtained from above to be 7.9±0.1 kyr B.P. We estimated the
effect of a small (up to 200yrs) hard water error might have on the 14C ages obtained
from 70 and 96 cm and propagated the combined errors including calibration,
reservoir age, and interpolation to the hardground horizon.
Case I: Assuming negligible hard water lake error and the propagation of error from
the combined error including calibration i.e. analytical uncertainty and interpolation
to the hardground horizon
The age of the end of hardground formation was estimated by linear extrapolation of
the 14C ages obtained from 70 and 96 cm, the slope of the regression line m, is given
by:
m
(7666  7155 )
(t 96  t 70 )

 19.65yr /cm
(96  70)
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where t70 and t96 is the calibrated age at 70 cm and 96 cm respectively.

Extrapolating upto the depth 108 cm, the age at 108cm, t108 is
t108 = (96-108)*m + t96 = 7901.8 yr (~7900 yr)……………(i)
Now if we consider, the calibration errors associated with t70 and t96 as t70 and t96
respectively then the new resultant slope (m’) of the line with the associated error, say
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m, is given by
m'  m  m  19.65 
(t96 mt 70 )
(96  70)
Using the upper
 and lower bounds of the analytical errors on the calibrated ages at 76
cm and 96 cm i.e. ±134 and ±59 yr respectively, the propagated error on slope (m) is
±2.9 and ±7.9 yr/cm.
Introducing this error in the calculation of the extrapolated age, t108, at 108cm
t108'  (96 108)m'(7666  t96 )
Substituting the corresponding values of the new slope m’ and rearranging the

equation:
t108'  (96 108)(m  m)  (7666  t96 )  (96 108)m  7666 12m  t 96

substituting (i), the age at 108 cm i.e. ~7900 yr in this equation, we have
t108'  7900  (12m  t96 )  t108  t108.............................(ii)
Hence the combined error propagated in the calculation of the extrapolated date at a

depth of 108 cm corresponding to the beginning of the hardground is
(12m  t96 )which following substitution of the m = ±2.9 and ±7.9 can be obtained
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
to be ±34.8±59 and ±88.8±59. The extrapolated age has been shown in the plot (Fig.
S9 ) along with the maximum (±147.8) and minimum (±24.2) range of errors
associated with obtained age at 108cm.
Figure S11 Error propagation on the age at 108 cm assuming negligible hard water
error. The maximum age range for the end of hardground formation is 8050-7750 yr
B.P.
Case II: Hard water lake error of 100 yrs
Depth
Cal. age
Age (14C yr)
2
HW error
Corrected
2 error
19
(cm)
error
(14C yr)
age (14C yr)
(yr B.P.)
70
6270
±45
100
6170
7088
148
96
6835
±30
100
6735
7592.5
67.5
Table S2: Age estimation at 108 cm using the equation (i) given in Case I is 7825 yr
B.P. and the propagated combined errors of calibration and linear extrapolation gives
±166.9 yr and ±30.3 yr as maximum and minimum uncertainties respectively. Hence,
the maximum age range would be 7992 – 7658 yr B.P.
Case III: Hard water lake error of 200 yrs
Depth
Cal. age
2
2 error
(cm)
Age (14C yr)
error
HW error
(14C yr)
Corrected
age (14C yr)
(yr B.P.)
70
6270
±45
200
6070
6908
120
96
6835
±30
200
6635
7519
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Table S3: Age estimation at 108 cm using the equation (i) given in Case I is 7800 yr
B.P. and the propagated combined errors of calibration and linear extrapolation gives
±135.8 and ±25.6 as maximum and minimum uncertainties respectively. Hence, the
maximum age range would be 7936 – 7664 yrs B.P.
The calibrated age corrected for hard water lake error for the onset of hardground
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formation lies between 8205-8100 yr B.P. which still corresponds well with the
radiometrically-dated speleothems age of weakening of the Asian and Indian
monsoons between ~8.2 and 8.0 kyr B.P. (Cheng et al., 2009; Fleitmann et al., 2003;
Liu et al., 2013; Morrill et al., 2013). For the end of the hardground formation, the
calibrated age corrected for combined errors i.e. hard water lake error of up to 200 yrs
and analytical error and error due to linear regression, gives a range of 7.9-7.7 kyr
B.P.
References:
Bhattacharya, S.K., Froehlich, K., Aggarwal, P.K., Kulkarni, K.M., 2003. Isotopic
variation in Indian Monsoon precipitation: Records from Bombay and New
Delhi. Geophys. Res. Lett. 30, 2285.
Cheng, H., Fleitmann, D., Edwards, R.L., Wang, X., Cruz, F.W., Auler, A.S.,
Mangini, A., Wang, Y., Kong, X., Burns, S.J., 2009. Timing and structure of
the 8.2 kyr BP event inferred from δ18O records of stalagmites from China,
Oman, and Brazil. Geology 37, 1007–1010.
Fleitmann, D., Burns, S.J., Mudelsee, M., Neff, U., Kramers, J., Mangini, A., Matter,
A., 2003. Holocene forcing of the Indian monsoon recorded in a stalagmite
from southern Oman. Science 300, 1737 –1739.
Liu, Y.-H., Henderson, G.M., Hu, C.-Y., Mason, A.J., Charnley, N., Johnson, K.R.,
Xie, S.-C., 2013. Links between the East Asian monsoon and North Atlantic
climate during the 8,200 year event. Nat. Geosci 6, 117–120.
Morrill, C., Anderson, D.M., Bauer, B.A., Buckner, R., Gille, E.P., Gross, W.S.,
Hartman, M., Shah, A., 2013. Proxy benchmarks for intercomparison of 8.2 ka
simulations. Clim. Past 9, 423–432.
Rozanski, K., Araguás-Araguás, L., Gonfiantini, R., 1993. Isotopic patterns in modern
global precipitation. Geophys. Monogr. Ser. 78, 1–36.
Sengupta, S., Sarkar, A., 2006. Stable isotope evidence of dual (Arabian Sea and Bay
of Bengal) vapour sources in monsoonal precipitation over north India. Earth
Planet. Sci. Lett. 250, 511–521.
Talbot, M.R., 1990. A review of the palaeohydrological interpretation of carbon and
oxygen isotopic ratios in primary lacustrine carbonates. Chem. Geol. Isot.
Geosci. Sect. 80, 261–279.
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