www.elsevier.com/locate/yqres

Quaternary Research 62 (2004) 19–28

Oxygen isotopes of bovid teeth as archives of paleoclimatic variations

in archaeological deposits of the Ganga plain, India

Shikha Sharma,a,b,* Michael M. Joachimski,a Heinz J. Tobschall,a Indra B. Singh,b

Devi P. Tewari,c and Rakesh Tewarid

a Institut fur Geologie und Mineralogie, Universitat Erlangen–Nurnberg, Schlossgarten 5, 91054 Erlangen, GermanybDepartment of Geology, Lucknow University, Lucknow 226007, India

cDepartment of Ancient Indian History and Archaeology, Lucknow University, Lucknow 226007, IndiadU.P. State Archaeological Department, Roshanud-daula Kothi, Lucknow, India

Received 30 June 2003

Available online 13 May 2004

Abstract

Oxygen isotope analysis was performed on enamel phosphate of mammalian teeth from archaeological sites Kalli Pachchhim and

Dadupur in the central Ganga plain and Charda in the northern Ganga plain. The bulk oxygen isotopic compositions of enamel phosphate

from third molars (M3) of Bos indicus individuals belonging to different cultural periods were used to understand the climatic changes during

the past 3600 cal yr B.P. Oxygen isotope ratios indicate humid conditions around 3600 cal yr B.P., followed by a trend toward drier

conditions until around 2800 cal yr B.P. Then from 2500 to 1500 cal yr B.P. there is a trend toward higher humidity, followed by the onset of

a dry period around 1300 cal yr B.P. The study of intratooth y18O variations in teeth from different periods demonstrates that the monsoon

seasonality was prominent. Spatial changes in the amount of annual rainfall are also reflected in the y18O values. Teeth derived from areas

with intense rainfall have lighter isotope ratios compared to teeth from regions receiving less rain, but they show similar seasonal patterns.

The long-term paleoclimatic variations reflected by fluctuations in bulk y18Op values from M3 teeth match well with the regional

paleoenvironmental records and show a good correlation to the cultural changes that took place during this time span in Ganga plain.

D 2004 University of Washington. All rights reserved.

Introduction enamel does not always reflect a closed system and may be

One of the most promising methods of continental

climate reconstruction is the analysis of the oxygen isotopic

composition of mammalian hard tissues. Of the various

oxygen-bearing hard tissues (e.g., bone, dentine, and enam-

el), tooth enamel is considered to retain the isotopic sig-

natures with high fidelity (Bryant et al., 1994; Fricke et al.,

1998; Kohn et al., 1998). This is because tooth enamel has a

lower organic content relative to dentine and bone phos-

phate, and it is precipitated as larger fully crystalline apatite

crystals. Due to its dense, well-crystallized nature, it is more

resistant to diagenetic alterations than other, less well

crystallized phosphatic hard parts. However, a recent study

by Lee-Thorp and Sponheimer (2003) demonstrates that

0033-5894/$ - see front matter D 2004 University of Washington. All rights rese

doi:10.1016/j.yqres.2004.03.003

* Corresponding author. Present address: Department of Geological

and Atmospheric Sciences, 253 Science 1, Iowa State University, Ames, IA

50011, USA.

E-mail address: ssharma@iastate.edu (S. Sharma).

prone to diagenesis. Nevertheless, it retains the biogenic

isotopic signals very well.

The nearly constant body temperature of mammals

makes it possible to interpret the oxygen isotopic composi-

tion of tooth enamel in terms of the isotopic composition of

the body water, which is related to the isotopic composition

of ingested meteoric water and food. Since the y18O value of

meteoric water is dependent on temperature and rainfall

intensity, the oxygen isotopic composition of tooth enamel

may provide a record of climatic changes. Oxygen is present

in both phosphate (PO43�) and carbonate (CO3

2�) phases in

enamel apatite. Both groups are cogenetic oxygen-bearing

phases in isotopic equilibrium with the same oxygen reser-

voir at the same temperature (of body water, 37jC). Thus, alinear correlation exists between the two phases (Bryant et

al., 1996; Iacumin et al., 1996). However, taking into

consideration that y18O values of the carbonate phase may

be modified more easily than y18O values of the phosphate

phase during diagenesis (Iacumin et al., 1996; Fricke et al.,

rved.

S. Sharma et al. / Quaternary Research 62 (2004) 19–2820

1998), we chose to measure the y18O values of enamel

phosphate.

In the present study we have made an attempt to interpret

climatic variations during the past 3600 yr using oxygen

isotope data from teeth enamel from archaeological sites in

the central alluvial plain of the Ganga river. This is the first

record of climatic variability in the Ganga plain during this

time frame. However, in a monsoon-dominated system,

there may be century- and decade-scale cycles of monsoon

activity (Sirocko et al., 1996). Considering the standard

deviation of radiocarbon dates, it is difficult to place a tooth

sample precisely within a century-scale cycle. The present

study is an initial step in the direction of more exhaustive

high-resolution studies, which are needed to ascertain these

paleoclimatic variations.

Study area

Large-scale human migration and settlement in the

Ganga plain began in the late Holocene when the people

transformed from hunter–gatherers to settled agriculturists.

Most of these late Holocene inhabitation sites are located on

mounds that represent natural levees or raised floodplains.

Fig. 1. Schematic map showing the geomorphic divisions of the Ganga plain along

and Charda, in the Himalayan foothills.

The present study was carried out on tooth samples from

three systematically excavated archaeological sites in the

Ganga plain. The archaeological sites of Kalli Pachchhim

(latitude 26j43V N, longitude 80j57V E) and Dadupur

(latitude 26j42VN, longitude 80j49VE) are located close

to the Lucknow township in the central Ganga plain,

whereas the archaeological site Charda (latitude 27j56V45W N, longitude 81j36V40W E) is located in the northern

part of Ganga plain, close to the Himalaya mountains (Fig.

1). A brief description of the archaeological periods is given

in Table 1.

The archaeological succession of the Kalli Pachchhim

site consists of Northern Black Polished Ware phase

(NBPW), Kushan, Gupta, post-Gupta, and Early Medieval

(EMP) periods. The Dadupur site encompasses three distinct

cultural periods: the Red Ware-dominated Early phase,

Painted Gray Ware (PGW) phase, and NBPW phase. The

cultural sequence recognized at the archaeological site of

Charda is the NBPW phase followed by Kushan, Gupta,

post-Gupta, and Medieval periods.

The archaeological sites of Kalli Pachchhim and Dadu-

pur lie in close proximity on the same latitude about 25 km

apart. Therefore, data from these two sites have been

grouped for paleoclimatic reconstruction. The Charda ar-

with the locations of the sites Kalli Pachchhim and Dadupur, near Lucknow,

Table 1

Archaeological strata, their ages, and cultural characteristics

Age (years B.P.) Archaeological strata Cultural characteristics

800–1400 Early Medieval period and post-Gupta period Period of urban decay and people restored to pastoralism.

There is description of frequent famines in literature of this

period (Dhavalikar, 2001).

1400–1700 Gupta period (post-Kushan period or Classical

period)

The ‘‘Golden Age’’ of Indian history, known for its prosperity,

dense population, and long-distance trade.

1700–2000 Kushan period Period of cultural prosperity.

2000–2600 Northern Black Polished Ware phase (NBPW)

(Early Historical period)

Period of urbanization and long-distance trade and intense

agriculture. Higher rainfall reported in several literary texts

from this period (Dhavalikar, 2001).

2600–3000 Pre-NBPW period (Painted Gray Wares in western

Ganga plain)

Village culture with agriculture and pastoral habits.

3000–3600 Red Ware-dominated Early phase (Ochre Colored

Pottery in western Ganga plain)

Agriculture activity and domestication of animals.

S. Sharma et al. / Quaternary Research 62 (2004) 19–28 21

chaeological site is discussed separately as it lies in the

Piedmont plain where mean annual rainfall is about 1200

mm, much higher than in the Lucknow region.

Fig. 2. Seasonal variations in y18O of precipitation, annual precipitation,

and surface air temperature from 1961 to 1971 for New Delhi (IAEA/WHO,

2001). y18O values and temperature values are given for all the years

individually. The symbols represent different years from 1961 to 1971.

Monthly precipitation is presented as average amount of rainfall for the

same period. V-SMOW is Vienna standard mean ocean water.

Oxygen isotopes and climate

The oxygen isotopic composition of mammalian tooth

enamel is directly related to the oxygen isotope composition

of body water. The body’s main oxygen sources are drinking

water, atmospheric oxygen, and oxygen-bearing organic

compounds. As the y18O value of atmospheric O2 is constant,

the enamel y18O is controlled primarily by the composition

of ingested water and, to a lesser degree, by the y18O of the

diet (Sponheimer and Lee-Thorp, 1999). It can be assumed

that the y18O of local meteoric water would be the primary

source of variations reflected in the y18O of tooth enamel for

animals of a given species with similar feeding habits.

As y18O values of enamel phosphate provide information

about y18O values of precipitation (y18Opt), it is necessary to

know modern annual variation of y18Opt values before

inferring past climatic variations. The y18O of precipitation

is influenced by a large number of factors, including

continentality, latitude, and altitude, as well as temperature

and amount of precipitation. The temperature effect is the

primary factor controlling y18Opt in areas beyond the

influence of the monsoonal rain. However, in the monsoonal

domain, y18Opt values are no longer correlated with ground

temperature, but with the ‘‘amount of precipitation’’ (Rozan-

ski et al., 1993; Wei and Gasse, 1999). In general, intense

and frequent rainfalls in warm humid regions have unusu-

ally low y18Opt values, probably because of condensation

cooling within rain clouds. In contrast, sparse rain over

warm and drier regions shows higher y18Opt values due to

evaporative enrichment of 18O in rain droplets (Dansgaard,

1964; Rozanski et al., 1993).

In the present study oxygen isotope data collected at New

Delhi (IAEA/WHO, 2001) are used as a reference because

the two archaeological sites of Kalli Pachchhim and Charda

are located 500 km east of New Delhi and experience the

same temperature and rainfall variations throughout the

year, with annual rainfall of f900 mm. The y18O data are

presented in Fig. 2.

The climate exhibits three seasons: cold, hot, and mon-

soon. The cold season (November to February) is charac-

terized by mean minimum and maximum temperatures of

7.6j and 21jC; the hot season (March to June) is marked by

S. Sharma et al. / Quaternary Research 62 (2004) 19–2822

hot northwestern winds and average mean minimum and

maximum temperatures of 27j and 32.5jC with peak

temperatures of 46jC in June; the monsoon (July–October)

is characterized by heavy rainfall. y18Opt values conversely

correlate with temperature: months with higher temperatures

show lower y18Opt values. The typical seasonal trend in

y18O is that months with heavy rainfall (July–September)

have significantly lower y18Opt values than months with less

intense rainfall (Fig. 2). Precipitation in June is usually more

enriched in y18Opt relative to July because evaporation

during hot and dry summers enriches 18O in rain droplets.

However, precipitation in September–November shows the

lowest y18Opt values, due to high humidity and low evap-

oration. The monsoonal rain fills ponds and lakes with water

relatively enriched in 16O. Little water is added during the

rest of the year. However, surface water evaporates and

some shallow ponds dry up completely. Because evapora-

tion enriches the remaining water body in 18O, ponds and

lakes are expected to show a seasonal variation in y18O,with lowest values during the monsoon and early cold

season and gradually increasing values thereafter.

At present, the Kalli Pachchhim and Dadupur archaeo-

logical sites have the same seasonal variation in rainfall and

temperature as New Delhi. On the other hand, the Charda

archaeological site located near the Himalayan foothills has

higher atmospheric humidity throughout the year, with

annual rainfall of 1200 mm, and lower maximum summer

temperatures.

Samples and methods

Herbivore teeth of a single genus (Bos indicus) were

chosen for this study because changes in genus-specific

dietary habits and metabolic processes may affect the y18Oof tooth enamel (Kohn, 1996; Fricke et al., 1998). Fur-

thermore, Clementz and Koch (2001) showed that con-

sumption of drinking water from different types of water

sources can contribute to y18O variability at the individual,

population, and species levels. In the present study, how-

ever, we presume that the animals were drinking water

from restricted sources. This presumption is based on the

fact that domestication of B. indicus in the Ganga plain

dates back to at least 3700 cal yr B.P. Thus it is reasonable

to assume that the animals drank water only from nearby

monsoon-dependent ponds and creeks, because under-

ground water resources had not yet been exploited by man.

It is well known that teeth formed early in an animal’s

life are enriched in 18O compared to meteoric water (pre-

weaning signal) as a result of metabolic processes (Bryant et

al., 1994). Generally, then, M3 teeth are analyzed to infer

y18O for meteoric water, because they form at a later stage

of the animal’s life when it is consuming an adult diet,

eliminating the effect of weaning. Consequently, we col-

lected and analyzed only M3 teeth of B. indicus, from

different stratigraphic layers at the three archaeological sites.

Two separate sampling strategies were followed. The

first strategy relied on the collection of bulk enamel samples

from different teeth. For the bulk sample, all teeth were

sampled lengthwise, the sample consisting of a vertical strip

2–3 mm wide and spanning the entire height of the tooth,

i.e., from apex to cervix. This sampling strategy gives an

integrated y18O signal for the entire growth period (Gadbury

et al., 2000). The second strategy was to take multiple

samples from the same tooth to study the seasonal varia-

tions. Sampling was done along the entire height of the

crown by milling a series of horizontal bands perpendicular

to the growth axis. This strategy, adopted by several workers

(Fricke and O’Neil, 1996; Stuart-Williams et al., 1997), is

justified by the fact that tooth development proceeds from

the apex toward the cervix of the crown. However, it has

been criticized by Wiedemann (2000) and Balasse (2002),

who argue that the horizontal direction might not always

coincide with the progression of the front of matrix secretion,

because enamel maturation or secondary mineralization

occurs in successive fronts moving in different directions

across the enamel layer. Consequently, a sample drilled

horizontally through the entire enamel layer may represent

a discontinuous time sequence.

A comparative study was done by Balasse (2003) on two

molars of a modern goat. A sequence of horizontal bands

was milled on the right molar, whereas on the left molar,

enamel was sampled at about 45j from the horizontal in the

direction of the hypoplasia line, which gives the direction of

the front of matrix secretion. Both the amplitude and the

profile of the isotopic variation along the two teeth were

very similar, suggesting that the time sequences obtained

from the two sampling procedures do not differ significant-

ly. This finding suggests that the sampling procedure

applied in this study is appropriate.

The radiocarbon ages of charcoal samples from the

Dadupur and Kalli Pachchhim sites were measured by the

liquid scintillation counting technique at the Birbal Sahni

Institute of Palaeobotany, Lucknow. The charcoal samples

from the Charda section were dated using the accelerator

mass spectrometry (AMS) technique at the Physics Depart-

ment of the University of Erlangen–Nuremberg. The cali-

brated ages were obtained using the INTCAL 98 calibration

program of Stuiver et al. (1998).

For isotopic analysis f1 mg of enamel powder was

soaked in 2.5% NaOCl for 24 h to remove organic matter.

Oxygen isotope analysis was performed on tri-silver phos-

phate prepared following a slightly modified method of

O’Neil et al. (1994) described in Wenzel et al. (2000), using

a high-temperature conversion elemental analyzer coupled

to a Thermo Finnigan DELTAplus mass spectrometer. Sam-

ples and standards were run in triplicate. Accuracy and

reproducibility of the measurements were checked by mul-

tiple analyses of tri-silver phosphate prepared from

NBS120c and several tri-silver phosphate reference samples

received from other laboratories. All y18O values are

reported as per mil deviation relative to V-SMOW (Vienna

Table 3

Oxygen isotope ratios (y18Op) of bovid M3 teeth from Kalli Pachchhim and

Dadupur

Sample

and

subsample

Position

(mm)

y18Op (x)

(serial

sampling)

y18Op (x)

(bulk

sampling)

Cultural

period

DDR-9 21.9 Pre-PGW

1 36.4–37.7 21.4

2 32.2–33.1 23.3

3 25.4–26.7 25.8

4 20.8–21.8 25.7

5 15.4–16.6 22.2

6 10.2–11.2 20.7

7 4.3–5.2 19.8

KPMT5-9 23.9 NBPW

1 51.0–52.9 21.9

2 47.2–49.3 23.0

3 43.0–45.6 22.3

4 38.2–39.2 23.6

5 32.4–34.2 25.4

6 26.6–28.7 26.7

7 21.8–23.6 26.7

8 17.2–19.0 26.9

9 11.7–13.6 24.6

10 5.0–7.2 22.2

11 2.5–4.0 22.6

KPK 22.2 Kushan

Table 2

Radiocarbon ages of the charcoal samples from different archaeological

periods

Sample

name

Lab No. 14C dates

(14C yr B.P.)

Calibrated dates

(cal yr B.P.)

XD 5-4a Archaeoclima

07/01-3

510F 50 560

YA 21-6a Archaeoclima

07/01-2

2130F 60 2150

YA 21-11a Archaeoclima

07/01-1

2340F 60 2440

KPM2a BS 1950 2390F 100 2520

DDR 3cb BS 1822 3270F 80 3470

DDR 3bb BS 1759 3380F 160 3630

DDR 3ab BS 1825 3430F 90 3660

The radiocarbon ages have been calibrated using the calibration program of

Stuiver et al. (1998).a Dated by the accelerator mass spectrometry technique in the Physics

Department at University of Erlangen-Nuremberg, Germany.b Dated by the liquid scintillation counting technique at the Birbal Sahni

Institute of Palaeobotany, Lucknow, India.

S. Sharma et al. / Quaternary R

standard mean ocean water). Accuracy and reproducibility

of the measurements is within 0.2x (1 standard deviation).

The mean y18O value of NBS120c was 22.3x V-SMOW,

which is 0.6x higher than the values reported by Crowson

et al. (1991) and Lecuyer et al. (1993), but relatively close to

the value of 22.58x determined recently by conventional

fluorination with BrF5 (Vennemann et al., 2002). The

oxygen isotopic composition of Ag3PO4 standard YR-2

(provided by R. Blake and T. Vennemann; see Vennemann

et al., 2002) was measured as 13.2x.

1 46.1–47.3 20.2

2 40.4–42.4 21.4

3 35.7–36.7 22.6

4 30.8–31.8 22.5

5 26.8–27.9 22.2

6 22.3–23.2 22.6

7 17.4–19.2 22.5

8 9.7–11.1 22.3

9 4.3–6.1 20.3

GU 6 a 20.3 Gupta

1 43.2–44.2 22.4

2 37.5–38.4 21.8

3 32.2–32.7 22.0

4 25.7–26.4 22.5

5 18.7–19.6 18.9

6 13.7–14.2 18.2

7 7.8–8.5 18.6

8 2.1–2.8 18.6

KPMT3-

EMP

24.2 EMP

1 36.9–38.7 24.4

2 31.8–33.3 25.5

3 27.9–29.3 25.4

4 23.7–25.2 25.4

5 18.5–20.7 24.6

6 13.8–17.9 23.8

7 7.8–11.9 23.2

8 3.5–6.5 20.8

The position of the sample represents the distance of the sample from the

cervical margin in serial sampling. All values relative to V-SMOW.

Results

Radiocarbon ages

The radiocarbon ages determined on the charcoal sam-

ples from the three sites are given in Table 2. In Dadupur

section the radiocarbon date of a charcoal sample from the

layer just below pre-PGW is 3430 F 90 14C yr B.P. (3660

cal yr B.P.). The charcoal samples from the layers contain-

ing samples DDR-10b and DDR-9 of the pre-PGW deposit

give ages of 3380 F 160 14C yr B.P. (3630 cal yr B.P) and

3270 F 80 14C yr B.P. (3470 cal yr B.P.), respectively. The

charcoal sample from the layer at the base of the NBPW

succession in Kalli Pachchhim (below the layer containing

tooth sample KPMT5-9) gave an age of 2390 F 100 14C yr

B.P. (2520 cal yr B.P.).

In Charda the uncalibrated 14C AMS dates of charcoal

samples from the base of the NBPW period and the topmost

layer of NBPW just below the Kushan period are 2340F 6014C yr B.P. (2440 cal yr B.P.) and 2130 F 60 14C yr B.P.

(2150 cal yr B.P), respectively. The charcoal sample from

the Medieval period gives an age of 510 F 50 14C yr B.P.

(560 cal yr B.P.).

Intratooth d18O variations as proxy for changes in

seasonality

The isotopic results of the serial sampling in five teeth

are listed in Table 3 and are plotted from apex (earliest

mineralized) to cervix (latest mineralized) in Fig. 3. Since

esearch 62 (2004) 19–28 23

Fig. 3. Comparison of intratooth variations in y18O measured on enamel of

the third (M3) molar of five individuals of B. indicus from different cultural

periods.

S. Sharma et al. / Quaternary Research 62 (2004) 19–2824

the specimen exhibit different stages of tooth wear, the

positions of the samples are determined by the distance from

the cervical margin (Zazzo et al., 2002). In modern B.

indicus more than 70% of the births occur during December

to March. The crown formation of M3 teeth in domestic

cattle begins at about 9.5 months after birth and continues

until the age of 24 months (Brown et al., 1960). Thus, the

Table 4

Oxygen isotope ratios (y18Op) of bovid M3 teeth from Charda

Sample

and

Subsample

Position

(mm)

y18Op (x)

(serial

sampling)

y18Op (x)

(bulk

sampling)

Cultural

period

CNBP 20.2 NBPW

1 45.5–47.1 20.1

2 41.3–42.6 19.9

3 34.2–35.5 21.1

4 30.4–31.9 22.1

5 25.4–27.1 22.5

6 20.5–22.5 23.0

7 16.4–18.1 22.2

8 10.9–12.4 19.2

2.5–4.4 18.6

YA21-18 20.6 Kushan

1 32.1–33.4 18.5

2 27.5–29.9 19.3

3 22.1–23.9 20.7

4 17.6–18.6 20.6

5 13.1–14.5 21.6

6 9.5–10.7 21.3

7 5.9–6.8 20.8

8 2.7–4.2 19.7

The position of the sample represents the distance of the sample from the

cervical margin in serial sampling. All values relative to V-SMOW.

growth of an M3 tooth is expected to represent a period of

approximately 1 yr. If we consider that cold season repre-

sents the season of birth and M3 formation starts at an age of

9.5 months, we can assume that crown formation of M3

initiated during the end of the monsoon (September–Octo-

ber) or at the beginning of the cold season (November).

Considering the pattern of seasonal variation in y18Opt

values (Fig. 2), it can be assumed that enamel phosphate

formed during this time will have lower y18O values

compared to the enamel phosphate formed during the late

cold or hot season.

This predicted pattern is recorded by tooth samples

DDR-9, KPMT5-9, and KPK along the length of the tooth.

The samples GU6a and KPMT3-EMP show incomplete

patterns (Fig. 3). The tooth KPMT5-9 from the beginning

of the NBPW period at the Kalli Pachchhim archaeological

site is the best preserved specimen, with almost no signs of

wear. The y18O values of the 11 subsamples collected from

Fig. 4. Comparison of intratooth y18O variations measured on enamel of the

third (M3) molar of B. indicus from Kalli Pachchhim and Charda belonging

to (top) the Northern Black Painted Ware period and (bottom) the Kushan

period. The patterns are similar, with generally lighter y18O values in the

Charda region.

S. Sharma et al. / Quaternary Research 62 (2004) 19–28 25

this tooth are in the range of 21.9 to 26.9x (Table 3, Fig. 3).

The low y18O values at the apex of the tooth indicate that

the oldest part of the enamel (represented by the first three

samples) formed during the end of monsoon and the

beginning of cold season (September to November). The

increase in y18O values in subsequent subsamples is inter-

preted to represent the peak cold and hot season. The

decrease in y18O from subsample 9 may be related to the

onset of the next monsoon season. We infer that complete

M3 crown formation of this tooth represents approximately

a 1-yr period.

The teeth DDR-9 from the pre-PGW cultural phase

(Dadupur site) and KPK from the Kushan period (Kalli

Fig. 5. Average enamel y18O values obtained by bulk sampling of eight teeth from

archaeological sites).

Pachchhim site) also exhibit low y18O values near the apex,

high values in the middle, and slightly lower y18O values at

the base of the tooth. The range between the minimum and

the maximum y18O value in tooth DDR-9 is large (6.0x),

whereas only a small difference (2.4x) is observed in tooth

KPK. Tooth GU6a from the Gupta period and tooth

KPMT3-EMP from the post-Gupta or Early Medieval

period (Kalli Pachchhim site) exhibit high y18O values near

the apex and low values toward the cervical margin (Fig. 3).

High y18O values measured near the apex of teeth GU6a and

KPMT3-EMP suggest formation of the oldest preserved

enamel during peak cold and hot season, when y18O values

of drinking water are expected to be elevated. The high y18O

B. indicus from different cultural periods (Kalli Pachchhim and Dadupur

S. Sharma et al. / Quaternary Research 62 (2004) 19–2826

values near the apex may be explained by the fact that these

two specimens are partially worn out and that the upper part

of the crown, having lower isotopic values, might have been

eroded. The other possible explanation for the higher values

in the upper part of the crown may be a 2- to 3-month shift

in the season of birth of the animal.

From the archaeological site of Charda, two teeth of B.

indicus have been analyzed: samples CNBP from the

NBPW period and YA21-18 from the Kushan period (Table

4). These teeth also exhibit a similar pattern, with low y18Ovalues near the apex, maximum values in the middle, and

again low values near the base. The y18O values of tooth

CNBP are in the range of 18.6 to 23x, while those of tooth

YA21-18 range from 18.5 to 20.8x (Fig. 4).

Intertooth d18O variation as a proxy for long-term climatic

changes

The oxygen isotope values of bulk enamel samples are

shown in Fig. 5. These samples are from the Dadupur and

Kalli Pachchhim sites, which are located close to each

other. Tooth DDR-11, from the lowermost layer, shows an

average y18O value of +20.8x, followed by tooth DDR-

10b (3630 cal yr B.P.), with a value of +21.4x, and by

DDR-9 (3470 cal yr B.P.), with a value of +21.9x. The

average y18O values indicate a gradual increase, probably

within a few hundred years. Charcoal from a layer just

below DDR-11 gives a radiocarbon age of 3660 cal yr B.P.

The y18O values of teeth from these layers dated in the pre-

PGW period are low in comparison to y18O values of teeth

from the overlying younger periods. Thus, we assume that

the pre-PGW period was characterized by intensified mon-

soonal rainfalls resulting in larger water bodies that were

affected to a minor degree by evaporation during the dry

season.

Sample DDR-7 is from the PGW period and corresponds

to an estimated age of 2800 cal yr B.P. The relatively high

average y18O value of +24.6x indicates a drier climatic

phase in comparison to the pre-PGW period.

The next younger sample (KPMT5-9) belongs to the

NBPW period and shows a slightly lighter y18O average

value of +23.9x. The date of charcoal from a layer just a

few centimeters below this sample is 2520 cal yr B.P. The

date of a charcoal sample from the uppermost part of the

NBPW period at Charda site is 2150 cal yr B.P. Thus, we

estimate sample KPMT5-9 to date from 2400 cal yr B.P.

The tooth KPK is from the lower part of the Kushan

period and dates from f1900 cal yr B.P. The y18O value of

this tooth is +22.2x, indicating a wetter climate relative to

the climate of the NBPW period. Tooth GU6a is from the

Gupta period at f1600 cal yr B.P. The average y18O value

is +20.3x, indicating a further increase in humidity.

Tooth KPMT3-EMP from the post-Gupta or Early Me-

dieval period dates from f1300 cal yr B.P. The average

y18O value of this tooth enamel is +24.2x, which suggests

a rather dry climate compared to the Gupta period.

Discussion

Mammalian tooth enamel is precipitated in isotopic

equilibrium with body water at a relatively constant tem-

perature of 37jC and forms incrementally from the crown

to the base of the tooth as it erupts. This growth occurs on

the order of months and preserves a time series of y18Ovalues along the direction of growth that reflects mainly

changes in the 18O/16O ratio of ingested water. Intratooth

variations in the y18O of individual bovid teeth were

taken as a proxy to record secular changes in the intensity

of precipitation and/or evaporation. Long-term climatic

changes were detected by comparing the average y18Ovalues of tooth enamel bulk samples, which are considered

a good indicator of the average y18O value of ingested water

over the period of enamel growth (Fricke and O’Neil,

1996).

The climate of any area is essentially controlled by two

parameters, temperature and rainfall. In monsoonal areas,

variation in the amount of annual rainfall controls climate

change, as the temperature varies only within a narrow

range. The y18O values of precipitation in such areas are not

correlated with ground temperature, but with the amount of

precipitation. However, quantitative interpretation of y18Ovalues of enamel phosphate in terms of corresponding y18Ovalues of local precipitation is difficult because physiolog-

ical, behavioral, and possible hydrological factors compli-

cate this relation. Exhaustive studies of teeth from well-

constrained populations of a particular species living under

a variety of environmental conditions are still needed for

such interpretations. With our limited knowledge at this

stage we can best interpret changes in y18O values in terms

of relative changes in rainfall intensity (i.e., more humid,

less humid, and dry).

The y18O values of samples DDR-7 and KPMT3-EMP

(from the PGW and post-Gupta periods, respectively) are

higher than the values of samples DDR-11 to 9, KPMT5-9,

KPK, and GU6a (from the pre-PGW, NBPW, Kushan, and

Gupta periods, respectively) and are interpreted to represent

a less humid climate. However, the pattern of y18O variation

within individual teeth is almost the same, suggesting

similar seasonality. This implies that the monsoon system

was operative throughout this period, and only the amount

of rainfall varied.

At present, the Charda site, which is located close to the

Himalayan foothills, is more humid relative to the Dadupur

and Kalli Pachchhim sites situated in the central Ganga

plain. It can be assumed that this rainfall gradient from the

Himalaya to the central Ganga plain was also present in the

past. To test this assumption, we compared the serial

variation of y18O values in individual teeth belonging to

the NBPW and Kushan periods from the two sites shown in

Fig. 4, top and bottom, respectively. For both time periods,

the y18O values of the teeth from Charda are lower relative

to those of the teeth from Kalli Pachchhim. However, the

pattern of seasonal variation is very similar. This supports

S. Sharma et al. / Quaternary Research 62 (2004) 19–28 27

the contention that the pattern of seasonality of the mon-

soonal system remained operative in space and time in the

study area.

The y18O values obtained from bulk samples of single

teeth are considered to be a better reflection of the average

y18O value of tooth enamel in comparison to mean values

calculated from the y18O values of serially sectioned

samples from a single tooth (Feranec and MacFadden,

2000). Further, the isotopic compositions of different indi-

viduals of the same genus (and of the same age) are

considered to be internally consistent by 0.2–0.3x (Kohn

et al., 1998). Bearing this in mind, an attempt has been

made to reconstruct long-term climatic changes in the

present study by using the average y18O values of M3

teeth of B. indicus from different cultural periods. Due to

restricted sample availability the current interpretations are

based on eight M3 teeth of B. indicus and each tooth is

representative of a particular archaeological period. Conse-

quently, analyses of several teeth from single well-dated

horizons are needed to interpret the paleoclimatic scenario

with higher certainty.

The plot of the average y18O values through time

clearly shows that after a humid phase in the lower part

of the pre-PGW period, climate became dryer in the PGW

period (Fig. 5). A pollen study from an alpine peat from

the central Himalaya by Phadtare (2000) indicates a

decrease in summer monsoon strength from 4000 to

3500 cal yr B.P. From 3500 to 2000 cal yr B.P. the

monsoon is considered to be highly unstable and gradu-

ally strengthening with two minor dry events at 3000 and

2000 cal yr B.P. Our results show a trend toward drier

conditions from 3660 to 2800 cal yr B.P. Around 2500

cal yr B.P. there is the onset of a trend toward wetter

climatic conditions. The dry episode around 2000 cal yr

B.P is not recorded by our data. This suggests that the

century-scale variations in monsoonal strength did not

affect the different parts of India at the same time and

more comprehensive investigations are needed to unravel

the regional differences in the paleoclimate. Alternatively,

it might also reflect the limitations of our sampling and

dating methodology.

At the beginning of the NBPW period, humidity gradu-

ally increased through time until 1500 cal yr B.P., encom-

passing the NBPW, Kushan, and Gupta periods as depicted

by a trend of decreasing y18O values (Fig. 5). The cultural

prosperity of people during these periods (Table 1) could be

a result of intensified rainfall. A detailed study based on

multiproxy data from a lake deposit of central Ganga plain

(Sharma et al., 2004) also shows evidence of climatic

amelioration at 1620 cal yr B.P. Higher humidity around

1500 cal yr B.P. is also inferred from pollen data of the

Dunde ice cap, Tibet (Liu et al., 1998), and a speleothem

from Pokahra Valley, Nepal (Denniston et al., 2000). The

higher y18O value of the sample from the post-Gupta or

Early Medieval period suggests drier conditions around

1300 cal yr B.P.

Conclusions

Oxygen isotope analysis of M3 teeth of B. indicus

collected from archaeological sites in the Ganga plain

indicate that the bulk y18O values of M3 teeth from

different archaeological horizons reflect climatic shifts over

large time scales. Samples from around 3600 cal yr B.P.

indicate humid conditions, which change to drier condi-

tions around 2800 cal yr B.P. From 2500 to 1500 cal yr

B.P. there is a trend of increasing humidity. Around 1300

cal yr B.P. climatic conditions again became less humid or

dry.

High-resolution records of individual M3 teeth using a

serial sampling technique permit us to reconstruct the

seasonal variability during a particular time span. The

y18O values of tooth samples from Charda (high annual

rainfall area) are lower in comparison to y18O values of

samples from Kalli Pachchhim (lower annual rainfall area).

However, y18O values of samples from the same archaeo-

logical period from the two sites show a similar seasonal

variation. It can be concluded that although the amount of

annual rainfall varied significantly in different parts of the

Ganga plain, the seasonal pattern remained the same every-

where. However, given the restricted sample availability the

interpretations have their limitations. High-resolution studies

on individual fossil teeth from closely spaced stratigraphic

intervals may help to establish a finer scaled climatic record

through time.

Acknowledgments

DAAD provided postdoctoral financial support for S.

Sharma. We are grateful to Professor Groiss for tooth

identification and to Dr. G. Morgenroth for AMS dating. We

thank Daniele Lutz for her help in the laboratory. Comments

from two anonymous reviewers improved the manuscript.

References

Balasse, M., 2002. Reconstructing dietary and environmental history from

enamel isotopic analysis: time resolution of intra-tooth sequential sam-

pling. International Journal of Osteoarchaeology 12, 155–165.

Balasse, M., 2003. Potential biases in sampling design and interpretation of

intra-tooth isotope analysis. International Journal of Osteoarchaeology

13, 3–10.

Brown, W.A.B., Christofferson, P.V., Massler, M., Weiss, M.B., 1960. Post

natal tooth development in cattle. American Journal of Veterinary Re-

search 21, 7–34.

Bryant, J.D., Koch, P.L., Froelich, P.N., Showers, W.J., Genna, B.J., 1996.

Oxygen isotope partitioning between phosphate and carbonate in mam-

malian apatite. Geochimica et Cosmochimica Acta 60, 5145–5148.

Bryant, J.D., Luz, B., Froelich, P.N., 1994. Oxygen isotopic composition of

fossil horse tooth phosphate as a record of continental palaeoclimate.

Palaeogeography, Palaeoclimatology, Palaeoecology 107, 303–316.

Clementz, M.T., Koch, P.L., 2001. Differentiating aquatic mammal habitat

and foraging ecology with stable isotopes in tooth enamel. Oecologia

129, 461–472.

S. Sharma et al. / Quaternary Research 62 (2004) 19–2828

Crowson, R.A., Showers, W.J., Wright, E.K., Hoering, T.C., 1991. Prepa-

ration of phosphate samples for oxygen isotope analysis. Analytical

Chemistry 63, 2397–2400.

Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus 16, 436–468.

Denniston, R.F., Gonzalez, L.U., Asmerom, Y., Sharma, R.H., Reagan,

M.K., 2000. Speleothem evidence for changes in Indian summer mon-

soon precipitation over last f2300 years. Quaternary Research 53,

196–202.

Dhavalikar, M.K., 2001. Green imperialism: monsoon in antiquity and

human response. Man and Environment XXXVI, 18–28.

Feranec, R.S., MacFadden, B.J., 2000. Evolution of the grazing niche

in Pleistocene mammals from Florida: evidence from stable iso-

topes. Palaeogeography, Palaeoclimatology, Palaeoecology 162,

155–169.

Fricke, H.C., Clyde, W.C., O’Neil, J.R., 1998. Intra-tooth variations in

yO18 (PO4) of mammalian tooth enamel as a record of seasonal varia-

tions in continental climate variables. Geochimica et Cosmochimica

Acta 62, 1839–1850.

Fricke, H.C., O’Neil, J.R., 1996. Inter- and intratooth variation in the

oxygen isotope composition of mammalian tooth enamel phosphate:

implications for palaeoclimatological and palaeobiological research.

Palaeogeography, Palaeoclimatology, Palaeoecology 126, 91–99.

Gadbury, C., Todd, L., Jahren, A.H., Amundson, R., 2000. Spatial and

temporal variations in the isotopic composition of bison tooth enamel

from the early Holocene Hudson–Meng bone bed, Nebraska. Palae-

ogeography, Palaeoclimatology, Palaeoecology 157, 79–93.

Iacumin, P., Bocherens, H., Mariotti, A., Longinelli, A., 1996. Oxygen

isotope analyses of co-existing carbonate and phosphate in biogenic

apatite: a way to monitor diagenetic alteration of bone phosphate? Earth

Planetary Science Letters 142, 1–6.

IAEA/WHO, 2001. Global Network of Isotopes in Precipitation. The GNIP

Database. International Atomic Energy Agency, Vienna, Austria. Ac-

cessible at http://isohis.iaea.org.

Kohn, M.J., 1996. Predicting animal y18O: accounting for diet and physio-

logical adaptation. Geochimica et Cosmochimica Acta 60, 4811–4829.

Kohn, M.J., Schoeninger, M.J., Valley, J.W., 1998. Variability in oxygen

isotope compositions of herbivore teeth: reflections of seasonality or

developmental physiology. Chemical Geology 152, 97–112.

Lecuyer, C., Grandjean, P., O’Neil, J.R., Capeta, H., Martineau, F., 1993.

Thermal excursions in the ocean at the Cretaceous–Tertiary boundary

(northern Morocco): y18O record of phosphatic fish debris. Palaeogeog-

raphy, Palaeoclimatology, Palaeoecology 105, 235–243.

Lee-Thorp, J., Sponheimer, M., 2003. Three case studies used to reassess

the reliability of fossil bone and enamel isotope signals for paleodietary

studies. Journal of Anthropological Archaeology 22, 208–216.

Liu, K.-B., Yao, Z., Thompson, L.G., 1998. A pollen record of Holocene

climatic changes from the Dunde ice cap, Quinghai–Tibetan Plateau.

Quaternary Research 26, 135–138.

O’Neil, J.R., Roe, J.L., Reinhardt, E., Blake, R.E., 1994. A rapid and

precise method of oxygen isotope analysis of biogenic phosphate. Israel

Journal of Earth Sciences 43, 203–212.

Rozanski, K., Araguas-Araguas, L., Gonfiantini, R., 1993. Isotopic patterns

in modern global precipitation. In: Swart, P.K., Lohmann, K.C.,

McKenzie, J., Savin, S. (Eds.), Climate change in continental isotopic

records, Geophysical Monograph, vol. 78. American Geophysical

Union, Washington, DC, pp. 1–36.

Sharma, S., Joachimski, M., Sharma, M., Tobschall, H.J., Singh, I.B.,

Sharma, C., Chauhan, M.S., Morgenroth, G., 2004. Late Glacial and

Holocene environmental changes in Ganga plain, northern India. Qua-

ternary Science Reviews 23, 139–153.

Sirocko, F., Garbe-Schonberg, D., McIntyre, A., Molfino, B., 1996. Tele-

connections between the subtropical monsoons and high-latitude cli-

mates during the last deglaciation. Science 272, 526–529.

Sponheimer, M., Lee-Thorp, J.A., 1999. Oxygen isotopes in enamel car-

bonate and their ecological significance. Journal of Archaeological Sci-

ence 120, 723–728.

Stuart-Williams, H., Le, Q., Schwarcz, H.P., 1997. Oxygen isotopic deter-

mination of climatic variation using phosphate from beaver bone, tooth

enamel and dentine. Geochimica et Cosmochimica Acta 61, 2539–2550.

Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A.,

Kromer, B., McCormac, F.G., Plicht, J.v.d., Spurk, M., 1998. Intcal98

radiocarbon age calibration, 24,000– 0 cal BP. Radiocarbon 40,

1041–1083.

Vennemann, T.W., Fricke, H.C., Blake, R.E., O’Neil, J.R., Colman, A.,

2002. Oxygen isotope analysis of phosphates: a comparison of techni-

ques for analysis of Ag3PO4. Chemical Geology 185, 321–336.

Wei, K., Gasse, F., 1999. Oxygen isotopes in lacustrine carbonates of west

China revisited: implications for post glacial changes in summer mon-

soon circulation. Quaternary Science Reviews 18, 1315–1334.

Wenzel, B., Lecuyer, C., Joachimski, M.M., 2000. Comparing oxygen

isotope records of Silurian calcite and phosphate—y18O compositions

of brachiopods and conodonts. Geochimica et Cosmochimica Acta 64,

1859–1872.

Wiedemann, F.B., 2000. Experimental design on enamel deposition in

sheep: implications for sampling strategies for stable analyses. Journal

of Human Evolution 38, A34.

Zazzo, A., Mariotti, A., Lecuyer, C., Heintz, E., 2002. Intra-tooth isotope

variations in late Miocene bovid enamel from Afghanistan: palaeobio-

logical, taphonomic and climatic implications. Palaeogeography, Palae-

oclimatology, Palaeoecology 186, 145–161.