balakrishnan et al, 2004

872019 Balakrishnan et al 2004

httpslidepdfcomreaderfullbalakrishnan-et-al-2004 116

Environmental significance of 13C 12C and 18O 16O ratios of modern

land-snail shells from the southern great plains of North America

Meena Balakrishnana Crayton J Yappa James L Theler bBrian J Carter c Don G Wyckoff d

a Department of Geological Sciences Southern Methodist University Dallas TX 75275-0395 USAbDepartment of Sociology and Archaeology University of Wisconsin-La Crosse La Crosse WI 54601 USA

cDepartment of Plant and Soil Sciences Oklahoma State University Stillwater OK 74078 USAdOklahoma Museum of Natural History University of Oklahoma Norman OK 73019 USA

Received 11 March 2004

Available online 26 November 2004

Abstract

13C 12C and 18O 16O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for

samples from twelve localities in a narrow eastndashwest corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of

the Sangre de Cristo Mountains in Northern New Mexico USA Across the study area shell y18O values (PDB scale) ranged from Agrave41x to

12x while y13C values ranged from Agrave132x to 00x y

18O values of the shell aragonite were predicted with a published steady state

evaporative flux balance model The predicted values differed (with one exception) by less than 1x from locality averages of measured y18O

values This similarity suggests that relative humidity at the time of snail activity is an important control on the y18O values of the aragonite

and emphasizes the seasonal nature of the climatic information preserved in the shells Correlated y13C values of coexisting Vallonia and

Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant

ecology Although there is considerable scatter multispecies transect average y13C values of the modern aragonite shells are related to

variations in the type of photosynthesis (ie C3 C4) in the local plant communities The results of this study emphasize the desirability of

obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among

individuals species etc and thus better represent the bneighborhoodQ scale temporal andor spatial environmental variations of interest in

studies of modern and ancient systems

D 2004 University of Washington All rights reserved

Keywords Land snails Oxygen isotopes Carbon isotopes Climate Relative humidity C3 plants C4 plants

Introduction

Studies of the isotopic compositions of the aragoniticshells of land snails from different parts of the world attest

to their value as environmental indicators (Goodfriend and

Ellis 2002 Goodfriend and Magaritz 1987 Goodfriend et

al 1989 Lecolle 1985 Magaritz and Heller 1980 1983

Magaritz et al 1981 Yapp 1979) y18O values of these

shells have been related to local climatic parameters and the

y18O of ambient meteoric water (eg Balakrishnan and

Yapp 2004 Goodfriend et al 1989 Lecolle 1985

Magaritz and Heller 1980 Magaritz et al 1981 Yapp1979) y13C values of shell aragonite may be correlated with

the y13C of local vegetation (eg Balakrishnan and Yapp

2004 Goodfriend and Magaritz 1987 Metref et al 2003

Stott 2002)

Goodfriend and Ellis (2002) conducted a study of the

y13C and y

18O variations of shell aragonite and shell organic

matrix in two species of land snails of the genus Rabdotus

along a transect from Northeast to Southwest Texas USA

They examined evidence for relationships between ambient

environmental parameters and the y13C or y18O values of

0033-5894$ - see front matter D 2004 University of Washington All rights reserved

doi101016jyqres200409009

Corresponding author Fax +1 214 768 2701

E-mail address cjyappmailsmuedu (CJ Yapp)

Quaternary Research 63 (2005) 15ndash30

wwwelseviercomlocateyqres



shell aragonite y13C values of shell aragonite were

correlated with y13C values of organic matrix in the shell

which suggests that the shell y13C reflects diet with an offset

associated with the snail physiology and equilibrium and

kinetic fractionation processes Relationships of y18O

variations of Rabdotus to the environmental variables

discussed by Goodfriend and Ellis (2002) appeared to bemore problematic than for carbon

In the current paper we present measurements of

variations in the carbon and oxygen isotope compositions

of shells of other species of modern land snails from a

different portion of the southern Great Plains of North

America Samples in t his study are described in the work of

Theler et al (2004) and are from a narrow eastndashwest

corridor extending across much of Oklahoma and into

Northeastern New Mexico USA The data are discussed in

terms of their relationship to modern environmental

variables to examine the likelihood that isotopic data from

ancient land snails in the region might have paleoenvir-onmental significance

Samples and study area

Samples

The modern snail population procured for this study

f ormed part of an extensive terrestrial gastropod survey

(Theler et al 2004 Wyckoff et al 1997) in the southern

Great Plains of North America Samples were collected at

12 localities along an eastndashwest corridor extending from

North Central Oklahoma to Northeastern New Mexico

between 36826VN t o 3 6858VN latitude and 96849VW to

104857VW longitude (Theler et al 2004 Wyckoff et al

1997) The site names and locations are depicted in Figure

1 The study corridor is 640 km long east to west and about

100 km wide and extends from the Flint Hills of North

Central Oklahoma to the foothills of the Sangre de Cristo

Mountains near Cimarron New Mexico (Fig 1) Elevation

in the study area slowly increases from 330 m above sea

level at the eastern end of the corridor to about 2290 m

above sea level at the western end

Vegetation

There are four distinct biotic districts in the sampled area

(Fig 1) Mixed-grass plains occupy the eastern section

(Blair and Hubbell 1938 Carpenter 1940 Ostlie et al

1997 Shelford 1963) This district marks the transition

from tall grass prairie in the east to short grass prairie in the

west and is characterized by several species of Ascoparius

(Ascoparius saccharoides Ascoparius furcatus Ascoparius

smithii) grama grasses (Bouteloua gracilis Bouteloua

racemosa Bouteloua hirsuta and Bouteloua curtipendula)

and buffalo grass (Buchloe dactyloides) (Blair and Hubbell

1938 Bruner 1931 Carpenter 1940 Kuchler 1964 Ostlie

et al 1997 Risser 1985 1990 Shelford 1963 Weaver and

Albertson 1956)

The second biotic region short grass prairie (immedi-

ately to the west of the mixed-grass prairie Fig 1) contains

vegetation that includes buffalo grass hairy grama (B

hirsuta) blue grama (B gracilis) and western wheatgrass

(Pascopyrum smithii) (Blair and Hubbell 1938 Bruner1931 Carpenter 1940 Kuchler 1964 Ostlie et al 1997

Risser 1990 Shelford 1963)

A third biotic district the pinyonndashjuniper shrub grass-

land Raton subsection (Blair and Hubbell 1938) extends

from the northwest corner of the panhandle into the

northeastern corner of New Mexico (Fig 1) Vegetation in

this region includes junipers (Juniperus monosperma

Juniperus osteosperma) oak (Quercus mohriana) and pine

(Pinus edulis Pinus monophylla) along with plants such as

silverbeard grass (A saccharoides) blue grama and some

species of prickly pear cactus (Opuntia sp) (Blair and

Hubbell 1938 Ostlie et al 1997)The dry pine forest at the western end of the study area

(Fig 1) is not strictly a Plains ecosystem (Shelford 1963)

Vegetation includes oak and pine along with hairy and blue

grama grasses (Shelford 1963 Theler et al 2004 Wyckoff

et al 1997)

Climate and isotopes in precipitation

Average annual precipitation on the southern plains

generally decreases from over 1020 mmyr in the east to

255 mmyr in the west (Ostlie et al 1997) The mean

annual temperatures in the mixed-grass prairie range from

158 t o 178C while the corresponding mean annual

precipitation ranges from 670 to 790 mm (Blair and

Hubbell 1938) Annual temperatures in the short grass

prairie range from 128 to 138C and mean annual precip-

itation from 450 to 560 mm (Blair and Hubbell 1938)

Average annual temperatures in the dry pine forest of the

foothills of the Sangre de Cristo mountains are about 118C

and average rainfall is about 400 mm (Climate Data Center

New Mexico State University at wwwweathernmsuedu)

Precipitation in these regions derives principally from three

locations (Elliot 1949 Nativ and Riggio 1990)

From late March into July moisture is derived primarily

from the Gulf of Mexico (curveb

aQ

Fig 2) From October to early March the Northern Pacific Ocean is the primary

moisture source (Nativ and Riggio 1990) (curve bcQ Fig

2) In the western end of the study area (Northeastern New

Mexico) both the Gulf of Mexico and the central Pacific

Ocean contribute moisture during the middle to late summer

and early fall (curves baQ and bbQ Fig 2) although

contributions from the Gulf of Mexico are predominant

The central Pacific component of this moisture is brought in

by the Mexican monsoons (Douglas et al 1993 Nativ and

Riggio 1990)

The temperature and relative humidity at which ocean

water evaporates the air mass history and the local

M Balakrishnan et al Quaternary Research 63 (2005) 15ndash3016



temperature of condensation are among the controls onthe isotopic composition of precipitation (Dansgaard

1964 Rozanski et al 1993) The different air masses

that contribute precipitation to the southern Plains impart

seasonally distinct y18O values to the rain andor snow

y18O values of summer rains originating from Gulf of

Mexico moisture are more positive than those of winter

precipitation originating from the North Pacific Ocean

(Nativ and Riggio 1990) This is primarily a consequence

of the higher elevations (lower temperatures) and longer

transport distances experienced by air masses from the

North Pacific (Nativ and Riggio 1990 Rozanski et al

1993)

Experimental

Sampling systematics

Results of an initial survey collection and documentation

of the modern gastropods in this region are found in Wyckoff

et al (1997) and Theler et al (2004) These include

description of the dominant vegetation types at each locality

Collections of the snails analyzed for the current work were

made at 12 localities along the 640-km sample corridor at

sites for which living snails could be expected (for sample

collection rationale see Theler et al 2004) Each sample

locality was restricted to a circle with a diameter of ~400 m

Figure 1 Map of the study area in the southern Great Plains of North America indicating the collection localities and the major ecological regions Localities 1

Kubic 2 Bluff Creek 3 Salt Fork 4 McDaniel 5 Burnham 6 Big Salt Plain 7 Skull Springs 8 Hitch 9 Black Mesa 10 Owensby 11 C S Ranch 12 Chase

(data sources Blair and Hubbell 1938 Carpenter 1940 Shelford 1963 Wyckoff et al 1997 Theler et al 2004)

M Balakrishnan et al Quaternary Research 63 (2005) 15ndash30 17



(Theler et al 2004 Wyckoff et al 1997) Each circle

contained several niches Niches (recognized by differences

in vegetation slope and aspect) favorable for snail habitation

were sampled along a linear btransect Q (Theler et al 2004

Wyckoff et al 1997) that was usually not more than 100 m in

length Along each transect there were three sample

collection sites (usually 10ndash20 m apart) called breplicationsQ

A B and C (Wyckoff et al 1997) The term bsampleQ was

substituted for breplicationQ by Theler et al (2004) However

in the current work we will retain breplicationQ (sensu

Wyckoff et al 1997) to avoid confusion with our more

generic use of the term bsampleQ which refers herein to any

collected material of interest Thus as an example the

sample locality bHitchQ has three transects (Hitch 21 Hitch

22 and Hitch 23) with each transect in Hitch in turn

comprised of three replications (eg Hitch 21A Hitch 21Band Hitch 21C) There is a total of 38 transects among the 12

localities and a total of 114 breplicationsQ summed over all of

the 38 transects (ie 3 Acirc 38) At each breplicationQ lower

parts of growing vegetation decaying vegetation and 2 cm

of topsoil from a 50 Acirc 50 cm area were collected (Wyckoff et

al 1997 Theler et al 2004) Wyckoff et al (1997) and

Theler et al (2004) sieved and sorted these samples in the

laboratory to extract the snail shells followed by identifica-

tion and population analyses

Because of the destructive nature of the isotopic analyses

and because it was necessary to retain snail shells for

archival purposes only those from sample sites represented

by large numbers of collected shells were analyzed Hence

of the total of 114 breplicationsQ among the 38 transects

only 71 replications from 34 transects are represented in this

study Most of the samples were collected in 1995

(collection from the Owensby site was made in 1996) and

were alive at the time or within 1 yr of collection (Theler et

al 2004 Wyckoff et al 1997)

Selection of species for isotopic analyses

Vallonia and Gastrocopta were the principal genera

employed for isotopic analyses of snail shells because they

are present throughout most or all of the study area (Theler

et al 2004 Wyckoff et al 1997) For some localities

snails representing a few other genera were also isotopically

analyzed but these other genera did not have the widedistribution exhibited by Vallonia or Gastrocopta The

genus Vallonia is represented by the species Vallonia

parvula at the lower elevations and Vallonia gracilicosta

at the higher elevations The latter is often associated with

deposits of Pleistocene age in the southern Great Plains

(Rossignol et al 2004 Theler et al 2004 Wyckoff et al

1997) Vallonia juveniles were also analyzed but could not

be identified at the species level (Theler et al 2004

Wyckoff et al 1997) The genus Gastrocopta was

represented by Gastrocopta contracta Gastrocopta holzin-

geri Gastrocopta pentodon Gastrocopta armifera Gastro-

copta cristata Gastrocopta pilsbryana Gastrocopta

Figure 2 Source regions and generalized trajectories of major moisture-bearing air masses that bring precipitation to the southern Great Plains of North

America Trajectory (a) March into July or August (b) middle to late summer and early fall (c) October to early March (see text) mP = maritime polar air

mass and mT = maritime tropical air mass (after Elliot 1949 Nativ and Riggio 1990) The shaded rectangle encompasses the land snail sites of Figure 1




procera and Gastrocopta pellucida The two latter species

exhibit relatively large distribution ranges However G

procera was notably absent at the higher altitudes in the

survey (Theler et al 2004 Wyckoff et al 1997)

Laboratory preparations and analyses

Each isotopically analyzed sample consisted of multiple

entire shells of adults of a particular species (or genus for

juveniles of Vallonia) from a breplicationQ The shells were

initially rinsed with deionized water then treated ultrasoni-

cally in deionized water to remove any adhering particles of

organic matter or other debris The shells were gently crushed

and treated with 5 reagent-grade sodium hypochlorite at

room temperature for about 7ndash8 h to remove organic matter

They were then rinsed thoroughly with deionized water and

dried in air at about 40ndash508C The shell fragments were

subsequently reacted overnight in vacuum with 100 H3PO4

at 258

C following the method of McCrea (1950) The CO2

prepared from the shell aragonite was analyzed for y13C and

y18O on a Finnigan MAT 252 mass spectrometer Analytical

uncertainty is about F01x The y values are defined as

y13C or y18O frac14 R sample=R standard

Agrave AacuteAgrave 1

Acirc AtildeAcirc 1000 x

where R = 13C 12C or 18O 16O y13C and y18O are reported

relative to the PDB standard (Craig 1957)

Results and discussions

Ranges of d18O and d13C of aragonite in land-snail shells

y18O and y

13C values were measured for 162 samples

from the 12 localities of Figure 1 (see Appendix A) y18O

values of the aragonite shells of these modern snails ranged

from Agrave41x to 12x (Fig 3) Published y18O values of

shells from globally distributed modern land snails that are

wholly subaerial (as opposed to semiaquatic) range from

Agrave117x to 45x (Goodfriend and Ellis 2002 Goodfriend

and Magaritz 1987 Goodfriend et al 1989 Lecolle 1985

Magaritz and Heller 1980 Magaritz et al 1981 Sharpe et

al 1994 Yapp 1979) In North America reported y18O

values of land-snail shells range from Agrave117x to 02x(Goodfriend and Ellis 2002 Sharpe et al 1994 Yapp

1979) If the results for a carnivorous cold-tolerant snail of

the genus Vitrina (Sharpe et al 1994) from Deer Creek

Nevada are excluded y18O values analyzed to date for

North America range from Agrave58x to 02x The current

work extends the upper range of North American values by

10x (Fig 3)

Previous studies of y13C values of shell aragonite from

snails in their natural settings reported values ranging from


and Magaritz 1987 Lecolle 1983 1984 Magaritz and

Heller 1980 1983 Magaritz et al 1981 Yapp 1979) For

North America published y13C values range from Agrave125x

to Agrave25x (Goodfriend and Ellis 2002 Yapp 1979) The

y13C values of snail shell aragonite studied for the current

work range from Agrave132x to 00x (Fig 3) By contrast

y13C values of shell aragonite of experimentally cultured

Helix aspersa that were fed a controlled diet ranged from

Agrave243x to 25x (Stott 2002) Controlled experiments also

indicate differences in y13C values among adults hatched

and 1-month-old individuals of H aspersa fed diets with

identical y13C values (Metref et al 2003)

Snail shell isotopic variation among populations

Variations in the isotopic composition of snail shells exist

among replications within a transect and also among species

in a replication (Appendix A) Within a sample locality

small-scale variations in topography vegetation local

moisture availability snail ages physiology etc are

expected Such variations might contribute to the observed

scatter in isotopic ratios among genera species or

individual samples

Isotopic analyses of Vallonia and Gastrocopta total 143

and represent the majority of the analyzed shell samples but

Figure 3 Ranges of Southern Great Plains land snails and snail shell y18O

and y13C values measured for breplicationsQ in the current study compared

with various published ranges (see text) Open portion of the range of North

Americany18

O values encompasses the values reported for shells from acarnivorous cold-tolerant snail (see text for reference)




there were also analyses (numbers in parentheses) of

bunderrepresentedQ genera as follows (see Appendix A)

Pupoides (9) Succineidae (3) Pupilla (2) Cionella (1)

Zonitoides (1) Helicodiscus (1) Glyphyalinia (1) and

Hawaiia (1) The ranges of y18O values for Vallonia and

Gastrocopta are about 28x and 20x respectively (Fig

4a) Corresponding y18O values of Vallonia and Gastrocopta

indicate no correlation among the various sites (Fig 4a) A

similar lack of correlation was evident when y18O values of

underrepresented genera were compared wit h values for

coexisting Vallonia (Fig 5a) or Gastrocopta (Fig 5b) The

particular origins of these differences are unknown Without

studies under controlled age and environmental conditions

(eg Metref et al 2003 Stott 2002) distinguishing micro-environmental effects from the effects of age andor species-

related physiological differences is not possible at present

The respective ranges of y13C values for Vallonia and

Gastrocopta shell aragonite are each about 8ndash9x and

samples from the same breplicationsQ show a significant

correlation (Fig 4b) This correlation could indicate similar

feeding habits in both genera making them potential sources

of isotopic information on the paleoecology of a locale

Because of this correlation of Vallonia and Gastrocopta y13C

values y13C values of eight other genera that coexisted with

one or both of these genera in the various breplicationsQ are

plotted against y13

C of either Vallonia or Gastrocopta in asingle figure (Fig 5c) There are insufficient data to establish

whether the y13C values of any of the bunderrepresentedQ

genera might be correlated with Vallonia or Gastrocopta but

overall there is considerable scatter among the species

Additional comparative analyses of and controlled experi-

ments on these genera are needed

An exploratory evaluation of the effect of life histories

and ages on the isotopic composition of snails was

attempted using the data for adult and juvenile Vallonia

(see Appendix A) y18O values of shells of coexisting adult

and juvenile Vall onia from the breplicationsQ are not

correlated (Fig 6a) The y18O values of the adult snails

represent averages over longer periods of time than those of

the juveniles Short time scale environmental conditions that

affect the y18O values of the body fluid in juveniles should

determine the y18O values of the shell aragonite and these

conditions might contrast with the longer term-averages of

the adults

The absence of a correlation in the y18O data of Figure 6a

contrasts with the good correlation of the y13C values of the

adults and juveniles in Figure 6b The y13C correlation

could indicate that in these locales the carbon isotope

Figure 4 Southern Great Plains land snails Comparison of average

isotopic compositions of the aragonitic shells of Gastrocopta and Vallonia

from the same breplicationsQ (see text) (a) comparison of y18O values and

(b) comparison of y13

C values Dashed line in panel a is the reference liney = x Solid line in panel b is the linear regression of the data with the

corresponding equation r 2 and P

Figure 5 Southern Great Plains land snails Comparison of y18O of the aragonitic shells of other species used in this study with that of coexisting (a) Vallonia

and (b) Gastrocopta in the breplicationsQ (c) Comparison of y13C values of the shell aragonite of other species with those of coexisting Vallonia andor

Gastrocopta in the same breplicationsQ (see text) Dashed lines are the reference lines y = x




composition of vegetation (as well as snail feeding patterns)

is not as variable on small scales as the oxygen isotope

composition of ambient moisture However the apparent

contrast in the respective oxygen and carbon isotope

relationships (adults or juveniles Figs 4 and 6) might also

be in part a consequence of the smaller ranges for the y18O

values Thus if the magnitude of the normal scatter in the

breplicationsQ data were comparable to the smaller total

range of the y18O values it would mask any evidence for a

broader y18

O correlation among genera or age groups

Snail shell isotope compositions and environmental

parameters

Carbon isotopes

As noted vegetation in the study area is dominantly

grasslands at lower elevations and trees at higher

elevations (Fig 1) Based on the nature of the photo-

synthetic pathway plants are classified as C3 C4 or CAM

(eg Jacobs et al 1999) y13C values of C3 plants range

from Agrave33x to Agrave21 x while y13C values of C4 plants

typically range from Agrave17x to Agrave9x (eg Cerling and

Quade 1993) CAM plants have y13C values that range

between the values for C3 and C4 plants (eg Cerling and

Quade 1993) Most of the grasses in the southern Great

Plains are C4 plants (Tieszen et al 1997) and the trees

and most of the forbs are C3 plants (Watson and Dallwitz

httpbiodiversityunoedudelta )

If snail shell y13C values are influenced by the y13C of their diets (eg Balakrishnan and Yapp 2004 Francey

1983 Goodfriend and Ellis 2002 Goodfriend and Magar-

itz 1987 Metref et al 2003 Stott 2002) the spatial

transitions in the ecology of the study corridor suggest that

the y13C values of the shells should be more negative at the

higher elevations toward the west y13C values of the shell

aragonite from all breplicationsQ (Appendix A) and their

averages for each transect (Table 1) are plotted against

elevation in Figures 7a and 7b respectively There is

considerable scatter but some suggestion of the expected

general shift to lower y13C values as altitude increases (Fig

7) However the regional vegetation trend does not explainthe very large range of snail shell y13C values at the lowest

elevations on the eastern end of the sample corridor (Figs

7a and 7b) Such a large range may be explained in part by

local variations in proportions of C3 and C4 plants

Wyckoff et al (1997) and Theler et al (2004)

identified plant species at each sample site in the study

corridor For the current work their identifications (no

quantitative estimates of type) were used to classify the

vegetation in each transect as C3-dominant C4-dominant

or mixed including CAM (Ehleringer et al 1997

Owensby et al 1997 Sage et al 1999 Appalachian

Farming Systems Research Center httpwwwarserrcgov

beckleyC3C4LISThtm ) The classifications are presented

in Table 1

The average y13C values of the land-snail shells from

each transect are listed in Table 1 and plotted in Figure 8

against the corresponding classification of local vegetation

which is arranged in a sequence from C4-dominant to C3-

dominant It is not known if the snails in the region ingest

CAM plants However examined in the manner of Figure

8 it is evident that the y13C values of snail shells of the

southern Great Plains are generally indicative of the type of

vegetation in their immediate environment although there

is still considerable scatter in the relationship In the

regions where C4 plants were identified as the dominant plant type the transect-average y

13C values of the snail

shell aragonite ranged from Agrave43x to Agrave19x with an

overall average of Agrave28x In localities where C3 plants

were documented to be the dominant type these transect-

average values ranged from Agrave101x to Agrave88x with an

overall average of Agrave90x (Fig 8) In the areas with mixed

vegetation types the shell y13C values are within the

extremes defined by the y13C values of the shells in areas

dominated by C3 or C4 plants These observations are in

agreement with earlier observations (Francey 1983 Good-

friend and Ellis 2002 Goodfriend and Magaritz 1987

Metref et al 2003 Stott 2002)

Figure 6 Comparison of coexisting adults and juveniles of southern Great

Plains Vallonia inb

replicationsQ

(see text) (a) y

18

O values of aragoniteshells and (b) y

13C values Solid line in panel b is the linear regression of

the data with the corresponding equation r 2 and P




For the transects representing the Owensby and Bluff

Creek localities the plant species were not documented but

the relatively negative land-snail shelly13C values suggestthe

possible local dominance of C3 vegetation(hence the question

mark by the C3 symbol on the far right of the abscissa of Fig

8) Some of the scatter in Figure 8 may be a result of the

complicating effects of incorporation of relatively13

C-richdietary carbonate from limestone (eg Goodfriendand Hood

1983 Metref et al 2003 Yates et al 2002)

Oxygen isotopes

Average annual y18O of meteoric water is about Agrave56x at

Norman Oklahoma (USGS unpublished data Martha

Scholl personal communication) in the east and Agrave98 x

at the higher elevations of Clovis New Mexico (Nativ and

Riggio 1990) in the west As suggested by Figure 2 some of

this difference may be a consequence of differing proportions

of precipitation from different moisture sources and air

masses with different histories Irrespective of the particular

mechanisms producing lower y18O values of average annual

precipitation at the higher western elevations if the dominant

control on the y18O value of the snail shell aragonite was the

y18O value of annual precipitation the shell y18O should be

lower at higher altitude Figure 9a depicts snail shell y18O

values plotted against altitude for all of the analyzed

breplications

Q (Appendix A) There is no correlation of shell

y18O with elevation evident in Figure 9a

Average y18O values of samples in each transect are listed

in Table 1 and plotted against elevation in Figure 9b For the

transect-average values in Figure 9b there may be a weak

relationship of shell y18O with altitude indicating some

tendency for a decrease of shell y18O with increasing

elevation For an increase in elevation of ~2000 m the slope

of the linear regression indicates a decrease in shell y18O of

only ~1x However even if this weak correlation in Figure

9b was significant a decrease of ~1x is much less than the

decrease of ~4x expected if the y18O of annual precipitation

were the principal control on shell y18O values

Table 1

Transect averages (all species) of measured shell y13C and y

18O

Locality Transect Elevationa (m) Plant type Transect average Average y18O Model calculations

y13C y

18O Calculated locality y18Ocalc D

18O

Kubic 6 329 C3 Agrave85 Agrave21 Agrave20 Agrave22 Agrave02

Kubic 5 351 C4 Agrave35 Agrave19

Kubic 2 360 C4 C3 Agrave48 Agrave21Kubic 4 360 C4 Agrave23 Agrave17


Bluff Creek 36 348 C3 Agrave84 Agrave12 Agrave12 Agrave15 Agrave03

Salt Fork 9 320 C3 Agrave101 Agrave19 Agrave19 Agrave15 04

McDaniel 11 375 C4 C3 Agrave76 Agrave22 Agrave22 Agrave14 08

Burnham 17 519 C4 C3 Agrave83 Agrave08 Agrave10 Agrave09 01

Burnham 16 567 C4 CAM C3 Agrave54 Agrave18

Burnham 12 607 C4 C3 Agrave58 Agrave23


Burnham 13 610 C4 Agrave43 Agrave01

Big Salt Plain 15 482 C3 Agrave89 Agrave04 Agrave04 Agrave09 Agrave05

Skull Springs 18 671 C4 CAM C3 Agrave60 Agrave16 Agrave16 Agrave03 13

Skull Springs 19 665 C4 C3 Agrave40 Agrave17

Hitch 22 915 C4 CAM Agrave51 Agrave15 Agrave18 Agrave25 Agrave07

Hitch 21 933 C4 CAM C3 Agrave50 Agrave06Hitch 23 881 C3 Agrave85 Agrave23

Black Mesa 27 1312 C4 C3 Agrave61 Agrave27 Agrave22 Agrave21 01

Black Mesa 26 1324 C4 CAM C3 Agrave66 Agrave15

Black Mesa 24 1488 C4 CAM Agrave26 Agrave17



Owensby 61 2193 C3 Agrave105 Agrave19 Agrave20 Agrave25 Agrave05

Owensby 60 2242 C3 Agrave96 Agrave30


CS Ranch 30 1922 C4 CAM C3 Agrave43 Agrave19 Agrave20 Agrave25 Agrave05

CS Ranch 29 1940 C4 CAM C3 Agrave49 Agrave25

Chase 34 1952 C4 C3 Agrave92 Agrave38 Agrave25 Agrave25 00

Chase 33 2184 C4 C3 Agrave86 Agrave22



Locality averages of measured y18O Also y

18O of shell at a locality as predicted from model calculations for diffusive evaporation (y18Ocalc) D18O =

y18Ocalc Agrave y

18Omeasa Sea level datum




The data of Figures 9a and 9b imply that factors other

than the y18O of annual precipitation are involved in

regulating the y18O values of the shells of land snails from

the southern Plains In general land snails are not active at

temperatures below 108C and above 278C (Cowie 1984

Thompson and Cheny 1996) nor are they active at values of

relative humidity (RH) of less than about 070mdashexpressing

RH as a decimal fraction (Van der Schalie and Getz 1961

1963) Thus land snails are active only at night or following

rains (Cook 1979 Edelstam and Palmer 1950 Gelperin

1974 Heatwole and Heatwole 1978 Newell 1966 Wardand Slotow 1992 Wells 1944) Moreover snail shells are

only precipitated when snails are active (Cowie 1984)

Therefore y18O values of snail shell aragonite should reflect

conditions within comparatively narrow ranges of high

relative humidities and moderate temperatures

The steady-state flux balance model of Balakrishnan and

Yapp (2004) may provide some insight into the oxygen

isotope systematics of the snail shells of this study The

relevant model inputs for calculations of expected shell

y18O values are temperatures relative humidities (RH) and

y18O values of precipitation estimated to be representative

of the local environments at the times of snail activity As

mentioned these periods of activity are primarily evenings

andor immediately after rainfall From the archives of the

Climate Data Center of New Mexico State University

(wwwweathernmsuedu) meteorological data for 1994

were available for one relevant station in New Mexico

(Clayton see Appendix A) For the year 1994 hourly

meteorological parameters for seven stations in Oklahoma(Appendix A) were available from Mesonet data (courtesy

of Oklahoma State University and University of Oklahoma)

Average temperatures characteristic of the aforementioned

conditions of land-snail activity appear to reasonably

represent the temperatures of the snail environment (Balak-

rishnan and Yapp 2004) and these temperatures were

employed in our calculations (excluding days when temper-

atures were below 108C or above 278C) We also used

averages of nighttime RH for RH N 070 and 108C b T b

278Cmdashie the range conditions for snail activity These

temperature and RH data are in Table 2 For th e

calculations it was assumed that essentially all of the water imbibed by the snail was lost via evaporation (ie h = 0)

and that the ambient vapor was in isotopic equilibrium with

the input rain (for an explanation of model assumptions and

definition of terms see Balakrishnan and Yapp 2004)

Isotopic compositions of active season precipitation

were only available from three sites in the vicinity of the

study area (1) Norman Oklahoma (USGS unpublished

data Martha Scholl personal communication) (2) Ama-

rillo Texas and (3) Paducah Texas (Nativ and Riggio

1990) The average for Norman represents the years 1996ndash Figure 7 y13C of southern Great Plains snail shell aragonite as a function of

elevation (a) y13C values for all breplicationsQ (b) average y13C values for

each transect (see text) Error bars in panel b represent one standard

deviation of the mean for the indicated transect

Figure 8 Southern Great Plains land-snail shells Open diamonds are

transect-averagey13C values of shells compared to the vegetation types at a

site (see text) Filled squares are average values of the respective transect

averages for each vegetation classification Error bars are one standard

deviation of the various means




2001 whereas the Amarillo data are for t he years 1984

1985 The average values are in Table 2 Model calcu-

lations for each snail locality used the geographically

nearest active season meteorological data and isotopic

compositions of rain (Table 2) Because the measured

environmental parameters are not precisely coincidenteither spatially or temporally with the respective snail

localities some unknown error is introduced into the

comparisons of calculated and measured shell y18O values

Nevertheless the comparisons are instructive

In the flux balance model of Balakrishnan and Yapp

(2004) it is assumed that the shell aragonite crystallized in

oxygen isotope equilibrium with snail body fluid that was

undergoing isotopic steady-state diffusive evaporation The

aragonitendashwater oxygen isotope fractionation equation of

Grossman and Ku (1986) is assumed to be applicable in

these model calculations Let D18O = y18Ocalc Agrave y

18Omeas

where y18Ocalc = the model-predicted y

18O of the aragonite

and y18Omeas = the measured y18O of the aragonite shell

Note that D18O values of zero represent exact agreement

between predicted and measured y18O For this compar-

ison averages (Table 1) of measured y18O values of all

analyzed species at each locality were employed with the

idea that variations associated with differences among

individuals species times of shell formation microenvir-

onments etc would be bsmoothed out Q and therefore

possibly better represent the average conditions reflected in

the meteorological data These locality-average D18O

values calculated with diffusive evaporation scatter

around zero and with one exception differ from zero by

1x or less (solid diamonds in Fig 10)In contrast for an assumption of oxygen isotopic

equilibrium between aragonite and land-snail body fluid

(local rain) that had experienced no evaporation prior to or

during snail activity predicted shell y18O values are

significantly different from measured values For this case

the calculated D18O values differ from zero by more than

30x (solid triangles Fig 10) and all of these D18O values

for no evaporation are negative (Agrave57 to Agrave34x)

The fact that locality averageD18O values for the diffusive

evaporation model scatter around and near zero suggests that

this evaporation model may approximate the processes

operating in these land snails of the southern Great Plains

and implies that the ambient relative humidity has an

important influence on the y18O values observed in the shells

(Balakrishnan and Yapp 2004 Yapp 1979) All other things

being equal the evaporation model predicts that a decimal

fraction decrease in RH of only 001 produces a predicted

increase in shell y

18

O of about 04x This apparent sensitivity to RH and the westward decrease of 003ndash006

in the average active season nighttime RH (Table 2) may

partially compensate for the somewhat lower y18O values of

Table 2

Active season temperature relative humidity and rainfall y18O

Weather station Summer T8C RHa y18O of summer rainb Rain isotope data station Proximal snail sample localities

Blackwell OK 220 091 Agrave51 Norman OK Kubic

Medford OK 224 089 Agrave51 Norman Bluff Creek Salt Fork

Cherokee OK 220 089 Agrave51 Norman McDaniel

Alva OK 212 088Agrave

51 Norman Burnham Big Salt PlainBeaver OK 223 086 Agrave50 Paducah TX Skull Springs

Goodwell OK 228 087 Agrave67 Amarillo TX Hitch

Boiser OK 228 086 Agrave67 Amarillo Black Mesa

Clayton NM 214 088 Agrave67 Amarillo Owensby CS Ranch Chase

a RH as a decimal fractionb See text for source of data

Figure 9 Southern Great Plains land-snail shells Measured y18O values of

snail shell aragonite as a function of elevation (a) y18O values of all

breplicationsQ and (b) average y18O values for each transect (see text) The

solid lines and associated equations in each figure represent the respective

linear regressions of the data




precipitation expected at the higher elevations and could

explain whyt heshell y18O values are not well correlated with

elevation (Fig 9)

Land snails of the genus Vallonia are commonly

associated with ancient sediments of the southern Great

Plains (Theler et al 2004 Wyckoff et al 1997) and the

diffusive evaporation model could provide a basis for

interpretation of many paleoenvironments in which this

genus was present Therefore y18O values of snail shell

aragonite predicted by the diffusive evaporation model

were compared only with the average measured y18O

values of adult Vallonia at each of the 12 modern

localities With one exception y18O values predicted by

the diffusive evaporation model (Balakrishnan and Yapp

2004) differed from the measured y18O values of Vallonia

by no more than 08x (shaded diamonds Fig 10) At

present we have no explanation for the single exception

In contrast for the case of no evaporation all predicted

y

18

O values of Vallonia were significantly different frommeasured y

18O values (28ndash54x more negative shaded

triangles Fig 10)

The approximate agreement between averages of meas-

ured shell y18O values of southern Great Plains land snails

and values predicted by the diffusive evaporation model is

in accord with the result obtained by Balakrishnan and Yapp

(2004) with reference to y18O data for western European

land snails measured by Lecolle (1985) Therefore the

steady-state isotopic effects of evaporation (thus relative

humidity) appear to be manifested in the y18O values of

land-snail shells of different species from two widely

separated regions with distinctly different climates

Conclusion

At various southern Great Plains sample sites transect-

average y13C values of land-snail shell aragonite are related

to the type of photosynthesis (ie C3 C4 or mixed) extant in

the local plant communities There is considerable scatter in

the relationship which suggests that caution should be

exercised in the interpretation of variations of shell y13C

values (eg Goodfriend and Hood 1983 Metref et al 2003

Yates et al 2002) However measured y13C values of

coexisting Vallonia and Gastrocopta are well-correlated

which appears to indicate similar feeding habits and suggests

that ancient samples of shells from these genera may be

useful sources of information on variations in southern Great

Plains plant ecology

Measured y18O values of land-snail shells averaged over

these sample localities appear to be controlled primarily by

the local temperature relative humidity and y18O value of

rain at the times of snail activity (ie nighttime or after rainfall in warmer months) This conclusion is supported by

the relatively good agreement between measured shell y18O

values and shell y18O values predicted with the evaporation

model of Balakrishnan and Yapp (2004)

Scatter of measured shell y18O values among and within

species at a site and among snails of different ages within a

genus (eg coexisting adults and juveniles of Vallonia)

indicates that the environmental information recorded by any

single small sample of land snails from the southern Great

Plains may depart significantly from the climatic bnormQ in a

locale For paleoclimatic studies such scatter emphasizes the

desirability of measuring if possible large numbers of

Figure 10 D18O vs average y18Omeas for each locality of southern Great Plains land snails D18O = (y18Ocalc Agrave y

18Omeas) Diamonds represent the comparison

of calculated and measured shell y18O for shell y18O values calculated with diffusive evaporation of snail body fluid (solid diamonds averages of all analyzed

specimens in a locality shaded diamonds averages of adult Vallonia only) Triangles represent D18O determined with the assumption that the snail shell was in

isotopic equilibrium with active season rain that experienced no evaporation either prior to or after being imbibed by the snails (solid triangles averages of all

analyzed species in a locality shaded triangles averages of adult Vallonia only)




individual snail shells from each defined sample to obtain

average values that might better represent the larger

(bneighborhoodQ ) scale temporal andor spatial variations of

ancient climate that are of interest The results presented here

for modern land-snail shells from the southern Great Plains of

North America suggest that meaningful climatic interpreta-

tions can be obtained from such averages but it must be kept in mind that the climatic information refers to the times of

snail activity and that more than one climatically relevant

parameter influences the shell y18O values

Acknowledgments

We thank Martha Scholl of the United States Geological

Survey for data on the isotopic composition of precipitation

in Norman Oklahoma and Mesonet of the University of

Oklahoma and Oklahoma State University for meteorolog-

ical data The paper benefited from the helpful comments of DD Rousseau and an anonymous reviewer This research

was supported in part by the Office of Graduate Studies at

SMU and NSF grant EAR-9614265 to CJY

Appendix A

Measured d13C and d18O values of Great Plains snails in this work

Locality Transect and replication Elevation (m) Plant type Land-snail species y13C y

18O

Kubic 6B 329 C3 G contractaAgrave

78Agrave

06Kubic 6C 329 C3 G contracta Agrave91 Agrave22

Kubic 6C 329 C3 G holzingeri Agrave94 Agrave17

Kubic 6C 329 C3 G pentodon Agrave91 Agrave21

Kubic 6C 329 C3 V parvula Agrave89 Agrave31

Kubic 6C 329 C3 Vallonia sp (juveniles) Agrave88 Agrave31

Kubic 6C 329 C3 Glyphyalinia indentata Agrave91 Agrave16

Kubic 6C 329 C3 Hawaiia minuscula Agrave61 Agrave26

Kubic 5B 351 C4 G procera Agrave34 Agrave14

Kubic 5B 351 C4 V parvula Agrave29 Agrave23

Kubic 5B 351 C4 Vallonia sp (juveniles) Agrave37 Agrave27

Kubic 5C 351 C4 G procera Agrave34 Agrave12


Kubic 1B 351 C4 G contracta Agrave25 Agrave26


Kubic 1C 351 C4 G procera Agrave22 Agrave19Kubic 2A 360 C4 C3 G pellucida Agrave43 Agrave25

Kubic 2A 360 C4 C3 G procera Agrave41 Agrave24

Kubic 2A 360 C4 C3 V parvula Agrave42 Agrave30

Kubic 2A 360 C4 C3 G contracta Agrave52 Agrave26

Kubic 2A 360 C4 C3 Vallonia sp (juveniles) Agrave54 Agrave09

Kubic 2A 360 C4 C3 Helicodiscus parallelus Agrave57 Agrave34

Kubic 2B 360 C4 C3 G armifera Agrave61 Agrave23

Kubic 2B 360 C4 C3 G holzingeri Agrave71 Agrave21

Kubic 2B 360 C4 C3 G pellucida Agrave65 Agrave15

Kubic 2B 360 C4 C3 G procera Agrave64 Agrave18

Kubic 2B 360 C4 C3 Pupoides albilabris Agrave21 Agrave17

Kubic 2B 360 C4 C3 V parvula Agrave49 Agrave25

Kubic 2B 360 C4 C3 Vallonia sp (juveniles) Agrave39 Agrave17

Kubic 2C 360 C4 C3 G pellucida Agrave39 Agrave17

Kubic 2C 360 C4 C3 G procera Agrave34 Agrave20Kubic 2C 360 C4 C3 Vallonia sp (juveniles) Agrave28 Agrave29

Kubic 4A 360 C4 G armifera Agrave24 Agrave12

Kubic 4A 360 C4 G contracta Agrave07 Agrave28

Kubic 4A 360 C4 G pellucida Agrave24 Agrave22

Kubic 4A 360 C4 G procera Agrave31 Agrave25


Kubic 4C 360 C4 G armifera Agrave18 Agrave16

Kubic 4C 360 C4 G contracta 00 Agrave16

Kubic 4C 360 C4 G pellucida Agrave16 Agrave17





Bluff Creek 36A 348 C3 G procera Agrave68 Agrave11




Appendix A (continued )


18O

Bluff Creek 36B 348 C3 G procera Agrave100 Agrave13

Salt Fork 9A 320 C3 G pellucida Agrave103 Agrave12

Salt Fork 9A 320 C3 V parvula Agrave99 Agrave20

Salt Fork 9A 320 C3 Vallonia sp (juveniles) Agrave101 Agrave21

Salt Fork 9B 320 C3 G pellucidaAgrave

106Agrave

20Salt Fork 9B 320 C3 V parvula Agrave100 Agrave21

Salt Fork 9B 320 C3 Vallonia sp (juveniles) Agrave100 Agrave18

Salt Fork 9C 320 C3 G pellucida Agrave100 Agrave17

Salt Fork 9C 320 C3 V parvula Agrave104 Agrave21

Salt Fork 9C 320 C3 Vallonia sp (juveniles) Agrave98 Agrave19

McDaniel 11C 375 C4 C3 G procera Agrave61 Agrave28

McDaniel 11A 375 C4 C3 G procera Agrave91 Agrave16

Burnham 17B 519 C4 C3 G pellucida Agrave94 Agrave08

Burnham 17B 519 C4 C3 G procera Agrave71 Agrave09

Burnham 16A 567 C4 CAM C3 G procera Agrave48 Agrave19

Burnham 16B 567 C4 CAM C3 G procera Agrave59 Agrave17

Burnham 12A 607 C4 C3 G pellucida Agrave54 Agrave23

Burnham 12A 607 C4 C3 G procera Agrave56 Agrave19

Burnham 12A 607 C4 C3 V parvula Agrave65 Agrave26

Burnham 14A 607 C4 CAM C3 G pellucida Agrave28 Agrave20Burnham 14A 607 C4 CAM C3 G procera Agrave31 Agrave02

Burnham 14B 607 C4 CAM C3 G pellucida Agrave59 Agrave07


Burnham 14C 607 C4 CAM C3 G pellucida Agrave49 Agrave09

Burnham 14C 607 C4 CAM C3 G procera Agrave41 Agrave16

Burnham 13A 610 C4 G pellucida Agrave30 11

Burnham 13A 610 C4 G procera Agrave38 04

Burnham 13B 610 C4 G pellucida Agrave38 12

Burnham 13B 610 C4 G procera Agrave55 Agrave18

Burnham 13C 610 C4 G procera Agrave49 Agrave14

Big Salt Plain 15A 482 C3 G pellucida Agrave81 Agrave10

Big Salt Plain 15A 482 C3 G procera Agrave93 Agrave06

Big Salt Plain 15B 482 C3 G procera Agrave94 05

Skull Springs 18A 671 C4 CAM C3 G procera Agrave51 Agrave22

Skull Springs 18A 671 C4 CAM C3 P albilabris Agrave47 Agrave16Skull Springs 18B 671 C4 CAM C3 G procera Agrave68 Agrave10

Skull Springs 18C 671 C4 CAM C3 G procera Agrave72 Agrave14

Skull Springs 19A 665 C4 C3 G cristata Agrave28 Agrave07

Skull Springs 19C 665 C4 C3 G cristata Agrave52 Agrave26

Hitch 22A 915 C4 CAM G procera Agrave42 Agrave15

Hitch 22A 915 C4 CAM P albilabris Agrave57 Agrave18

Hitch 22A 915 C4 CAM Succineidae Agrave65 Agrave03

Hitch 22B 915 C4 CAM Succineidae Agrave46 Agrave15

Hitch 22B 915 C4 CAM G procera Agrave44 Agrave22

Hitch 21A 933 C4 CAM C3 G procera Agrave34 Agrave01

Hitch 21A 933 C4 CAM C3 P albilabris Agrave56 00

Hitch 21C 933 C4 CAM C3 Succineidae Agrave59 Agrave16

Hitch 23A 881 C3 G cristata Agrave90 Agrave26

Hitch 23A 881 C3 G procera Agrave89 Agrave14

Hitch 23A 881 C3 P albilabris Agrave93 Agrave25Hitch 23A 881 C3 V parvula Agrave99 Agrave27

Hitch 23A 881 C3 Vallonia sp (juveniles) Agrave94 Agrave32

Hitch 23B 881 C3 G cristata Agrave82 Agrave16

Hitch 23B 881 C3 V parvula Agrave88 Agrave22

Hitch 23B 881 C3 Vallonia sp (juveniles) Agrave89 Agrave28

Hitch 23C 881 C3 G cristata Agrave37 Agrave18

Black Mesa 27A 1312 C4 C3 V gracilicosta Agrave86 Agrave27

Black Mesa 27A 1312 C4 C3 Vallonia sp (juveniles) Agrave93 Agrave16

Black Mesa 27B 1312 C4 C3 G procera Agrave51 Agrave23

Black Mesa 27B 1312 C4 C3 V gracilicosta Agrave45 Agrave26

Black Mesa 27B 1312 C4 C3 Vallonia sp (juveniles) Agrave53 Agrave29

Black Mesa 27C 1312 C4 C3 Vallonia sp (juveniles) Agrave58 Agrave30

Black Mesa 27C 1312 C4 C3 G pellucida Agrave57 Agrave25

(continued on next page)




References

Balakrishnan M Yapp CJ 2004 Flux balance models for the oxygen

and carbon isotope compositions of land snail shells Geochimica et

Cosmochimica Acta 68 2007ndash2024

Blair WF Hubbell TH 1938 The biotic districts of Oklahoma

American Midland Naturalist 20 425ndash455

Bruner WE 1931 The vegetation of Oklahoma Ecological Mono-

graphs 2 100ndash188

Carpenter JR 1940 The grassland biome Ecological Monographs 10

617ndash684

Cerling TE Quade J 1993 Stable carbon and oxygen isotopes in soil

carbonates In Swart PK Lohman KC McKenzie J Savin S

(Eds) Climate change in continental isotopic records Geophy-



18O

Black Mesa 27C 1312 C4 C3 G procera Agrave62 Agrave25

Black Mesa 27C 1312 C4 C3 P albilabris Agrave36 Agrave24

Black Mesa 27C 1312 C4 C3 V gracilicosta Agrave63 Agrave31

Black Mesa 27C 1312 C4 C3 V parvula Agrave68 Agrave41

Black Mesa 26A 1324 C4 CAM C3 V gracilicostaAgrave

77Agrave

10Black Mesa 26A 1324 C4 CAM C3 Vallonia sp (juveniles) Agrave59 Agrave19

Black Mesa 26B 1324 C4 CAM C3 G pellucida Agrave38 Agrave14

Black Mesa 26B 1324 C4 CAM C3 G procera Agrave71 Agrave30

Black Mesa 26B 1324 C4 CAM C3 V gracilicosta Agrave83 Agrave07

Black Mesa 26B 1324 C4 CAM C3 Vallonia sp (juveniles) Agrave67 Agrave25

Black Mesa 24B 1488 C4 CAM P albilabris Agrave26 Agrave17

Black Mesa 25A 1464 C4 CAM C3 G pellucida Agrave57 Agrave14

Black Mesa 25A 1464 C4 CAM C3 G procera Agrave68 Agrave05

Black Mesa 25A 1464 C4 CAM C3 V gracilicosta Agrave68 Agrave34

Black Mesa 25A 1464 C4 CAM C3 Vallonia sp (juveniles) Agrave79 Agrave25




Black Mesa 25C 1464 C4 CAM C3 G pellucida Agrave65 Agrave19

Black Mesa 25C 1464 C4 CAM C3 V gracilicosta Agrave73 Agrave38Black Mesa 25C 1464 C4 CAM C3 Vallonia sp (juveniles) Agrave65 Agrave26








Black Mesa 35C 1464 C4 CAM C3 Pupilla muscorum Agrave87 Agrave17

Black Mesa 35C 1464 C4 CAM C3 V gracilicosta Agrave84 Agrave08

Black Mesa 35C 1464 C4 CAM C3 Vallonia sp (juveniles) Agrave81 Agrave05

Owensby 61A 2193 C3 P muscorum Agrave132 Agrave18

Owensby 61A 2193 C3 V gracilicosta Agrave111 Agrave17

Owensby 61A 2193 C3 Vallonia sp (juveniles) Agrave93 Agrave23

Owensby 61C 2193 C3 V gracilicosta Agrave84 Agrave16Owensby 60B 2242 C3 Vallonia sp (juveniles) Agrave96 Agrave30



Owensby 59B 2288 C3 V gracilicosta Agrave109 Agrave13

Owensby 59B 2288 C3 Vallonia sp (juveniles) Agrave115 Agrave37

Owensby 59C 2288 C3 V gracilicosta Agrave117 Agrave10

CS Ranch 30A 1922 C4 CAM C3 P albilabris Agrave43 Agrave19

CS Ranch 29B 1940 C4 CAM C3 G pellucida Agrave47 Agrave24


CS Ranch 29C 1940 C4 CAM C3 P albilabris Agrave50 Agrave10

Chase 34A 1952 C4 C3 V gracilicosta Agrave92 Agrave38

Chase 33A 2184 C4 C3 G pilsbryana Agrave69 Agrave33

Chase 33B 2184 C4 C3 Cionella lubrica Agrave88 Agrave15

Chase 33B 2184 C4 C3 G pilsbryana Agrave93 Agrave25

Chase 33B 2184 C4 C3 G pellucida Agrave92 Agrave16Chase 31C 2220 C4 C3 G pilsbryana Agrave85 Agrave13

Chase 31C 2220 C4 C3 Zonitoides arboreus Agrave94 Agrave37

Chase 32C 2233 C4 C3 V gracilicosta Agrave93 Agrave18

Chase 32C 2233 C4 C3 Vallonia sp (juveniles) Agrave86 Agrave27




sical Monograph vol 78 American Geophysical Union Washington

pp 217ndash231

Cook A 1979 Homing in the gastropoda Malacologia 18 315ndash318

Cowie RH 1984 The life-cycle and productivity of the land snail

Theba pisana (Mollusca Helicidae) Journal of Animal Ecology 53

311ndash325

Craig H 1957 Isotopic standard for carbon and oxygen and correction

factors for mass spectrometric analysis of carbon dioxide Geochimicaet Cosmochimica Acta 12 133ndash149

Douglas MW Maddox RA Howard K 1993 The Mexican monsoon

Journal of Climate 6 1665ndash1677

Dansgaard W 1964 Stable isotopes in precipitation Tellus 16

436ndash469

Edelstam C Palmer C 1950 Homing behaviour in gastropods Okios 2

259ndash270

Ehleringer JR Cerling TE Helliker BR 1997 C4 photosynthesis

atmospheric CO2 and climate Oecologia 112 285ndash299

Elliot RD 1949 Forecasting the weathermdashThe weather types of North

America Weatherwise 2 15ndash 18

Francey RJ 1983 A comment on 13C 12C in land snail shells Earth and

Planetary Science Letters 63 142 ndash 143

Gelperin A 1974 Olfactory basis of homing in the giant garden slug

Limax maximus Proceedings of the National Academy of ScienceUnited States of America 71 966ndash970

Goodfriend GA Ellis GL 2002 Stable carbon and oxygen isotopic

variations in modern Rabdotus land snail shell in the southern Great

Plains USA and their relation to environment Geochimica et


Goodfriend GA Hood DJ 1983 Carbon isotope analysis of land snail

shells implications for carbon sources and radiocarbon dating Radio-

carbon 25 810ndash830

Goodfriend GA Magaritz M 1987 Carbon and oxygen isotope

composition of shell carbonate of desert land snails Earth and Planetary

Science Letters 86 377ndash388

Goodfriend GA Magaritz M Gat JR 1989 Stable isotope

composition of land snail body water and its relation to environmental

waters and shell carbonate Geochimica et Cosmochimica Acta 53

3215ndash3221Grossman EL Ku T-L 1986 Oxygen and carbon isotope fractiona-

tion in biogenic aragonite temperature effects Chemical Geology 59

59ndash74

Heatwole H Heatwole A 1978 Ecology of the Puerto Rican Camaenid

tree-snails Malacologia 17 241ndash315

Kuchler AW 1964 Potential vegetation of the conterminous United

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Jacobs BF Kingston JD Jacobs LL 1999 The origin of grass-

dominated ecosystems Annals of the Missouri Botanical Gardens 86

590ndash643

Lecolle P 1983 Relation entre les teneurs en 18O et 13C des tests de

Gasteropodes terrestres et le climat oceanique et alpin Comptes

Rendus de lrsquoAcademie des Sciences Serie II 297 863 ndash 866

Lecolle P 1984 Influence de lrsquoaltitude en climat mediterraneen sur les

teneurs en oxygene-18 et carbone-13 des coquilles de Gasteropodesterrestres Comptes Rendus de lrsquoAcademie des Sciences Serie II 298

211ndash214

Lecolle P 1985 The oxygen isotope composition of land snail shells as a

climatic indicator applications to hydrogeology and paleoclimatology

Chemical Geology 58 157ndash 181

Magaritz M Heller J 1980 A desert migration indicator-oxygen isotopic

composition of land snail shells Palaeogeography Palaeoclimatology

Palaeoecology 32 153ndash162

Magaritz M Heller J 1983 A comment of 13C 12C in land snail shells-

reply Earth and Planetary Science Letters 63 144ndash145

Magaritz M Heller J Volokita M 1981 Land-air boundary

environment as recorded by the 18O 16O and 13C 12C isotope ration

in the shells of land snails Earth and Planetary Science Letters 52

101ndash106

McCrea JM 1950 On the isotopic chemistry of carbonates and a

paleotemperature scale Journal of Chemical Physics 18 849ndash857

Metref S Rousseau D-D Bentaleb I Labonne M Vianey-Liaud M

2003 Study of the diet effect on y13C of shell carbonate of the land

snail Helix aspersa in experimental conditions Earth and Planetary

Science Letters 211 381 ndash 393

Nativ R Riggio R 1990 Precipitation in the Southern High Plains

meteorologic and isotopic features Journal of Geophysical Research95 22559ndash 22564

Newell PF 1966 The nocturnal behaviour of slugs Medical Biology

Illustrated 16 146 ndash 159

Ostlie WR Schneider RE Aldrich JM Faust TM McKim RLB

Chaplin SJ 1997 The Status of Biodiversity in the Great Plains The

Nature Conservancy Arlington VA USA

Owensby CE Ham JM Knapp AK Bremer D Auen LM 1997

Water vapour fluxes and their impact under elevated CO2 in a C4-

tallgrass prairie Global Change Biology 3 189ndash195

Risser PG 1985 Grasslands In Chabot BF Mooney HA (Eds)

Physiological Ecology of North American Plant Communities Chap-

man and Hall New York pp 232ndash256

Risser PG 1990 Landscape processes and the vegetation of the North

American grassland In Collins SL Wallace LL (Eds) Fire in

North American Tallgrass Prairies University of Oklahoma PressNorman pp 133ndash146

Rossignol J Moine O Rousseau D-D 2004 The Buzzardrsquos Roost and

Eustis mollusc sequences comparison between the paleoenvironments

of two sites in the Wisconsinan loess of Nebraska USA Boreas 33

145ndash154

Rozanski K Araguas-Araguas L Gonfiantini R 1993 Isotopic patterns

in modern global precipitation In Swart PK Lohman KC

McKenzie J Savin S (Eds) Climate Change in Continental Isotopic

Records Geophysical Monograph vol 78 American Geophysical

Union Washington pp 1 ndash 36

Sage RF Li M Monson RK 1999 The taxonomic distribution of C4

photosynthesis In Sage RF Monson RK (Eds) C4 Plant Biology

Academic Press pp 551ndash 584

Sharpe SE Forester RM Whelan JF McConnaughey T 1994

Molluscs as climate indicators preliminary stable isotope and com-munity analyses Proceedings of the 5th International High-level

Radioactive Waste Management Conference and Exposition Las Vegas

Nevada pp 2538ndash 2544

Shelford VE 1963 The Ecology of North America University of Illinois

Press Urbana

Stott LD 2002 The influence of diet on the y13C of shell carbon in the

pulmonate snail Helix aspersa Earth and Planetary Science Letter 195

249ndash259

Theler JL Wyckoff DG Carter BJ 2004 The Southern Plains

gastropod survey the distribution of land snail populations in an

American grassland environment American Malacological Bulletin 18

(12) 1ndash16

Thompson R Cheny S 1996 Raising snails National Agriculture

Library Special Reference Briefs NAL SRB 96-05

Tieszen L Reed BC Bliss NB Wylie BK DeJong DD 1997NDVI C3 and C4 production and distribution in great plains grassland

land cover classes Ecological Applications 7 59ndash78

Van der Schalie A Getz LL 1961 Comparison of adult and young

Pomatiopsis cincinnatiensis (lea) in respect to moisture requirements

Transactions of the American Microscopical Society 80 211 ndash 220

Van der Schalie A Getz LL 1963 Comparison of temperature and

moisture responses of the snail genera Pomatiopsis and Oncomelania

Ecology 44 73ndash83

Ward D Slotow R 1992 The effects of water availability on the life

history of the desert snail Trochoidea seetzeni An experimental field

manipulation Oecologia 90 572ndash580

Weaver JE Albertson FW 1956 Grasslands of the Great Plains Their

Nature and Use Johnsen Publishing Co Lincoln NE

Wells GP 1944 The water relations of snails and slugs III Factors




determining the activity of Helix pomatia L Journal of Experimental

Biology 44 73ndash83

Wyckoff DG Theler JL Carter BJ 1997 Southern Plains gastropods

modern occurrences prehistoric implications Final Report to the

National Geographic Society 46 pp

Yapp CJ 1979 Oxygen and carbon isotope measurements of land snail

shell carbonate Geochimica et Cosmochimica Acta 43 629ndash635

Yates TJS Spiro BF Vita-Finzi C 2002 Stable isotope variability and

the selection of terrestrial mollusk shell samples for 14C dating

Quaternary International 87 87ndash100




shell aragonite y13C values of shell aragonite were

correlated with y13C values of organic matrix in the shell

which suggests that the shell y13C reflects diet with an offset

associated with the snail physiology and equilibrium and

kinetic fractionation processes Relationships of y18O

variations of Rabdotus to the environmental variables

discussed by Goodfriend and Ellis (2002) appeared to bemore problematic than for carbon

In the current paper we present measurements of

variations in the carbon and oxygen isotope compositions

of shells of other species of modern land snails from a

different portion of the southern Great Plains of North

America Samples in t his study are described in the work of

Theler et al (2004) and are from a narrow eastndashwest

corridor extending across much of Oklahoma and into

Northeastern New Mexico USA The data are discussed in

terms of their relationship to modern environmental

variables to examine the likelihood that isotopic data from

ancient land snails in the region might have paleoenvir-onmental significance

Samples and study area

Samples

The modern snail population procured for this study

f ormed part of an extensive terrestrial gastropod survey

(Theler et al 2004 Wyckoff et al 1997) in the southern

Great Plains of North America Samples were collected at

12 localities along an eastndashwest corridor extending from

North Central Oklahoma to Northeastern New Mexico

between 36826VN t o 3 6858VN latitude and 96849VW to

104857VW longitude (Theler et al 2004 Wyckoff et al

1997) The site names and locations are depicted in Figure

1 The study corridor is 640 km long east to west and about

100 km wide and extends from the Flint Hills of North

Central Oklahoma to the foothills of the Sangre de Cristo

Mountains near Cimarron New Mexico (Fig 1) Elevation

in the study area slowly increases from 330 m above sea

level at the eastern end of the corridor to about 2290 m

above sea level at the western end

Vegetation

There are four distinct biotic districts in the sampled area

(Fig 1) Mixed-grass plains occupy the eastern section

(Blair and Hubbell 1938 Carpenter 1940 Ostlie et al

1997 Shelford 1963) This district marks the transition

from tall grass prairie in the east to short grass prairie in the

west and is characterized by several species of Ascoparius

(Ascoparius saccharoides Ascoparius furcatus Ascoparius

smithii) grama grasses (Bouteloua gracilis Bouteloua

racemosa Bouteloua hirsuta and Bouteloua curtipendula)

and buffalo grass (Buchloe dactyloides) (Blair and Hubbell

1938 Bruner 1931 Carpenter 1940 Kuchler 1964 Ostlie

et al 1997 Risser 1985 1990 Shelford 1963 Weaver and

Albertson 1956)

The second biotic region short grass prairie (immedi-

ately to the west of the mixed-grass prairie Fig 1) contains

vegetation that includes buffalo grass hairy grama (B

hirsuta) blue grama (B gracilis) and western wheatgrass

(Pascopyrum smithii) (Blair and Hubbell 1938 Bruner1931 Carpenter 1940 Kuchler 1964 Ostlie et al 1997

Risser 1990 Shelford 1963)

A third biotic district the pinyonndashjuniper shrub grass-

land Raton subsection (Blair and Hubbell 1938) extends

from the northwest corner of the panhandle into the

northeastern corner of New Mexico (Fig 1) Vegetation in

this region includes junipers (Juniperus monosperma

Juniperus osteosperma) oak (Quercus mohriana) and pine

(Pinus edulis Pinus monophylla) along with plants such as

silverbeard grass (A saccharoides) blue grama and some

species of prickly pear cactus (Opuntia sp) (Blair and

Hubbell 1938 Ostlie et al 1997)The dry pine forest at the western end of the study area

(Fig 1) is not strictly a Plains ecosystem (Shelford 1963)

Vegetation includes oak and pine along with hairy and blue

grama grasses (Shelford 1963 Theler et al 2004 Wyckoff

et al 1997)

Climate and isotopes in precipitation

Average annual precipitation on the southern plains

generally decreases from over 1020 mmyr in the east to

255 mmyr in the west (Ostlie et al 1997) The mean

annual temperatures in the mixed-grass prairie range from

158 t o 178C while the corresponding mean annual

precipitation ranges from 670 to 790 mm (Blair and

Hubbell 1938) Annual temperatures in the short grass

prairie range from 128 to 138C and mean annual precip-

itation from 450 to 560 mm (Blair and Hubbell 1938)

Average annual temperatures in the dry pine forest of the

foothills of the Sangre de Cristo mountains are about 118C

and average rainfall is about 400 mm (Climate Data Center

New Mexico State University at wwwweathernmsuedu)

Precipitation in these regions derives principally from three

locations (Elliot 1949 Nativ and Riggio 1990)

From late March into July moisture is derived primarily

from the Gulf of Mexico (curveb

aQ

Fig 2) From October to early March the Northern Pacific Ocean is the primary

moisture source (Nativ and Riggio 1990) (curve bcQ Fig

2) In the western end of the study area (Northeastern New

Mexico) both the Gulf of Mexico and the central Pacific

Ocean contribute moisture during the middle to late summer

and early fall (curves baQ and bbQ Fig 2) although

contributions from the Gulf of Mexico are predominant

The central Pacific component of this moisture is brought in

by the Mexican monsoons (Douglas et al 1993 Nativ and

Riggio 1990)

The temperature and relative humidity at which ocean

water evaporates the air mass history and the local















1993)

Experimental



























































































at 258












y18O and y

















10x (Fig 3)
























individual samples






Americany18





























plotted against y13


















the adults


























broader y18



parameters

Carbon isotopes






































in Table 1

























Plains Vallonia inb

replicationsQ

(see text) (a) y

18
















Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16












































1993)

Experimental



























































































at 258












y18O and y

















10x (Fig 3)
























individual samples






Americany18





























plotted against y13


















the adults


























broader y18



parameters

Carbon isotopes






































in Table 1

























Plains Vallonia inb

replicationsQ

(see text) (a) y

18
















Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16











































































































at 258












y18O and y

















10x (Fig 3)
























individual samples






Americany18





























plotted against y13


















the adults


























broader y18



parameters

Carbon isotopes






































in Table 1

























Plains Vallonia inb

replicationsQ

(see text) (a) y

18
















Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16

























































plotted against y13


















the adults


























broader y18



parameters

Carbon isotopes






































in Table 1

























Plains Vallonia inb

replicationsQ

(see text) (a) y

18
















Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16










































broader y18



parameters

Carbon isotopes






































in Table 1

























Plains Vallonia inb

replicationsQ

(see text) (a) y

18
















Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16










































Oxygen isotopes















breplications














Table 1


18O


y13C y


18O


































y18Ocalc Agrave y

















































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16













































































































18Omeas
































increase in shell y

18




Table 2






















elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16



































elevation (Fig 9)
















y

18



triangles Fig 10)











Conclusion















































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16










































Acknowledgments








Appendix A



18O


78Agrave
















































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16



































18O






106Agrave




























































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16

































References









617ndash684






18O






77Agrave



















































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16


































pp 217ndash231




311ndash325






436ndash469


259ndash270
























59ndash74







590ndash643






211ndash214












101ndash106


























145ndash154














Press Urbana



249ndash259




(12) 1ndash16































balakrishnan et al, 2004

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