This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 73 (2009) 4077–4099 www.elsevier.com/locate/gca Oxygen and carbon stable isotopes of modern land snail shells as environmental indicators from a low-latitude oceanic island Yurena Yanes a,*, Christopher S. Romanek a, Antonio Delgado b, Heather A. Brant a, John E. Noakes c, Marı´a R. Alonso d, Miguel Iba´n˜ez d a Department of Geology and Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, USA b Laboratorio de Biogeoquı´mica de Iso´topos Estables, Estacio´n Experimental del Zaidı´n (CSIC), Granada. Prof. Albareda 1, 18008 Granada, Spain c Center for Applied Isotopes Studies, University of Georgia, 120 Riverbend Road, Athens, GA 30602, USA d Departamento de Biologı´a Animal, Facultad de Biologı´a, Universidad de La Laguna, Avda. Astrofı´sico Fco. Sa´nchez, s/n. 38206 La Laguna, Tenerife, Canary Islands, Spain Received 26 December 2008; accepted in revised form 27 April 2009; available online 3 May 2009 Abstract Land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells, which are generally highly abundant and well-preserved in the fossil record, contain a temporal record of environmental change in the form of isotope codes. To evaluate the utility of this approach for a low-latitude oceanic setting, 207 modern shells of 18 species of land snail were analyzed for their oxygen and carbon isotope composition along a north and south facing altitudinal gra- dient (10–2160 m a.s.l.) in Tenerife Island (28°N) of the Canary Archipelago. Shells collected at each locality showed a relatively large range in isotope composition which was greater along the south facing transect (drier and hotter), suggesting that the variance in shell isotope values may be related to water-stress. Although pooled isotope values did not generally show strong relationships with environmental variables (i.e., altitude, temperature and precipitation), mean isotope values were strongly associated with some climatic factors when grouped by site. The mean d18O 18 value of the shell (d Oshell) by site displayed a negative correlation with elevation, which is consistent with the positive rela- 18 18 18 tionship observed between temperature and the d O value of rain (d Orain). Calculated d O values of the snail body water 18 18 (d Obody) derived from observed temperatures and d Oshell values (using the equation of Grossman and Ku [Grossman E. L. and Ku T. L. (1986) Oxygen and carbon isotope fractionation in biogenic aragonite. Chem. Geol. (Isotope Geosci. Sec.) 59, 59–74]) displayed a trend with respect to altitude that was similar to measured and hypothetical d18O values for local rain 18 water. The calculated d Obody values from the shell declined 0.17& (VSMOW) per 100 m, which is consistent with the ‘‘alti- tude effect” observed for tropical rains in Western Africa, and it correlated negatively with rainfall amount. Accordingly, low- 18 18 er d Oshell values indicate lower temperatures, lower d Orain values and possibly, higher rainfall totals. A positive correlation 13 13 between the mean d C values of shells (d Cshell) and plants by site suggests that shells potentially record information about 13 the surrounding vegetation. The d Cshell values varied between À15.7 and À0.6& (VPDB), indicating that snails consumed 13 C3 and C4/CAM plants, where more negative d Cshell values probably reflects the preferential consumption of C3 plants 13 which are favored under wetter conditions. Individuals with more positive d Cshell values consumed a larger percentage of C4 plants (other potential factors such as carbonate ingestion or atmospheric CO2 contribution were unlikely) that were more common at lower elevations of the hotter and drier south facing transect. The relatively wide range of shell isotope values within a single site requires the analysis of numerous shells for meaningful paleoclimatic studies. Although small differences were observed in isotope composition among snail species collected at a single sampling site, they were not significant, * Corresponding author. Fax: +1 803 725 3309. E-mail address: [email protected] (Y. Yanes). 0016-7037/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2009.04.021 Author's personal copy 4078 Y. Yanes et al. / Geochimica et Cosmochimica Acta 73 (2009) 4077–4099 suggesting that isotope signatures extracted from multi-taxa snail data sets may be used to infer environmental conditions over a broad range of habitats. Ó 2009 Elsevier Ltd. All rights reserved. 1. INTRODUCTION of Tenerife Island. Consequently, a study of the stable isotope composition of land snails is a useful baseline Land snails are one of the most widely used organisms to better understand isotope profiles extracted from fos- to estimate climatic characteristics of both modern and an- sil shells in future paleoclimatic studies of low latitude cient terrestrial ecosystems (e.g., Yapp, 1979; Magaritz and environments. Heller, 1980, 1983; Goodfriend and Magaritz, 1987; Good- In the present study, the oxygen and carbon isotope friend et al., 1989; Goodfriend, 1992, 1999; Goodfriend and composition of multiple species of modern land snails were Ellis, 2002; Balakrishnan and Yapp, 2004; Balakrishnan determined from individual shells collected along an altitu- et al., 2005a,b; Colonese et al., 2007). dinal gradient from Tenerife Island, Canary Archipelago 18 18 The d O value of the shell (d Oshell) represents the (from 10 to 2160 m a.s.l.) to determine the relationships be- combined effects of relative humidity, ambient water vapor, tween isotope signatures and various environmental param- water ingested by the snail and the temperature at which eters, that may be useful indicators of climate dynamics for the shell precipitated (Balakrishnan and Yapp, 2004), low-latitude oceanic settings. which may vary differentially depending on the study local- ity and species. Consequently, many studies performed on modern land snail shells have documented a relationship 2. GEOGRAPHICAL AND ENVIRONMENTAL 18 18 between the d O value of rain water (d Orain) and the CONTEXT snail shell (e.g., Yapp, 1979; Le´colle, 1985; Zanchetta et al., 2005; Yanes et al., 2008), in addition to other impor- Tenerife is a low latitude (28°N) volcanic island lo- tant factors such as relative humidity (Balakrishnan and cated in the center of the Canary Archipelago, which is sit- Yapp, 2004). However, this relationship has not been uated about 110 km off of the Moroccan coast, NW Africa proven in arid areas (Goodfriend et al., 1989; Colonese (Fig. 1). The island is the largest (2034 km2) of the archipel- et al., 2007). ago, reaching the highest altitude in the Atlantic Ocean The relationship between the d13C value of the shell basin (3718 m a.s.l.). 13 13 (d Cshell) and the plants (d Cplants) that a snail assimi- Tenerife has a Mediterranean climate characterized by lates is well established in both natural (e.g., Goodfriend hot and dry summers, and wet and warm winters. Never- and Ellis, 2002; Baldini et al., 2007; Yanes et al., 2008) theless, multiple micro-climates and ecosystems are recog- and laboratory settings (Stott, 2002; Metref et al., 2003). nized due to the altitudinal temperature gradient, the Thus, the carbon isotope composition of the shell should influence of the humid trade winds and the Canarian record the integrated d13C value of plants assimilated by cool ocean current, and the variety of volcanic soil types the organisms, which in part is a reflection of the humidity on the island (Del-Arco et al., 2006; Ferna´ndez-Palacios or aridity of an environment (e.g., Goodfriend and Mag- and Whittaker, 2008). As a consequence, plant communi- aritz, 1987; Goodfriend, 1992, 1999; Goodfriend and Ellis, ties are spatially distinct on the island and are highly cor- 2000, 2002). related with altitude, wind-exposure, temperature and Landscapes that contain altitudinal gradients are sen- precipitation (Ferna´ndez-Palacios, 1992). Five main bio- sitive environments for testing ecological and evolution- climatic belts (terrestrial zonal habitats) are defined with ary responses of biota to climate change over short altitude (e.g., Bramwell and Bramwell, 1974; Ferna´ndez- spatial scales because many environmental variables such Palacios, 1992; Del-Arco et al., 2006; Ferna´ndez-Palacios as temperature and atmospheric pressure change over and Whittaker, 2008)(Fig. 2): (1) arid (sub-desert) coast- relatively short distances (Ko¨rner, 2007). Tenerife Island al scrub up to 600 m with African ecosystem affinities, of the Canary Archipelago is a unique site to study the which is dominated by succulent endemic Euphorbia effect of climate on land snails along an altitudinal gra- shrubs (including C4 and CAM plant types); (2) semiarid dient for several reasons: (1) Tenerife is the third highest thermophilous woodlands from 300 to 1100 m, which is a oceanic island in the world after two Hawaiian Islands, Mediterranean-like ecosystem; (3) humid ‘‘laurel” (ever- reaching up to 3718 m at the volcanic peak of El Teide green) forest in a cloud belt (on windward slopes) from in the center of the island (Rivas-Martı´nez et al., 1993); 600 to 1200 m, which is a relict sub-tropical ecosystem (2) the island is strongly influenced by the trade winds; with abundant paleo-endemic tree species; (4) humid to and (3) the island contains a great variety of volcanic dry temperate pine forest from 1100 to 2200 m, domi- soil types.