Pleistocene–Holocene environmental change in the Canary Archipelago as inferred from the stable isotope composition of land snail shells

Abstract

The isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern Canary Islands (28–29°N) over the last ~ 50 ka. Shell δ13C values range from −8.9‰ to 3.8‰. At various times during the glacial interval (~ 15 to ~ 50 ka), moving average shell δ13C values were 3‰ higher than today, suggesting a larger proportion of C4 plants at those periods. Shell δ18O values range from −1.9‰ to 4.5‰, with moving average δ18O values exhibiting a noisy but long-term increase from 0.1‰ at ~ 50 ka to 1.6–1.8‰ during the LGM (~ 15–22 ka). Subsequently, the moving average δ18O values range from 0.0‰ at ~ 12 ka to 0.9‰ at present. Calculations using a published snail flux balance model for δ18O, constrained by regional temperatures and ocean δ18O values, suggest that relative humidity at the times of snail activity fluctuated but exhibited a long-term decline over the last ~ 50 ka, eventually resulting in the current semiarid conditions of the eastern Canary Islands (consistent with the aridification process in the nearby Sahara). Thus, low-latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical/subtropical environmental change.

Transitional environments of the lower Maastrichtian South-Pyrenean Basin (Catalonia, Spain): The Fumanya Member tidal flat

“…For land snails (terrestrial gastropod pulmonates) d 18 O in shells is related to the d 18 O of the water that the snails absorb through their skin or drink from the upper layers of the soil, and to the temperature (Balakrishnan, Yapp, Meltzer, & Theler, 2005;Yanes et al, 2011;Zanchetta, Leone, Fallick, & Bonadonna, 2005). The d 18 O of the shells is linked to the d 18 O values of precipitation (environmental water) and correlate with the annual mean temperature.…”

“…The d 13 C for shells from terrestrial-shell carbonate may be mainly explained by the relative contribution of metabolic CO 2 and ingested carbonates (Yanes et al, 2011). Moreover, the d 13 C in landsnail shells are also linked to the predominant photosynthetic pathways (C3, C4) in the local plant communities.…”

The ancient forests of La Gomera, Canary Islands, and their sensitivity to environmental change

“…This is partly because of the poor preservation of proxies (e.g., fossil pollen) due to the volcanic nature of the sediments and lack of permanent lakes. However, recent analyses of d 18 O from land snails shells from the eastern islands (Lanzarote, Fuerteventura, and Alegranza, La Graciosa and Montaña Clara islets) have been used to infer a decline in humidity during the Late Holocene (Yanes et al 2011). There is evidence to suggest that Mediterranean regions in the Iberian Peninsula (e.g., eastern Betic Mountains) also became increasingly arid during the period 5000 to 4000 cal.…”

Food Water Contribution to the Oxygen Isotope Composition of Land Snail Body Water and Its Environmental Implication

“…The flux balance model using snail shell d 18 O values has been widely applied to both modern and paleo studies (e.g. Balakrishnan et al, 2005aBalakrishnan et al, , 2005bColonese et al, 2011Colonese et al, , 2014Yanes, 2015;Yanes & Romanek, 2013;Yanes et al, 2009Yanes et al, , 2011Yanes et al, , 2012Yanes et al, , 2013aYanes et al, , 2013b. For example, based on the model by Yanes et al (2012), the environment from 12.1 to10.9 ka BP was drier than both the 8.4 to 6.3 ka BP interval and today.…”