Seasonal Cyclicity in Trace Elements and Stable Isotopes of Modern Horse Enamel.

Niels J. de Winter,Christophe Snoeck,Philippe Claeys

doi:10.1371/journal.pone.0166678

Abstract

The study of stable isotopes in fossil bioapatite has yielded useful results and has shown that bioapatites are able to faithfully record paleo-environmental and paleo-climatic parameters from archeological to geological timescales. In an effort to establish new proxies for the study of bioapatites, intra-tooth records of enamel carbonate stable isotope ratios from a modern horse are compared with trace element profiles measured using laboratory micro X-Ray Fluorescence scanning. Using known patterns of tooth eruption and the relationship between stable oxygen isotopes and local temperature seasonality, an age model is constructed that links records from six cheek upper right teeth from the second premolar to the third molar. When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios. While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal’s diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal. The latter explanation is in agreement with seasonal changes observed in carbon isotopes of the same teeth. This external forcing of trace element composition in mammal tooth enamel implies that trace element ratios may be used as proxies for seasonal changes in paleo-environment and paleo-diet.

Highlights

Records from fossil tooth bioapatite have often been used to reconstruct paleo-diet and paleoenvironment (e.g. [1] [2] [3]; [4] [5] [6])
When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios
While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal’s diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal

Summary

Introduction

Records from fossil tooth bioapatite have often been used to reconstruct paleo-diet and paleoenvironment (e.g. [1] [2] [3]; [4] [5] [6]). Records from fossil tooth bioapatite have often been used to reconstruct paleo-diet and paleoenvironment Horse molars and premolars grow to about 8–9 cm length and their relatively fast growth rate of 3–4 cm/yr ([34]) allows the construction of multi-year geochemical records with a high (monthly) temporal resolution. The eruption and mineralization sequence of modern horses varies between races, but the timing of mineralization of horse cheek teeth is known within a 1 to 3 months range ([34]). This knowledge allows construction of a composite time series from multiple individual teeth. The total sequence of teeth covers a timespan of over 4 years ([34] [38])

Methods

Findings

Discussion

Conclusion