Zinc Isotope Ratios as Indicators of Diet and Trophic Level in Arctic Marine Mammals

Abstract

Carbon and nitrogen stable isotope ratios of bone collagen are an established method for dietary reconstruction, but this method is limited by the protein preservation. Zinc (Zn) is found in bioapatite and the isotopic compositions of this element constitute a very promising dietary indicator. The extent of fractionation of Zn isotopes in marine environments, however, remains unknown. We report here on the measurement of zinc, carbon and nitrogen isotopes in 47 marine mammals from the archaeological site of Arvik in the Canadian Arctic. We undertook this study to test and demonstrate the utility of Zn isotopes in recent mammal bone minerals as a dietary indicator by comparing them to other isotopic dietary tracers. We found a correlation between δ66Zn values and trophic level for most species, with the exception of walruses, which may be caused by their large seasonal movements. δ6Zn values can therefore be used as a dietary indicator in marine ecosystems for both modern and recent mammals.

Fig 1. Expected distribution of δ⁶⁶Zn values in animal tissues based on values obtained in modern terrestrial food webs and experimental animals [14,15,16].

Fig 2. Map showing the location of the site, Zn-Pb deposits (green circles) and the Polaris mine.

The map is adapted from the one of Le Moine et al [29].

Fig 3

A. Relationship between the Zn concentration and δ⁶⁶Zn values of cancellous (black circles) and cortical part of bones of walruses (circles) and other mammals (crosses), found in surface (green colors) and subsurface deposits (black colors). All the cancellous bone samples fall on a regression line. B. δ⁶⁶Zn values of cancellous and cortical fractions of walrus bones. Lines define the average and two standard deviation area of cortical values. Green rectangles frame values for same individuals.

Fig 4. Cortical bone isotopic values of arctic mammals for C, N, and Zn.

A) δ⁶⁶Zn_bioapatite vs. δ¹³C_collagen values for four species of marine mammals (B) δ⁶⁶Zn_bioapatite vs. δ¹⁵N_collagen values, (C) δ¹⁵N_collage vs. δ¹³C_collagen and (D) 3D plot showing that Zn, N and C isotopic compositions of marine mammals enables a distinguishing of the different species. Measurement uncertainties are given by the white boxes.