Nitrogen Isotopes Suggest a Change in Nitrogen Dynamics between the Late Pleistocene and Modern Time in Yukon, Canada

Authors

Farnoush Tahmasebi, The University of Western Ontario
Fred J. Longstaffe, The University of Western OntarioFollow
Grant Zazula, Government of Yukon Territory

Document Type

Article

Publication Date

2018

Volume

13

Issue

2

Journal

PLoS ONE

First Page

1

URL with Digital Object Identifier

https://doi.org/10.1371/journal. pone.0192713

Last Page

31

Abstract

A magnificent repository of Late Pleistocene terrestrial megafauna fossils is contained in ice-rich loess deposits of Alaska and Yukon, collectively eastern Beringia. The stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope compositions of bone collagen from these fossils are routinely used to determine paleodiet and reconstruct the paleoecosystem. This approach requires consideration of changes in C- and N-isotope dynamics over time and their effects on the terrestrial vegetation isotopic baseline. To test for such changes between the Late Pleistocene and modern time, we compared δ¹³C and δ¹⁵N for vegetation and bone collagen and structural carbonate of some modern, Yukon, arctic ground squirrels with vegetation and bones from Late Pleistocene fossil arctic ground squirrel nests preserved in Yukon loess deposits. The isotopic discrimination between arctic ground squirrel bone collagen and their diet was measured using modern samples, as were isotopic changes during plant decomposition; Over-wintering decomposition of typical vegetation following senescence resulted in a minor change (~0±1 ½) in δ¹³C of modern Yukon grasses. A major change (~2±10 ½) in δ¹⁵N was measured for decomposing Yukon grasses thinly covered by loess. As expected, the collagen-diet C-isotope discrimination measured for modern samples confirms that modern vegetation δ¹³C is a suitable proxy for the Late Pleistocene vegetation in Yukon Territory, after correction for the Suess effect. The N-isotope composition of vegetation from the fossil arctic ground squirrel nests, however, is determined to be ~2.8‰ higher than modern grasslands in the region, after correction for decomposition effects. This result suggests a change in N dynamics in this region between the Late Pleistocene and modern time.