Tahmasebi Farnoush, Longstaffe Fred J, Zazula Grant
Department of Earth Sciences, The University of Western Ontario, London, Ontario, Canada.
Yukon Palaeontology Program, Department of Tourism & Culture, Government of Yukon, Whitehorse, Yukon Territory, Canada.
PLoS One. 2018 Feb 15;13(2):e0192713. doi: 10.1371/journal.pone.0192713. eCollection 2018.
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 ‰) in δ13C of modern Yukon grasses. A major change (2-10 ‰) 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.
阿拉斯加和育空地区（统称为东白令陆桥）富含冰的黄土沉积物中蕴藏着晚更新世陆地巨型动物化石的宏伟宝库。这些化石骨胶原的稳定碳（δ13C）和氮（δ15N）同位素组成通常用于确定古饮食并重建古生态系统。这种方法需要考虑碳和氮同位素动力学随时间的变化及其对陆地植被同位素基线的影响。为了测试晚更新世和现代之间的这种变化，我们比较了一些现代育空北极地松鼠的植被、骨胶原和结构碳酸盐的δ13C和δ15N，以及育空黄土沉积物中保存的晚更新世化石北极地松鼠巢穴的植被和骨骼的δ13C和δ15N。利用现代样本测量了北极地松鼠骨胶原与其饮食之间的同位素分馏，以及植物分解过程中的同位素变化；现代育空地区草类在衰老后的越冬分解导致δ13C有微小变化（约0-1‰）。对被黄土薄层覆盖的育空地区分解草类测量到δ15N有较大变化（约2-10‰）。正如预期的那样，对现代样本测量的胶原-饮食碳同位素分馏证实，在对苏士效应进行校正后，现代植被的δ13C是育空地区晚更新世植被的合适替代指标。然而，在对分解效应进行校正后，化石北极地松鼠巢穴中植被的氮同位素组成被确定比该地区现代草原高约2.8‰。这一结果表明该地区在晚更新世和现代之间氮动力学发生了变化。
