Stable carbon isotope compositions of Eastern Beringian grasses and sedges: Investigating their potential as paleoenvironmental indicators

摘要

The nature of vegetation cover present in Beringia during the last glaciation remains unclear. Uncertainty rests partly with the limitations of conventional paleoecological methods. A lack of sufficient taxonomic resolution most notably associated with the grasses and sedges restricts the paleoccological inferences that can be made. Stable isotope measurements of subfossil plants are frequently used to enhance paleoenvironmental reconstructions. We present an investigation of the stable carbon isotope composition (delta C-13) of modern and subfossil grasses and sedges (graminoids) from Eastern Beringia. Modern grasses from wet habitats had a mean delta C-13 of -29.1 parts per thousand. (standard deviation [SD] = 2.1 parts per thousand, n = 75), while those from dry habitats had a mean of -26.9 parts per thousand (SD = 1.19, n = 27). Sedges (n = -50) from dry, wet, marsh, and sand dune habitats had specific habitat ranges. Four modern C-4 grasses had delta C-13 values typical Of C4 plants. Analyses were also conducted using subfossil graminoid remains from several sedimentary paleoecological contexts (e.g., arctic ground squirrel nests, loess, permafrost, and paleosols) in Eastern Beringia. Results from these subfossil samples, ranging in age from > 40,000 to ca. 11,000 cal. yr BP, illustrate that the delta C-13 of graminoid remains has altered during the past. The range of variation in the subfossil samples is within the range from modern graminoid specimens from dry and wet habitats. The results indicate that stable isotopes could contribute to a comprehensive and multiproxy reconstruction of Beringian paleoenvironments.