N-Alkanes in fresh snow in Hokkaido, Japan: Implications for ice core studies

摘要

Plant waxes (e.g. long-chain n-alkanes) in ice cores are a promising paleovegetation proxy. However, much work needs to be done to assess how n-alkanes are transported from source areas to, and incorporated into, glacial archives. In this paper we present analyses of n-alkanes in seasonal snow and assess the information on source vegetation. n-Alkanes with carbon numbers C_(18) to C_(43) were extracted from snow samples collected at two sites in Hokkaido, northern Japan, during winter 2009-2010. Molecular distributions revealed that the majority of the n-alkanes originated from higher vegetation (ca. 65%), rather than anthropogenic sources. The distribution characteristics confirmed that the n-alkane signal had a wide regional origin, rather than a local source. We determined stable carbon and hydrogen isotopic compositions for the C_(27)n-alkane. The δ~(13)C of the C_(27) (- 28.2 to - 33.0‰) was more representative of C _3 than C_4 vegetation, while the δD of the C _(27) (- 169.9 to - 223.1%‰) indicated growth latitudes more northerly than Hokkaido. The n-alkanes in the snow preserve information about the source vegetation type (photosynthetic group, growth site), confirming that if deposited with seasonal snows that firnify to form glacial ice, they have potential to record broad, regional vegetation changes over time.