1. Glasgow Molecular Organic Geochemistry Laboratory (G-MOL), School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, U.K.
2. Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo 060-0819, Japan
3. Field Science Center for Northern Biosphere, Hokkaido University, Tokuda 250, Nayoro 096-0071, Japan
4. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.