Division of Earth Sciences, National Institute of Polar Research, Itabashi, Tokyo, 173-8515 Japan ; Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska Fairbanks, PO Box 755860, Fairbanks, AK 99775-5860 United States
Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska Fairbanks, PO Box 755860, Fairbanks, AK 99775-5860 United States