Depositional and summer snow melting features in 2007-2011 on the upstream side of Potanin Glacier, Mongolian Altai, reconstructed by pollen and oxygen isotope analysis

摘要

This study analyzed pollen in snow pits dug in late summer (2008-2011) on the upstream side of Potanin Glacier, a summer accumulation-type glacier in the Mongolian Altai, to reconstruct the recent snow depositional environment, particularly melting conditions. Annual snow pit observations were performed at sites 0 and 4 (3752 and 3890 ma.s.l., respectively). Seasonal layers in the pits were identified according to the presence of pollen from three taxa (Betulaceae, Pinus, and Artemisia), which have different pollen seasons typically between May and early September. The pollen-dating method was successful in snow pits where conventional methods such as ice layer dating and use of delta O-18 records were unreliable due to significant melting. Depths of pollen concentration peaks for the three taxa differed annually at both sites. In some years, concentration peaks of the three pollen taxa were found at different depths, but in other years, peaks associated with each taxon were found at the same depth. This difference was explained by summer temperature. Snow melting during the relatively warm summers of 2007 and 2008 caused pollen grains to concentrate on the glacier surface, producing peaks at the same depth. In contrast, snow melting during the relatively cool summer of 2009 did not substantially alter pollen grain location, and each peak thus retained its original depth. The median temperatures in 2010 and 2011 corresponded to pollen concentrating on the glacier surface at site 0 but retaining their original position at site 4.