ABSTRACT: The Mount Logan (Yukon) ice cores: Preliminary results.

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Abstract

Three ice cores were taken at different elevations on or near My Logan in the years 2001 and 2002. The summit core (PRCol) comes from the summit plateau ( 5340 masl, length 187 m to bedrock, mean temperature -29 C ) and was done by the Geological Survey of Canada. The NIPR group cored 210m on the flanks of the mountain at King Col (4200 masl mean temperature -16C) and the UNH group cored 20 km from the mountain at Eclipse "Dome" (3015 masl,length 345 m mean temperature -5C) . The three cores were done cooperatively by GSC, NIPR and UNH and cover nominally 30 ka, 1 ka and 2ka respectively . Located very close to the Gulf of Alaska these core records are thought to reflect the climate history of the Pacific Ocean and having three widely spaced elevations, the sites "see" different distances to different sources. The lowest site (Eclipse) has excellent seasonals but a very muted $\delta^{18}$O history with no obvious little ice age, whereas the most recent 1ka of the PRCol summit sites contains two very large and sudden $\delta^{18}$O and d (deuterium excess) shifts at 1850 AD and ~ 800 AD. The $\delta^{18}$O shifts which happen from one year to the next are about 4 o/oo . The summit site (PRCol) $\delta^{18}$O response is "backwards", ie the Little Ice Age $\delta^{18}$O values are 4 o/oo more positive than recent ones. The PRCol $\delta^{18}$O and d suggest that the source water can either be ‰local¡ (Gulf of Alaska) or very distant (tropics) . The Eclipse site seems only to get the local water . A massive dust storm originating in central Asia (Gobi) in April 2001 dumped a visible layer all over the St Elias Mountains and this layer was sampled, to provide a calibration "Asian dust event". The satellite and isotoic signatures both agreed that Gobi was the source. The PRCol record covers the Holocene and well back into the ice age. The transition is defined by a sudden ECM shift on the flanks of a more gradual O18 shift.

Bibliography of Canadian Geomorphology