A new Himalayan ice core CHsub4/sub record: possible hints at the preindustrial latitudinal gradient

摘要

Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on thenortheast saddle of Mt. Qomolangma (Everest) (28°01' N,86°58' E, 6518 m above sea level) give access to a tentativerecord of past Himalayan atmospheric mixing ratio of CH₄ spanning thepast 1200 yr. The major part of the record is affected by artifacts probablydue to in situ production. After selecting what may represent the trueatmospheric mixing ratio, an average of 749 ± 25 ppbv of CH₄ isestimated for the late preindustrial Holocene, which is ~ 36 ± 17(~ 73 ± 18) ppbv higher than the atmospheric levels recorded inthe Greenland (Antarctic) ice cores. A comparison of these new data withmodel simulations of the CH₄ latitudinal gradient suggests either thatthe models do not get a correct balance between high and low latitudeCH₄ sources, or that the filtered CH₄ profile from the ER coresremains biased by small artifacts.