ABSTRACT: Controls on the stable water isotope composition of precipitation in the southwestern Yukon.

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

The goal of our work is to better understand controls on the stable water isotope (SWI) composition of precipitation in the southwestern Yukon, and in particular, to better-interpret the SWI signal from the Mount Logan ice core. One feature of interest in the Mt. Logan ice core record is a significant drop in d18O in the 1850’s towards more depleted values, which is thought to have resulted from a shift in North Pacific circulation towards a deeper Aleutian Low and moisture from more southerly sources. Because of their greater arrival times, these air masses would have undergone a greater isotopic depletion than moisture from closer, colder sources under a more zonal flow regime. Although physically plausible, it is possible that the d18O drop caused by this proposed shift might be offset by warmer source evaporation conditions and warmer air mass trajectories. To test the plausibility of the meridional hypothesis, we conducted numerical experiments with the NASA GISS ModelE isotopically-equipped general circulation model. We found that positive d18O anomalies in the SW Yukon were in fact associated with a deeper Aleutian Low and stronger meridional transport. It would appear as though the effect of a longer transit is offset by a warmer moisture transport pathway, in disagreement with the current moisture shift explanation. Our results are in agreement with recent tree-ring reconstructions of the North Pacific Index, which suggest an 1850’s shift towards a weaker Aleutian Low. We also found that the degree of control on the SW Yukon isotope signal is highly dependent on seasonality. During the summer months, the underlying circulation controls on d18O are largely absent,whereas during the winter months, the circulation features become much more enhanced. This suggests that much information can be gained by separating the winter from summer signals in the Mt. Logan ice core record.

Bibliography of Canadian Geomorphology