An improved method for delta 15N measurements in ice cores F. S. Mani1, P. Dennis1, W. T. Sturges1, R. Mulvaney2, and M. Leuenberger3 1School of Environmental Sciences, University of East Anglia, Norwich, UK 2British Antarctic Survey, Natural Environment Research Council, Cambridge, UK 3Climate and Environmental Physics, Physics Institute, University of Berne, Berne, Switzerland
Abstract. The use of isotopic ratios of nitrogen gas (δ15N) trapped in
ice cores as a paleothermometer to characterise abrupt climate changes is
becoming a widespread technique. The versatility of the technique could be
enhanced, for instance in quantifying small temperature changes during the
last glacial period in Antarctic ice cores, by using high precision methods.
In this paper, we outline a method for measuring δ15N to a
precision of 0.006\permil (1σ, n=9) from replicate ice core samples. The
high precision results from removing oxygen, carbon dioxide and water vapour
from the air extracted from ice cores. The advantage of the technique is
that it does not involve correction for isobaric interference due to
CO+ ions. We also highlight the importance of oxygen removal from the
sample, and how it influences δ15N measurements. The results
show that a small amount of oxygen in the sample can be detrimental to
achieving an optimum precision in δ15N measurements of
atmospheric nitrogen trapped ice core samples.
Citation: Mani, F. S., Dennis, P., Sturges, W. T., Mulvaney, R., and Leuenberger, M.: An improved method for delta 15N measurements in ice cores, Clim. Past Discuss., 4, 149-171, doi:10.5194/cpd-4-149-2008, 2008.