25th International Meeting on Organic Geochemistry IMOG 2011

O-45
Advancing trace-level analysis of marker compounds in ice
cores to generate records of South American fire activity
Matthew Makou 1 , Lonnie Thompson 1 , Timothy Eglinton 2 , Daniel Montluçon 2
1 Byrd Polar Research Center, Ohio State University, Columbus, OH, United States of America, 2 ETH Zurich,
Zurich, Switzerland (corresponding author:makou.1@osu.edu)
Stir bar sorptive extraction, which provides a
means of quickly and quantitatively recovering semivolatile
lipids from aqueous samples, was applied in
conjunction with coupled thermal desorption and gas
chromatography/time-of-flight mass spectrometry to
measure trace-level marker compounds preserved in
an ice core. We generated multi-molecular records
from the Quelccaya Ice Cap in Peru, which is situated
along the eastern flank of the Andes and thus is well
positioned for deposition of higher plant-derived
compounds originating from both the Amazon Basin
and higher elevations. Our analytical approach proved
effective in recovering several different types of
compounds from small volumes of melted ice (10-30
ml), resulting in century-scale fire and vegetation
records at better-than-annual resolution. For example,
we successfully recovered and analyzed diterpenoids,
fatty acids, and alkyl amides with mean
concentrations as low as 10 pg/ml. Diterpenoids such
as dehydroabietin and a variant of phenanthrenone
represent the biomarkers of greatest utility due to their
inferred specificity for conifer burning. Abrupt changes
in compound abundance are superimposed on
decadal variability (see figure) and are not strictly
associated with high-altitude temperature and aridity
changes inferred from inorganic ice core climate
proxies. This suggests that our approach provides
new lines of climate evidence indicative of tropical
carbon cycling. Inputs of organic carbon to the Andes
likely reflect a combination of sources from
anthropogenic burning and natural fires related to
aridity, and include both high and low elevation
vegetation. We are presently applying these
techniques to older ice to develop records of tropical
burning related to late Holocene climate variability
and Amazon Basin societal change.
Fig. 1. Records of selected marker compounds
preserved in the Quelccaya ice core. Elevated relative
concentrations suggest enhanced deposition of firederived
aerosols. Disparities between records likely
arise from the vegetation source specificity of each
compound.
105