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Abstract

This thesis presents research into the global carbon cycle using measurements
of atmospheric composition made at the Commonwealth Scientific and Industrial
Research Organisation's (CSIRO) Global Atmospheric Sampling LABoratory
(GASLAB). The focus is on high precision measurement of atmospheric 021N2 and
its application to deduction of carbon fluxes due to surface exchange and
atmospheric transport processes. A key theme is the use of multiple species (gas
concentrations and isotopomer ratios) constraints to enhance both the interpretation
of atmospheric data and the diagnosis of experimental artefacts.
Behaviour of the linked carbon and oxygen cycles in the contemporary
atmosphere is examined on three timescales, in each case addressing important but
unresolved scientific issues:
• The long term trend in atmospheric 02/N2 constrains the partitioning of uptake
of anthropogenic CO2between the oceans and the land biosphere. The
partitioning is deduced here by determination of trends at.Cape Grim, Tasmania,
based on 5 years of biweekly flask sampling and by reconstruction of a 23-year
record using archived air. The results favour a small net global biospheric sink,
implying significant oceanic and terrestrial (after allowance for land clearing)
carbon uptake between 1978 and 2001.
• More than forty years of atmospheric CO2monitoring at Mauna Loa, Hawaii has
revealed strong correlation in interannual variability (IAV) of CO 2growth rate
with the El Nirio Southern Oscillation (ENSO). GASLAB multi-species
measurements during the 1990s showed correlation of ENSO and global IAV in most of the measured species. They include CO 2 . established tracers of terrestrial
carbon exchange (021N2 and 8' 3C) and other species (H2, CO and CH4) whose
atmospheric budgets are not as obviously linked to CO 2 . A multi-species
analysis implicates biomass burning as a major influence on IAV in all species.
• Seasonal cycling in composition of background Southern Hemisphere air is
investigated by ground-based flask sampling of the marine boundary layer at
Cape Grim and from aircraft-based vertical profiling of the troposphere to
altitudes of 6-8 km above Cape Grim. Seasonal variations in the vertical 0211•12
gradient are useful as a constraint of vertical mixing rates. Measurements of
CO2, 02/N2 and other relevant tracers are used to explore the relative
contributions of multiple processes (atmospheric transport, terrestrial and air-sea
exchange) to seasonal signals.
Measurement of 021N2 to the precision required for global carbon cycle,
studies is a major challenge. Extensive consideration is therefore given to the
technical aspects of this measurement program, especially in relation to the mass
spectrometric analytical technique and to gas handling procedures. Numerous causes
of significant 02/N2 artefacts were identified, in some cases shedding light on
artefacts previously observed, but not understood, for other species (e.g. CO2).

Item Type:	Thesis - PhD
Authors/Creators:	Langenfelds, RL
Keywords:	Carbon cycle (Biogeochemistry), Atmospheric carbon dioxide
Copyright Holders:	The Author
Copyright Information:	Copyright 2002 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references
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