Graduate Thesis Or Dissertation

 

The Impact of Hydrological and Climatic Variations on the Oxygen-18 Content of Atmospheric CO2 Public Deposited

https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/jw827b894
Abstract
  • The 18O composition of atmospheric CO2 is a potentially valuable tracer of global interactions between the hydrologic and carbon cycles. The observed 18O composition of atmospheric CO2 (hereafter δCa, where δ=(R/Rstandard-1) ~ 1000 and R is the molar ratio of heavy to light isotopes) does not show a clear long-term trend, though almost all monitoring stations observed an impressive decrease in δCa from 1992 to 1998. The cause(s) of this and other interannual δCa variations are still relatively unknown, and this work aims to better understand the driving mechanisms that caused the observed interannual δCa variations.

    Observed interannual δCa anomalies from Mauna Loa were correlated with anomalies of certain meteorological variables that could potentially affect δCa. Negative correlation existed between δCa and both relative humidity and precipitation amount within parts of the tropics. Positive correlations existed between δCa variations and the 18O content of precipitation for the same tropical regions. Rough estimates suggest that about 20% of the decrease in δCa during the 1990s was due to increases in relative humidity and about 80% of the decrease was due to decreases in the δ18O value of precipitation (and likely a consequence of increases in the amount of precipitation).

    A global model was constructed to simulate atmospheric CO2 and CO18O (and thus δCa). This model employed an isotopic land model (ISOLSM) and the Community Atmosphere Model (CAM). The model is used for a series of sensitivity experiments to better understand how both steady-state and interannual varying δCa respond to changes in relative humidity, δ18O values of precipitation and water vapor, temperature, and light levels. δCa responded the most to changes in the δ18O values of precipitation and water vapor, with moderate responses to relative humidity changes. Model results suggest that the decrease in δCa during the 1990s was due primarily to decreases in the 18O composition of precipitation with a smaller a contribution from increased relative humidity. Thus, observations of δCa may become a powerful integrative tool in the coming decades for monitoring large scale changes in the hydrological cycle should it accelerate under a warming climate, as predicted.

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  • 2010
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  • 2020-01-23
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