Decadal Delta O-17 record of tropospheric CO2: Verification of a stratospheric component in the troposphere

摘要

abstract_textpFor quantification and prediction of global warming due to anthropogenic carbon dioxide (CO2) emissions, high-resolution determination of carbon cycle reservoir size and rates of exchange is vital. Isotope ratio measurements of C-13 and O-18 in CO2 have proven their utility in resolving the carbon cycle. Here we report a long-term record of triple oxygen isotopic composition of tropospheric CO2. A presence of a steady state stratospheric component (Delta O-17=ln(delta O-17 + 1) - 0.522 ln(delta O-18 + 1) = 0.08 +/- 0.04 parts per thousand) is observed in tropospheric CO2 after modeling via a long-term spline fit of the record, adding an additional technique for quantification of CO2 fluxes. The delta O-18 of CO2 (measured as O-2 for oxygen triple isotopic composition) from the present study is compared to the measurements of the Scripps Institute of Oceanography CO2 network (measured as CO2 for delta C-13 and delta O-18) and found to be comparable. We note that the triple oxygen isotopic signal (Delta O-17) significantly decreased to 0.02 +/- 0.02 from the steady state value of 0.08 +/- 0.04 during the 1997-1999 time period. The possible causes for this depletion are evaluated and discussed. An enhanced role of global primary productivity, facilitating water-CO2 isotope exchange is possible, and future measurements and modeling strategies may develop this further./p/abstract_text