Observations of radiocarbon in CO<sub>2</sub> at La Jolla, California, USA 1992-2007: Analysis of the long-term trend

Graven, HD, Guilderson TP, Keeling RF.  2012.  Observations of radiocarbon in CO2 at La Jolla, California, USA 1992-2007: Analysis of the long-term trend. Journal of Geophysical Research-Atmospheres. 117

Date Published:



airborne measurements, atmospheric co2, biosphere, carbon-dioxide, diffusion-model, EARTHS ATMOSPHERE, fossil-fuel co2, gas transfer velocity, quasi-biennial oscillation, terrestrial, tropospheric (co2)-c-14


High precision measurements of Delta C-14 were performed on CO2 sampled at La Jolla, California, USA over 1992-2007. A decreasing trend in Delta C-14 was observed, which averaged -5.5 parts per thousand yr(-1) yet showed significant interannual variability. Contributions to the trend in global tropospheric Delta C-14 by exchanges with the ocean, terrestrial biosphere and stratosphere, by natural and anthropogenic C-14 production and by C-14-free fossil fuel CO2 emissions were estimated using simple models. Dilution by fossil fuel emissions made the strongest contribution to the Delta C-14 trend while oceanic C-14 uptake showed the most significant change between 1992 and 2007, weakening by 70%. Relatively steady positive influences from the stratosphere, terrestrial biosphere and C-14 production moderated the decreasing trend. The most prominent excursion from the average trend occurred when Delta C-14 decreased rapidly in 2000. The rapid decline in Delta C-14 was concurrent with a rapid decline in atmospheric O-2, suggesting a possible cause may be the anomalous ventilation of deep C-14-poor water in the North Pacific Ocean. We additionally find the presence of a 28-month period of oscillation in the Delta C-14 record at La Jolla.






Scripps Publication ID: