About

AOS 270 Seminars

WHEN:

Wednesday, January 18th

WHO:

 Joseph Biello, University of California, Davis

TIME:

3:30pm

WHERE:  

Math Science 7124
TOPIC: "A novel method for estimating global terrestrial photosynthesis: Using the ENSO signal in oxygen isotopes of atmospheric CO2"

Abstract:

Three decades of oxygen isotope ratios in atmospheric CO2 measured in the SIO global flask network have revealed a strong correlation with ENSO. Station d18O-CO2 time series are positively correlated with predictions of the d18O of precipitation in Southeast Asia and Northern South America from the IsoGSM model, and are negatively correlated with relative humidity in these same regions. We suggest that the redistribution of moisture and rainfall in the tropics during El Niño increases the 18O/16O of precipitation and plant water, and this signal is then passed onto atmospheric CO2 by vegetation-atmosphere gas exchange. Further exchange with the ocean and the biosphere, including the extra-tropics, provides damping of the d18O-CO2 to stable background levels. We use a simple two box-model to estimate that the global turnover time of O-isotopes in atmospheric CO­2 from fitting the decay of the El Niño anomalies is 1.1 – 1.7 yrs. We show how the decay time of the El Niño anomalies in this dataset can be useful in constraining global gross primary production. Our analysis shows a rapid recovery from El Niño, implying a faster cycling time of CO2 with respect to the terrestrial biosphere and oceans than previously estimated. Our analysis suggests that current estimates of global terrestrial gross primary production (GPP) of 120 Pg C yr-1 may be too low, and that a best guess of 150-175 better reflects the observed rapid cycling of CO2. Although still tentative, such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models.