Global 3‐D Simulations of the Triple Oxygen Isotope Signature Δ17O in Atmospheric CO2. Issue 15 (4th August 2019) - Koren, Gerbrand
Abstract: The triple oxygen isotope signature Δ 17 O in atmospheric CO2, also known as its " 17 O excess, " has been proposed as a tracer for gross primary production (the gross uptake of CO2 by vegetation through photosynthesis). We present the first global 3‐D model simulations for Δ 17 O in atmospheric CO2 together with a detailed model description and sensitivity analyses. In our 3‐D model framework we include the stratospheric source of Δ 17 O in CO2 and the surface sinks from vegetation, soils, ocean, biomass burning, and fossil fuel combustion. The effect of oxidation of atmospheric CO on Δ 17 O in CO2 is also included in our model. We estimate that the global mean Δ 17 O (defined as Δ 17 O = ln ( δ 17 O + 1 ) − λ RL · ln ( δ 18 O + 1 ) with λ RL = 0.5229) of CO2 in the lowest 500 m of the atmosphere is 39.6 per meg, which is ∼20 per meg lower than estimates from existing box models. We compare our model results with a measured stratospheric Δ 17 O in CO2 profile from Sodankylä (Finland), which shows good agreement. In addition, we compare our model results with tropospheric measurements of Δ 17 O in CO2 from Göttingen (Germany) and Taipei (Taiwan), which shows some agreement but we also find substantial discrepancies that are subsequently discussed. Finally, we show model results for Zotino (Russia), Mauna Loa (United States), Manaus (Brazil), and South Pole, which we propose as possible locations for future measurements of Δ 17 O in tropospheric CO2 that can help to further increase our understanding of the global budget of Δ 17 O in atmospheric CO2 . Key Points: This work presents a first view on possible spatial and temporal gradients of Δ 17 O in CO2 across the globe Tropical, boreal, and Southern Hemisphere observations of Δ 17 O in CO2 could be of great interest We implemented spatially and temporally explicit sources and sinks of Δ 17 O in CO2 in a 3‐D model framework