Long-term variability in Southern Hemisphere Δ14CO2 observed at Wellington, New Zealand

Abstract:

Atmospheric Δ¹⁴CO₂ measurements have been made at Wellington, New Zealand, since December 1954. This is the longest ¹⁴CO₂ record available from anywhere in the world, predating the ¹⁴C bomb spike by several years and documenting the movement of the bomb spike into the Southern Hemisphere and other parts of the global carbon cycle. In more recent times, the spatial and temporal changes in Δ¹⁴CO₂ are thought to be dominated by two main drivers: (i) the addition of ¹⁴C-free, fossil-fuel derived CO₂, which occurs mainly over Northern Hemisphere continents, and (ii) the net flux of ¹⁴C-depleted CO₂ into the atmosphere from the oceans, most strongly from the Southern Ocean. Thus Δ¹⁴CO₂ measurements can provide key information on both the source and fate of fossil fuel CO₂ emissions. In particular, Southern Hemisphere Δ¹⁴CO₂ records have the potential to elucidate the mechanisms that drive Southern Ocean carbon exchange, a key component of the global carbon cycle.

We will present an updated Wellington Δ¹⁴CO₂ record. It is primarily based on ~2 week integrated samples collected by CO₂ absorption into NaOH solution. The results have now been thoroughly reviewed, revised where necessary, and extended through to 2014. In addition, we use a series of new measurements on archived “NaOH” samples, archived whole air flask samples and tree rings to span gaps in the main record and to re-measure key periods, thereby producing a record with lower variability and higher precision. We use new modeling tools to examine the causes of the temporal variability in the Wellington ¹⁴CO₂ record.