Sixty years of radiocarbon dioxide measurements at Wellington, New Zealand: 1954–2014
We present 60 years of Δ<sup>14</sup>CO<sub>2</sub> measurements from Wellington, New Zealand (41° S, 175° E). The record has been extended and fully revised. New measurements have been used to evaluate the existing record and to replace original measurements where warrant...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/17/14771/2017/acp-17-14771-2017.pdf |
| Summary: | We present 60 years of Δ<sup>14</sup>CO<sub>2</sub> measurements from Wellington,
New Zealand (41° S, 175° E). The record has been extended
and fully revised. New measurements have been used to evaluate the existing
record and to replace original measurements where warranted. This is the
earliest direct atmospheric Δ<sup>14</sup>CO<sub>2</sub> record and records the rise
of the <sup>14</sup>C <q>bomb spike</q> and the subsequent decline in
Δ<sup>14</sup>CO<sub>2</sub> as bomb <sup>14</sup>C moved throughout the carbon cycle and
increasing fossil fuel CO<sub>2</sub> emissions further decreased atmospheric
Δ<sup>14</sup>CO<sub>2</sub>. The initially large seasonal cycle in the 1960s
reduces in amplitude and eventually reverses in phase, resulting in a small
seasonal cycle of about 2 ‰ in the 2000s. The seasonal
cycle at Wellington is dominated by the seasonality of cross-tropopause
transport and differs slightly from that at Cape Grim, Australia, which is
influenced by anthropogenic sources in winter. Δ<sup>14</sup>CO<sub>2</sub> at Cape
Grim and Wellington show very similar trends, with significant differences
only during periods of known measurement uncertainty. In contrast, similar
clean-air sites in the Northern Hemisphere show a higher and earlier bomb
<sup>14</sup>C peak, consistent with a 1.4-year interhemispheric exchange time.
From the 1970s until the early 2000s, the Northern and Southern Hemisphere
Δ<sup>14</sup>CO<sub>2</sub> were quite similar, apparently due to the balance of
<sup>14</sup>C-free fossil fuel CO<sub>2</sub> emissions in the north and
<sup>14</sup>C-depleted ocean upwelling in the south. The Southern Hemisphere sites
have shown a consistent and marked elevation above the Northern Hemisphere sites
since the early 2000s, which is most likely due to reduced upwelling of
<sup>14</sup>C-depleted and carbon-rich deep waters in the Southern Ocean, although
an underestimate of fossil fuel CO<sub>2</sub> emissions or changes in biospheric
exchange are also possible explanations. This developing
Δ<sup>14</sup>CO<sub>2</sub> interhemispheric gradient is consistent with recent
studies that indicate a reinvigorated Southern Ocean carbon sink since the
mid-2000s and suggests that the upwelling of deep waters plays an important role
in this change. |
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| ISSN: | 1680-7316 1680-7324 |