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      Sixty years of radiocarbon dioxide measurements at Wellington, New Zealand: 1954–2014

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          Abstract

          <p><strong>Abstract.</strong> We present 60 years of Δ<sup>14</sup>CO<sub>2</sub> measurements from Wellington, New Zealand (41°<span class="thinspace"></span>S, 175°<span class="thinspace"></span>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<span class="thinspace"></span>‰ 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.</p>

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          Recent trends and drivers of regional sources and sinks of carbon dioxide

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            AGE OF SOIL ORGANIC MATTER AND SOIL RESPIRATION: RADIOCARBON CONSTRAINTS ON BELOWGROUND C DYNAMICS

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              The reinvigoration of the Southern Ocean carbon sink.

              Several studies have suggested that the carbon sink in the Southern Ocean-the ocean's strongest region for the uptake of anthropogenic CO2 -has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized.
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                Author and article information

                Journal
                Atmospheric Chemistry and Physics
                Atmos. Chem. Phys.
                Copernicus GmbH
                1680-7324
                2017
                December 12 2017
                : 17
                : 23
                : 14771-14784
                Article
                10.5194/acp-17-14771-2017
                236de026-9b68-4b62-82ad-3f870374ba14
                © 2017

                https://creativecommons.org/licenses/by/3.0/

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