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

Abstract

<p><strong>Abstract.</strong> 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 atmospheric Δ<sup>14</sup>CO<sub>2</sub> record and records the rise of the <sup>14</sup>C "bomb spike", 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, Northern Hemisphere clean air sites 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 show 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. 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 upwelling of deep waters plays an important role in this change.</p>

Age structure of the Australian lungfish (Neoceratodus forsteri)

“…Freshwater mussel tissue samples contained F 14 C values ranging between 1.035–1.047 (Fig 6), while the mussel shell carbonate F 14 C values ranged between 1.034–1.044 (Fig 6). The corresponding atmospheric CO 2 F 14 C ranges from ~1.036–1.044 F 14 C between 2012–2015 are highlighted (Fig 6, [40]). These results demonstrate that a major food source for lungfish, freshwater mussels, does not contain older, more depleted sources of carbon that would potentially be metabolized by lungfish and affect the resultant age estimations from radiocarbon dating.…”

Mobilization of aged and biolabile soil carbon by tropical deforestation

“…Soil samples were combusted and graphitized following Steinhof et al (2017) 62 prior to analysis on a MICADAS 14 C AMS system (Ionplus AG, Dietikon, Switzerland). Leaf litter samples were assigned a modern radiocarbon value (+25‰) based on the 2016-2017 atmospheric CO 2 radiocarbon content 63 .…”

Changes to Carbon Isotopes in Atmospheric CO2 Over the Industrial Era and Into the Future

“…The changes in atmospheric δ 13 CO 2 and Δ 14 CO 2 over the Industrial Period have been quantified using a combination of direct sampling of the atmosphere and records of atmospheric composition from tree rings, ice cores, and firn. Regular observations of δ 13 CO 2 and Δ 14 CO 2 have been made by direct measurements of air samples since the 1970s for δ 13 CO 2 (Allison & Francey, 2007; Keeling et al, 2005; Vaughn et al, 2010) and the 1950s for Δ 14 CO 2 (Levin et al, 2010; Turnbull et al, 2016). Records of δ 13 CO 2 and Δ 14 CO 2 prior to direct measurements have been constructed using measurements of air in ice cores and firn for δ 13 CO 2 (Rubino et al, 2013) and tree ring cellulose and other materials for Δ 14 CO 2 (Hogg et al, 2013; Reimer et al, 2013).…”