Observations of CFCs and SF<sub>6</sub> as Ocean Tracers

Fine, Rana A.

doi:10.1146/annurev.marine.010908.163933

Cited by 85 publications

(77 citation statements)

References 138 publications

(168 reference statements)

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“…Figure 1 shows pCFC-12 changes for a section in the South Pacific (P16, see Fig. 2A), but similar changes in pCFC-12 are observed for other South Pacific sections and for sections in the southern Indian and Atlantic Oceans (16).…”

supporting

confidence: 61%

“…S1). Because of this time dependence, CFC measurements can provide constraints on the rates and pathways of ocean transport (15,16).…”

mentioning

confidence: 99%

“…1A). [We express the measurements as the partial pressure of CFC-12 ( pCFC-12), defined as the seawater concentration divided by the solubility (16). This enables direct comparison with the atmospheric history of CFC-12.]…”

mentioning

confidence: 99%

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Recent Changes in the Ventilation of the Southern Oceans

Waugh

Primeau

DeVries

et al. 2013

Science

153

166

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Surface westerly winds in the Southern Hemisphere have intensified over the past few decades, primarily in response to the formation of the Antarctic ozone hole, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid-to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans.T he transport of surface waters into the interior ("ventilation") of the southern oceans plays an important role in global climate and the cycling of carbon, oxygen, and nutrients in the oceans (1-3). Over the past few decades, the southern oceans have warmed at roughly twice the rate of the global mean ocean (1), and around 40% of the anthropogenic carbon in the oceans entered south of 40°S (4). Southern ocean ventilation is driven primarily by the westerly winds (5), which have strengthened and shifted poleward over recent decades, primarily as a consequence of Antarctic stratospheric ozone depletion (6). Modeling studies suggest that this has caused changes in the ocean's overturning circulation (7-9), and carbon uptake (10, 11). However, the sensitivity of the southern ocean circulation and ventilation to decadal changes in wind stresses is under debate (12)(13)(14).Information on ventilation rates can be obtained from measurements of chlorofluorocarbons (CFCs). These compounds are conserved within the oceans, and their atmospheric concentrations have increased rapidly from when they were first produced in the 1930s until the mid1990s ( fig. S1). Because of this time dependence, CFC measurements can provide constraints on the rates and pathways of ocean transport (15, 16).We used CFC-12 measurements made along several sections in the southern oceans in the early 1990s as part of the World Ocean Circulation Experiment (WOCE) and resampled in mid-to late 2000s as part of the Climate Variability and Predictability (CLIVAR) and CO 2 repeat hydrography program (supplementary materials) to examine changes in the ventilation of the southern oceans over the past two decades.The measurements during WOCE show largest pCFC-12 at the surface, with values decreasing with depth along isopycnals (e.g., Fig. 1A). [We express the measurements as the partial pressure of CFC-12 ( pCFC-12), defined as the seawater concentration divided by the solubility (16). This enables direct comparison with the atmospheric history of CFC-12.] The repeat occupations 14 to 16 years later show large increases in pCFC-12 in the subtropical thermocline (~25°t o 45°S, 200 to 1000 m), which correspond to the waters formed by the transport of surface waters along surfaces of constant density (e.g., Fig. 1B). ...

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supporting

confidence: 61%

“…S1). Because of this time dependence, CFC measurements can provide constraints on the rates and pathways of ocean transport (15,16).…”

mentioning

confidence: 99%

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Recent Changes in the Ventilation of the Southern Oceans

Waugh

Primeau

DeVries

et al. 2013

Science

153

166

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“…In order to obtain the N 2 O equilibrium concentrations at every depth, the age of the water mass and then the atmospheric N 2 O concentration during the year of the water mass formation was estimated by using CFC-11 and CFC-12 concentrations from the P19 and P21 transects of WOCE, according to Fine (2011). The water samples collected in this study were assumed to be the same age as the calculated water mass age from WOCE.…”

Section: Discussionmentioning

confidence: 99%

Following the N<sub>2</sub>O consumption in the oxygen minimum zone of the eastern South Pacific

Cornejo¹

2012

Biogeosciences

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“…Fine, 2011). This time information can then be used to determine current states of ventilation and in the case of transient tracer time series also changes or trends in ventilation.…”

Section: Introductionmentioning

confidence: 99%