Contour dos suggests reconstruction of one's ratios off CFC-11/CFC-several and CFC-113/CFC-a dozen inside the remote Us heavens. The fresh new ratio from CFC-11/CFC-several in air increased drastically throughout the late 1940s in order to from the 1977, and this out-of CFC-113/CFC-12 got a moderate increase during the eighties.

Matchmaking with other Atmospheric Gases, Sulfurhexafluoride

The slowing and turnover of CFC atmospheric mixing ratios in the 1990s has resulted in ambiguity in CFC-based apparent age. Sulphur hexafluoride (SF_six) has been developed as an alternative to CFCs for gas-solubility dating of water (Busenberg and Plummer, 1997). Significant production of SF₆ began in the 1960s for use in high voltage electrical switches. SF₆ is extremely stable, with an estimated atmospheric lifetime of 800 (Morris et al., 1995) to 3200 years (Ravishankara et al., 1993). SF₆ can be analysed by GC-ECD techniques to a precision of 1-3% (Wanninkhof et al., 1991; Law et al., 1994), so, even though atmospheric mixing ratios are small (currently about 10 pptv), dating is possible from about 1970 to the present.

Once we are able to use Henry's laws so you can interpret visible CFC decades to possess personal CFC ingredients, there are also variations in the ratios out-of atmospheric CFC density that can be used getting dating

The earliest reported measurement of the atmospheric concentration of SF₆ was 0.03 pptv in 1970 (Lovelock, 1971). SF₆ is accumulating rapidly in the atmosphere with a current growth rate of more than 7% per year. The historical atmospheric mixing ratio of SF₆ has been reconstructed from production records and atmospheric measurements (Ko et al., 1993; Elkins et al., 1996; Maiss et al., 1996; Geller et al., 1997; Levin and Hesshaimer, 1996), and retrieved from concentrations measured in seawater (Law et al., 1994) and in previously-dated groundwater (Busenberg and Plummer, unpub. https://datingmentor.org/escort/abilene/ data). Figure 1 shows a preliminary reconstruction of northern hemisphere SF₆ mixing ratios. As atmospheric CFC concentrations fall, an even more sensitive dating tool will be the ratio of SF₆ to, for example, CFC-12 (Figure 2). However, because of the low solubility of SF₆ (Mroczek, 1997), apparent ages can be very sensitive to excess air, so this needs to be accurately determined.

Busenberg and Plummer (1997) used SF₆ successfully to date shallow groundwater on the Delmarva Peninsula, Maryland, and water from springs in the Blue Ridge Mountains of Virginia. Although SF₆ is mostly of anthropogenic origin, concentrations between one and two orders of magnitude higher than that possible for modern air-water equilibrium were measured in groundwater from volcanic rift zones in New Mexico and Idaho (Busenberg and Plummer, 1997). There is likely a natural, igneous source of SF₆ that will complicate dating in some environments. SF₆ has also been used as an artificial tracer (Wilson and Mackay, 1996; Schlatter et al., 1997) that is injected into groundwater or surface water. Clark et al. (1995b) found that wastewater discharged to the Hudson River at New York City was contaminated with SF₆. Busenberg and Plummer (1997) found minor contamination of SF₆ in Rio Grande water near an outfall from a sewage treatment plant. All other surface waters had SF₆ concentrations near equilibrium with air.

Of a lot procedure exist throughout recharge plus the brand new groundwater ecosystem one can impact CFC levels past those lay because of the heavens-liquids balance, and consequently apply at interpretation out-of obvious years. Dining table dos directories one techniques, their impact on apparent CFC age, and cousin pros.

Profile step 3 Concentrations off CFC-eleven, CFC-a dozen, and you may CFC-113 in the water recharged ranging from 1940 and you will 1998 from the temperatures regarding 5 so you can 25 °C on sea level.

magnitude old problems you to result from concerns inside the recharge temperature. Like, in case your CFC-eleven quantity was 600 pg kilogram -1 in a specific water decide to try one billed at fifteen°C, however, charge heat was mistakenly thought as 5°C, a noticeable decades that is some several many years too old create become tasked, predicated on CFC-eleven. An uncertainty for the cost heat away from ± 2°C leads to age uncertainties out-of three-years or faster to possess h2o charged just before throughout the 1990 (Busenberg et al., 1993). Over-quote out of charge temperature results in apparent decades too young, and less than-quote provides decades which can be biased old. Uncertainty from inside the charge heat from ± 2°C causes uncertainty inside the visible CFC chronilogical age of 1 year or less to own drinking water recharged ahead of the middle-seventies. Yet not, just like the air fusion rates peaked regarding the mid- and you will late-90s, CFC noticeable ages became most responsive to concerns for the demand temperatures.