Measurement of the 36Cl deposition flux in central Japan: natural background levels and seasonal variability

Abstract

Essential parameters for the applications of 36 Cl as a tracer in groundwater studies include the initial 36 Cl/Cl ratio, at the time of recharge, and/or the natural background deposition flux of 36 Cl in the recharge area. To facilitate the hydrological use of 36 Cl in central Japan, this study aims to obtain a precise estimate of the long-term average local 36 Cl flux and to characterize its seasonal variability. 36 Cl in precipitation was continuously monitored in Tsukuba, central Japan 2 over a period of >5 years. The 36 Cl flux showed a clear seasonal variation with an annual peak during the spring, which is attributed to the seasonal variability of tropopause height. The long-term average 36 Cl flux (32 ± 2 atoms m −2 s −1), estimated from the measured data, is consistent with the prediction from the 36 Cl latitudinal fallout model scaled using the global mean production rate of 20 atoms m −2 s −1. The initial 36 Cl/Cl ratio was estimated to be (41 ± 6) × 10 −15 , which is similar to that of pre-bomb groundwater in the Tsukuba Upland. An observation period covering an 11-year solar cycle would yield more accurate estimates of the values, given the increased 36 Cl flux during the solar minimum.

Temporal variation of iodine-129 in rainwater at Tsukuba before and after the Fukushima Daiichi Nuclear Power Plant accident

“…Concentration of 127 I was in the range 0.701-3.43 mg L -1 , with an average of 1.78 ± 0.62 mg L -1 (Fig. 2b), consistent with earlier studies (Aldahan et al, 2009;Xu et al, 2013Xu et al, , 2016, and with a narrower range than reported for Cl - (Tosaki et al, 2012). Periodic changes in 127 I concentrations were insufficient to affect the 129 I/ 127 I ratio, indicating that variations in the ratio were due mainly to 129 I variations (Xu et al, 2013;Fig.…”

“…Total monthly deposition of rainwater has been measured since March 2009 on the roof of the Tandem Accelerator Complex building (36.11∞N, 140.10∞E), University of Tsukuba, located ~170 km southwest of the FDNPP, Japan. A funnel-and-bottle collection system was used, with a funnel diameter of 21 cm and a 5 L high-density polyethylene bottle, as described by Tosaki et al (2012). To avoid loss of iodine during storage, rainwater samples were filtered first through glass-fiber filters (Whatman GF/B), then stored with lids in a dark environment until preparation of chemical separation.…”

Modern Meteoric 36Cl Deposition in the Atacama Desert, Chile

“…Measurements of low‐level 36 Cl concentrations by the accelerator mass spectrometry (AMS) were first adopted for 36 Cl analysis of meteorites, ice cores, or precipitations/water samples to determine ages of meteorites/ice or detect “ 36 Cl bomb pulses” generated by thermonuclear tests in the 1950s (Elmore et al, 1982; Finkel et al, 1980; Nishiizumi et al, 1993; Phillips et al, 1990; Suter et al, 1987; Synal et al, 1990). Later, 36 Cl was measured in precipitation of Israel (Herut et al, 1992), the United States (Hainsworth et al, 1994; Knies et al, 1994), Australia (Keywood et al, 1998), Japan (Tosaki et al, 2012), across the Europe (Johnston & McDermott, 2008; Pupier et al, 2016; Santos et al, 2004), and at other places around the planet (Scheffel et al, 1999). Moysey et al (2003) explored the nationwide 36 Cl/Cl ratios of meteoric groundwater to show the spatial patterns of meteoric 36 Cl/Cl ratio across the United States.…”