Cosmogenic ³⁶Cl in karst waters from Bunker Cave North Western Germany - A tool to derive local evapotranspiration?

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• 作者：C. Mü ; nsterer^a ; ^b ; ^{muensterer@phys.ethz.ch} ; J. Fohlmeister^b ; M. Christl^a ; A. Schrö ; der-Ritzrau^b ; V. Alfimov^a ; S. Ivy-Ochs^a ; A. Wackerbarth^b ; A. Mangini^b
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2012
• 出版时间：1 June, 2012
• 年：2012
• 卷：86
• 期：Complete
• 页码：138-149
• 全文大小：679 K

文摘

Monthly rain and drip waters were collected over a period of 10 months at Bunker Cave, Germany. The concentration of ³⁶Cl and the ³⁶Cl/Cl-ratios were determined by accelerator mass spectrometry (AMS), while stable ^(35+37)Cl concentrations were measured with both, ion chromatography (IC) and AMS. The measured ³⁶Cl-fluxes of (0.97 ¡À 0.57) ¡Á 10⁴ atoms cm^? month^? (0.97 atoms m^? month^?) in precipitation were on average twice as high as the global mean atmospheric production rate. This observation is consistent with the local fallout pattern, which is characterized by a maximum at mid-latitudes. The stable chloride concentration in drip waters (ranging from 13.2 to 20.9 mg/l) and the ³⁶Cl-concentrations (ranging from 16.9 ¡Á 10⁶ to 35.3 ¡Á 10⁶ atoms/l) are a factor of 7 and 10 above the values expected from empirical evapotranspiration formulas and the rain water concentrations, respectively. Most likely the additional stable Cl is due to human impact from a nearby urban conglomeration. The large ³⁶Cl-enrichment is attributed to the local evapotranspiration effect, which appears to be higher than the calculated values and to additional bomb-derived ³⁶Cl from nuclear weapons tests in the 1950s and 60s stored in the soil above the cave. In the densely vegetated soil above Bunker Cave, ³⁶Cl seems not to behave as a completely conservative tracer. The bomb derived ³⁶Cl might be retained in the soil due to uptake by minerals and organic material and is still being released now. Based on our data, the residence time of ³⁶Cl in the soil is estimated to be about 75-85 years.