Cosmogenic 3He production rates from Holocene lava flows in Iceland

We measured cosmogenic 3He production rates in olivine phenocrysts from four radiocarbon-dated postglacial basaltic lava flows in the Western Volcanic Zone of Iceland. These measurements provide important new calibrations of cosmogenic nuclide production rates near sea level at high latitudes. Calibration sites from Lambahraun (4040 ± 250 cal yr BP; n = 4), Leitahraun (5210 ± 110 cal yr BP; n = 5), Búrfellshraun (8060 ± 120 cal yr BP; n = 6), and Þingvallahraun (10,330 ± 80 cal yr BP; n = 4) yield a mean production rate of 132 ± 5 atoms 3He g− 1 yr− 1 (± 1σ; normalized to sea level at high latitudes with the standard atmosphere). Mean production rates from the four flows agree within uncertainty, indicating that these calibrations establish a reproducible local 3He production rate that will significantly increase the accuracy of exposure dating in Iceland. The 3He production rate in Iceland is ∼ 17% higher than the mean of normalized Holocene values previously determined in the western USA. The high production rates in Iceland are attributed to the influence of persistent low atmospheric pressure over Iceland (the Icelandic Low) through the Holocene, which yielded higher cosmic ray fluxes. The Icelandic calibrations thus support previous suggestions that cosmogenic isotope production rates should be adjusted for regional variations in long-term atmospheric pressure. By extending the latitudinal extent of previous calibration studies, these results are also useful for evaluating scaling models.