The SPICE Project: The SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations

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Our proposed SPICE project will measure, for the first time and at one calibration site, accurate cross-calibrated production rates of each of the most commonly used cosmogenic nuclides (He-3, Be-10, C-14, Ne-21, Al-26, and Cl-36) integrated over the past 72 ka. The formally named SP Flow is a quartz-, olivine- and pyroxene-bearing basalt with an Ar-40/Ar-39age of 72. We are not aware of any other location worldwide where these minerals coexist in an uneroded, well-dated lava flow. The flow is preserved in the arid desert climate of northern Arizona, USA, and its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion. Preliminary He-3 and Ne-21 data in pyroxene from the SP flow are consistent with a 72 ka eruption age and yield production rates (with 7 percent uncertainty) in excellent agreement with other rates reported in recent literature. The uncertainties are low due to the high-precision Ar-40/Ar-39 age.The SPICE Project will increase the accuracy of six cosmogenic nuclide production rates, and thus, will impact every published study, as well as future studies that use cosmogenic nuclides to quantify earth-surface processes. Cosmogenic nuclides have revolutionized Quaternary geology by allowing us to quantify large-scale, long-term (Myr time-scale) landscape evolution, as well as the generation and movement of sediment through drainage systems. Scientists also use cosmogenic nuclides to date glacial moraines, debris flows, landslides, lava flows, and fluvial deposits all over the world. The Quaternary science community has used this technique to study global climate change (e.g., in the Northern and Southern Hemispheres) and to assess links between climate regimes and landscape evolution. Nearly all Quaternary paleoclimate synthesis studies make use of glacial geology/chronology studies, and most of them rely in large part on cosmogenic nuclide data. Exposure-age data have contributed significantly to the climate-change debate, and exposure ages are often compared to other Quaternary age-dating methods in global-climate studies. The majority of glacial-climate scientists strive to correlate exposure-dated moraines in their own research projects with each other or with independently dated (i.e., radiocarbon, U-series, OSL, etc.) climate events at millennial time scales; however, these scientists make inferences about these correlations that are simply not justifiable when uncertainties in the absolute values of nuclide production rates and in production-rate scaling are currently estimated at 10 to 15 percent. Though impressive progress has been made over the past 20 years in determining cosmogenic nuclide production rates and improving scaling schemes, research is still needed to minimize these uncertainties to less than 5 percent. The SPICE project puts us one step closer to obtaining this lower uncertainty.