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Nathaniel Lifton, Marek Zreda, Darin Desilets, John Clem. Background Objectives Present-Day Fluxes Instrumental Measurements Modeling Time-Integrated Fluxes In Situ 14 C in Saturated Surfaces. Cosmic-Ray Fluxes Present and Past. CRONUS-Earth. Background.
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Nathaniel Lifton, Marek Zreda, Darin Desilets, John Clem Background Objectives Present-Day Fluxes Instrumental Measurements Modeling Time-Integrated Fluxes In Situ 14C in Saturated Surfaces Cosmic-Ray FluxesPresent and Past CRONUS-Earth
Background • Production Rates Well-Established at Few Sites • Scaling Models Predict Production Rates Elsewhere • Current Scaling Models Based on Modern Cosmic-Ray Measurements • Lal, 1991; Stone, 2000; Dunai, 2000, 2001; Desilets & Zreda, 2003; Lifton et al., in prep • Neutron Monitors (NM) • Other Instruments/Techniques • Problems • Need to Tie CR Measurements to CN Production in Rocks • Limited Empirical Testing of Models Over Millenial Time Scales • Scarcity of Samples of Well-Established Age CRONUS-Earth
Objectives • Relate NM Measurements to CN Production Rates • Global NM Network Data, Published Surveys CRONUS-Earth
Global Neutron Monitor Network CRONUS-Earth
Global Neutron Monitor Network CRONUS-Earth
Objectives • Relate NM Measurements to CN Production Rates • Global NM Network Data, Published Surveys • Selected Low-Energy Neutron Detector Measurements • Using NM Data as a Basis for CN Scaling • Can a Single Scaling Model Apply to the Entire Neutron Energy Spectrum? • Detailed NM Response to Secondary Cosmic Rays? • NMs More Sensitive to High Energies • Are Rocks as Well? • Physically Relate NM Response and CN Production in Rock • Test Scaling Models over Millenial Time Scales • In Situ 14C in Saturated Surfaces CRONUS-Earth
Present-Day Fluxes • Measurements (Zreda, Desilets) • Modeling (Zreda, Desilets, Clem) CRONUS-Earth
Time-Integrated Scaling From In Situ 14C Production Rates • Short Half-Life • 5,730 yr • Secular Equilibrium by About 25 kyr • Insensitive to Moderate Erosion Rates • Many Geomorphic Settings Suitable for Production Rate Determinations CRONUS-Earth
In Situ Cosmogenic 14C(In Situ 14C) • Extract From Quartz • Opportunity for Thorough Empirical Testing of Scaling Models • Integrated Over Millenial Time Scales CRONUS-Earth
Existing Altitude Transects CRONUS-Earth
In Situ 14C Production Rate Scaling • Produced by Nucleons and Muons • 83% spallation, 15% slow muon, 2% fast muon(Heisinger et al, 2002) • Preliminary AntarcticData Suggest Low Muogenic Production CRONUS-Earth
Antarctic Altitude Transect CRONUS-Earth
In Situ 14C Production Rate Scaling • Produced by Nucleons and Muons • 83% spallation, 15% slow muon, 2% fast muon(Heisinger et al, 2002) • Preliminary AntarcticData Suggest Low Muogenic Production • Scale to SL, High Latitude • Time-integrated production rate • Account for geomagnetic and solar variability • Test atmospheric models • Test For Bias With Sample Altitude and Latitude CRONUS-Earth
Identifying Scaling Model Biases CRONUS-Earth
Uncertainties • Scatter in Preliminary Data CRONUS-Earth
Observed Scatter CRONUS-Earth
Uncertainties • Scatter in Preliminary Data • Low Values = Geologic Factors • Address with Many Analyses • High Values = Inadequate Pretreatment? • Identify and Minimize Lab Sources of Scatter • Different Workers • Different Sample Prep Techniques • Different Degrees of Etching? • Objective Indicator of Etching Amount • Ba, Al, Zr? CRONUS-Earth
Stepwise Dissolution CRONUS-Earth
Uncertainties • Scatter in Preliminary Data • Low Values = Geologic Factors • Address with Many Analyses • High Values = Inadequate Pretreatment? • Identify and Minimize Lab Sources of Scatter • Different Workers • Different Sample Prep Techniques • Different Degrees of Etching? • Objective Indicator of Etching Amount • Ba, Al, Zr? • Spallogenic/Muogenic Production Proportions • Antarctic Altitude Transect • 5-10 m Drill Cores from Geological Calibration CRONUS-Earth
Timeline and Deliverables • Year 1 • Identify Global Sample Set for Saturated 14C Analysis • Already Collected by Other Investigators • Evidence for 14C Saturation • Stable/Long-Lived CN Data • Geomorphic/Geologic Indicators • Years 1-5 • Analyses • Year 5 • Results Compared with Other CRONUS Data • Geomagnetic & Solar Variation Effects • Atmospheric Effects • Spallogenic/Muogenic Production • Incorporate into Parameter Estimation Model • Write Papers CRONUS-Earth