Climatological effects on surface exposure dating

Shan Ye

Abstract: Cosmogenic surface exposure dating is a widely applied tool in glaciated landscapes for determining the history of past glaciations. In the western North America exposure dating with ¹⁰Be have been measured on moraine boulders deposited by alpine glaciers in order to determine stable glacier positions and infer past climate conditions. The production rate of ¹⁰Be varies in space, so a geographic scaling is required in the age calibration. However, the effect of many geologic and climatologic processes on surface exposure ages are not quantified and incorporated into this geographic scaling, which could lead to discrepancies amongst ages across relatively large geographic ranges and obscure our knowledge of glacial histories. Here, we compile a dataset of 1140 ¹⁰Be based surface exposure ages from 46 alpine moraines across the western North America and archive our data in our newly developed Sparrow database. The surface exposure ages span the past 20 ka and the moraines are spread across a large geographic area and a complex mountainous topography. Steep climatologic gradients across this mountainous terrain can influence surface exposure dating techniques in several ways but most notably in snow shielding of the moraine deposits and surface erosion of the moraine boulders. To test the potential effects of snow shielding, we apply a regional scale model to test the potential effects of climatology on surface exposure dating. To begin, we utilize modern remote sensing and snow reanalysis data to reconstruct the history of snow coverage, depth, and density in North America to determine the potential influence of the snow cover on the ¹⁰Be production rates at the moraine locations. This modeling approach assumes that the climatology across our modeling study have remained stationary over the past 20 ka, so future work will incorporate simulated snowfall data from transient modeling simulations across this time period to test the sensitivity of snow cover on the surface exposure ages. Future work will also incorporate the effects of erosion on the moraine ages and apply an erosion model based on local climatological and geological information and consistently scaled across our model domain. This work will then be applied to the existing moraine ages to provide better uncertainty estimates of the ¹⁰Be based ages and insight into past glacier changes.

Time: April 22nd (11:15)

Advisor: Shaun Marcott

Co-Authors: Shaun Marcott, Daven Quinn

Stream: Zoom

Email: shan.ye@wisc.edu