GLACIAL CHRONOLOGY AND LANDSCAPE EVOLUTION ON BAFFIN ISLAND, CANADA, CONSTRAINED BY A COMPILATION OF PAIRED 26AL/10BE ANALYSES

Constraining glacial history through cosmogenic isotope analysis in areas of cold-based ice can be challenging because the lack of deep erosion violates the assumption of no inheritance. On Baffin Island, cosmogenic isotope measurements indicate that the land surface, especially at high elevations, has been progressively modified but not deeply eroded over multiple glacial/interglacial cycles. The Baffin Island landscape preserves a long and rich history of glacial events, so it is important to constrain erosion efficiency and develop approaches for extracting information about past glaciation from landscapes with complex exposure/erosion histories.

Here, we compile the data from 149 paired ¹⁰Be and ²⁶Al analyses of Baffin Island samples prepared at University of Vermont. All apparent exposure ages have been recalculated in CRONUS. Measured ¹⁰Be concentrations in samples range from 3.5 to 180·10⁴ atoms g^-1, yielding calculated apparent exposure ages of 6.3 to 160 ka. Measured ²⁶Al concentrations in samples range from 1.2 to 83·10⁵ atoms g^-1, yielding calculated apparent exposure ages of 4.3 to 124 ka. Calculated ²⁶Al/¹⁰Be ratios range from 3.3-8.7, excluding three outliers that likely had measurement error in one or both isotopes.

The dataset allows us to use a large number of samples to construct a three-part test for inherited cosmogenic nuclides indicative of complex exposure histories resulting from ineffective erosion and repeated exposure. For the 149 samples compiled here, ¹⁰Be and ²⁶Al apparent exposure ages are closely related (R² = 0.97, p < 0.01), but ²⁶Al ages are consistently lower (regression line slope = 0.77). For paired bedrock/boulder samples, bedrock apparent exposure ages exceed boulder ages in 8 of the 11 bedrock-boulder pairs for which the sample ages differ by more than the one-sigma analytical uncertainties. Finally, both bedrock (R² = 0.35, p = <0.01) and boulder (R² = 0.22, p = <0.01) sample ages increase with elevation (although the ²⁶Al/¹⁰Be ratio has no trend with elevation, possibly due to poorer ²⁶Al data reproducibility, as shown with both field and laboratory replicate analyses). The above observations are consistent with a relatively thin ice sheet with limited erosive capabilities that led to the development of surfaces with complex exposure histories.