Cosmogenic ²⁶Al/¹⁰Be surface production ratio in Greenland

Abstract

The assumed value for the cosmogenic 26Al/10Be surface production rate ratio in quartz is an important parameter for studies investigating the burial or subaerial erosion of long‐lived surfaces and sediments. Recent models and data suggest that the production ratio is spatially variable and may be greater than originally thought. Here we present measured 26Al/10Be ratios for 24 continuously exposed bedrock and boulder surfaces spanning ~61–77°N in Greenland. Empirical measurements, such as ours, include nuclides produced predominately by neutron‐induced spallation with percent‐level contributions by muon interactions. The slope of a York regression line fit to our data is 7.3 ± 0.3 (1σ), suggesting that the 26Al/10Be surface production ratio exceeds the commonly used value of 6.75, at least in the Arctic. A higher 26Al/10Be production ratio has implications for multinuclide cosmogenic isotope studies because it results in greater modeled burial durations and erosion rates.

The Northwestern Greenland Ice Sheet During The Early Pleistocene Was Similar To Today

“…These data suggest the presence of a largely persistent, yet dynamic, ice sheet in northwestern Greenland by the Early Pleistocene . Decay-corrected 10 Be concentrations in diamict resemble 10 Be measurements of sediment discharged from the GrIS today ( Figure 2) and the decay-corrected 26 Al i / 10 Be i ratio, while uncertain, exceeds the observed Greenland surface production ratio (Corbett, Bierman, Rood, et al, 2017). These observations suggest that most subglacial material we analyzed was sourced from regions with high erosion rates.…”

“…This early Pleistocene diamict is sourced from an area with minimal exposure and high erosion rates, and thus comprised of deeply eroded materials. The 1.9 Ma decay-corrected 26 Al i / 10 Be i ratio of this diamict (9.1 ± 1.5; weighted mean ± 1 sigma), while variable, is greater than the contemporary Greenland surface production ratio of 7.3 ± 0.3 (Corbett, Bierman, Rood, et al, 2017) (Table S6 and Figure S4). 26 Al i / 10 Be i ratios >7 are indicative of muon-induced production at depths of tens of meters for short (~100 kyr) periods (Balco, 2017).…”

Tectonic controls of Holocene erosion in a glaciated orogen

“…In landscapes where the cosmogenic nuclide inventories are a function of constant exposure or constant erosion, the ratio of 26 Al to 10 Be within sediments can be predicted based on the modeled (Lal, 1991;Balco et al, 2008) or measured (Corbett et al, 2017) ratios. Recent studies indicate that our samples should have natural 26 Al / 10 Be ratios of ∼ 6.75 (Balco et al, 2008), a value that is close to most of our measured ratios (Fig.…”

Response to RC1

“…In landscapes where the cosmogenic nuclide inventories are a function of constant exposure or constant erosion, the ratio of 26 Al to 10 Be within sediments can be predicted based on the modeled (Lal, 1991;Balco et al, 2008) or measured (Corbett et al, 2017) ratios. Recent studies indicate that our samples should have natural 26 Al / 10 Be ratios of ∼ 6.75 (Balco et al, 2008), a value that is close to most of our measured ratios (Fig.…”