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1. Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides

   Koester, A. J. (April 2021, GSA Special Paper)

   Richard B. Waitt; Glenn D. Thackray; Alan R. Gillespie (Ed.)

   The northward retreat history of the Laurentide ice sheet through the lowlands of the northeastern United States during the last deglaciation is well constrained, but its vertical thinning history is less well known because of the lack of direct constraints on ice thickness through time and space. In addition, the highest elevations in New England are characterized by gently sloping upland surfaces and weathered block fields, features with an uncertain history. To better constrain ice-sheet history in this area and its relationship to alpine geomorphology, we present 20 new 10Be and seven in situ 14C cosmogenic nuclide measurements along an elevation transect at Mount Washington, New Hampshire, the highest mountain in the northeastern United States (1917 m above sea level [a.s.l.]). Our results suggest substantially different exposure and erosion histories on the upper and lower parts of the mountain. Above 1600 m a.s.l., 10Be and in situ 14C measurements are consistent with upper reaches of the mountain deglaciating by 18 ka. However, some 10Be ages are up to several times greater than the age of the last deglaciation, consistent with weakly erosive, cold-based ice that did not deeply erode preglacial surfaces. Below 1600 m a.s.l., 10Be ages are indistinguishable over a nearly 900 m range in elevation and imply rapid ice-surface lowering ca. 14.1 ± 1.1 ka (1 standard deviation; n = 9). This shift from slow thinning early in the deglaciation on the upper part of the mountain to abrupt thinning across the lower elevations coincided with accelerated ice-margin retreat through the region recorded by Connecticut River valley varve records during the Bølling interstadial. The Mount Washington cosmogenic nuclide vertical transect and the Connecticut River valley varve record, along with other New England cosmogenic nuclide records, suggest rapid ice-volume loss in the interior northeastern United States in response to Bølling warming. 

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2. Hurricanes alter ¹⁰ Be concentrations in tropical river sediment but do not change regional erosion rate estimates

   https://doi.org/10.1002/esp.5310  

   Quock, Melinda; Schmidt, Amanda H.; Corbett, Lee B.; Bierman, Paul R.; Hidy, Alan J.; Caffee, Marc (March 2022, Earth Surface Processes and Landforms)

   Abstract Tropical islands, including many in island arcs, are subjected to recurring disturbances from extreme storms such as tropical cyclones. To test whether such storms influence cosmogenic nuclide concentrations such that they do not reflect long‐term rates of erosion, we measured meteoric andin situ¹⁰Be in river sediment samples from Dominica, an andesitic island in the Caribbean, before and after category five Hurricane Maria (in 2017). Populations of before‐ and after‐storm concentrations are statistically indistinguishable (n = 7 pairs forin‐situ¹⁰Be,n = 11 pairs for meteoric¹⁰Be).¹⁰Be concentrations vary from −138% to +73% within before–after sample pairs relative to the mean of the pair. These new data suggest that the effects of extreme storms on the depth and amount of near‐surface erosion on Dominica vary spatially. Our data support the calculations of Niemi et al. (2005) and Yanites et al. (2009) suggesting that basin‐by‐basin comparisons of erosion rates based on cosmogenic nuclides should be approached with caution in small (<~100 km²) watersheds affected by mass movements and extreme storms. Erosion rates determined fromin‐situ¹⁰Be on Dominica (geometric mean = 0.102 mm y⁻¹,n = 12) are low compared to similarly steep and wet areas globally and correlate positively with the spatial density of mass movements. 

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3. Increased Erosion Rates Following the Onset of Pleistocene Periglaciation at Bear Meadows, Pennsylvania, USA

   https://doi.org/10.1029/2021GL096739  

   Del Vecchio, J.; DiBiase, R. A.; Corbett, L. B.; Bierman, P. R.; Caffee, M. W.; Ivory, S. J. (February 2022, Geophysical Research Letters)

   Abstract Direct measurements of erosional response to past climate change are scarce, but mid‐latitude landscapes can record how shifts between cold and warm periods altered erosion outside glacial margins. To study hillslope responses to periglaciation, we measured bulk geochemistry and cosmogenic¹⁰Be and²⁶Al concentrations in colluvium and weathered bedrock in an 18 m regolith core from Bear Meadows, Pennsylvania, ∼100 km south of maximum glacial extent. Using core lithology, cosmogenic nuclide concentrations, and regional¹⁰Be‐derived erosion rates, we show the onset of 100‐Kyr glacial cycles at the Mid‐Pleistocene Transition (1.2–0.7 Ma) instigated multiple periglacial episodes in central Appalachia, increasing erosion rates compared to the relatively warmer Neogene. Our results show the higher efficiency of periglacial versus temperate erosion processes and highlight a pervasive Pleistocene periglacial erosion signal preserved in the¹⁰Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes. 

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4. Production rate calibration for cosmogenic ¹⁰ Be in pyroxene by applying a rapid fusion method to ¹⁰ Be-saturated samples from the Transantarctic Mountains, Antarctica

   https://doi.org/10.5194/gchron-6-491-2024  

   Bergelin, Marie; Balco, Greg; Corbett, Lee B; Bierman, Paul R (August 2024, Geochronology)

   Abstract. Measurements of multiple cosmogenic nuclides in a single sample are valuable for various applications of cosmogenic nuclide exposure dating and allow for correcting exposure ages for surface weathering and erosion and establishing exposure–burial history. Here we provide advances in the measurement of cosmogenic 10Be in pyroxene and constraints on the production rate that provide new opportunities for measurements of multi-nuclide systems, such as 10Be/3He, in pyroxene-bearing samples. We extracted and measured cosmogenic 10Be in pyroxene from two sets of Ferrar Dolerite samples collected from the Transantarctic Mountains in Antarctica. One set of samples has 10Be concentrations close to saturation, which allows for the production rate calibration of 10Be in pyroxene by assuming production–decay equilibrium. The other set of samples, which has a more recent exposure history, is used to determine if a rapid fusion method can be successfully applied to samples with Holocene to Last Glacial Maximum exposure ages. From measured 10Be concentrations in the near-saturation sample set we find the production rate of 10Be in pyroxene to be 3.74 ± 0.10 atoms g−1 yr−1, which is consistent with 10Be/3He paired nuclide ratios from samples assumed to have simple exposure. Given the high 10Be concentration measured in this sample set, a sample mass of ∼ 0.5 g of pyroxene is sufficient for the extraction of cosmogenic 10Be from pyroxene using a rapid fusion method. However, for the set of samples that have low 10Be concentrations, measured concentrations were higher than expected. We attribute spuriously high 10Be concentrations to failure in removing all meteoric 10Be and/or a highly variable and poorly quantified procedural blank background correction. 

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5. Cosmogenic nuclide and solute flux data from central Cuban rivers emphasize the importance of both physical and chemical mass loss from tropical landscapes

   https://doi.org/10.5194/gchron-4-435-2022  

   Campbell, Mae Kate; Bierman, Paul R.; Schmidt, Amanda H.; Sibello Hernández, Rita; García-Moya, Alejandro; Corbett, Lee B.; Hidy, Alan J.; Cartas Águila, Héctor; Guillén Arruebarrena, Aniel; Balco, Greg; et al (January 2022, Geochronology)

   Abstract. We use 25 new measurements of in situ produced cosmogenic 26Al and 10Bein river sand, paired with estimates of dissolved load flux in river water,to characterize the processes and pace of landscape change in central Cuba.Long-term erosion rates inferred from 10Be concentrations in quartzextracted from central Cuban river sand range from3.4–189 Mg km−2 yr−1 (mean 59, median 45). Dissolved loads (10–176 Mg km−2 yr−1; mean 92, median 97), calculated from stream soluteconcentrations and modeled runoff, exceed measured cosmogenic-10Be-derived erosion rates in 18 of 23 basins. This disparity mandatesthat in this environment landscape-scale mass loss is not fully representedby the cosmogenic nuclide measurements. The 26Al / 10Be ratios are lower than expected for steady-state exposure or erosion in 16 of 24 samples. Depressed 26Al / 10Be ratios occur in many of the basins that have the greatest disparity between dissolved loads (high) and erosion rates inferred from cosmogenic nuclide concentrations (low). Depressed 26Al / 10Be ratios are consistentwith the presence of a deep, mixed, regolith layer providing extendedstorage times on slopes and/or burial and extended storage during fluvialtransport. River water chemical analyses indicate that many basins with lower 26Al / 10Be ratios and high 10Be concentrations are underlain at least in part by evaporitic rocks that rapidly dissolve. Our data show that when assessing mass loss in humid tropical landscapes,accounting for the contribution of rock dissolution at depth is particularly important. In such warm, wet climates, mineral dissolution can occur many meters below the surface, beyond the penetration depth of most cosmic rays and thus the production of most cosmogenic nuclides. Our data suggest the importance of estimating solute fluxes and measuring paired cosmogenic nuclides to better understand the processes and rates of mass transfer at a basin scale. 

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