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Abstract While there are no ice sheets in the Northern Hemisphere outside of Greenland today, it is uncertain whether this was also the case during most other Quaternary interglacials. We show, using in situ cosmogenic nuclides in ice-rafted debris, that the Laurentide Ice Sheet was likely more persistent during Quaternary interglacials than often thought. Low 26Al/10Be ratios (indicative of burial of the source area) in marine core sediment suggest sediment source areas experienced only brief (on the order of thousands of years) and/or infrequent ice-free interglacials over the past million years. These results imply that complete Laurentide deglaciation may have only occurred when climate forcings reached levels comparable to those of the early Holocene, making our current interglacial unusual relative to others of the mid-to-late Pleistocene. 

Past interglacial climates with smaller ice sheets offer analogs for ice sheet response to future warming and contributions to sea level rise; however, well-dated geologic records from formerly ice-free areas are rare. Here we report that subglacial sediment from the Camp Century ice core preserves direct evidence that northwestern Greenland was ice free during the Marine Isotope Stage (MIS) 11 interglacial. Luminescence dating shows that sediment just beneath the ice sheet was deposited by flowing water in an ice-free environment 416 ± 38 thousand years ago. Provenance analyses and cosmogenic nuclide data and calculations suggest the sediment was reworked from local materials and exposed at the surface <16 thousand years before deposition. Ice sheet modeling indicates that ice-free conditions at Camp Century require at least 1.4 meters of sea level equivalent contribution from the Greenland Ice Sheet.

 

Abstract. Long-term erosion rates in Tasmania, at the southern end of Australia's Great Dividing Range, are poorly known; yet, this knowledge is critical for making informed land-use decisions and improving the ecological health of coastal ecosystems. Here, we present quantitative, geologically relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in situ-produced 10Be (10Bei) measured from stream sand at two trunk channel sites and seven tributaries (mean: 24.1±1.4 Mgkm-2yr-1; 1σ). These new10Bei-based erosion rates are strongly related to elevation, which appears to control mean annual precipitation and temperature,suggesting that elevation-dependent surface processes influence rates of erosion in northeast Tasmania. Erosion rates are not correlated with slopein contrast to erosion rates along the mainland portions of Australia's Great Dividing Range. We also extracted and measured meteoric 10Be(10Bem) from grain coatings of sand-sized stream sediment at each site, which we normalize to measured concentrations of reactive 9Beand use to estimate 10Bem-based denudation rates for the George River. 10Bem/9Bereac denudation ratesreplicate 10Bei erosion rates within a factor of 3 but are highly sensitive to the value of 9Be that is found in bedrock(9Beparent), which was unmeasured in this study. 10Bem/9Bereac denudation rates seem sensitive to recentmining, forestry, and agricultural land use, all of which resulted in widespread topsoil disturbance. Our findings suggest that10Bem/9Bereac denudation metrics will be most useful in drainage basins that are geologically homogeneous, where recentdisturbances to topsoil profiles are minimal, and where 9Beparent is well constrained. 

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. 

Abstract. Glaciers preserve climate variations in their geologicaland geomorphological records, which makes them prime candidates for climatereconstructions. Investigating the glacier–climate system over the pastmillennia is particularly relevant first because the amplitude andfrequency of natural climate variability during the Holocene provides theclimatic context against which modern, human-induced climate change must beassessed. Second, the transition from the last glacial to the currentinterglacial promises important insights into the climate system duringwarming, which is of particular interest with respect to ongoing climatechange. Evidence of stable ice margin positions that record cooling during the past12 kyr are preserved in two glaciated valleys of the Silvretta Massif in theeastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mappedand dated moraines in these catchments including historical ridges usingberyllium-10 surface exposure dating (10Be SED) techniques andcorrelate resulting moraine formation intervals with climate proxy recordsto evaluate the spatial and temporal scale of these cold phases. The newgeochronologies indicate the formation of moraines during the early Holocene (EH), ca. 11.0 ± 0.7 ka (n = 19). Boulder ages along historical moraines (n = 6) suggest at least two glacier advances during the Little Ice Age (LIA; ca. 1250–1850 CE) around 1300 CE and in the second half of the 18th century. An earlier advance to the same position may have occurredaround 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence thatmillennial-scale EH warming was superimposed by centennial-scale cooling.The timing of EH moraine formation coincides with brief temperature dropsidentified in local and regional paleoproxy records, most prominently withthe Preboreal Oscillation (PBO) and is consistent with moraine depositionin other catchments in the European Alps and in the Arctic region. Thisconsistency points to cooling beyond the local scale and therefore aregional or even hemispheric climate driver. Freshwater input sourced fromthe Laurentide Ice Sheet (LIS), which changed circulation patterns in theNorth Atlantic, is a plausible explanation for EH cooling and moraineformation in the Nordic region and in Europe. 

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.