Meteoric 10-Be, produced in the atmosphere and delivered in precipitation, is an important tracer... more Meteoric 10-Be, produced in the atmosphere and delivered in precipitation, is an important tracer of sediment and geomorphic processes. This talk will review several decades of work measuring 10-Be adhered to soil and sediment collected from varied terrains around the world. We will then present new data and modeling approaches demonstrating the rich potential but complex, dynamic nature of this isotope system. Considering all of these data, we will examine the utility of meteoric10-Be, produced in the atmosphere and delivered in precipitation, as a tracer of watershed and hillslope sediment transport processes at a variety of spatial scales. We will finish the talk by examining uncertainties that require additional research to resolve.
After Hurricane Isabel in 2003, Great Falls on the Potomac River was overwhelmed by muddy floodwa... more After Hurricane Isabel in 2003, Great Falls on the Potomac River was overwhelmed by muddy floodwater carrying soil washed from historic upland farms. Precise measurement of soil erosion over large areas is a crucial part of learning sustainable farming practices, but is notoriously hard to do given the variability of nature.
To quantify short-term sediment movement rates across Mojave Desert piedmonts, 1600 painted and n... more To quantify short-term sediment movement rates across Mojave Desert piedmonts, 1600 painted and numbered pebbles were laid out in paired, orthogonal, 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later. Pebble lines cross shallow (5-15 cm), ephemeral channels and adjacent unconsolidated interfluves, the latter being the dominant landform at all sites. Two sites are located on surfaces that have been or are impacted by military training activities, including the use of tracked vehicles. The two other sites have not been disturbed by human impact. Three different processes transport pebbles. Episodic streamflow in ephemeral channels transports a few pebbles long distances (decimeters to meters) down gradient. Bioturbation moves many pebbles small distances (centimeters) in any direction, and vehicular disturbance transports pebbles varying distances (centimeters to meters) in any direction. Significant down-gradient sediment movement occurred dominantly in channels where flowing water was concentrated. Interfluves were stable surfaces where little transport occurred. Off-road vehicle use is coincident with accelerated pebble movement. Pebbles moved further and faster down gradient at the disturbed Iron Mountain and East Range Road sites (mean speeds of 0.18 and 0.34 m yr À1 , respectively) than at the undisturbed Chemehuevi and Goldstone sites, (mean speeds of 0.17 and 0.02 m yr À1 , respectively). Mean pebble movement is highly and negatively correlated with vegetation density. Short-term pebble movement rates are several times lower than long-term (10 3 to 10 4 year) rates, suggesting the importance of rare, extreme precipitation events for sediment transport such as those of fall and winter 2004.
In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea l... more In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC) that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to forecast changes in the state of Earth's surface as a result of likely future C&LUC. We also propose strategies for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration across disciplines are necessary. The main body of the paper addresses cross-cutting issues, including the importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment transport, as well as the importance of alternate stable states and extreme, rare events for understanding and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process zones (global-scale assessments and fluvial, aeolian, glacial/periglacial, and coastal process zones) in detail.
Debris flows, both the erosion they cause and the sediment they deposit, are significant natural ... more Debris flows, both the erosion they cause and the sediment they deposit, are significant natural hazards in the high-relief, passive margin of eastern Brazil. To determine the source of debris flow sediment and the return interval of flows significant enough to transport large boulders, we sampled and measured two sets of boulders deposited by prehistoric debris flows and one set of boulders deposited in 2011. To determine the likelihood of inheritance of nuclides from prior exposure on basin slopes, we sampled 5 boulders (1.2 to 2.2 m) in the channel above Posse, at Campo Grande close to Teresópolis city. These boulders were moved in 2011 debris flows and 4 of 5 have relatively low concentrations of Be-10 (20,000; 26,000; 32,000 and 66,000 atoms/g), the equivalent of 3 to 10 ky of surface exposure. One boulder contains 320,000 atoms/g, the equivalent of 48 ky of exposure. These data suggest that most boulders carried by debris flows contain modest concentrations of Be-10 (few 10s of thousands of atoms/g) generated from prior exposure on slopes before transport and deposition in the lowlands. We sampled 5 prehistoric debris-flow boulders from several meters above the active channel in Posse, about 6 km NW of Teresopolis, an area devastated by 2011 debris flows. These boulders have a wide range Be-10 concentrations (32,000; 120,000; 300,000; 411,000 and 440,000 atoms/g) and exposure ages (5, 19, 48, 66, and 72 ky). Considered along with the data from active-channel boulders, it appears likely that debris flows repeatedly deposited boulders in this area during the later Pleistocene. Three large prehistoric debris flow boulders (5 to 6 m) sampled 5 km west of Bom Sucesso contain high concentrations of Be-10 (800,000 to 900,000 atoms/g) and thus have very long exposure ages, 117-132 ky. These boulders are many meters above the adjacent channel and several meters above the adjacent farmland. Sandy sediment deposited by 2011 debris flows and sampled at three different locations contains 340,000 to 490,000 atoms/g of Be-10, more than most debris flow boulders. Because the sandy sediment contains high concentrations of Be-10, it must be sourced from more stable parts of the landscape than the boulders, perhaps stable channel margin deposits eroded and reworked by the debris flows or from the rocky outcrops, so common in the area?
We measured the concentration of 10 Be in fluvial sediment collected in 2011 from rivers draining... more We measured the concentration of 10 Be in fluvial sediment collected in 2011 from rivers draining the Kangerlussuaq (n=11) and Narsarsuaq (n=12) regions on the west and south coasts of Greenland. The concentration of 10 Be, measured in quartz, can be used as a tracer of sediment transport from the ice margin across the landscape. In Kangerlussuaq, we collected samples along the length of the Watson River, which flows from the ice margin to the fjord mouth. Concentrations of 10 Be in Watson River sediment were 2.3, 2.9, and 2.1 x 10 4 atoms/gram. Watson River sediment had lower concentrations of 10 Be than sediments from the ice margin, other drainages, and the fjord mouth, where concentrations were between 3.3 and 5.7 x 10 4 atoms/gram of 10 Be. One interpretation is that sediment coming out of the ice today has 10 Be concentrations between 3 and 6 x 10 4 atoms/gram. Lower 10 Be concentrations in Watson River sediment may be due to jökulhlaup events in 2007 and 2008, which significantly increased river discharge, mixing higher concentration sediments from the ice margin with lower concentration sediments from bank material stored in lake and channel bottoms. In Narsarsuaq, sediments from two rivers flowing from the ice margin to the fjord mouth had concentrations between 2.1 and 6.4 x 10 4 atoms/gram of 10 Be. In both rivers, 10 Be concentration increased downstream, likely because as the rivers approach the fjord, they drain an increasingly large area of deglaciated terrain, which has been accumulating 10 Be during the current interglacial. Sediments from rivers draining exclusively deglaciated landscapes had greater abundances of 10 Be than sediments from partially glaciated terrain with concentrations ranging between 8.6 and 34.7 x 10 4 atoms/gram. Initial results suggest that sediment being discharged by the 6/15/2018
at Kangerlussuaq. As post-glacial uplift continued and local sea level fell, the gravel terrace w... more at Kangerlussuaq. As post-glacial uplift continued and local sea level fell, the gravel terrace was incised, sequentially exposing four samples on a bedrock rib-the equivalent of a slip off surface. The rate of terrace incision (gravel stripping and exposure of our sample sites) matched the rate of relative sea-level fall until a bedrock sill downstream was exposed 4500 /-200 years ago providing a local base-level for the river. The Watson River 10-Be data confirm the inner Kangerlussuaq Fjord emergence curve of Ten Brink (1974), which we calibrated for changes in marine 14-C over time, and provide critical control for the mid-Holocene (2-7 ky) when emergence rates slowed and shell dating becomes less certain.
The timing of initial gully incision into valley bottoms, the processes controlling incision, and... more The timing of initial gully incision into valley bottoms, the processes controlling incision, and the emplacement mechanism for gully-derived sedimentary deposits on the southeastern Tablelands of New South Wales, Australia, have been debated for several decades. We use single-grain optically stimulated luminescence (OSL) to establish the timing of these sedimentary units and conclude that they were deposited after the arrival of Europeans to the region (ca. calendar years 1801-1914). We thus refer to these sediments as post-European materials (PEM) as they are likely the result of European land-use changes. Gully erosion and its relationship to PEM have been extensively studied on the Tablelands of southeastern Australia. We test the long-held geomorphic interpretation that gully incision was initiated in water-saturated swampy meadow environments along pre-European valley bottoms. We measure concentrations of meteoric 10 Be and the OSL of bulk sediment samples from two PEM profiles derived from initial erosion in Birchams Creek. Bulk sediment OSL data collected from two upstream reference profiles that could each potentially serve as the source material for PEM-swampy meadow sediments and weathered regolith derived from sandstone bedrock-show two possible depth-sources from both the swampy meadow profile (39-87 cm and 102-147 cm) and the regolith profile (9-18 cm and 63-99 cm). Homogeneous concentrations of meteoric 10 Be measured from PEM deposits (8.4-9.4 x 10 8 atoms/g) show that PEM was well mixed during fluvial transport before deposition. Meteoric 10 Be results show that PEM could only be derived from shallow erosion (~12-15 cm) of the swampy meadow source profile and not the deep incision indicated by bulk sediment OSL data. PEM could be derived from the regolith source up to depths of 81 cm, which agrees with potential depths suggested by bulk OSL analysis. We interpret these data to suggest that incision leading to gully erosion throughout the Tablelands region did not begin in swampy meadows. European-induced reductions of vegetation on valley bottoms in the late 1800s to early 1900s was an attempt to improve the land for livestock grazing-a change in land-use that ultimately led to removal of PEM sediment from its source and the incision of erosional gullies, many of which are still active.
As part of the NSF-funded program CRONUS-Earth, a series of natural reference materials for in si... more As part of the NSF-funded program CRONUS-Earth, a series of natural reference materials for in situ produced 26 Al, 10 Be, 14 C, and 36 Cl were prepared and circulated to United States, Australian, and European laboratories for analysis to explore the comparability of results from the different laboratories and generate preliminary consensus values for a range of reference material. Such reference materials, which did not exist for these isotopes, assist laboratories in independently assessing quality and are useful to quantify precision and accuracy. Currently, most researchers report only internal analytical uncertainties for all results. While researchers have acknowledged the need for realistic inter-laboratory uncertainties for in situ produced cosmogenic isotopes, few previous studies have addressed this issue. Two samples (denoted A and N) were provided for 26 Al, 10 Be and in situ 14 C analysis, one from the Antarctic, high in 26 Al and 10 Be and the other from Australia, lower in both 26 Al and 10 Be. Both samples were prepared to quartz at the University of Vermont. For each sample, results have been summarised in terms of the mean reported concentration, standard deviation both between (inter) and within (intra) laboratories to describe inter-and intra-laboratory variability. Coefficients of variation (CoV) expressed as a percentage of the mean are also reported. For in-situ 14 C, a small number of laboratories reported results, so they are summarised separately. Initial uncorrected results for samples A and N showed significant variation (greater than 8% CoV) in results, due to differences in standardization. When corrected to a common basis, the CoV was 2.9% for 10 Be measurements of sample A (high concentration) and to 4.1% for sample N (lower concentration), which is closer to typical cosmogenic samples. 26 Al measurements had greater variation; a CoV of 4.9% was achieved for sample A (high concentration) but for the lower concentration sample N, the CoV was 10.1%. Highlights: • We report on an intercomparison study between different CRONUS laboratories • We find high-concentration 10 Be samples give interlab results within <5% error • In the best cases <3% error is achieved • We find higher errors for 26 Al at ~5% and 10% for lower-level samples • A series of references materials have been characterised
The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine ... more The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine are identified using 14 C and highresolution (cm-by-cm) particle size analysis of sediment cores taken from six post-glacial lakes (*0.1-1.4 km 2). A total of nine sediment cores (4.5-6 m long) were taken near the base of stream delta foreslopes. End-member modeling of the particle-size frequency distributions from each core produces 3-5 representative end member distributions, or end members (EMs). Concurrent increases in mean and median particle size, and in the relative abundance of the coarsest EM(s), indicate increased transport capacity of inflowing tributaries, resulting from rainstorms. In all 9 cores, particle size data show clear signs of episodic, high-energy sediment transport events where proxy measurements such as loss-on-ignition and magnetic susceptibility do not, demonstrating the sensitivity of particle size analysis in paleostorm investigations made using lake sediment cores. Floods caused by storms in this region peaked around 1.4, 2.1, 3.0, 3.9, 6.8, 8.2, and 11.5 ka cal BP, and presently appear to be increasing in frequency. Periods of storminess in New Hampshire and Maine correlate well with other records of precipitation and climate in the northeastern United States during the Holocene, further supporting modern records which show tropical air masses as a primary driver of extreme precipitation events in New England (Ludlum 1996; Konrad 2001; Sisson and Gyakum 2004).
Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soi... more Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soil cohesion are commonly invoked to explain topographic asymmetry that depends on aspect, few studies have directly quantified the efficiency of regolith transport along hillslopes of opposing aspect. We utilize meteoric 10 Be concentrations in regolith (n = 74) to determine mass flux along equatorial-and polar-facing hillslopes in three forested, upland watersheds in and adjacent to the Susquehanna Shale Hills Critical Zone Observatory (SSHO) in central Pennsylvania. In combination with regolith depth measurements and high resolution topography, these fluxes allow us to evaluate transport rate laws and the efficiency of regolith creep. Concentrations of meteoric 10 Be in regolith along six separate transects imply that regolith flux is similar along all hillslopes, despite differences in topographic gradient and regolith thickness. Comparison of flux with regolith depth and topographic gradient reveals that transport depends on regolith depth, and that regolith creep is twice as efficient along low-gradient, southfacing slopes with thin regolith as compared to steep, north-facing slopes mantled with thicker
Meteoric 10-Be, produced in the atmosphere and delivered in precipitation, is an important tracer... more Meteoric 10-Be, produced in the atmosphere and delivered in precipitation, is an important tracer of sediment and geomorphic processes. This talk will review several decades of work measuring 10-Be adhered to soil and sediment collected from varied terrains around the world. We will then present new data and modeling approaches demonstrating the rich potential but complex, dynamic nature of this isotope system. Considering all of these data, we will examine the utility of meteoric10-Be, produced in the atmosphere and delivered in precipitation, as a tracer of watershed and hillslope sediment transport processes at a variety of spatial scales. We will finish the talk by examining uncertainties that require additional research to resolve.
After Hurricane Isabel in 2003, Great Falls on the Potomac River was overwhelmed by muddy floodwa... more After Hurricane Isabel in 2003, Great Falls on the Potomac River was overwhelmed by muddy floodwater carrying soil washed from historic upland farms. Precise measurement of soil erosion over large areas is a crucial part of learning sustainable farming practices, but is notoriously hard to do given the variability of nature.
To quantify short-term sediment movement rates across Mojave Desert piedmonts, 1600 painted and n... more To quantify short-term sediment movement rates across Mojave Desert piedmonts, 1600 painted and numbered pebbles were laid out in paired, orthogonal, 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later. Pebble lines cross shallow (5-15 cm), ephemeral channels and adjacent unconsolidated interfluves, the latter being the dominant landform at all sites. Two sites are located on surfaces that have been or are impacted by military training activities, including the use of tracked vehicles. The two other sites have not been disturbed by human impact. Three different processes transport pebbles. Episodic streamflow in ephemeral channels transports a few pebbles long distances (decimeters to meters) down gradient. Bioturbation moves many pebbles small distances (centimeters) in any direction, and vehicular disturbance transports pebbles varying distances (centimeters to meters) in any direction. Significant down-gradient sediment movement occurred dominantly in channels where flowing water was concentrated. Interfluves were stable surfaces where little transport occurred. Off-road vehicle use is coincident with accelerated pebble movement. Pebbles moved further and faster down gradient at the disturbed Iron Mountain and East Range Road sites (mean speeds of 0.18 and 0.34 m yr À1 , respectively) than at the undisturbed Chemehuevi and Goldstone sites, (mean speeds of 0.17 and 0.02 m yr À1 , respectively). Mean pebble movement is highly and negatively correlated with vegetation density. Short-term pebble movement rates are several times lower than long-term (10 3 to 10 4 year) rates, suggesting the importance of rare, extreme precipitation events for sediment transport such as those of fall and winter 2004.
In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea l... more In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC) that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we have the tools to forecast the geomorphic responses to likely future C&LUC. Fully exploiting these models and utilizing these tools will require close collaboration among Earth-surface scientists and Earth-system modelers. This paper assesses the state-of-the-art tools and data that are being used or could be used to forecast changes in the state of Earth's surface as a result of likely future C&LUC. We also propose strategies for filling key knowledge gaps, emphasizing where additional basic research and/or collaboration across disciplines are necessary. The main body of the paper addresses cross-cutting issues, including the importance of nonlinear/threshold-dominated interactions among topography, vegetation, and sediment transport, as well as the importance of alternate stable states and extreme, rare events for understanding and forecasting Earth-surface response to C&LUC. Five supplements delve into different scales or process zones (global-scale assessments and fluvial, aeolian, glacial/periglacial, and coastal process zones) in detail.
Debris flows, both the erosion they cause and the sediment they deposit, are significant natural ... more Debris flows, both the erosion they cause and the sediment they deposit, are significant natural hazards in the high-relief, passive margin of eastern Brazil. To determine the source of debris flow sediment and the return interval of flows significant enough to transport large boulders, we sampled and measured two sets of boulders deposited by prehistoric debris flows and one set of boulders deposited in 2011. To determine the likelihood of inheritance of nuclides from prior exposure on basin slopes, we sampled 5 boulders (1.2 to 2.2 m) in the channel above Posse, at Campo Grande close to Teresópolis city. These boulders were moved in 2011 debris flows and 4 of 5 have relatively low concentrations of Be-10 (20,000; 26,000; 32,000 and 66,000 atoms/g), the equivalent of 3 to 10 ky of surface exposure. One boulder contains 320,000 atoms/g, the equivalent of 48 ky of exposure. These data suggest that most boulders carried by debris flows contain modest concentrations of Be-10 (few 10s of thousands of atoms/g) generated from prior exposure on slopes before transport and deposition in the lowlands. We sampled 5 prehistoric debris-flow boulders from several meters above the active channel in Posse, about 6 km NW of Teresopolis, an area devastated by 2011 debris flows. These boulders have a wide range Be-10 concentrations (32,000; 120,000; 300,000; 411,000 and 440,000 atoms/g) and exposure ages (5, 19, 48, 66, and 72 ky). Considered along with the data from active-channel boulders, it appears likely that debris flows repeatedly deposited boulders in this area during the later Pleistocene. Three large prehistoric debris flow boulders (5 to 6 m) sampled 5 km west of Bom Sucesso contain high concentrations of Be-10 (800,000 to 900,000 atoms/g) and thus have very long exposure ages, 117-132 ky. These boulders are many meters above the adjacent channel and several meters above the adjacent farmland. Sandy sediment deposited by 2011 debris flows and sampled at three different locations contains 340,000 to 490,000 atoms/g of Be-10, more than most debris flow boulders. Because the sandy sediment contains high concentrations of Be-10, it must be sourced from more stable parts of the landscape than the boulders, perhaps stable channel margin deposits eroded and reworked by the debris flows or from the rocky outcrops, so common in the area?
We measured the concentration of 10 Be in fluvial sediment collected in 2011 from rivers draining... more We measured the concentration of 10 Be in fluvial sediment collected in 2011 from rivers draining the Kangerlussuaq (n=11) and Narsarsuaq (n=12) regions on the west and south coasts of Greenland. The concentration of 10 Be, measured in quartz, can be used as a tracer of sediment transport from the ice margin across the landscape. In Kangerlussuaq, we collected samples along the length of the Watson River, which flows from the ice margin to the fjord mouth. Concentrations of 10 Be in Watson River sediment were 2.3, 2.9, and 2.1 x 10 4 atoms/gram. Watson River sediment had lower concentrations of 10 Be than sediments from the ice margin, other drainages, and the fjord mouth, where concentrations were between 3.3 and 5.7 x 10 4 atoms/gram of 10 Be. One interpretation is that sediment coming out of the ice today has 10 Be concentrations between 3 and 6 x 10 4 atoms/gram. Lower 10 Be concentrations in Watson River sediment may be due to jökulhlaup events in 2007 and 2008, which significantly increased river discharge, mixing higher concentration sediments from the ice margin with lower concentration sediments from bank material stored in lake and channel bottoms. In Narsarsuaq, sediments from two rivers flowing from the ice margin to the fjord mouth had concentrations between 2.1 and 6.4 x 10 4 atoms/gram of 10 Be. In both rivers, 10 Be concentration increased downstream, likely because as the rivers approach the fjord, they drain an increasingly large area of deglaciated terrain, which has been accumulating 10 Be during the current interglacial. Sediments from rivers draining exclusively deglaciated landscapes had greater abundances of 10 Be than sediments from partially glaciated terrain with concentrations ranging between 8.6 and 34.7 x 10 4 atoms/gram. Initial results suggest that sediment being discharged by the 6/15/2018
at Kangerlussuaq. As post-glacial uplift continued and local sea level fell, the gravel terrace w... more at Kangerlussuaq. As post-glacial uplift continued and local sea level fell, the gravel terrace was incised, sequentially exposing four samples on a bedrock rib-the equivalent of a slip off surface. The rate of terrace incision (gravel stripping and exposure of our sample sites) matched the rate of relative sea-level fall until a bedrock sill downstream was exposed 4500 /-200 years ago providing a local base-level for the river. The Watson River 10-Be data confirm the inner Kangerlussuaq Fjord emergence curve of Ten Brink (1974), which we calibrated for changes in marine 14-C over time, and provide critical control for the mid-Holocene (2-7 ky) when emergence rates slowed and shell dating becomes less certain.
The timing of initial gully incision into valley bottoms, the processes controlling incision, and... more The timing of initial gully incision into valley bottoms, the processes controlling incision, and the emplacement mechanism for gully-derived sedimentary deposits on the southeastern Tablelands of New South Wales, Australia, have been debated for several decades. We use single-grain optically stimulated luminescence (OSL) to establish the timing of these sedimentary units and conclude that they were deposited after the arrival of Europeans to the region (ca. calendar years 1801-1914). We thus refer to these sediments as post-European materials (PEM) as they are likely the result of European land-use changes. Gully erosion and its relationship to PEM have been extensively studied on the Tablelands of southeastern Australia. We test the long-held geomorphic interpretation that gully incision was initiated in water-saturated swampy meadow environments along pre-European valley bottoms. We measure concentrations of meteoric 10 Be and the OSL of bulk sediment samples from two PEM profiles derived from initial erosion in Birchams Creek. Bulk sediment OSL data collected from two upstream reference profiles that could each potentially serve as the source material for PEM-swampy meadow sediments and weathered regolith derived from sandstone bedrock-show two possible depth-sources from both the swampy meadow profile (39-87 cm and 102-147 cm) and the regolith profile (9-18 cm and 63-99 cm). Homogeneous concentrations of meteoric 10 Be measured from PEM deposits (8.4-9.4 x 10 8 atoms/g) show that PEM was well mixed during fluvial transport before deposition. Meteoric 10 Be results show that PEM could only be derived from shallow erosion (~12-15 cm) of the swampy meadow source profile and not the deep incision indicated by bulk sediment OSL data. PEM could be derived from the regolith source up to depths of 81 cm, which agrees with potential depths suggested by bulk OSL analysis. We interpret these data to suggest that incision leading to gully erosion throughout the Tablelands region did not begin in swampy meadows. European-induced reductions of vegetation on valley bottoms in the late 1800s to early 1900s was an attempt to improve the land for livestock grazing-a change in land-use that ultimately led to removal of PEM sediment from its source and the incision of erosional gullies, many of which are still active.
As part of the NSF-funded program CRONUS-Earth, a series of natural reference materials for in si... more As part of the NSF-funded program CRONUS-Earth, a series of natural reference materials for in situ produced 26 Al, 10 Be, 14 C, and 36 Cl were prepared and circulated to United States, Australian, and European laboratories for analysis to explore the comparability of results from the different laboratories and generate preliminary consensus values for a range of reference material. Such reference materials, which did not exist for these isotopes, assist laboratories in independently assessing quality and are useful to quantify precision and accuracy. Currently, most researchers report only internal analytical uncertainties for all results. While researchers have acknowledged the need for realistic inter-laboratory uncertainties for in situ produced cosmogenic isotopes, few previous studies have addressed this issue. Two samples (denoted A and N) were provided for 26 Al, 10 Be and in situ 14 C analysis, one from the Antarctic, high in 26 Al and 10 Be and the other from Australia, lower in both 26 Al and 10 Be. Both samples were prepared to quartz at the University of Vermont. For each sample, results have been summarised in terms of the mean reported concentration, standard deviation both between (inter) and within (intra) laboratories to describe inter-and intra-laboratory variability. Coefficients of variation (CoV) expressed as a percentage of the mean are also reported. For in-situ 14 C, a small number of laboratories reported results, so they are summarised separately. Initial uncorrected results for samples A and N showed significant variation (greater than 8% CoV) in results, due to differences in standardization. When corrected to a common basis, the CoV was 2.9% for 10 Be measurements of sample A (high concentration) and to 4.1% for sample N (lower concentration), which is closer to typical cosmogenic samples. 26 Al measurements had greater variation; a CoV of 4.9% was achieved for sample A (high concentration) but for the lower concentration sample N, the CoV was 10.1%. Highlights: • We report on an intercomparison study between different CRONUS laboratories • We find high-concentration 10 Be samples give interlab results within <5% error • In the best cases <3% error is achieved • We find higher errors for 26 Al at ~5% and 10% for lower-level samples • A series of references materials have been characterised
The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine ... more The frequency and timing of Holocene paleofloods in the hilly terrain of New Hampshire and Maine are identified using 14 C and highresolution (cm-by-cm) particle size analysis of sediment cores taken from six post-glacial lakes (*0.1-1.4 km 2). A total of nine sediment cores (4.5-6 m long) were taken near the base of stream delta foreslopes. End-member modeling of the particle-size frequency distributions from each core produces 3-5 representative end member distributions, or end members (EMs). Concurrent increases in mean and median particle size, and in the relative abundance of the coarsest EM(s), indicate increased transport capacity of inflowing tributaries, resulting from rainstorms. In all 9 cores, particle size data show clear signs of episodic, high-energy sediment transport events where proxy measurements such as loss-on-ignition and magnetic susceptibility do not, demonstrating the sensitivity of particle size analysis in paleostorm investigations made using lake sediment cores. Floods caused by storms in this region peaked around 1.4, 2.1, 3.0, 3.9, 6.8, 8.2, and 11.5 ka cal BP, and presently appear to be increasing in frequency. Periods of storminess in New Hampshire and Maine correlate well with other records of precipitation and climate in the northeastern United States during the Holocene, further supporting modern records which show tropical air masses as a primary driver of extreme precipitation events in New England (Ludlum 1996; Konrad 2001; Sisson and Gyakum 2004).
Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soi... more Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soil cohesion are commonly invoked to explain topographic asymmetry that depends on aspect, few studies have directly quantified the efficiency of regolith transport along hillslopes of opposing aspect. We utilize meteoric 10 Be concentrations in regolith (n = 74) to determine mass flux along equatorial-and polar-facing hillslopes in three forested, upland watersheds in and adjacent to the Susquehanna Shale Hills Critical Zone Observatory (SSHO) in central Pennsylvania. In combination with regolith depth measurements and high resolution topography, these fluxes allow us to evaluate transport rate laws and the efficiency of regolith creep. Concentrations of meteoric 10 Be in regolith along six separate transects imply that regolith flux is similar along all hillslopes, despite differences in topographic gradient and regolith thickness. Comparison of flux with regolith depth and topographic gradient reveals that transport depends on regolith depth, and that regolith creep is twice as efficient along low-gradient, southfacing slopes with thin regolith as compared to steep, north-facing slopes mantled with thicker
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Papers by Paul Bierman