Articles | Volume 3, issue 1
https://doi.org/10.5194/gchron-3-1-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-3-1-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
07 Jan 2021
Research article |
| 07 Jan 2021
| 07 Jan 2021
Atmospherically produced beryllium-10 in annually laminated late-glacial sediments of the North American Varve Chronology
Greg Balco
CORRESPONDING AUTHOR
Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA, USA
Benjamin D. DeJong
Vanasse Hangen Brustlin, Inc., Montpelier, VT, USA
Department of Geology, University of Vermont, Burlington, VT, USA
John C. Ridge
Department of Earth and Ocean Sciences, Tufts University, Medford, MA, USA
Paul R. Bierman
Department of Geology, University of Vermont, Burlington, VT, USA
Dylan H. Rood
Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, London, UK
Earth Research Institute, University of California, Santa Barbara, CA 93106, USA
Department of Earth and Environmental Science & A. E. Lalonde AMS Laboratory, University of Ottawa, Ottawa, Ontario, Canada
Related authors
Marie Bergelin, Andrew Gorin, Greg Balco, and William Cassata
EGUsphere, https://doi.org/10.5194/egusphere-2025-928, https://doi.org/10.5194/egusphere-2025-928, 2025
This preprint is open for discussion and under review for Geochronology (GChron).
Short summary
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Helium gas accumulates over time in minerals, but loss can occur depending on temperature. If partially retained, its loss can potentially be used for determining past surface temperatures. This study uses a model that accounts for complex gas loss to analyze helium retention in two minerals commonly found on the surface of Antarctica. We find one of the minerals retains helium while the other loses nearly all of the gas within hundred years, making it unsuitable as a climate reconstruction.
Greg Balco
EGUsphere, https://doi.org/10.5194/egusphere-2025-149, https://doi.org/10.5194/egusphere-2025-149, 2025
Short summary
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This paper describes measurements of cosmogenic neon-21 concentrations in a widely distributed mineral standard material that is routinely used for quality control and interlaboratory comparison for measurements of other cosmic-ray-produced nuclides useful for various geochronology applications. Broadly, this facilitates improvement of precision and accuracy of these measurements and their applications in geochronology.
Joanne S. Johnson, John Woodward, Ian Nesbitt, Kate Winter, Seth Campbell, Keir A. Nichols, Ryan A. Venturelli, Scott Braddock, Brent M. Goehring, Brenda Hall, Dylan H. Rood, and Greg Balco
The Cryosphere, 19, 303–324, https://doi.org/10.5194/tc-19-303-2025, https://doi.org/10.5194/tc-19-303-2025, 2025
Short summary
Short summary
Determining where and when the Antarctic ice sheet was smaller than present requires recovery and exposure dating of subglacial bedrock. Here we use ice sheet model outputs and field data (geological and glaciological observations, bedrock samples, and ground-penetrating radar) to assess the suitability for subglacial drilling of sites in the Hudson Mountains, West Antarctica. We find that no sites are perfect, but two are feasible, with the most suitable being Winkie Nunatak (74.86°S, 99.77°W).
Gordon R. M. Bromley, Greg Balco, Margaret S. Jackson, Allie Balter-Kennedy, and Holly Thomas
Clim. Past, 21, 145–160, https://doi.org/10.5194/cp-21-145-2025, https://doi.org/10.5194/cp-21-145-2025, 2025
Short summary
Short summary
We constructed a geologic record of East Antarctic Ice Sheet thickness from deposits at Otway Massif to directly assess how Earth's largest ice sheet responds to warmer-than-present climate. Our record confirms the long-term dominance of a cold polar climate but lacks a clear ice sheet response to the mid-Pliocene Warm Period, a common analogue for the future. Instead, an absence of moraines from the late Miocene–early Pliocene suggests the ice sheet was less extensive than present at that time.
Joseph P. Tulenko, Greg Balco, Michael A. Clynne, and L. J. Patrick Muffler
Geochronology, 6, 639–652, https://doi.org/10.5194/gchron-6-639-2024, https://doi.org/10.5194/gchron-6-639-2024, 2024
Short summary
Short summary
Cosmogenic nuclide exposure dating is an exceptional tool for reconstructing glacier histories, but reconstructions based on common target nuclides (e.g., 10Be) can be costly and time-consuming to generate. Here, we present a cost-effective proof-of-concept 21Ne exposure age chronology from Lassen Volcanic National Park, CA, USA, that broadly agrees with nearby 10Be chronologies but at lower precision.
Greg Balco, Andrew J. Conant, Dallas D. Reilly, Dallin Barton, Chelsea D. Willett, and Brett H. Isselhardt
Geochronology, 6, 571–584, https://doi.org/10.5194/gchron-6-571-2024, https://doi.org/10.5194/gchron-6-571-2024, 2024
Short summary
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This paper describes how krypton isotopes produced by nuclear fission can be used to determine the age of microscopic particles of used nuclear fuel. This is potentially useful for international safeguard applications aimed at tracking and identifying nuclear materials, as well as geoscience applications involving dating post-1950s sediments or understanding environmental transport of nuclear materials.
Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke
Clim. Past, 20, 2167–2190, https://doi.org/10.5194/cp-20-2167-2024, https://doi.org/10.5194/cp-20-2167-2024, 2024
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We date sedimentary deposits showing that the southeastern Laurentide Ice Sheet was at or near its southernmost extent from ~ 26 000 to 21 000 years ago, when sea levels were at their lowest, with climate records indicating glacial conditions. Slow deglaciation began ~ 22 000 years ago, shown by a rise in modeled local summer temperatures, but significant deglaciation in the region did not begin until ~ 18 000 years ago, when atmospheric CO2 began to rise, marking the end of the last ice age.
Marie Bergelin, Greg Balco, Lee B. Corbett, and Paul R. Bierman
Geochronology, 6, 491–502, https://doi.org/10.5194/gchron-6-491-2024, https://doi.org/10.5194/gchron-6-491-2024, 2024
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Cosmogenic nuclides, such as 10Be, are rare isotopes produced in rocks when exposed at Earth's surface and are valuable for understanding surface processes and landscape evolution. However, 10Be is usually measured in quartz minerals. Here we present advances in efficiently extracting and measuring 10Be in the pyroxene mineral. These measurements expand the use of 10Be as a dating tool for new rock types and provide opportunities to understand landscape processes in areas that lack quartz.
Greg Balco, Alan J. Hidy, William T. Struble, and Joshua J. Roering
Geochronology, 6, 71–76, https://doi.org/10.5194/gchron-6-71-2024, https://doi.org/10.5194/gchron-6-71-2024, 2024
Short summary
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We describe a new method of reconstructing the long-term, pre-observational frequency and/or intensity of wildfires in forested landscapes using trace concentrations of the noble gases helium and neon that are formed in soil mineral grains by cosmic-ray bombardment of the Earth's surface.
Benoit S. Lecavalier, Lev Tarasov, Greg Balco, Perry Spector, Claus-Dieter Hillenbrand, Christo Buizert, Catherine Ritz, Marion Leduc-Leballeur, Robert Mulvaney, Pippa L. Whitehouse, Michael J. Bentley, and Jonathan Bamber
Earth Syst. Sci. Data, 15, 3573–3596, https://doi.org/10.5194/essd-15-3573-2023, https://doi.org/10.5194/essd-15-3573-2023, 2023
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The Antarctic Ice Sheet Evolution constraint database version 2 (AntICE2) consists of a large variety of observations that constrain the evolution of the Antarctic Ice Sheet over the last glacial cycle. This includes observations of past ice sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. The database is intended to improve our understanding of past Antarctic changes and for ice sheet model calibrations.
Allie Balter-Kennedy, Joerg M. Schaefer, Roseanne Schwartz, Jennifer L. Lamp, Laura Penrose, Jennifer Middleton, Jean Hanley, Bouchaïb Tibari, Pierre-Henri Blard, Gisela Winckler, Alan J. Hidy, and Greg Balco
Geochronology, 5, 301–321, https://doi.org/10.5194/gchron-5-301-2023, https://doi.org/10.5194/gchron-5-301-2023, 2023
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Cosmogenic nuclides like 10Be are rare isotopes created in rocks exposed at the Earth’s surface and can be used to understand glacier histories and landscape evolution. 10Be is usually measured in the mineral quartz. Here, we show that 10Be can be reliably measured in the mineral pyroxene. We use the measurements to determine exposure ages and understand landscape processes in rocks from Antarctica that do not have quartz, expanding the use of this method to new rock types.
Greg Balco, Nathan Brown, Keir Nichols, Ryan A. Venturelli, Jonathan Adams, Scott Braddock, Seth Campbell, Brent Goehring, Joanne S. Johnson, Dylan H. Rood, Klaus Wilcken, Brenda Hall, and John Woodward
The Cryosphere, 17, 1787–1801, https://doi.org/10.5194/tc-17-1787-2023, https://doi.org/10.5194/tc-17-1787-2023, 2023
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Samples of bedrock recovered from below the West Antarctic Ice Sheet show that part of the ice sheet was thinner several thousand years ago than it is now and subsequently thickened. This is important because of concern that present ice thinning in this region may lead to rapid, irreversible sea level rise. The past episode of thinning at this site that took place in a similar, although not identical, climate was not irreversible; however, reversal required at least 3000 years to complete.
Anna Ruth W. Halberstadt, Greg Balco, Hannah Buchband, and Perry Spector
The Cryosphere, 17, 1623–1643, https://doi.org/10.5194/tc-17-1623-2023, https://doi.org/10.5194/tc-17-1623-2023, 2023
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This paper explores the use of multimillion-year exposure ages from Antarctic bedrock outcrops to benchmark ice sheet model predictions and thereby infer ice sheet sensitivity to warm climates. We describe a new approach for model–data comparison, highlight an example where observational data are used to distinguish end-member models, and provide guidance for targeted sampling around Antarctica that can improve understanding of ice sheet response to climate warming in the past and future.
Jonathan R. Adams, Joanne S. Johnson, Stephen J. Roberts, Philippa J. Mason, Keir A. Nichols, Ryan A. Venturelli, Klaus Wilcken, Greg Balco, Brent Goehring, Brenda Hall, John Woodward, and Dylan H. Rood
The Cryosphere, 16, 4887–4905, https://doi.org/10.5194/tc-16-4887-2022, https://doi.org/10.5194/tc-16-4887-2022, 2022
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Glaciers in West Antarctica are experiencing significant ice loss. Geological data provide historical context for ongoing ice loss in West Antarctica, including constraints on likely future ice sheet behaviour in response to climatic warming. We present evidence from rare isotopes measured in rocks collected from an outcrop next to Pope Glacier. These data suggest that Pope Glacier thinned faster and sooner after the last ice age than previously thought.
Natacha Gribenski, Marissa M. Tremblay, Pierre G. Valla, Greg Balco, Benny Guralnik, and David L. Shuster
Geochronology, 4, 641–663, https://doi.org/10.5194/gchron-4-641-2022, https://doi.org/10.5194/gchron-4-641-2022, 2022
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We apply quartz 3He paleothermometry along two deglaciation profiles in the European Alps to reconstruct temperature evolution since the Last Glacial Maximum. We observe a 3He thermal signal clearly colder than today in all bedrock surface samples exposed prior the Holocene. Current uncertainties in 3He diffusion kinetics do not permit distinguishing if this signal results from Late Pleistocene ambient temperature changes or from recent ground temperature variation due to permafrost degradation.
Marie Bergelin, Jaakko Putkonen, Greg Balco, Daniel Morgan, Lee B. Corbett, and Paul R. Bierman
The Cryosphere, 16, 2793–2817, https://doi.org/10.5194/tc-16-2793-2022, https://doi.org/10.5194/tc-16-2793-2022, 2022
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Glacier ice contains information on past climate and can help us understand how the world changes through time. We have found and sampled a buried ice mass in Antarctica that is much older than most ice on Earth and difficult to date. Therefore, we developed a new dating application which showed the ice to be 3 million years old. Our new dating solution will potentially help to date other ancient ice masses since such old glacial ice could yield data on past environmental conditions on Earth.
Mae Kate Campbell, Paul R. Bierman, Amanda H. Schmidt, Rita Sibello Hernández, Alejandro García-Moya, Lee B. Corbett, Alan J. Hidy, Héctor Cartas Águila, Aniel Guillén Arruebarrena, Greg Balco, David Dethier, and Marc Caffee
Geochronology, 4, 435–453, https://doi.org/10.5194/gchron-4-435-2022, https://doi.org/10.5194/gchron-4-435-2022, 2022
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We used cosmogenic radionuclides in detrital river sediment to measure erosion rates of watersheds in central Cuba; erosion rates are lower than rock dissolution rates in lowland watersheds. Data from two different cosmogenic nuclides suggest that some basins may have a mixed layer deeper than is typically modeled and could have experienced significant burial after or during exposure. We conclude that significant mass loss may occur at depth through chemical weathering processes.
Joanne S. Johnson, Ryan A. Venturelli, Greg Balco, Claire S. Allen, Scott Braddock, Seth Campbell, Brent M. Goehring, Brenda L. Hall, Peter D. Neff, Keir A. Nichols, Dylan H. Rood, Elizabeth R. Thomas, and John Woodward
The Cryosphere, 16, 1543–1562, https://doi.org/10.5194/tc-16-1543-2022, https://doi.org/10.5194/tc-16-1543-2022, 2022
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Recent studies have suggested that some portions of the Antarctic Ice Sheet were less extensive than present in the last few thousand years. We discuss how past ice loss and regrowth during this time would leave its mark on geological and glaciological records and suggest ways in which future studies could detect such changes. Determining timing of ice loss and gain around Antarctica and conditions under which they occurred is critical for preparing for future climate-warming-induced changes.
Jamey Stutz, Andrew Mackintosh, Kevin Norton, Ross Whitmore, Carlo Baroni, Stewart S. R. Jamieson, Richard S. Jones, Greg Balco, Maria Cristina Salvatore, Stefano Casale, Jae Il Lee, Yeong Bae Seong, Robert McKay, Lauren J. Vargo, Daniel Lowry, Perry Spector, Marcus Christl, Susan Ivy Ochs, Luigia Di Nicola, Maria Iarossi, Finlay Stuart, and Tom Woodruff
The Cryosphere, 15, 5447–5471, https://doi.org/10.5194/tc-15-5447-2021, https://doi.org/10.5194/tc-15-5447-2021, 2021
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Understanding the long-term behaviour of ice sheets is essential to projecting future changes due to climate change. In this study, we use rocks deposited along the margin of the David Glacier, one of the largest glacier systems in the world, to reveal a rapid thinning event initiated over 7000 years ago and endured for ~ 2000 years. Using physical models, we show that subglacial topography and ocean heat are important drivers for change along this sector of the Antarctic Ice Sheet.
Allie Balter-Kennedy, Gordon Bromley, Greg Balco, Holly Thomas, and Margaret S. Jackson
The Cryosphere, 14, 2647–2672, https://doi.org/10.5194/tc-14-2647-2020, https://doi.org/10.5194/tc-14-2647-2020, 2020
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We describe new geologic evidence from Antarctica that demonstrates changes in East Antarctic Ice Sheet (EAIS) extent over the past ~ 15 million years. Our data show that the EAIS was a persistent feature in the Transantarctic Mountains for much of that time, including some (but not all) times when global temperature may have been warmer than today. Overall, our results comprise a long-term record of EAIS change and may provide useful constraints for ice sheet models and sea-level estimates.
Greg Balco
Geochronology, 2, 169–175, https://doi.org/10.5194/gchron-2-169-2020, https://doi.org/10.5194/gchron-2-169-2020, 2020
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Geologic dating methods generally do not directly measure ages. Instead, interpreting a geochemical measurement as an age requires a middle layer of calculations and supporting data, and the fact that this layer continually improves is an obstacle to synoptic analysis of geochronological data. This paper describes a prototype data management and analysis system that addresses this obstacle by making the middle-layer calculations transparent and dynamic to the user.
Michal Ben-Israel, Ari Matmon, Alan J. Hidy, Yoav Avni, and Greg Balco
Earth Surf. Dynam., 8, 289–301, https://doi.org/10.5194/esurf-8-289-2020, https://doi.org/10.5194/esurf-8-289-2020, 2020
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Early-to-mid Miocene erosion rates were inferred using cosmogenic 21Ne measured in chert pebbles transported by the Miocene Hazeva River (~ 18 Ma). Miocene erosion rates are faster compared to Quaternary rates in the region. Faster Miocene erosion rates could be due to a response to topographic changes brought on by tectonic uplift, wetter climate in the region during the Miocene, or a combination of both.
Keir A. Nichols, Brent M. Goehring, Greg Balco, Joanne S. Johnson, Andrew S. Hein, and Claire Todd
The Cryosphere, 13, 2935–2951, https://doi.org/10.5194/tc-13-2935-2019, https://doi.org/10.5194/tc-13-2935-2019, 2019
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We studied the history of ice masses at three locations in the Weddell Sea Embayment, Antarctica. We measured rare isotopes in material sourced from mountains overlooking the Slessor Glacier, Foundation Ice Stream, and smaller glaciers on the Lassiter Coast. We show that ice masses were between 385 and 800 m thicker during the last glacial cycle than they are at present. The ice masses were both hundreds of metres thicker and remained thicker closer to the present than was previously thought.
Greg Balco, Kimberly Blisniuk, and Alan Hidy
Geochronology, 1, 1–16, https://doi.org/10.5194/gchron-1-1-2019, https://doi.org/10.5194/gchron-1-1-2019, 2019
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This article applies a new geochemical dating method to determine the age of sedimentary deposits useful in reconstructing slip rates on a major fault system.
Marie Bergelin, Andrew Gorin, Greg Balco, and William Cassata
EGUsphere, https://doi.org/10.5194/egusphere-2025-928, https://doi.org/10.5194/egusphere-2025-928, 2025
This preprint is open for discussion and under review for Geochronology (GChron).
Short summary
Short summary
Helium gas accumulates over time in minerals, but loss can occur depending on temperature. If partially retained, its loss can potentially be used for determining past surface temperatures. This study uses a model that accounts for complex gas loss to analyze helium retention in two minerals commonly found on the surface of Antarctica. We find one of the minerals retains helium while the other loses nearly all of the gas within hundred years, making it unsuitable as a climate reconstruction.
Greg Balco
EGUsphere, https://doi.org/10.5194/egusphere-2025-149, https://doi.org/10.5194/egusphere-2025-149, 2025
Short summary
Short summary
This paper describes measurements of cosmogenic neon-21 concentrations in a widely distributed mineral standard material that is routinely used for quality control and interlaboratory comparison for measurements of other cosmic-ray-produced nuclides useful for various geochronology applications. Broadly, this facilitates improvement of precision and accuracy of these measurements and their applications in geochronology.
Joanne S. Johnson, John Woodward, Ian Nesbitt, Kate Winter, Seth Campbell, Keir A. Nichols, Ryan A. Venturelli, Scott Braddock, Brent M. Goehring, Brenda Hall, Dylan H. Rood, and Greg Balco
The Cryosphere, 19, 303–324, https://doi.org/10.5194/tc-19-303-2025, https://doi.org/10.5194/tc-19-303-2025, 2025
Short summary
Short summary
Determining where and when the Antarctic ice sheet was smaller than present requires recovery and exposure dating of subglacial bedrock. Here we use ice sheet model outputs and field data (geological and glaciological observations, bedrock samples, and ground-penetrating radar) to assess the suitability for subglacial drilling of sites in the Hudson Mountains, West Antarctica. We find that no sites are perfect, but two are feasible, with the most suitable being Winkie Nunatak (74.86°S, 99.77°W).
Gordon R. M. Bromley, Greg Balco, Margaret S. Jackson, Allie Balter-Kennedy, and Holly Thomas
Clim. Past, 21, 145–160, https://doi.org/10.5194/cp-21-145-2025, https://doi.org/10.5194/cp-21-145-2025, 2025
Short summary
Short summary
We constructed a geologic record of East Antarctic Ice Sheet thickness from deposits at Otway Massif to directly assess how Earth's largest ice sheet responds to warmer-than-present climate. Our record confirms the long-term dominance of a cold polar climate but lacks a clear ice sheet response to the mid-Pliocene Warm Period, a common analogue for the future. Instead, an absence of moraines from the late Miocene–early Pliocene suggests the ice sheet was less extensive than present at that time.
Jonathan R. Adams, Dylan H. Rood, Klaus Wilcken, Stephen J. Roberts, and Joanne S. Johnson
Geochronology Discuss., https://doi.org/10.5194/gchron-2024-34, https://doi.org/10.5194/gchron-2024-34, 2024
Preprint under review for GChron
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Ice sheet mass loss is adding to sea-level rise, and is expected to increase, but by how much and how fast remains uncertain. Isotopes produced in rock at the Earth’s surface provide records of past ice sheet thinning which help predict future change but are more effective if they are precise enough to determine past changes to the nearest thousand years. The precision of carbon-14, an isotope which is guaranteed to record past change since the last ice age, can be improved.
Joseph P. Tulenko, Greg Balco, Michael A. Clynne, and L. J. Patrick Muffler
Geochronology, 6, 639–652, https://doi.org/10.5194/gchron-6-639-2024, https://doi.org/10.5194/gchron-6-639-2024, 2024
Short summary
Short summary
Cosmogenic nuclide exposure dating is an exceptional tool for reconstructing glacier histories, but reconstructions based on common target nuclides (e.g., 10Be) can be costly and time-consuming to generate. Here, we present a cost-effective proof-of-concept 21Ne exposure age chronology from Lassen Volcanic National Park, CA, USA, that broadly agrees with nearby 10Be chronologies but at lower precision.
Greg Balco, Andrew J. Conant, Dallas D. Reilly, Dallin Barton, Chelsea D. Willett, and Brett H. Isselhardt
Geochronology, 6, 571–584, https://doi.org/10.5194/gchron-6-571-2024, https://doi.org/10.5194/gchron-6-571-2024, 2024
Short summary
Short summary
This paper describes how krypton isotopes produced by nuclear fission can be used to determine the age of microscopic particles of used nuclear fuel. This is potentially useful for international safeguard applications aimed at tracking and identifying nuclear materials, as well as geoscience applications involving dating post-1950s sediments or understanding environmental transport of nuclear materials.
Nicolas Bakken-French, Stephen J. Boyer, B. Clay Southworth, Megan Thayne, Dylan H. Rood, and Anders E. Carlson
The Cryosphere, 18, 4517–4530, https://doi.org/10.5194/tc-18-4517-2024, https://doi.org/10.5194/tc-18-4517-2024, 2024
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Repeat photography, field mapping, and remote sensing find that glaciers on Mt. Hood, Oregon, have lost about 25 % of their area in the first 2 decades of the 21st century and 17 % of their area in the last 7–8 years. The 21st century recession rate is more than 3 times faster than the 20th century average and 1.9 times faster than the fastest period of retreat within the 20th century. This unprecedented retreat corresponds to regional summer warming of 1.7–1.8°C relative to the early 1900s.
Allie Balter-Kennedy, Joerg M. Schaefer, Greg Balco, Meredith A. Kelly, Michael R. Kaplan, Roseanne Schwartz, Bryan Oakley, Nicolás E. Young, Jean Hanley, and Arianna M. Varuolo-Clarke
Clim. Past, 20, 2167–2190, https://doi.org/10.5194/cp-20-2167-2024, https://doi.org/10.5194/cp-20-2167-2024, 2024
Short summary
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We date sedimentary deposits showing that the southeastern Laurentide Ice Sheet was at or near its southernmost extent from ~ 26 000 to 21 000 years ago, when sea levels were at their lowest, with climate records indicating glacial conditions. Slow deglaciation began ~ 22 000 years ago, shown by a rise in modeled local summer temperatures, but significant deglaciation in the region did not begin until ~ 18 000 years ago, when atmospheric CO2 began to rise, marking the end of the last ice age.
Paul R. Bierman, Andrew J. Christ, Catherine M. Collins, Halley M. Mastro, Juliana Souza, Pierre-Henri Blard, Stefanie Brachfeld, Zoe R. Courville, Tammy M. Rittenour, Elizabeth K. Thomas, Jean-Louis Tison, and François Fripiat
The Cryosphere, 18, 4029–4052, https://doi.org/10.5194/tc-18-4029-2024, https://doi.org/10.5194/tc-18-4029-2024, 2024
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In 1966, the U.S. Army drilled through the Greenland Ice Sheet at Camp Century, Greenland; they recovered 3.44 m of frozen material. Here, we decipher the material’s history. Water, flowing during a warm interglacial when the ice sheet melted from northwest Greenland, deposited the upper material which contains fossil plant and insect parts. The lower material, separated by more than a meter of ice with some sediment, is till, deposited by the ice sheet during a prior cold period.
Christopher Halsted, Paul Bierman, Alexandru Codilean, Lee Corbett, and Marc Caffee
Geochronology Discuss., https://doi.org/10.5194/gchron-2024-22, https://doi.org/10.5194/gchron-2024-22, 2024
Revised manuscript accepted for GChron
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Sediment generation on hillslopes and transport through river networks are complex processes that influence landscape evolution. In this study compiled sand from over 600 river basins and measured its (very subtle) radioactivity to unravel timelines of sediment routing around the world. With this data we empirically confirm that sediment from large lowland basins in tectonically stable regions typically experiences long periods of burial, while sediment moves rapidly through small upland basins.
Marie Bergelin, Greg Balco, Lee B. Corbett, and Paul R. Bierman
Geochronology, 6, 491–502, https://doi.org/10.5194/gchron-6-491-2024, https://doi.org/10.5194/gchron-6-491-2024, 2024
Short summary
Short summary
Cosmogenic nuclides, such as 10Be, are rare isotopes produced in rocks when exposed at Earth's surface and are valuable for understanding surface processes and landscape evolution. However, 10Be is usually measured in quartz minerals. Here we present advances in efficiently extracting and measuring 10Be in the pyroxene mineral. These measurements expand the use of 10Be as a dating tool for new rock types and provide opportunities to understand landscape processes in areas that lack quartz.
Peyton M. Cavnar, Paul R. Bierman, Jeremy D. Shakun, Lee B. Corbett, Danielle LeBlanc, Gillian L. Galford, and Marc Caffee
EGUsphere, https://doi.org/10.5194/egusphere-2024-2233, https://doi.org/10.5194/egusphere-2024-2233, 2024
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To investigate the Laurentide Ice Sheet’s erosivity before and during the Last Glacial Maximum, we sampled sand deposited by ice in eastern Canada before final deglaciation. We also sampled modern river sand. The 26Al and 10Be measured in glacial deposited sediments suggests that ice remained during some Pleistocene warm periods and was an inefficient eroder. Similar concentrations of 26Al and 10Be in modern sand suggests that most modern river sediment is sourced from glacial deposits.
Catherine M. Collins, Nicolas Perdrial, Pierre-Henri Blard, Nynke Keulen, William C. Mahaney, Halley Mastro, Juliana Souza, Donna M. Rizzo, Yves Marrocchi, Paul C. Knutz, and Paul R. Bierman
EGUsphere, https://doi.org/10.5194/egusphere-2024-2194, https://doi.org/10.5194/egusphere-2024-2194, 2024
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The Camp Century sub-glacial core stores information about past climates, glacial and interglacial processes in northwest Greenland. In this study, we investigated the core archive making large scale observations using CT scans and micron scale observation observing physical and chemical characteristics of individual grains. We find evidence of past ice-free conditions, weathering processes during warmer periods, and past glaciations.
Greg Balco, Alan J. Hidy, William T. Struble, and Joshua J. Roering
Geochronology, 6, 71–76, https://doi.org/10.5194/gchron-6-71-2024, https://doi.org/10.5194/gchron-6-71-2024, 2024
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We describe a new method of reconstructing the long-term, pre-observational frequency and/or intensity of wildfires in forested landscapes using trace concentrations of the noble gases helium and neon that are formed in soil mineral grains by cosmic-ray bombardment of the Earth's surface.
Eric W. Portenga, David J. Ullman, Lee B. Corbett, Paul R. Bierman, and Marc W. Caffee
Geochronology, 5, 413–431, https://doi.org/10.5194/gchron-5-413-2023, https://doi.org/10.5194/gchron-5-413-2023, 2023
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New exposure ages of glacial erratics on moraines on Isle Royale – the largest island in North America's Lake Superior – show that the Laurentide Ice Sheet did not retreat from the island nor the south shores of Lake Superior until the early Holocene, which is later than previously thought. These new ages unify regional ice retreat histories from the mainland, the Lake Superior lake-bottom stratigraphy, underwater moraines, and meltwater drainage pathways through the Laurentian Great Lakes.
Benoit S. Lecavalier, Lev Tarasov, Greg Balco, Perry Spector, Claus-Dieter Hillenbrand, Christo Buizert, Catherine Ritz, Marion Leduc-Leballeur, Robert Mulvaney, Pippa L. Whitehouse, Michael J. Bentley, and Jonathan Bamber
Earth Syst. Sci. Data, 15, 3573–3596, https://doi.org/10.5194/essd-15-3573-2023, https://doi.org/10.5194/essd-15-3573-2023, 2023
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The Antarctic Ice Sheet Evolution constraint database version 2 (AntICE2) consists of a large variety of observations that constrain the evolution of the Antarctic Ice Sheet over the last glacial cycle. This includes observations of past ice sheet extent, past ice thickness, past relative sea level, borehole temperature profiles, and present-day bedrock displacement rates. The database is intended to improve our understanding of past Antarctic changes and for ice sheet model calibrations.
Allie Balter-Kennedy, Joerg M. Schaefer, Roseanne Schwartz, Jennifer L. Lamp, Laura Penrose, Jennifer Middleton, Jean Hanley, Bouchaïb Tibari, Pierre-Henri Blard, Gisela Winckler, Alan J. Hidy, and Greg Balco
Geochronology, 5, 301–321, https://doi.org/10.5194/gchron-5-301-2023, https://doi.org/10.5194/gchron-5-301-2023, 2023
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Cosmogenic nuclides like 10Be are rare isotopes created in rocks exposed at the Earth’s surface and can be used to understand glacier histories and landscape evolution. 10Be is usually measured in the mineral quartz. Here, we show that 10Be can be reliably measured in the mineral pyroxene. We use the measurements to determine exposure ages and understand landscape processes in rocks from Antarctica that do not have quartz, expanding the use of this method to new rock types.
Jennifer R. Shadrick, Dylan H. Rood, Martin D. Hurst, Matthew D. Piggott, Klaus M. Wilcken, and Alexander J. Seal
Earth Surf. Dynam., 11, 429–450, https://doi.org/10.5194/esurf-11-429-2023, https://doi.org/10.5194/esurf-11-429-2023, 2023
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This study uses a coastal evolution model to interpret cosmogenic beryllium-10 concentrations and topographic data and, in turn, quantify long-term cliff retreat rates for four chalk sites on the south coast of England. By using a process-based model, clear distinctions between intertidal weathering rates have been recognised between chalk and sandstone rock coast sites, advocating the use of process-based models to interpret the long-term behaviour of rock coasts.
Greg Balco, Nathan Brown, Keir Nichols, Ryan A. Venturelli, Jonathan Adams, Scott Braddock, Seth Campbell, Brent Goehring, Joanne S. Johnson, Dylan H. Rood, Klaus Wilcken, Brenda Hall, and John Woodward
The Cryosphere, 17, 1787–1801, https://doi.org/10.5194/tc-17-1787-2023, https://doi.org/10.5194/tc-17-1787-2023, 2023
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Samples of bedrock recovered from below the West Antarctic Ice Sheet show that part of the ice sheet was thinner several thousand years ago than it is now and subsequently thickened. This is important because of concern that present ice thinning in this region may lead to rapid, irreversible sea level rise. The past episode of thinning at this site that took place in a similar, although not identical, climate was not irreversible; however, reversal required at least 3000 years to complete.
Anna Ruth W. Halberstadt, Greg Balco, Hannah Buchband, and Perry Spector
The Cryosphere, 17, 1623–1643, https://doi.org/10.5194/tc-17-1623-2023, https://doi.org/10.5194/tc-17-1623-2023, 2023
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This paper explores the use of multimillion-year exposure ages from Antarctic bedrock outcrops to benchmark ice sheet model predictions and thereby infer ice sheet sensitivity to warm climates. We describe a new approach for model–data comparison, highlight an example where observational data are used to distinguish end-member models, and provide guidance for targeted sampling around Antarctica that can improve understanding of ice sheet response to climate warming in the past and future.
Jonathan R. Adams, Joanne S. Johnson, Stephen J. Roberts, Philippa J. Mason, Keir A. Nichols, Ryan A. Venturelli, Klaus Wilcken, Greg Balco, Brent Goehring, Brenda Hall, John Woodward, and Dylan H. Rood
The Cryosphere, 16, 4887–4905, https://doi.org/10.5194/tc-16-4887-2022, https://doi.org/10.5194/tc-16-4887-2022, 2022
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Glaciers in West Antarctica are experiencing significant ice loss. Geological data provide historical context for ongoing ice loss in West Antarctica, including constraints on likely future ice sheet behaviour in response to climatic warming. We present evidence from rare isotopes measured in rocks collected from an outcrop next to Pope Glacier. These data suggest that Pope Glacier thinned faster and sooner after the last ice age than previously thought.
Natacha Gribenski, Marissa M. Tremblay, Pierre G. Valla, Greg Balco, Benny Guralnik, and David L. Shuster
Geochronology, 4, 641–663, https://doi.org/10.5194/gchron-4-641-2022, https://doi.org/10.5194/gchron-4-641-2022, 2022
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We apply quartz 3He paleothermometry along two deglaciation profiles in the European Alps to reconstruct temperature evolution since the Last Glacial Maximum. We observe a 3He thermal signal clearly colder than today in all bedrock surface samples exposed prior the Holocene. Current uncertainties in 3He diffusion kinetics do not permit distinguishing if this signal results from Late Pleistocene ambient temperature changes or from recent ground temperature variation due to permafrost degradation.
Adrian M. Bender, Richard O. Lease, Lee B. Corbett, Paul R. Bierman, Marc W. Caffee, James V. Jones, and Doug Kreiner
Earth Surf. Dynam., 10, 1041–1053, https://doi.org/10.5194/esurf-10-1041-2022, https://doi.org/10.5194/esurf-10-1041-2022, 2022
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To understand landscape evolution in the mineral resource-rich Yukon River basin (Alaska and Canada), we mapped and cosmogenic isotope-dated river terraces along the Charley River. Results imply widespread Yukon River incision that drove increased Bering Sea sedimentation and carbon sequestration during global climate changes 2.6 and 1 million years ago. Such erosion may have fed back to late Cenozoic climate change by reducing atmospheric carbon as observed in many records worldwide.
Marie Bergelin, Jaakko Putkonen, Greg Balco, Daniel Morgan, Lee B. Corbett, and Paul R. Bierman
The Cryosphere, 16, 2793–2817, https://doi.org/10.5194/tc-16-2793-2022, https://doi.org/10.5194/tc-16-2793-2022, 2022
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Glacier ice contains information on past climate and can help us understand how the world changes through time. We have found and sampled a buried ice mass in Antarctica that is much older than most ice on Earth and difficult to date. Therefore, we developed a new dating application which showed the ice to be 3 million years old. Our new dating solution will potentially help to date other ancient ice masses since such old glacial ice could yield data on past environmental conditions on Earth.
Mae Kate Campbell, Paul R. Bierman, Amanda H. Schmidt, Rita Sibello Hernández, Alejandro García-Moya, Lee B. Corbett, Alan J. Hidy, Héctor Cartas Águila, Aniel Guillén Arruebarrena, Greg Balco, David Dethier, and Marc Caffee
Geochronology, 4, 435–453, https://doi.org/10.5194/gchron-4-435-2022, https://doi.org/10.5194/gchron-4-435-2022, 2022
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We used cosmogenic radionuclides in detrital river sediment to measure erosion rates of watersheds in central Cuba; erosion rates are lower than rock dissolution rates in lowland watersheds. Data from two different cosmogenic nuclides suggest that some basins may have a mixed layer deeper than is typically modeled and could have experienced significant burial after or during exposure. We conclude that significant mass loss may occur at depth through chemical weathering processes.
Klaus M. Wilcken, Alexandru T. Codilean, Réka-H. Fülöp, Steven Kotevski, Anna H. Rood, Dylan H. Rood, Alexander J. Seal, and Krista Simon
Geochronology, 4, 339–352, https://doi.org/10.5194/gchron-4-339-2022, https://doi.org/10.5194/gchron-4-339-2022, 2022
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Cosmogenic nuclides are now widely applied in the Earth sciences; however, more recent applications often push the analytical limits of the technique. Our study presents a comprehensive method for analysis of cosmogenic 10Be and 26Al samples down to isotope concentrations of a few thousand atoms per gram of sample, which opens the door to new and more varied applications of cosmogenic nuclide analysis.
Joanne S. Johnson, Ryan A. Venturelli, Greg Balco, Claire S. Allen, Scott Braddock, Seth Campbell, Brent M. Goehring, Brenda L. Hall, Peter D. Neff, Keir A. Nichols, Dylan H. Rood, Elizabeth R. Thomas, and John Woodward
The Cryosphere, 16, 1543–1562, https://doi.org/10.5194/tc-16-1543-2022, https://doi.org/10.5194/tc-16-1543-2022, 2022
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Recent studies have suggested that some portions of the Antarctic Ice Sheet were less extensive than present in the last few thousand years. We discuss how past ice loss and regrowth during this time would leave its mark on geological and glaciological records and suggest ways in which future studies could detect such changes. Determining timing of ice loss and gain around Antarctica and conditions under which they occurred is critical for preparing for future climate-warming-induced changes.
Leah A. VanLandingham, Eric W. Portenga, Edward C. Lefroy, Amanda H. Schmidt, Paul R. Bierman, and Alan J. Hidy
Geochronology, 4, 153–176, https://doi.org/10.5194/gchron-4-153-2022, https://doi.org/10.5194/gchron-4-153-2022, 2022
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This study presents erosion rates of the George River and seven of its tributaries in northeast Tasmania, Australia. These erosion rates are the first measures of landscape change over millennial timescales for Tasmania. We demonstrate that erosion is closely linked to a topographic rainfall gradient across George River. Our findings may be useful for efforts to restore ecological health to Georges Bay by determining a pre-disturbance level of erosion and sediment delivery to this estuary.
Jamey Stutz, Andrew Mackintosh, Kevin Norton, Ross Whitmore, Carlo Baroni, Stewart S. R. Jamieson, Richard S. Jones, Greg Balco, Maria Cristina Salvatore, Stefano Casale, Jae Il Lee, Yeong Bae Seong, Robert McKay, Lauren J. Vargo, Daniel Lowry, Perry Spector, Marcus Christl, Susan Ivy Ochs, Luigia Di Nicola, Maria Iarossi, Finlay Stuart, and Tom Woodruff
The Cryosphere, 15, 5447–5471, https://doi.org/10.5194/tc-15-5447-2021, https://doi.org/10.5194/tc-15-5447-2021, 2021
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Understanding the long-term behaviour of ice sheets is essential to projecting future changes due to climate change. In this study, we use rocks deposited along the margin of the David Glacier, one of the largest glacier systems in the world, to reveal a rapid thinning event initiated over 7000 years ago and endured for ~ 2000 years. Using physical models, we show that subglacial topography and ocean heat are important drivers for change along this sector of the Antarctic Ice Sheet.
Jennifer R. Shadrick, Martin D. Hurst, Matthew D. Piggott, Bethany G. Hebditch, Alexander J. Seal, Klaus M. Wilcken, and Dylan H. Rood
Earth Surf. Dynam., 9, 1505–1529, https://doi.org/10.5194/esurf-9-1505-2021, https://doi.org/10.5194/esurf-9-1505-2021, 2021
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Here we use topographic and 10Be concentration data to optimise a coastal evolution model. Cliff retreat rates are calculated for two UK sites for the past 8000 years and, for the first time, highlight a strong link between the rate of sea level rise and long-term cliff retreat rates. This method enables us to study past cliff response to sea level rise and so to greatly improve forecasts of future responses to accelerations in sea level rise that will result from climate change.
Andrew J. Christ, Paul R. Bierman, Jennifer L. Lamp, Joerg M. Schaefer, and Gisela Winckler
Geochronology, 3, 505–523, https://doi.org/10.5194/gchron-3-505-2021, https://doi.org/10.5194/gchron-3-505-2021, 2021
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Cosmogenic nuclide surface exposure dating is commonly used to constrain the timing of past glacier extents. However, Antarctic exposure age datasets are often scattered and difficult to interpret. We compile new and existing exposure ages of a glacial deposit with independently known age constraints and identify surface processes that increase or reduce the likelihood of exposure age scatter. Then we present new data for a previously unmapped and undated older deposit from the same region.
Melisa A. Diaz, Lee B. Corbett, Paul R. Bierman, Byron J. Adams, Diana H. Wall, Ian D. Hogg, Noah Fierer, and W. Berry Lyons
Earth Surf. Dynam., 9, 1363–1380, https://doi.org/10.5194/esurf-9-1363-2021, https://doi.org/10.5194/esurf-9-1363-2021, 2021
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We collected soil surface samples and depth profiles every 5 cm (up to 30 cm) from 11 ice-free areas along the Shackleton Glacier, a major outlet glacier of the East Antarctic Ice Sheet (EAIS), and measured meteoric beryllium-10 and nitrate concentrations to understand the relationship between salts and beryllium-10. This relationship can help inform wetting history, landscape disturbance, and exposure duration.
Allie Balter-Kennedy, Gordon Bromley, Greg Balco, Holly Thomas, and Margaret S. Jackson
The Cryosphere, 14, 2647–2672, https://doi.org/10.5194/tc-14-2647-2020, https://doi.org/10.5194/tc-14-2647-2020, 2020
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We describe new geologic evidence from Antarctica that demonstrates changes in East Antarctic Ice Sheet (EAIS) extent over the past ~ 15 million years. Our data show that the EAIS was a persistent feature in the Transantarctic Mountains for much of that time, including some (but not all) times when global temperature may have been warmer than today. Overall, our results comprise a long-term record of EAIS change and may provide useful constraints for ice sheet models and sea-level estimates.
Greg Balco
Geochronology, 2, 169–175, https://doi.org/10.5194/gchron-2-169-2020, https://doi.org/10.5194/gchron-2-169-2020, 2020
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Geologic dating methods generally do not directly measure ages. Instead, interpreting a geochemical measurement as an age requires a middle layer of calculations and supporting data, and the fact that this layer continually improves is an obstacle to synoptic analysis of geochronological data. This paper describes a prototype data management and analysis system that addresses this obstacle by making the middle-layer calculations transparent and dynamic to the user.
Michal Ben-Israel, Ari Matmon, Alan J. Hidy, Yoav Avni, and Greg Balco
Earth Surf. Dynam., 8, 289–301, https://doi.org/10.5194/esurf-8-289-2020, https://doi.org/10.5194/esurf-8-289-2020, 2020
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Early-to-mid Miocene erosion rates were inferred using cosmogenic 21Ne measured in chert pebbles transported by the Miocene Hazeva River (~ 18 Ma). Miocene erosion rates are faster compared to Quaternary rates in the region. Faster Miocene erosion rates could be due to a response to topographic changes brought on by tectonic uplift, wetter climate in the region during the Miocene, or a combination of both.
Hannah S. Weiss, Paul R. Bierman, Yves Dubief, and Scott D. Hamshaw
The Cryosphere, 13, 3367–3382, https://doi.org/10.5194/tc-13-3367-2019, https://doi.org/10.5194/tc-13-3367-2019, 2019
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Climate change is devastating winter tourism. High-elevation, high-latitude ski centers have turned to saving snow over the summer. We present results of two field seasons to test and optimize over-summer snow storage at a midlatitude, low-elevation nordic ski center in the northeastern USA. In 2018, we tested coverings and found success overlaying 20 cm of wet woodchips with a reflective sheet. In 2019, we employed this strategy to a large pile and stored sufficient snow to open the ski season.
Keir A. Nichols, Brent M. Goehring, Greg Balco, Joanne S. Johnson, Andrew S. Hein, and Claire Todd
The Cryosphere, 13, 2935–2951, https://doi.org/10.5194/tc-13-2935-2019, https://doi.org/10.5194/tc-13-2935-2019, 2019
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We studied the history of ice masses at three locations in the Weddell Sea Embayment, Antarctica. We measured rare isotopes in material sourced from mountains overlooking the Slessor Glacier, Foundation Ice Stream, and smaller glaciers on the Lassiter Coast. We show that ice masses were between 385 and 800 m thicker during the last glacial cycle than they are at present. The ice masses were both hundreds of metres thicker and remained thicker closer to the present than was previously thought.
Greg Balco, Kimberly Blisniuk, and Alan Hidy
Geochronology, 1, 1–16, https://doi.org/10.5194/gchron-1-1-2019, https://doi.org/10.5194/gchron-1-1-2019, 2019
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This article applies a new geochemical dating method to determine the age of sedimentary deposits useful in reconstructing slip rates on a major fault system.
Martin D. Hurst, Dylan H. Rood, and Michael A. Ellis
Earth Surf. Dynam., 5, 67–84, https://doi.org/10.5194/esurf-5-67-2017, https://doi.org/10.5194/esurf-5-67-2017, 2017
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Beryllium-10 is a rare isotope that only forms near to the Earth surface, allowing rock surfaces to be dated. In this paper we develop a numerical model for the evolution of shore platforms and associated 10Be concentrations to explore the potential for this method to reveal long-term rates of sea cliff retreat. Tides, sea level, cliffs and beaches all modify how rapidly 10Be accumulates on the shore platform, but there is great potential to measure rates of cliff retreat and platform erosion.
Amanda H. Schmidt, Thomas B. Neilson, Paul R. Bierman, Dylan H. Rood, William B. Ouimet, and Veronica Sosa Gonzalez
Earth Surf. Dynam., 4, 819–830, https://doi.org/10.5194/esurf-4-819-2016, https://doi.org/10.5194/esurf-4-819-2016, 2016
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In order to test the assumption that erosion rates derived from Be-10 are not affected by increases in erosion due to contemporary agricultural land use, we measured erosion rates in three tributaries of the Mekong River. We find that in the most heavily agricultural landscapes, the apparent long-term erosion rate correlates best with measures of modern land use, suggesting that agriculture has eroded below the mixed layer and is affecting apparent erosion rates derived from Be-10.
Related subject area
Other
Krypton-85 chronometry of spent nuclear fuel
Comparison of basin-scale in situ and meteoric 10Be erosion and denudation rates in felsic lithologies across an elevation gradient at the George River, northeast Tasmania, Australia
A 62 kyr geomagnetic palaeointensity record from the Taymyr Peninsula, Russian Arctic
Greg Balco, Andrew J. Conant, Dallas D. Reilly, Dallin Barton, Chelsea D. Willett, and Brett H. Isselhardt
Geochronology, 6, 571–584, https://doi.org/10.5194/gchron-6-571-2024, https://doi.org/10.5194/gchron-6-571-2024, 2024
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This paper describes how krypton isotopes produced by nuclear fission can be used to determine the age of microscopic particles of used nuclear fuel. This is potentially useful for international safeguard applications aimed at tracking and identifying nuclear materials, as well as geoscience applications involving dating post-1950s sediments or understanding environmental transport of nuclear materials.
Leah A. VanLandingham, Eric W. Portenga, Edward C. Lefroy, Amanda H. Schmidt, Paul R. Bierman, and Alan J. Hidy
Geochronology, 4, 153–176, https://doi.org/10.5194/gchron-4-153-2022, https://doi.org/10.5194/gchron-4-153-2022, 2022
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This study presents erosion rates of the George River and seven of its tributaries in northeast Tasmania, Australia. These erosion rates are the first measures of landscape change over millennial timescales for Tasmania. We demonstrate that erosion is closely linked to a topographic rainfall gradient across George River. Our findings may be useful for efforts to restore ecological health to Georges Bay by determining a pre-disturbance level of erosion and sediment delivery to this estuary.
Stephanie Scheidt, Matthias Lenz, Ramon Egli, Dominik Brill, Martin Klug, Karl Fabian, Marlene M. Lenz, Raphael Gromig, Janet Rethemeyer, Bernd Wagner, Grigory Federov, and Martin Melles
Geochronology, 4, 87–107, https://doi.org/10.5194/gchron-4-87-2022, https://doi.org/10.5194/gchron-4-87-2022, 2022
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Levinson-Lessing Lake in northern central Siberia provides an exceptional opportunity to study the evolution of the Earth's magnetic field in the Arctic. This is the first study carried out at the lake that focus on the palaeomagnetic record. It presents the relative palaeointensity and palaeosecular variation of the upper 38 m of sediment core Co1401, spanning ~62 kyr. A comparable high-resolution record of this time does not exist in the Eurasian Arctic.
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Short summary
The North American Varve Chronology (NAVC) is a sequence of 5659 annual sedimentary layers that were deposited in proglacial lakes adjacent to the retreating Laurentide Ice Sheet ca. 12 500–18 200 years ago. We attempt to synchronize this record with Greenland ice core and other climate records that cover the same time period by detecting variations in global fallout of atmospherically produced beryllium-10 in NAVC sediments.
The North American Varve Chronology (NAVC) is a sequence of 5659 annual sedimentary layers that...
