| 1. |
- Codilean, A. T., et al.
(författare)
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OCTOPUS database (v.2)
- 2022
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 14:8, s. 3695-3713
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Tidskriftsartikel (refereegranskat)abstract
- OCTOPUS v.2 is an Open Geospatial Consortium (OGC) compliant web-enabled database that allows users to visualise, query, and download cosmogenic radionuclide, luminescence, and radiocarbon ages and denudation rates associated with erosional landscapes, Quaternary depositional landforms, and archaeological records, along with ancillary geospatial (vector and raster) data layers. The database follows the FAIR (Findability, Accessibility, Interoperability, and Reuse) data principles and is based on open-source software deployed on the Google Cloud Platform. Data stored in the database can be accessed via a custom-built web interface and via desktop geographic information system (GIS) applications that support OGC data access protocols. OCTOPUS v.2 hosts five major data collections. CRN Denudation and ExpAge consist of published cosmogenic Be-10 and Al-26 measurements in modern fluvial sediment and glacial samples respectively. Both collections have a global extent; however, in addition to geospatial vector layers, CRN Denudation also incorporates raster layers, including a digital elevation model, gradient raster, flow direction and flow accumulation rasters, atmospheric pressure raster, and CRN production scaling and topographic shielding factor rasters. SahulSed consists of published optically stimulated luminescence (OSL) and thermoluminescence (TL) ages for fluvial, aeolian, and lacustrine sedimentary records across the Australian mainland and Tasmania. SahulArch consists of published OSL, TL, and radiocarbon ages for archaeological records, and FosSahul consists of published late-Quaternary records of direct and indirect non-human vertebrate (mega)fauna fossil ages that have been systematically quality rated. Supporting data are comprehensive and include bibliographic, contextual, and sample-preparation- and measurement-related information. In the case of cosmogenic radionuclide data, OCTOPUS also includes all necessary information and input files for the recalculation of denudation rates using the open-source program CAIRN. OCTOPUS v.2 and its associated data curation framework allow for valuable legacy data to be harnessed that would otherwise be lost to the research community. The database can be accessed at https://octopusdata.org (last access: 1 July 2022). The individual data collections can also be accessed via their respective digital object identifiers (DOIs) (see Table 1).
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| 2. |
- Dalton, April S., et al.
(författare)
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Deglaciation of the north American ice sheet complex in calendar years based on a comprehensive database of chronological data: NADI-1
- 2023
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Ingår i: QUATERNARY SCIENCE REVIEWS. - 0277-3791 .- 1873-457X. ; 321
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Tidskriftsartikel (refereegranskat)abstract
- The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of Be-10, 459 measurements of Al-26 and 35 measurements of Cl-36 from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly 'unzipping' of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km(2). All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
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| 3. |
- Hall, Adrian M., et al.
(författare)
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Glacial ripping: geomorphological evidence from Sweden for a new process of glacial erosion
- 2020
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Ingår i: Geografiska Annaler Series a-Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 2:4, s. 333-53
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Tidskriftsartikel (refereegranskat)abstract
- In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultantboulder spreadsare covers of large, angular boulders, many with glacial transport distances of 1-100 m. Boulder spreads occur alongside partly disintegrated roches moutonnees and associated fracture caves, and are associated withdisrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1-4 m. This compares with 0.6-1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Henceglacial rippingis a highly effective process of glacial erosion.
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| 4. |
- Moon, S., et al.
(författare)
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Present-Day Stress Field Influences Bedrock Fracture Openness Deep Into the Subsurface
- 2020
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:23
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Tidskriftsartikel (refereegranskat)abstract
- Fracturing of bedrock promotes water-rock interactions and influences the formation of the life-sustaining layer of soil at Earth's surface. Models predict that present-day stress fields should influence bedrock fracture openness, but testing this prediction has proven difficult because comprehensive fracture data sets are rarely available. We model the three-dimensional present-day stress field beneath the deglaciated, low-relief landscape of Forsmark, Sweden. We account for ambient regional stresses, pore pressure, topography, sediment weight, and seawater loading. We then compare the modeled stresses to a data set of similar to 50,000 fractures reaching depths of 600 m at Forsmark. We show that modeled failure proxies correlate strongly with the fraction of observed open fractures to depths of similar to 500 m. This result implies that the present-day regional stress field, affected by surface conditions and pore pressure, influences fracture openness in bedrock hundreds of meters beneath the surface, thereby preparing the rock for further weathering. Plain Language Summary The "critical zone"-the life-sustaining part of the Earth that extends from the top of the tree canopy to the bottom of permeable bedrock-is essential for ecosystems and agriculture. The opening of bedrock fractures and onset of water-rock interaction are crucial to the formation of the critical zone. Within the bedrock, the intensities of horizontal regional forces and vertical gravitational forces typically increase with depth. These force intensities, or stresses, are modified by surface effects associated with topography, the weight of overlying seawater and sediment, and by groundwater pressure. However, the influence of these surface effects on fractures has been difficult to observe because comprehensive fracture data sets are rare. In this study, we examine whether, and to what depths, bedrock may fracture under the influence of stress associated with surficial conditions. We compare bedrock stress calculations with similar to 50,000 fractures from 18 cores reaching depths of 600 m at Forsmark, Sweden. We find that the present-day stress field influences the opening of fractures to depths of 500 m, contributing to the formation of the critical zone and the preparation of rock for weathering hundreds of meters beneath the surface, much deeper than previously thought.
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| 5. |
- Moon, Seulgi, et al.
(författare)
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Present-Day Stress Field Influences Bedrock Fracture Openness Deep Into the Subsurface
- 2020
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:23
-
Tidskriftsartikel (refereegranskat)abstract
- Fracturing of bedrock promotes water-rock interactions and influences the formation of the life-sustaining layer of soil at Earth's surface. Models predict that present-day stress fields should influence bedrock fracture openness, but testing this prediction has proven difficult because comprehensive fracture data sets are rarely available. We model the three-dimensional present-day stress field beneath the deglaciated, low-relief landscape of Forsmark, Sweden. We account for ambient regional stresses, pore pressure, topography, sediment weight, and seawater loading. We then compare the modeled stresses to a data set of similar to 50,000 fractures reaching depths of 600 m at Forsmark. We show that modeled failure proxies correlate strongly with the fraction of observed open fractures to depths of similar to 500 m. This result implies that the present-day regional stress field, affected by surface conditions and pore pressure, influences fracture openness in bedrock hundreds of meters beneath the surface, thereby preparing the rock for further weathering. Plain Language Summary The "critical zone"-the life-sustaining part of the Earth that extends from the top of the tree canopy to the bottom of permeable bedrock-is essential for ecosystems and agriculture. The opening of bedrock fractures and onset of water-rock interaction are crucial to the formation of the critical zone. Within the bedrock, the intensities of horizontal regional forces and vertical gravitational forces typically increase with depth. These force intensities, or stresses, are modified by surface effects associated with topography, the weight of overlying seawater and sediment, and by groundwater pressure. However, the influence of these surface effects on fractures has been difficult to observe because comprehensive fracture data sets are rare. In this study, we examine whether, and to what depths, bedrock may fracture under the influence of stress associated with surficial conditions. We compare bedrock stress calculations with similar to 50,000 fractures from 18 cores reaching depths of 600 m at Forsmark, Sweden. We find that the present-day stress field influences the opening of fractures to depths of 500 m, contributing to the formation of the critical zone and the preparation of rock for weathering hundreds of meters beneath the surface, much deeper than previously thought.
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| 6. |
- Patton, H., et al.
(författare)
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The extreme yet transient nature of glacial erosion
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet—the third largest Quaternary ice mass that spanned 49°Nto82°N—to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatialandtemporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a−1 and anetvolume equating to ~130,000 km3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion—critically modulated by transient ice-sheet dynamics—with its capacity to impart a profound but piecemeal geological legacy across mid- and highlatitudes.
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| 7. |
- Ye, S., et al.
(författare)
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A quantitative assessment of snow shielding effects on surface exposure dating from a western North American Be-10 data compilation
- 2023
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- To better assess the spatiotemporal variations of the snow shielding effect on surface exposure dating, we compiled a dataset of 1341 Be-10 ages from alpine moraines and glacially eroded valleys across western North America, and conducted a sensitivity test with both modern and time-integrated snow data covering the same region. Our analyses reveal significant differences in snow shielding both across our geographic domain and through time. In our time-integrated experiments we find snow-based exposure age corrections as low as 3.5% in the Great Basin region and high as 28.4% in the Pacific Northwest for samples dating to the Last Glacial Maximum (LGM) when no wind-sweeping is assumed. As demonstrated with our time-varying snow conditions with a global climate model and a positive degree day model, modern snow conditions across western North America cannot account for the varying snow patterns under large scale climate shifts since the LGM. The snowbased exposure age corrections from the modern data differ from those calculated by our time-varying model by up to 17% across our model domain. In addition, we find that the Be-10 ages calculated under two end-member scenarios regarding wind-sweeping effects, specifically whether boulders were shielded only when the total snow accumulation exceeded boulder heights or were always shielded when the snow was present, can differ by similar to 7.6% on average for LGM aged samples. Our analyses provide a model-based estimates of the spatiotemporal variability and complexity of snow shielding effects on surface exposure dates across western North America and highlight the need to consider snow depth variations both spatially and temporally when conducting surface exposure dating in terrains where snowfall accumulation is significant.
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