scholarly journals Supplemental Material: Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

2020 ◽  
Author(s):  
Perry Spector ◽  
Greg Balco
Keyword(s):  
Polar Desert ◽  
Exposure Age ◽  
Exposure Ages ◽  
Desert Climate

Table S1 (sample and exposure-age information for all samples in the ICE-D:ANTARCTICA database that have Miocene apparent exposure ages).<br>

scholarly journals Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 91-95
Author(s):  
Perry Spector ◽  
Greg Balco
Keyword(s):  
Liquid Water ◽  
High Elevation ◽  
Polar Desert ◽  
Cosmogenic Nuclide ◽  
Erosion Processes ◽  
Exposure Age ◽  
Antarctic Continent ◽  
The Antarctic ◽  
Exposure Ages ◽  
Desert Climate

Abstract High-elevation rock surfaces in Antarctica have some of the oldest cosmogenic-nuclide exposure ages on Earth, dating back to the Miocene. A compilation of all available 3He, 10Be, and 21Ne exposure-age data from the Antarctic continent shows that exposure histories recorded by these surfaces extend back to, but not before, the mid-Miocene cooling at 14–15 Ma. At high elevation, this cooling entailed a transition between a climate in which liquid water and biota were present and could contribute to surface weathering and erosion, and a polar desert climate in which virtually all weathering and erosion processes had been shut off. This climate appears to have continued uninterrupted between the mid-Miocene and the present.

scholarly journals Supplemental Material: Exposure-age data from across Antarctica reveal mid-Miocene establishment of polar desert climate

2020 ◽  
Author(s):  
Perry Spector ◽  
Greg Balco
Keyword(s):  
Polar Desert ◽  
Exposure Age ◽  
Exposure Ages ◽  
Desert Climate

Table S1 (sample and exposure-age information for all samples in the ICE-D:ANTARCTICA database that have Miocene apparent exposure ages).<br>

Palaeoclimatic and morphodynamic implications of Holocene boulder-dominated periglacial and paraglacial landforms in Rondane, South Norway

2021 ◽  
Author(s):  
Philipp Marr ◽  
Stefan Winkler ◽  
Svein Olaf Dahl ◽  
Jörg Löffler
Keyword(s):  
Slope Failure ◽  
Rock Slope ◽  
Control Point ◽  
Alluvial Fan ◽  
Age Dating ◽  
The Holocene ◽  
Holocene Thermal Maximum ◽  
Exposure Age ◽  
Thermal Maximum ◽  
Exposure Ages

&lt;p&gt;Periglacial, paraglacial and related boulder-dominated landforms constitute a valuable, but often unexplored source of palaeoclimatic and morphodynamic information. The timing of landform formation and stabilization can be linked to past cold climatic conditions which offers the possibility to reconstruct cold climatic periods. In this study, Schmidt-hammer exposure-age dating (SHD) was applied to a variety of boulder-dominated landforms (sorted stripes, blockfield, paraglacial alluvial fan, rock-slope failure) in Rondane, eastern South Norway for the first time. On the basis of an old and young control point a local calibration curve was established from which surface exposure ages of each landform were calculated. The investigation of formation, stabilization and age of the respective landforms permitted an assessment of Holocene climate variability in Rondane and its connectivity to landform evolution. The obtained SHD age estimates range from 11.15 &amp;#177; 1.22 to 3.99 &amp;#177; 1.52 ka which shows their general inactive and relict character. Most surface exposure ages of the sorted stripes cluster between 9.62 &amp;#177; 1.36 and 9.01 &amp;#177; 1.21 ka and appear to have stabilized towards the end of the &amp;#8216;Erdalen Event&amp;#8217; or in the following warm period prior to &amp;#8216;Finse Event&amp;#8217;. The blockfield age with 8.40 &amp;#177; 1.16 ka indicates landform stabilization during &amp;#8216;Finse Event&amp;#8217;, around the onset of the Holocene Thermal Maximum (~8.0&amp;#8211;5.0 ka). The paraglacial alluvial fan with its four subsites shows age ranges from 8.51 &amp;#177; 1.63 to 3.99 &amp;#177; 1.52 ka. The old exposure age points to fan aggradation follow regional deglaciation due to paraglacial processes, whereas the younger ages can be explained by increasing precipitation during the onset neoglaciation at ~4.0 ka. Surface exposure age of the rock-slope failure with 7.39 &amp;#177; 0.74 ka falls into a transitional climate period towards the Holocene Thermal Maximum (~8.0&amp;#8211;5.0 ka). This indicates that climate-driven factors such as decreasing permafrost depth and/or increasing hydrological pressure negatively influence slope stability. Our obtained first surface exposure ages from boulder-dominated landforms in Rondane give important insights to better understand the palaeoclimatic variability in the Holocene.&lt;/p&gt;

scholarly journals Cosmic Ray Exposure Age Determinations of Cosmic Spherules from Marine Sediments

1985 ◽  
Vol 85 ◽  
pp. 179-181
Author(s):  
Kazuo Yamakoshi
Keyword(s):  
Mass Spectrometry ◽  
Cosmic Ray ◽  
High Energy ◽  
High Energy Accelerator ◽  
Exposure Age ◽  
Cosmic Spherules ◽  
Inner Region ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Age ◽  
Cosmic Ray Exposure Ages

AbstractThe cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.

Late Pleistocene Cosmogenic 36Cl Glacial Chronology of the Southwestern Ahklun Mountains, Alaska

2001 ◽  
Vol 56 (2) ◽  
pp. 148-154 ◽  
Author(s):  
Jason P. Briner ◽  
Terry W. Swanson ◽  
Marc Caffee
Keyword(s):  
Late Pleistocene ◽  
Outlet Glacier ◽  
Ice Volume ◽  
Ice Cap ◽  
Global Ice Volume ◽  
Exposure Age ◽  
Alpine Glaciers ◽  
Glacial Chronology ◽  
Glacier Advance ◽  
Exposure Ages

AbstractThirty-two cosmogenic 36Cl surface exposure ages constrain the timing of two late Pleistocene glacial advances in the western Ahklun Mountains, southwestern Alaska. Boulders were sampled from one early Wisconsin (sensu lato) and six late Wisconsin moraines deposited by ice-cap outlet glaciers and local alpine glaciers. Four moraine boulders deposited during an extensive early Wisconsin ice-cap outlet glacier advance have a mean surface exposure age of 60,300±3200 yr. A moraine deposited by an ice-cap outlet glacier during the restricted late Wisconsin advance has a mean surface exposure age of 19,600±1400 yr. Five moraines deposited by late Wisconsin alpine glaciers have mean ages that range between 30,000 and 17,000 yr. The 36Cl ages are consistent with limiting 14C and thermoluminescence ages from related deposits and indicate that Ahklun Mountains glaciers reached their most extensive position of the last glaciation early during the late Pleistocene, in contrast to the deep-sea isotopic record of global ice volume.1

scholarly journals 3. Fragmentation of Asteroids and Delivery of Fragments to Earth

1977 ◽  
Vol 39 ◽  
pp. 283-291 ◽  
Author(s):  
G. W. Wetherill
Keyword(s):  
Cosmic Ray ◽  
Asteroid Belt ◽  
Combined Effects ◽  
Iron Meteorites ◽  
Exposure Age ◽  
Impact Rate ◽  
Dynamical Time ◽  
Spectrophotometric Data ◽  
Exposure Ages ◽  
Cosmic Ray Exposure Ages

Earth-impacting meteoroids are derived from both comets and asteroids, and some uncertainty still exists regarding with which of these bodies some stone meteorites should be identified. In contrast, the long cosmic ray exposure ages of iron meteorites strongly suggest a long-lived asteroidal source capable of providing ~108 g/yr of this material to the earth’s surface over at least much of solar system history. Spectrophotometric data show that differentiated asteroids are concentrated in the inner portion of the asteroid belt. The orbital histories of fragments of inner belt asteroids are investigated, considering the combined effects of close planetary encounters, secular perturbations, and secular resonances. Particular attention is given to the low inclination (<15°) objects with small semimajcr axis (2.1 to 2.6 A.U.), which can make fairly close approaches to Mars (<0.1 A.U.). It is found that the annual yield and dynamical lifetime of collision fragments of these asteroids is in agreement with the observed impact rate and exposure age of iron meteorites. A smaller yield of stone meteorites (-107 g/yr) is expected, because elimination of these objects by collision is probable on the long dynamical time scaTe. Achondrites could be produced in this way; the yield is probably too low to account for chondrites. Chondrites could possibly be derived indirectly from these bodies insofar as these asteroids are also sources of Apollo and Amor objects.

Das Strahlungsalter der Eisenmeteorite aus Chlor-36-Messungen

1961 ◽  
Vol 16 (4) ◽  
pp. 379-384 ◽  
Author(s):  
Else Vilcsek ◽  
H. Wanke
Keyword(s):  
Cosmic Ray ◽  
Decay Rates ◽  
Sikhote Alin ◽  
Iron Meteorites ◽  
Exposure Age ◽  
Exposure Ages ◽  
Chlorine 36

Chlorine 36, which is produced by the interaction of cosmic ray particles with nuclei in meteorites, was measured in seven iron meteorites and in one stone meteorite. The decay rates for chlorine-36 in iron meteorites varied between 6.5 and 20.2 dpm/kg. From these and from the concentration of stable spallation products, the exposure ages of these meteorites were calculated. In this way we found for six of the meteorites examined exposure ages close to 500 million years. Only for the Sikhote Alin meteorite the quite different exposure age of 60 million years was measured. As this value is also definitely lower than that found by other authors for this meteorite, it is suggested that the Sikhote Alin had been part of a bigger meteorite which was broken into pieces about 60 million years ago by a collision with another meteorite.

scholarly journals Rapid thinning of the Welsh Ice Cap at 20–19 ka Based on 10Be Ages

2016 ◽  
Vol 85 (1) ◽  
pp. 107-117 ◽  
Author(s):  
Philip D. Hughes ◽  
Neil F. Glasser ◽  
David Fink
Keyword(s):  
Arithmetic Mean ◽  
Last Deglaciation ◽  
Mountain Areas ◽  
Ice Cap ◽  
Ice Surface ◽  
Exposure Age ◽  
Vertical Range ◽  
North Wales ◽  
Complete Dataset ◽  
Exposure Ages

New 10Be ages from the summits of three mountain areas of North Wales reveal a very similar exposure timing as the Welsh Ice Cap thinned after the global Last Glacial Maximum. Eight bedrock and one boulder sample gave a combined arithmetic mean exposure age of 19.08 ± 0.80 ka (4.2%, 1σ). Similar exposure ages over a 320 m vertical range (824 to 581 m altitude) show that ice cap thinning was very rapid and spatially uniform. Using the same production rate and scaling scheme, we recalculated six published 10Be exposure ages from the nearby Arans, which also covered a similar elevation range from 608 to 901 m and obtained an arithmetic mean of 19.41 ± 1.45 ka (7.5%, 1σ). The average exposure age of all 15 accepted deglaciation ages is 19.21 ± 1.07 (5.6%, 1σ). The complete dataset from North Wales provides very strong evidence indicating that these summits became exposed as nunataks at 20–19 ka. This result provides important insight to the magnitude of ice surface lowering and behavior of the Welsh Ice Cap during the last deglaciation that can be compared to other ice masses that made up the British-Irish Ice Sheet.

Cosmogenic nuclide exposure age constraints on the glacial history of the Lake Wellman area, Darwin Mountains, Antarctica

2010 ◽  
Vol 22 (6) ◽  
pp. 603-618 ◽  
Author(s):  
B.C. Storey ◽  
D. Fink ◽  
D. Hood ◽  
K. Joy ◽  
J. Shulmeister ◽  
...  
Keyword(s):  
Ross Ice Shelf ◽  
Ice Volume ◽  
Model Interpretation ◽  
Ice Surface ◽  
Exposure Age ◽  
Glacier Ice ◽  
History Of ◽  
Age Model ◽  
Elevation Model ◽  
Exposure Ages

AbstractWe present direct terrestrial evidence of ice volume change of the Darwin and Hatherton glaciers which channel ice from the Transantarctic Mountains into the Ross Ice Shelf. Combining glacial geomorphology with cosmogenic exposure ages from 25 erratics indicates a pre-LGM ice volume at least 600 m thicker than current Hatherton ice elevation was established at least 2.2 million years ago. In particular, five erratics spread across a drift deposit at intermediate elevations located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, give a well-constrained single population with mean 10Be age of 37.0 ± 5.5 ka (1σ). At lower elevations of 50–100 m above the surface of Lake Wellman, a further five samples from within a younger drift deposit range in exposure age from 1 to 19 ka. Our preferred age model interpretation, which is partly dependent on the selection of a minimum or maximum age-elevation model, suggests that LGM ice volume was not as large as previously estimated and constrains LGM ice elevation to be within ± 50 m of the modern Hatherton Glacier ice surface, effectively little different from what is observed today.

scholarly journals Very low inheritance in cosmogenic surface exposure ages of glacial deposits: A field experiment from two Norwegian glacier forelands

The Holocene ◽  
2017 ◽  
Vol 27 (9) ◽  
pp. 1406-1414 ◽  
Author(s):  
John A Matthews ◽  
Richard A Shakesby ◽  
Derek Fabel
Keyword(s):  
Field Experiment ◽  
Ice Sheets ◽  
Viable Alternative ◽  
Rock Fragments ◽  
Perceived Need ◽  
Cosmogenic Nuclide ◽  
Exposure Age ◽  
Cosmogenic Nuclide Dating ◽  
Southern Norway ◽  
Exposure Ages

Terrestrial cosmogenic nuclide dating has been widely used to estimate the surface exposure age of bedrock and boulder surfaces associated with deglaciation and Holocene glacier variations, but the effect of inherited age has been rarely directly addressed. In this study, small clasts, embedded in flute surfaces on two cirque glacier forelands in Jotunheimen, southern Norway and deposited within the last ~60 years, were used to test whether such clasts have the modern surface exposure age expected in the absence of inheritance. Two different approaches were taken involving dating of (1) a single clast of cobble size from the proglacial area of Austanbotnbreen, and (2) 75 clasts mostly of pebble size from the proglacial area of Storbreen crushed and treated as a single sample. 10Be surface exposure ages were 99 ± 98 and 368 ± 90 years, respectively, with 95% confidence (±2σ). It is concluded that (1) these small glaciers have eroded and deposited rock fragments with a cosmogenic zero or near-zero concentration, (2) the likelihood of inherited cosmogenic nuclide concentrations in similar rock fragments deposited by larger warm-based glaciers and ice sheets should be small, and (3) combining a large number of small rock particles into one sample rather than using single large clasts of boulder size may provide a viable alternative to the commonly perceived need for five or more independent estimates of exposure age per site.

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