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>

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>

Lichens of the Oasis Molodyozhnyi and adjacent areas (Enderby Land, Antarctic)

2013 ◽  
Vol 47 ◽  
pp. 167-178 ◽  
Author(s):  
M. P. Andreev
Keyword(s):  
Liquid Water ◽  
Climate Conditions ◽  
Water Ice ◽  
Buellia Frigida ◽  
Antarctic Continent ◽  
Harsh Climate ◽  
The Antarctic ◽  
First Time ◽  
Lichen Flora

Lichen flora and vegetation in the vicinity of the Russian base «Molodyozhnaya» (Enderby Land, Antarctica) were investigated in 2010–2011 in details for the first time. About 500 specimens were collected in 100 localities in all available ecotopes. The lichen flora is the richest in the region and numbers 39 species (21 genera, 11 families). The studied vegetation is very poor and sparse, but typical for coastal oases of the Antarctic continent. The poorness is caused by the extremely harsh climate conditions, insufficient availability of liquid water, ice-free land, and high insolation levels. The dominant and most common lichens are Rinodina olivaceobrunnea, Amandinea punctata, Candelariella flava, Physcia caesia, Caloplaca tominii, Lecanora expectans, Caloplaca ammiospila, Lecidea cancriformis, Pseudephebe minuscula, Lecidella siplei, Umbilicaria decussata, Buellia frigida, Lecanora fuscobrunnea, Usnea sphacelata, Lepraria and Buellia spp.

scholarly journals Low Antarctic continental climate sensitivity due to high ice sheet orography

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Hansi A. Singh ◽  
Lorenzo M. Polvani
Keyword(s):  
Moisture Transport ◽  
Climate Models ◽  
Ice Sheet ◽  
High Elevation ◽  
Moisture Convergence ◽  
Warm Temperature ◽  
Atmospheric Concentration ◽  
Antarctic Continent ◽  
The Antarctic ◽  
Continental Climate

Abstract The Antarctic continent has not warmed in the last seven decades, despite a monotonic increase in the atmospheric concentration of greenhouse gases. In this paper, we investigate whether the high orography of the Antarctic ice sheet (AIS) has helped delay warming over the continent. To that end, we contrast the Antarctic climate response to CO2-doubling with present-day orography to the response with a flattened AIS. To corroborate our findings, we perform this exercise with two different climate models. We find that, with a flattened AIS, CO2-doubling induces more latent heat transport toward the Antarctic continent, greater moisture convergence over the continent and, as a result, more surface-amplified condensational heating. Greater moisture convergence over the continent is made possible by flattening of moist isentropic surfaces, which decreases humidity gradients along the trajectories on which extratropical poleward moisture transport predominantly occurs, thereby enabling more moisture to reach the pole. Furthermore, the polar meridional cell disappears when the AIS is flattened, permitting greater CO2-forced warm temperature advection toward the Antarctic continent. Our results suggest that the high elevation of the present AIS plays a significant role in decreasing the susceptibility of the Antarctic continent to CO2-forced warming.

Constraints from cosmogenic nuclides on the glaciation and erosion history of Dove Bugt, northeast Greenland

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2282-2294 ◽  
Author(s):  
Daniel Søndergaard Skov ◽  
J.L. Andersen ◽  
J. Olsen ◽  
B.H. Jacobsen ◽  
M.F. Knudsen ◽  
...  
Keyword(s):  
Ice Cover ◽  
High Elevation ◽  
Cosmogenic Nuclide ◽  
Erosion History ◽  
Minimum Age ◽  
History Of ◽  
Subglacial Topography ◽  
Ice Sheet Dynamics ◽  
Cosmogenic 10Be ◽  
Exposure Ages

Abstract The intricate interplay between subglacial topography and ice-sheet dynamics is key to the evolution of large ice sheets, but in Greenland as elsewhere the effects of long-term glacial history on landscape evolution remain poorly constrained. Here we measure abundances of cosmogenic 10Be and 26Al in bedrock and transported boulders to unveil the glaciation and erosion history of Dove Bugt, northeast Greenland. In agreement with studies of west Greenland, we find that apparent exposure ages increase with elevation from 9 ka to 13 ka in low-lying valleys to 21 ka to 204 ka on high-elevation, blockfield-covered plateaus. We employ a Markov chain Monte Carlo inversion framework to constrain the probability of various erosion histories, and we quantify the residence time of samples within the upper 2 m of the bedrock subsurface—a measure defined as the cosmogenic nuclide memory. This cosmogenic nuclide memory exceeds 600 ka on the highest plateaus but is limited to less than 500 ka in most other high-elevation samples and to less than 100 ka at low-elevations. Our results define maximum limits for the fraction of ice cover during the past 1 Ma to ∼70% on the Store Koldewey peaks and ∼90% farther inland at Pusterdal, respectively. Minimum limits to ice cover, however, cannot be reliably constrained by the data. Finally, we propose that limited erosion on the highest plateaus of Store Koldewey since 0.6–1.0 Ma indicates a minimum age for fjord-plateau formation within this area of northeast Greenland.

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.

Slow regolith degradation without creep determined by cosmogenic nuclide measurements in Arena Valley, Antarctica

2008 ◽  
Vol 69 (2) ◽  
pp. 242-249 ◽  
Author(s):  
Jaakko Putkonen ◽  
Greg Balco ◽  
Daniel Morgan
Keyword(s):  
Indirect Evidence ◽  
Soil Surface ◽  
Ice Cover ◽  
Surface Erosion ◽  
Dry Valleys ◽  
Cosmogenic Nuclide ◽  
Exposure Age ◽  
Excellent Preservation ◽  
Exposure Ages ◽  
Landslide Deposit

Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring10Be and26Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma−1) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation.

Felsenmeer persistence under non-erosive ice in the Torngat and Kaumajet mountains, Quebec and Labrador, as determined by soil weathering and cosmogenic nuclide exposure dating

2004 ◽  
Vol 41 (1) ◽  
pp. 19-38 ◽  
Author(s):  
Geneviève C Marquette ◽  
James T Gray ◽  
John C Gosse ◽  
François Courchesne ◽  
Lisa Stockli ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
High Elevation ◽  
Secondary Minerals ◽  
Soil Weathering ◽  
Exposure Dating ◽  
Cosmogenic Nuclide ◽  
Late Wisconsinan ◽  
Exposure Ages ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Soil analyses and terrestrial cosmogenic nuclide exposure dating are combined and a conceptual model proposed to explain altitudinal weathering contrasts in high-latitude highlands. We show that summits in the Torngat and Kaumajet mountains were covered by ice during the Last Glacial Maximum, and that their felsenmeer cover probably survived multiple glaciation events. For similar lithologies, soils on felsenmeer covered summits are signigicantly more weathered than those below the felsenmeer limit, displaying higher concentrations of crystalline iron, amorphous aluminium, and silicium extracted with oxalate. Secondary minerals such as gibbsite and kaolinite occur in felsenmeer soils, whereas those formed in till lacked these secondary minerals. 10Be and 26Al exposure ages for nine of ten samples, from high-elevation tors and autochthonous felsenmeer blocks, range from 73 ± 6 to 157 ± 15 ka. By contrast, ages of 11.4 ± 1.0 and 11.7 ± 1.0 ka are measured for bedrock in the much lower Saglek zone, indicating extensive (>3 m) glacial erosion of this zone during Late Wisconsinan glaciation. 26Al/10Be ratios demonstrate that exposure of the high-elevation surfaces was interrupted during at least one cosmic ray shielding event by either ice or till cover. In either case, Late Wisconsinan glaciers could not have extensively eroded these surfaces. Five erratics dated above the Saglek zone, including one in the felsenmeer zone, have exposure ages ranging from 11.6 ± 1.0 to 13.6 ± 0.7 ka. This indicates that valley and high-elevation ice persisted through the Younger Dryas Chron and provides further evidence that the highlands were not nunataks during the Late Wisconsinan period.

Synoptic analysis of globally-distributed data sets of cosmogenic-nuclide exposure ages

2021 ◽  
Author(s):  
Greg Balco
Keyword(s):  
Global Analysis ◽  
Glacier Change ◽  
Data Sets ◽  
Distributed Data ◽  
Data Set ◽  
Cosmogenic Nuclide ◽  
Synoptic Analysis ◽  
Exposure Age ◽  
Exposure Ages ◽  
Globally Distributed

&lt;p&gt;This abstract describes a project to make large data sets of cosmogenic-nuclide measurements useable for synoptic global analysis of paleoclimate, glacier change, and landscape change. It is based on the 'ICE-D' (Informal Cosmogenic-nuclide Exposure-age Database), a transparent-middle-layer infrastructure for compiling and storing cosmogenic-nuclide measurements and generating internally consistent exposure-age data. The prototype implementation of this project focuses on a global data set of exposure ages from glacial deposits that are, potentially, useful for synoptic analysis of glacier change and paleoclimate. The aim is to address a number of messy data-management and analysis problems associated with cosmogenic-nuclide data, thus making it possible to apply unbiased, automated quantitative analysis to the entire globally-distributed data set. The presentation will highlight (i) examples of error-tolerant hypothesis testing using this approach; (ii) means of quantifying the importance of the details of cosmogenic-nuclide production-rate calculations to global paleoclimate inferences, and (iii) likewise, approaches to understanding the importance of geomorphic processes and landform evolution to global paleoclimate inferences drawn from exposure-dated landforms.&lt;/p&gt;

scholarly journals Outlet Glacier and Landscape Evolution of Victoria Land, Antarctica

2021 ◽  
Author(s):  
◽  
Ross Whitmore
Keyword(s):  
Erosion Rate ◽  
Ice Sheet ◽  
Outlet Glacier ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Ice Surface ◽  
Victoria Land ◽  
Bedrock Erosion ◽  
The Antarctic ◽  
Exposure Ages

<p>Terrestrial cosmogenic exposure studies are an established and rapidly evolving tool for landscapes in both polar and non-polar regions. This thesis takes a multifaceted approach to utilizing and enhancing terrestrial cosmogenic methods. The three main components of this work address method development, reconstructing surface-elevation-changes in two large Antarctic outlet glaciers, and evaluating bedrock erosion rates in Victoria Land, Antarctica. Each facet of this work is intended to enhance its respective field, as well as benefit the other sections of this thesis. Quartz purification is a necessary and critical step to producing robust and reproducible results in terrestrial cosmogenic nuclide studies. Previous quartz purification work has centred on relatively coarse sample material (1 mm-500 μm) and is effective down to 125 μm. However, sample material finer than that poses significant purification challenges and this material is usually discarded. The new purification procedure outlined in this thesis shows that very fine sand size material (125-63 μm) can be reliably cleaned for use in terrestrial cosmogenic nuclide studies. The results below show that 35% mass loss in very fine-grained quartz is sufficient to remove major elements (Al, Ti, Na, K, Fe, Mg, Ca, Mn,) and trace elements (9Be, and 10B) along with meteoric 10Be. Insufficient leaching is most detrimental to Al concentration, however errors up to 27% in exposure age and up to 29% in erosion rate are possible if meteoric 10Be is not fully removed from quartz during the HF leaching stages. Outlet glaciers have been well observed since the beginning of the satellite era, approximately 60 years ago. However, we do not currently know how these important glaciers, which drain a significant portion of the Antarctic Ice Sheet, have behaved on centennial to millennial timescales. Dating glacial erratics deposited by a thinning outlet glacier provides a window into the long-term outlet glacier and ice sheet response to climatic forcing. New results in this thesis constrain the thinning history of Mawson and Tucker glaciers over the last several thousand years. Mawson Glacier undergoes rapid thinning from at least ~6.5 kya to ~4.9 kya then transitions to slower thinning until ~1 kya, with a minimum of 250 m of ice-surface-lowering. While Tucker Glacier ~450 km north undergoes gradual thinning from ~19 kya to ~5 kya with ~300 m of ice-surface-lowering. The results of this work show that either the Tucker Glacier was not significantly affected by the Ross Ice Shelf grounding line, or that Antarctic mountain glaciers respond differently to the outlet glaciers connected to the Easty Antarctic Ice Sheet. The style, rate, magnitude, and duration of thinning is unique to each outlet glacier, even with similar climate forcing. The results of this work shed light on the style and duration of outlet glacier thinning and retreat that is possible following a climate perturbation. Antarctica’s average bedrock erosion rate is consistently lower than 4.5 m/Myr, the lowest bedrock erosion rates for any region on Earth. Therefore, many cosmogenic dating studies assume zero erosion when calculating exposure ages. However, previous erosion rate work in Antarctica is biased to arid high-elevation inland sites (~60% of work) and the hyperarid ice-free McMurdo Dry Valleys (~40% of work). These studies do not capture the effects of coastal maritime climates, where many outlet glacier studies are conducted, on the rate of bedrock erosion. New results presented in this thesis show that the Northern Victoria Land coast has the highest known erosion rate in Antarctica. Two sample sites were selected, one coastal and one in the interior. The coastal bedrock erosion rates are 8.86±0.78 m/Myr and 7.15±0.6 m/Myr while the interior bedrock erosion rates are 1.07±0.08 m/Myr and 0.42±0.03 m/Myr. The coastal erosion rates are average for non-polar cold climates while the inland sites are below average for polar erosion rates. The results suggest a strong gradient in the rate of erosion is present from the Antarctic coastline inland. If exposure ages are not calculated with an appropriate erosion rate the apparent age may under-estimate the actual age by as much as 12%, which is thousands of years for Holocene thinning histories like those found in this thesis.</p>

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