Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46�S, Argentina

2005 ◽  
Vol 63 (3) ◽  
pp. 301-315 ◽  
Author(s):  
Michael R. Kaplan ◽  
Daniel C. Douglass ◽  
Bradley S. Singer ◽  
Robert P. Ackert ◽  
Marc W. Caffee
Keyword(s):  
Northern Hemisphere ◽  
Erosion Rate ◽  
Buenos Aires ◽  
Glacial Cycles ◽  
Rate Estimate ◽  
Oxygen Isotope Stage ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Stage 4 ◽  
Glacial Advance

At Lago Buenos Aires, Argentina, 10Be, 26Al, and 40Ar/39Ar ages range from 190,000 to 109,000 yr for two moraines deposited prior to the last glaciation, 23,000�16,000 yr ago. Two approaches, maximum boulder ages assuming no erosion, and the average age of all boulders and an erosion rate of 1.4 mm/103 yr, both yield a common estimate age of 150,000�140,000 yr for the two moraines. The erosion rate estimate derives from 10Be and 26Al concentrations in old erratics, deposited on moraines that are >760,000 yr old on the basis of interbedded 40Ar/39Ar dated lavas. The new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid-latitude Andes. The next five youngest moraines correspond to stage 2. There is no preserved record of a glacial advance during stage 4. The distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760,000 and >200,000 yr ago. The mid-latitude Patagonian glacial record, which is well preserved because of low erosion rates, indicates that during the last two glacial cycles major glaciations in the southern Andes have been in phase with growth and decay of Northern Hemisphere ice sheets, especially at the 100,000 yr periodicity. Thus, glacial maxima are global in nature and are ultimately paced by small changes in Northern Hemisphere insolation.

scholarly journals Centennial- and orbital-scale erosion beneath the Greenland Ice Sheet

2021 ◽  
Author(s):  
Allie Balter-Kennedy ◽  
Nicolás Young ◽  
Jason Briner ◽  
Brandon Graham ◽  
Joerg Schaefer
Keyword(s):  
Erosion Rate ◽  
Ice Sheets ◽  
Greenland Ice Sheet ◽  
Flow Dynamics ◽  
Surface Process ◽  
Earth Surface ◽  
Ice Flow ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Historical Times

Erosion beneath glaciers and ice sheets is a fundamental Earth-surface process dictating landscape development, which in turn influences ice-flow dynamics and the climate sensitivity of ice masses. The rate at which subglacial erosion takes place, however, is notoriously difficult to observe because it occurs beneath modern glaciers in a largely inaccessible environment. Here, we present 1) cosmogenic-nuclide measurements from bedrock surfaces with well constrained exposure and burial histories fronting Jakobshavn Isbræ in western Greenland to constrain centennial-scale erosion rates, and 2) a new method combining cosmogenic nuclide measurements in a shallow bedrock core with cosmogenic-nuclide modelling to constrain orbital-scale erosion rates across the same landscape. Twenty-six 10Be measurements in surficial bedrock constrain the erosion rate during historical times to 0.4–0.8 mm yr-1. Seventeen 10Be measurements in a 4-m-long bedrock core corroborate this centennial-scale erosion rate, and reveal that 10Be concentrations below ~2 m depth are greater than what is predicted by an idealized production-rate depth profile. We utilize this excess 10Be at depth to constrain orbital-scale erosion rates at Jakobshavn Isbræ to 0.1–0.3 mm yr-1. The broad similarity between centennial- and orbital-scale erosion rates suggests that subglacial erosion rates have remained relatively uniform throughout the Pleistocene at Jakobshavn Isbræ.

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>

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>

Periglacial Climate at the 2.5 Ma Onset of Northern Hemisphere Glaciation Inferred from the Whippoorwill Formation, Northern Missouri, USA

2010 ◽  
Vol 73 (1) ◽  
pp. 151-161 ◽  
Author(s):  
Charles W. Rovey ◽  
Greg Balco
Keyword(s):  
Northern Hemisphere ◽  
Soil Profile ◽  
Ice Sheet ◽  
Glacial Till ◽  
Laurentide Ice Sheet ◽  
Erosion Rates ◽  
Cosmogenic Nuclide ◽  
Active Mixing ◽  
Climate Cooling

The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic–nuclide burial ages show that it was deposited between the Matuyama–Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic–nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1–2 m/Ma. However, cosmogenic–nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape.

Lithostratigraphy and limiting optical ages of the Pleistocene fill in Fraser River valley near Clinton, south-central British Columbia

2001 ◽  
Vol 38 (5) ◽  
pp. 839-850 ◽  
Author(s):  
Olav B Lian ◽  
Stephen R Hicock
Keyword(s):  
Oxygen Isotope ◽  
River Valley ◽  
Fraser River ◽  
Oxygen Isotope Stage ◽  
Valley Fill ◽  
The North ◽  
South Central ◽  
Last Glaciation ◽  
Stage 4 ◽  
Glacial Advance

The Fraser River valley near Clinton contains a thick sediment fill that is presently incised down to bedrock. The sequence, approximately 500 m thick, is generally upward fining and consists of up to 100 m of glacigenic debris flow diamicton and glaciofluvial–deltaic gravel and sand at the base, overlain by about 350 m of glaciolacustrine sediments and minor diamicton, which is in turn capped by several metres of till. The sequence is interpreted to represent (i) valley aggradation in response to glaciation, followed by (ii) the impoundment of the valley by sediment and (or) ice, and the formation of a large proglacial lake(s), and finally (iii) overriding of the valley fill by glaciers. This glacial advance sequence can be readily correlated with previously studied units situated immediately to the north, most of which have been associated with the last glaciation; however, the age of these units has been based only on stratigraphic relations. We introduce limiting optical ages from a widespread glaciolacustrine unit that show that the glacial advance sequence was formed, at the earliest, during the penultimate Okanagan Centre Glaciation (oxygen isotope stage 4; ca. 74–59 ka), but almost certainly during the (last) Fraser Glaciation (oxygen isotope stage 2; ca. 24–12 ka). It could not have been deposited during oxygen isotope stage 6, or during an older glaciation.

scholarly journals Impacts of oak deforestation and rainfed cultivation on soil redistribution processes across hillslopes using 137Cs techniques

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Shamsollah Ayoubi ◽  
Nafiseh Sadeghi ◽  
Farideh Abbaszadeh Afshar ◽  
Mohammad Reza Abdi ◽  
Mojtaba Zeraatpisheh ◽  
...  
Keyword(s):  
Land Use ◽  
Magnetic Susceptibility ◽  
Soil Erosion ◽  
Erosion Rate ◽  
Land Use Changes ◽  
Soil Samples ◽  
Natural Forest ◽  
Oak Forests ◽  
Erosion Rates ◽  
Rainfed Farming

Abstract Background As one of the main components of land-use change, deforestation is considered the greatest threat to global environmental diversity with possible irreversible environmental consequences. Specifically, one example could be the impacts of land-use changes from oak forests into agricultural ecosystems, which may have detrimental impacts on soil mobilization across hillslopes. However, to date, scarce studies are assessing these impacts at different slope positions and soil depths, shedding light on key geomorphological processes. Methods In this research, the Caesium-137 (137Cs) technique was applied to evaluate soil redistribution and soil erosion rates due to the effects of these above-mentioned land-use changes. To achieve this goal, we select a representative area in the Lordegan district, central Iran. 137Cs depth distribution profiles were established in four different hillslope positions after converting natural oak forests to rainfed farming. In each hillslope, soil samples from three depths (0–10, 10–20, and 20–50 cm) and in four different slope positions (summit, shoulder, backslope, and footslope) were taken in three transects of about 20 m away from each other. The activity of 137Cs was determined in all the soil samples (72 soil samples) by a gamma spectrometer. In addition, some physicochemical properties and the magnetic susceptibility (MS) of soil samples were measured. Results Erosion rates reached 51.1 t·ha− 1·yr− 1 in rainfed farming, whereas in the natural forest, the erosion rate was 9.3 t·ha− 1·yr− 1. Magnetic susceptibility was considerably lower in the cultivated land (χhf = 43.5 × 10− 8 m3·kg− 1) than in the natural forest (χhf = 55.1 × 10− 8 m3·kg− 1). The lower soil erosion rate in the natural forest land indicated significantly higher MS in all landform positions except at the summit one, compared to that in the rainfed farming land. The shoulder and summit positions were the most erodible hillslope positions in the natural forest and rainfed farming, respectively. Conclusions We concluded that land-use change and hillslope positions played a key role in eroding the surface soils in this area. Moreover, land management can influence soil erosion intensity and may both mitigate and amplify soil loss.

scholarly journals Assessment of Soil Erosion Vulnerability in the Heavily Populated and Ecologically Fragile Communities in Motozintla De Mendoza, Chiapas, Mexico

2017 ◽  
Author(s):  
Selene B. González-Morales ◽  
Alex Mayer ◽  
Neptalí Ramírez-Marcial
Keyword(s):  
Soil Erosion ◽  
Erosion Rate ◽  
Negative Response ◽  
Attitudes And Practices ◽  
Erosion Rates ◽  
Soil Erosion Rate ◽  
Kap Survey ◽  
Level Of Knowledge ◽  
Steep Slopes ◽  
Knowledge Attitudes And Practices

Abstract. The physical aspects and knowledge of soil erosion in six communities in rural Chiapas, Mexico were assessed. Average erosion rates estimated with the RUSLE model ranged from 200 to 1,200 ha−1 yr−1. Most erosion rates are relatively high due to steep slopes, sandy soils and bare land cover. The lowest rates occur where corn is cultivated for much of the year and slopes are relatively low. The results of a knowledge, attitudes and practices (KAP) survey showed that two-thirds of respondents believed that the major cause of soil erosion was hurricanes or rainfall and only 14 % of respondents identified human activities as causes of erosion. Forty-two percent of respondents indicated that the responsibility for solving soil erosion problems lies with government, as opposed to 26 % indicating that the community is responsible. More than half of respondents believed that reforestation is a viable option for reducing soil erosion, but only a third of respondents were currently applying reforestation practices and another one-third indicated that they were not following any conservation practices. The KAP results were used to assess the overall level of knowledge and interest in soil erosion problems and their solutions by compiling negative responses. The community of Barrio Vicente Guerrero may be most vulnerable to soil erosion, since it had the highest average negative response and the second highest soil erosion rate. However, Poblado Cambil had the highest estimated soil erosion rate and a relatively low average negative response rate, suggesting that soil conservation efforts should be prioritized for this community. We conclude that as long as the economic and productive needs of the communities are not solved simultaneously, the risk of soil erosion will increase in the future, which threatens the survival of these communities.

scholarly journals Estimation of soil loss using remote sensing and GIS-based universal soil loss equation in northern catchment of Lake Tana Sub-basin, Upper Blue Nile Basin, Northwest Ethiopia

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Veera Narayana Balabathina ◽  
R. P. Raju ◽  
Wuletaw Mulualem ◽  
Gedefaw Tadele
Keyword(s):  
Remote Sensing ◽  
Land Use ◽  
Soil Erosion ◽  
Soil Loss ◽  
Erosion Rate ◽  
Soil Erodibility ◽  
Lake Tana ◽  
Erosion Rates ◽  
Soil Erosion Rate ◽  
Soil Loss Equation

Abstract Background Soil erosion is one of the major environmental challenges and has a significant impact on potential land productivity and food security in many highland regions of Ethiopia. Quantifying and identifying the spatial patterns of soil erosion is important for management. The present study aims to estimate soil erosion by water in the Northern catchment of Lake Tana basin in the NW highlands of Ethiopia. The estimations are based on available data through the application of the Universal Soil Loss Equation integrated with Geographic Information System and remote sensing technologies. The study further explored the effects of land use and land cover, topography, soil erodibility, and drainage density on soil erosion rate in the catchment. Results The total estimated soil loss in the catchment was 1,705,370 tons per year and the mean erosion rate was 37.89 t ha−1 year−1, with a standard deviation of 59.2 t ha−1 year−1. The average annual soil erosion rare for the sub-catchments Derma, Megech, Gumara, Garno, and Gabi Kura were estimated at 46.8, 40.9, 30.9, 30.0, and 29.7 t ha−1 year−1, respectively. Based on estimated erosion rates in the catchment, the grid cells were divided into five different erosion severity classes: very low, low, moderate, high and extreme. The soil erosion severity map showed about 58.9% of the area was in very low erosion potential (0–1 t ha−1 year−1) that contributes only 1.1% of the total soil loss, while 12.4% of the areas (36,617 ha) were in high and extreme erosion potential with erosion rates of 10 t ha−1 year−1 or more that contributed about 82.1% of the total soil loss in the catchment which should be a high priority. Areas with high to extreme erosion severity classes were mostly found in Megech, Gumero and Garno sub-catchments. Results of Multiple linear regression analysis showed a relationship between soil erosion rate (A) and USLE factors that soil erosion rate was most sensitive to the topographic factor (LS) followed by the support practice (P), soil erodibility (K), crop management (C) and rainfall erosivity factor (R). Barenland showed the most severe erosion, followed by croplands and plantation forests in the catchment. Conclusions Use of the erosion severity classes coupled with various individual factors can help to understand the primary processes affecting erosion and spatial patterns in the catchment. This could be used for the site-specific implementation of effective soil conservation practices and land use plans targeted in erosion-prone locations to control soil erosion.

scholarly journals Mid-Pleistocene transition in glacial cycles explained by declining CO2and regolith removal

2019 ◽  
Vol 5 (4) ◽  
pp. eaav7337 ◽  
Author(s):  
M. Willeit ◽  
A. Ganopolski ◽  
R. Calov ◽  
V. Brovkin
Keyword(s):  
Climate Variability ◽  
Carbon Cycle ◽  
Northern Hemisphere ◽  
Seasonal Variations ◽  
Ice Sheets ◽  
Glacial Cycles ◽  
Solar Insolation ◽  
The Past ◽  
Transient Simulations

Variations in Earth’s orbit pace the glacial-interglacial cycles of the Quaternary, but the mechanisms that transform regional and seasonal variations in solar insolation into glacial-interglacial cycles are still elusive. Here, we present transient simulations of coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. We show that a gradual lowering of atmospheric CO2and regolith removal are essential to reproduce the evolution of climate variability over the Quaternary. The long-term CO2decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations, while the combined effect of CO2decline and regolith removal controls the timing of the transition from a 41,000- to 100,000-year world. Our results suggest that the current CO2concentration is unprecedented over the past 3 million years and that global temperature never exceeded the preindustrial value by more than 2°C during the Quaternary.

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