Atmospheric 10Be, a cosmogenic nuclide, was used to quasicontinuously date these sedimentary units. This chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock. The travel time of water moving through a landscape influences nutrient dynamics and biogeochemical cycles.
Constraining water travel times helps to understand the functioning of the critical zone. Water travel times cannot be observed directly but can be constrained by measurements of cosmogenic radioactive isotopes. We studied a small 4. We analyzed a combination of three cosmogenic radioactive isotopes with half-lives varying from 87 days sulfur , 2. Water stable isotopes and solute chemistry aided the interpretation of the cosmogenic isotopes. Tritium samples 1L are analyzed by noble gas mass spectrometry after helium-3 accumulation.
Samples for sulfur and sodium are collected by processing L of water through an anion and cation exchange column in-situ. Sulfur is analyzed by liquid scintillation counting after chemical purification and precipitation. Sodium is analyzed by gamma counting after eluting the cations into a 4L Marinelli beaker. Monthly collected precipitation samples show variability of deposition rate for tritium and sulfur Sodium levels in cumulative yearly precipitation samples are consistent with recent studies in the US and Japan.
The observed variability of deposition rates complicates direct use as decaying age tracers. The level and variability of tritium in monthly stream samples indicate a mean residence time on the order of 10 years and only small contributions of younger water during high flow conditions.
Cosmogenic isotopes – University of Copenhagen
Sulfur and sodium concentrations were critically interpreted considering possible uptake by vegetation and cation exchange. Angel, Isandra; Audemard M. This paper contributes with 24 exposure ages of glacial landforms sampled in the Gavidia valley. Exposure ages were obtained based on terrestrial cosmogenic nuclide 10Be dating. The glacier retreated in two different phases. A combination of topographic features and changes in the paleoclimate conditions at the end of the El Caballo Stadial seems leaded the fastest former glacier extinction. The topographic feature which seems contributed to the fastest glacier extinction was the low valley bottom slopes.
Asynchronous deglaciation histories were observed. Local paleotemperatures and paleoprecipitations contrasts, different valleys aspects, insolation and catchments steepness could explain different deglaciation histories. A new sampling strategy for cosmogenic surface exposure dating of moraines: Cosmogenic surface exposure dating has been applied to date numerous moraines worldwide. The geochronological data obtained from these studies have improved our knowledge on the timing of glaciation and allow us to reconstruct the paleoclimate.
Generally, the ages on a well-preserved moraine surface show unimodal normal distribution. Frequently, erosion, exhumation and boulder toppling are blamed for the younger outliers. On the other hand, although infrequent, older outliers will indicate inherited nuclide concentration from pre-exposure to cosmic radiation. To obtain the true age of a moraine deposit, one needs to collect several samples that not only greatly increases the budget of the project but also is time consuming.
To overcome this problem, we developed a new sampling strategy for dating moraine surfaces by cosmogenic nuclides. Fourteen to 32 boulders were chosen for sampling every 20 m. All rock chips were amalgamated to make one sample. The age results from the two Late Pleistocene moraines and one rock glacier surface show no difference in terms of boulder exposure ages. This work is supported by the U. Determining timing of Alaska Range exhumation and glaciation through cosmogenic nuclide burial dating. The Alaska Range is a transpressional orogen with modern exhumation initiating 6 Ma.
The stratigraphic record of unroofing and uplift of the foreland basin is largely preserved along the northern flank of the Alaska Range in the Pliocene-Pleistocene aged Nenana Gravel, an extensive alluvial fan and braidplain deposit. Chronometric control on the Nenana Gravel is largely lacking, with the limited available age control based on a single Ar-Ar tephra date in an underlying unit and via stratigraphic inferences for the upper portions.
Higher-resolution dating of the Nenana Gravel unit is imperative in order to quantify deposition rates and the timing of uplift and deformation of the foreland basin. Furthermore, a glacial unit has been found to lie unconformably on top of the unit at Suntrana Creek and may represent the initiation of glacial advances in the Alaska Range. Three samples from the lower Nenana Gravel yield an isochron burial age of 4.
Two samples collected from the middle of the Nenana Gravel unit produced an average simple burial age of 2. Two samples from the upper-most portion of the Nenana Gravel yielded an average simple burial age of 1. In addition, the age of the glacial unit provides a minimum age for inception of foreland basin uplift and abandonment of the Nenana Gravel in this region.
Isotopic abundances of the noble gases were measured in the following Martian meteorites: These glass samples, when combined with literature data on a separate single glass inclusion from EET and a glass vein from Zagami, permit examination of the isotopic composition of Ne, Ar, Kr, and Xe trapped from the Martian atmosphere in greater detail. The isotopic composition of Martian Ne, if actually present in these glasses, remains poorly defined. Martian atmospheric Kr appears to be enriched in lighter isotopes by approx.
Cosmogenic gases indicate space exposure ages of The space exposure age for Y is 4. Using cosmogenic nuclides to date the stabilisation age of relict rockglaciers. Active rockglaciers are periglacial landforms which are creeping down mountain slopes due to plastic deformation of the interstitial ice. The occurrence of active rockglaciers is an indicator of Alpine permafrost. Relict rockglaciers are not moving anymore because the ice melted, but they give evidence for the earlier existence of permafrost. In the Alps, relict rockglaciers can often be found below today's tree line raising the question of when these landforms have last been active.
Judging from the present position of the relict rockglaciers, the lower permafrost limit during the time of their activity must have been hundreds of meters lower than it is today. Already in the early days of rockglacier research, the potential of relict rockglaciers as a paleoclimate proxy was recognised Barsch , Haeberli However, obtaining absolute ages on relict rockglaciers has always been a major difficulty. Lately it has been shown that with cosmogenic nuclides it is possible to date the stabilisation age of relict rockglaciers, but it has been applied only in a few cases Ivy-Ochs et al.
According to Reitner , the lowest relict rockglaciers of the eastern Alps, the Tandl rockglaciers, are located in the Province of Carinthia Austria. The Tandl rockglaciers are a complex series of rockglaciers spanning from around m down to m a. Therefore, samples from the entire rockglacier series were taken for 10Be exposure dating. Furthermore, the close proximity of the rockglaciers to moraines associated to the Gschnitz stadial allow comparing the dating results to equilibrium line depression reconstructions.
Less than 10 km to the southwest, a second rockglacier series, the Norbert rockglaciers, was sampled. In contrast to the. Glacier retreat in polar areas has major implications at a local, regional and even planetary scale. Global average sea level rise is the most obvious and socio-economically relevant, but there are others such as the arrival of new fauna to deglaciated areas, plant colonisation or permafrost formation and degradation.
Ice-cap glacier retreat chronology will be revealed by the use of cosmogenic isotopes mainly 36Cl on glacially originated sedimentary and erosive records.
Cosmogenic dating will be complemented by other dating methods C14 and OSL , which will permit the validation of these methods in regions with cold-based glaciers. Given the geomorphological evidences and the obtained ages, a deglaciation calendar will be proposed and we will use a GIS methodology to reconstruct the glacier extent and the ice thickness. The results emerging from this project will allow to assess whether the high glacier retreat rates observed during the last decades were registered in the past, or if they are conversely the consequence and evidence of the Global Change in Antarctica.
Recent summer warming has now raised the equilibrium line above almost all ice caps on Baffin Island, resulting in surface lowering and marginal recession everywhere. As cold-based ice recedes it frequently exposes in situ tundra plants that were living at the time ice expanded across the site. Radiocarbon dates for each plant records when cold summers dropped regional snowline below the site, killing the plants, and snowline remained below the site until the collection date. The kill dates also represent the last time that the climate was warm enough to expose the sampling location.
Radiocarbon dead sites north of the Penny Ice cap experienced significantly more exposure over their lifetimes than their counterparts east of the Penny Ice cap, suggesting significant differences in local and regional land ice fluctuations over the last 2 million years.
Accessing the application of in situ cosmogenic 14C to surface exposure dating of amorphous SiO2. We assess the feasibility and utility of in situ cosmogenic 14C as a geochronometer for landforms composed of amorphous SiO2 through the comparison of 14C surface exposure ages to independently determined eruption ages on Obsidian Dome, California. Landforms composed of amorphous SiO2 phases are difficult to date by conventional cosmogenic nuclide methods due to several complications that may arise e.
The onset of an increased understanding of production rates and analytical measurement of in situ 14C in SiO2 provides an opportunity to address this limitation. Obsidian Dome is a year-old phreatomagmatic dome of the Mono-Inyo Craters located in Inyo County, California, and consists of vesicular pumice, obsidian, and rhyolite.
Measurement of 14C concentrations in shielded, subsurface samples will assist in isolating the atmospheric 14C component and aid in correcting the surface exposure ages. Hydrological travel times are studied on scales that span six orders of magnitude, from daily event water in stream flow to pre-Holocene groundwater in wells.
Groundwater vulnerability to contamination, groundwater surface water interactions and catchment response are often focused on "modern" water that recharged after the introduction of anthropogenic tritium in precipitation in Shorter residence times are expected in smaller catchments, resulting in immediate vulnerability to contamination. Tritium samples 1 L are analyzed by noble gas mass spectrometry after helium-3 accumulation. The observed variability of deposition rates complicates direct estimation of stream water age fractions. Estimates of subsurface storage are in agreement with estimates from geophysical studies.
In order to determine the age of the relatively younger fans, the erosion rate of the boulders and the cosmogenic nuclide inheritance from exposure prior to deposition in the fan were established. Cosmogenic nuclide inheritance values that range between 8. Boulder erosion rate, ranging between 17 and mm k. Since the boulders on the fans represent the most resistant rocks in this environment, we used the lowest rate for the age calculations.
Monte Carlo simulations were used to determine ages of 16?? Older fans older than ka were dated by analyzing 10Be and 26Al concentrations in buried sand samples. The ages of the three oldest fans range between ?? Although fan age determinations are accompanied by large uncertainties, the results of this study show a clear trend of increasing fan ages with increasing distance from the source near Little Rock Creek and provide a long-term slip rate along this section of the San Andreas fault.
Slip rate along the Mojave section of the San Andreas fault for the past k. The average slip rate calculated from the individual fan ages is 4. A linear regression through the data points implies a slip rate of 3. A most probable slip rate of 3. Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India. Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya.
The glacial stages that have been identified are: The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation.
Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene. Deglacial history of the Pensacola Mountains, Antarctica from glacial geomorphology and cosmogenic nuclide surface exposure dating. The retreat history of the Antarctic Ice Sheet is important for understanding rapid deglaciation, as well as to constrain numerical ice sheet models and ice loading models required for glacial isostatic adjustment modelling. There is particular debate about the extent of grounded ice in the Weddell Sea embayment at the Last Glacial Maximum, and its subsequent deglacial history.
Here we provide a new dataset of geomorphological observations and cosmogenic nuclide surface exposure ages of erratic samples that constrain the deglacial history of the Pensacola Mountains, adjacent to the present day Foundation Ice Stream and Academy Glacier in the southern Weddell Sea embayment. We show there is evidence of at least two glaciations, the first of which was relatively old and warm-based, and a more recent cold-based glaciation. During the most recent glaciation ice thickened by at least m in the Williams Hills and at least m on Mt Bragg. Progressive thinning from these sites was well underway by 10 ka BP and ice reached present levels by 2.
The thinning history is consistent with, but does not mandate, a Late Holocene retreat of the grounding line to a smaller-than-present configuration, as has been recently hypothesized based on ice sheet and glacial isostatic modelling. The data also show that clasts with complex exposure histories are pervasive and that clast recycling is highly site-dependent. These new data provide constraints on a reconstruction of the retreat history of the formerly-expanded Foundation Ice Stream, derived using a numerical flowband model. Cosmic ray exposure dating with in situ produced cosmogenic 3He: In an effort to determine the in situ production rate of spallation-produced cosmogenic 3He, and evaluate its use as a surface exposure chronometer, we have measured cosmogenic helium contents in a suite of Hawaiian radiocarbon- dated lava flows.
The lava flows, ranging in age from to 13, years, were collected from Hualalai and Mauna Loa volcanoes on the island of Hawaii. Because cosmic ray surface-exposure dating requires the complete absence of erosion or soil cover, these lava flows were selected specifically for this purpose. The 3He production rate, measured within olivine phenocrysts, was found to vary significantly, ranging from 47 to atoms g-1 yr-1 normalized to sea level. Although there is considerable scatter in the data, the samples younger than 10, years are well-preserved and exposed, and the production rate variations are therefore not related to erosion or soil cover.
Explaining the science of Antarctic glaciers
Data averaged over the past years indicate a sea-level 3He production rate of ?? The longer record suggests a minimum in sea level normalized 3He production rate between and years 55?? The minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength, as indicated by archeomagnetic data. However, the production rate variations a factor of 2. Calculations using the atmospheric production model of O'Brien , and the method of Lal and Peters , predict smaller production rate variations for similar variation in dipole moment a factor of 1.
Because the production rate variations, archeomagnetic data. Surface exposure dating of Holocene basalt flows and cinder cones in the Kula volcanic field western Turkey using cosmogenic 3He and 10Be. The Kula volcanic field is the youngest volcanic province in western Anatolia and covers an area of about km2 around the town Kula Richardson-Bunbury, Its alkali basalts formed by melting of an isotopically depleted mantle in a region of long-lived continental extension and asthenospheric upwelling Prelevic et al.
In this study, we analysed cosmogenic 3He in olivine phenocrysts from three basalt flows and one cinder cone to resolve the Holocene history of volcanic eruptions in more detail. In addition, we applied 10Be exposure dating to two quartz-bearing xenoliths found at the surface of one flow and at the top of one cinder cone. Our results show that the Late Holocene lava flows are not coeval but formed over a period of a few thousand years. Ultrapotassic mafic rocks as geochemical proxies for post-collisional dynamics of orogenic lithospheric mantle: Journal of Petrology, 53, The Kula Volcanic Field, western Turkey: Geological Magazine, , The rates and chronologies of valley incision are closely modulated by the tectonic uplift of active mountain ranges and were controlled by repeated climate changes during the Quaternary.
The continental collision between the Iberian and Eurasian plates induced a double vergence orogen, the Pyrenees, which has been considered as a mature mountain range in spite of significant seismicity e. Nevertheless, recent studies indicate that the range may have never reached a steady state Ford et al.
One option for resolving this controversy is to quantify the incision rates since the Miocene by reconstructing the vertical movement of geometric markers such as fluvial terraces. However, the few available ages from the Pyrenean terrace systems do not exceed the middle Pleistocene. Thus, to enlarge the time span of this dataset, we studied alluvium-filled horizontal epiphreatic passages in limestone karstic networks.
Such landforms are used as substitutes of fluvial terraces because they represent former valley floors e. Palmer, ; Audra et al. They record the transient position of former local base levels during the process of valley deepening. Preliminary results indicate a history of valley deepening in successive stages. Decoding mass-independent fractionation of sulfur isotopes in modern atmosphere using cosmogenic 35S: A five- isotope approach and possible implications for Archean sulfur isotope records.
The signature of sulfur isotopic mass-independent fractionation S-MIF observed in Archean sediments have been interpreted as a proxy of the origins and evolution of atmospheric oxygen and early life on Earth . Photochemistry of SOx in the short cosmogenic 35S a stratospheric tracer  and all four stable sulfur isotopes in the same modern atmospheric sulfate samples to define the mechanisms.
The significant role of volcanic OCS in the Archean atmosphere has been called for in terms of its ability to provide a continual SO2 high altitude source for photolysis . The strong but previously underappreciated stratospheric signature of S-MIF in tropospheric sulfates suggests that a more careful investigation of wavelength-dependent sulfur isotopic fractionation at different altitudes are required.
Although combustion is unlikely in Archean, recombination reactions may occur in other previously unappreciated processes such as volcanism and may contribute in part to the heavily depleted 36S in some Paleoarchean records [5,7]. The roles of both photochemical and non. The field area is situated 25 km due south of the archaeological site of Machu Picchu. Cosmogenic 10Be surface exposure dating of granitic boulders sampled on the Salcantay moraines is underway and has provided the first numerical ages for these deposits.
Initial results indicate ages of 8. The outer and inner moraine ages correspond to glacial events during the early and latest Holocene, respectively. Further 10Be dating of the mapped moraines and similar deposits observed in adjacent drainages on Nevado Salcantay is anticipated to yield a high-resolution chronology of valley glaciation in this segment of the southern Peruvian Andes.
The new results bridge an important gap between existing Andean glacier records to the north and south, and complement available ice core and lacustrine paleoclimate records in the vicinity, thereby expanding spatial and temporal coverage for identifying patterns of Holocene climate change in the tropical Andes. Notably, the inner moraine age correlates with the timing of the Little Ice Age as defined in northern mid- and high latitude glacier records, and suggests considerable expansion of valley glaciers in the southern Peruvian Andes during this climatic minimum.
Apart from their paleoclimatic significance, the initial results also demonstrate.
Combining cosmogenic radionuclides and amino acid racemization to date late Pliocene glacial deposits exposed on Baffin Island, Nunavut, Canada. Sequences of glacial deposits spanning the Quaternary are valuable archives recording the effects of glaciation on landscapes through time, but determining the age of such deposits has long challenged geologists.
The recent advances in cosmogenic radionuclide CRN measurement has made it possible to date some of these deposits, but dating buried glacial sediments in most settings remains problematic. This formation, approximately 40 m thick, includes interlayered shell-bearing marine, glaciomarine, and glacial sediments deposited along the northern margin of the Laurentide Ice Sheet and earlier continental ice sheets.
In this region we compare river profiles and incision rates between these rivers to resolve controls on river evolution. Disequilibrium profiles in both rivers are evident by numerous knickpoints and convexities which we analyze in the context of a new compilation of incision rate data, including new isochron cosmogenic burial dates on early Quaternary terraces. The Lees Ferry knickpoint is interpreted to be an upstream-migrating knickpoint initiated by integration of the Colorado system through Grand Canyon about 6 Ma.
An isochron cosmogenic burial date of 1. This date is 3x older than a cosmogenic surface date from the same terrace suggesting that high terraces dated by surface cosmogenic techniques are minimum dates. A burial date of 2. The Hite data show significantly more scatter, and additional samples have been collected to clarify the age. On the Green River, a new isochron cosmogenic burial date of 1.
Glacial and volcanic evolution on Nevado Coropuna Tropical Andes based on cosmogenic 36Cl surface exposure dating. Journal of Quaternary Science, 26 1: One Isotope , Two Tales: As the cryosphere continues to undergo rapid and accelerating change, it is more important than ever to understand past glacier activity to predict the future of the cryosphere. However, continuous Holocene glacier records are notoriously difficult to reconstruct because an advancing glacier will re-incorporate previous deposits so that moraines typically only record the farthest downvalley glacier expansion.
Here we combine dates of ice margin advance from in situ dead vegetation with in situ cosmogenic 14C in situ 14C from preserved bedrock surfaces at the same locations to further constrain the timing of ice-free episodes during the Holocene following deglaciation on southern Baffin Island. Radiocarbon ages from recently exposed in situ plants suggest that ice last advanced over sample locations at 9. Associated in situ 14C inventories are variable, but well above background levels, suggesting some amount of Holocene in situ 14C production. Using plant 14C ages representing the beginning of ice coverage and in situ 14C inventories representative of exposure prior to ice coverage, a simple model of cosmogenic in situ 14C production accounting for muon production through ice provides constraints timing and duration of ice-free times at sample locations prior to their most recent burial.
Using conservative Holocene ice thicknesses, the locations buried at 9. This suggests these locations were ice free by at least 10 ka and likely earlier. The in situ 14C inventory at the location buried at 3. These pilot data show that valuable information regarding periods of exposure is contained within in situ 14C inventories. Additional paired plant and. Fossil debris-covered glaciers in Demanda Sierra Northern Spain: The Demanda Sierra, at altitudes above m.
The most relevant evidences of Pleistocene glaciation are found in small cirques above m a. These cirques hosted small-size glaciers with ice tongues Cosmogenic Exposure Dating CED , 10Be, applied to 18 quartzite samples taken from stable boulders over moraine ridges or fossil debris-covered glaciers; 3 glacier reconstruction for modelling the glacier evolution at different stages; 4 Equilibrium Line Altitude ELA calculation. Late Pleistocene ages for the most recent volcanism and glacial-pluvial deposits at Big Pine volcanic field, California, USA, from cosmogenic 36Cl dating.
The Big Pine volcanic field is one of several Quaternary volcanic fields that poses a potential volcanic hazard along the tectonically active Owens Valley of east-central California, and whose lavas are interbedded with deposits from Pleistocene glaciations in the Sierra Nevada Range. Field mapping and petrology reveal approximately 15 vents and 6 principal flow units with variable geochemical composition and mineralogy. The tectonic trough of the fault zone defines the boundary between the Central and Eastern Taurides Ranges.
The presence of faulted alluvial fans and colluvium within this trough provide favorable conditions to unravel the Late Quaternary slip-rate of the fault zone by cosmogenic surface exposure dating. Geomorphic mapping and topographic surveying indicate four different alluvial fan levels deposited along the main strand. We dated the surface of the AF1 with 13 cosmogenic 36Cl samples. Our results indicate that the AF1 surface was abandoned maximum Accordingly, we propose 0. The surface exposure age of the colluvium yielded Our results reveal significant Quaternary deformation, and low strain rates might indicate very long earthquake recurrence intervals along the fault zone.
In many instances the radioactive ones are readily distinguished from the anthropogenic and meteoritic backgrounds. Measurements of these cosmogenic radionuclides RCN can contribute to the solution of a variety of geophysical problems [Lai and Peters, ].
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We summarize here the symposium presentations. The use of 36Cl cosmogenic nuclide as a paleoseismological tool for normal faults in the Mediterranean has revolutionized our understanding of their seismic cycle Gran Mitchell et al. Here we synthetized results obtained on 13 faults in Central Italy. Those records cover a period of 8 to 45 ka. The mean recurrence time of retrieved seismic events is 5. Most retrieved events correspond to single events according to scaling relationships. This is also supported by the 2 m-high co-seismic slip observed on the Mt Vettore fault after the October 30, M6.
Our results suggest that all faults have experienced one or several periods of slip acceleration with bursts of seismic activity, associated with very high slip-rate of 1. The duration of those bursts is variable from a fault to another from The last glaciation of Bear Peninsula, central Amundsen Sea Embayment of Antarctica: Constraints on timing and duration revealed by in situ cosmogenic 14C and 10Be dating. Ice streams in the Pine Island-Thwaites region of West Antarctica currently dominate contributions to sea level rise from the Antarctic ice sheet.
Predictions of future ice-mass loss from this area rely on physical models that are validated with geological constraints on past extent, thickness and timing of ice cover. However, terrestrial records of ice sheet history from the region remain sparse, resulting in significant model uncertainties. We report glacial-geological evidence for the duration and timing of the last glaciation of Hunt Bluff, in the central Amundsen Sea Embayment. A multi-nuclide approach was used, measuring cosmogenic 10Be and in situ14C in bedrock surfaces and a perched erratic cobble.
Bedrock 10Be ages ka reflect multiple periods of exposure and ice-cover, not continuous exposure since the last interglacial as had previously been hypothesized. In situ14C dating suggests that the last glaciation of Hunt Bluff did not start until Thickening of ice at Hunt Bluff most likely post- dated the maximum extent of grounded ice on the outer continental shelf. Flow re-organisation provides a possible explanation for this, with the date for onset of ice-cover at Hunt Bluff providing a minimum age for the timing of convergence of the Dotson and Getz tributaries to form a single palaeo-ice stream.
This is the first time that timing of onset of ice cover has been constrained in the Amundsen Sea Embayment. This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka.
Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano.
Constraining the age of Aboriginal rock art using cosmogenic Be and Al dating of rock shelter collapse in the Kimberley region, Australia. The Kimberley region, northwest Australia, possesses an extensive and diverse collection of aboriginal rock art that potentially dates to more than 40, years ago. However, dating of such art using conventional techniques remains problematic. In the upper atmosphere several radioactive isotopes are produced when cosmic rays collide with atmospheric molecules at high speed.
These isotopes are known as cosmogenic isotopes.
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The production rate of the cosmogenic isotopes depends on the strength of the cosmic radiation, which again varies with the strength of the Earth magnetic field and with the solar activity. Therefore, records of cosmogenic isotope production rates are invaluable for understanding the relation between past climate change, the Earth magnetic field, and variations in the solar activity.
Currently, the exact influence of past and future variations in the solar activity on climate is much debated. The cosmogenic ice core profiles provide one of the key records to resolve this controversy. The Earth magnetic field is shielding the Earth from charged cosmic particles such that a relatively strong magnetic field reduces the production of radiogenic isotopes. From Wikipedia, the free encyclopedia. Chemistry of the Elements 2nd ed.