10Be Production Research Articles

10Be in Lake Lisan sediments — A proxy for production or climate?

The geochemical behavior of 10Be in the modern Dead Sea hydrological–limnological system was studied in order to evaluate the feasibility of using Dead Sea and Lake Lisan (the late Pleistocene precursor of the Dead Sea) sediments as archives of the variations in the 10Be production rate. 10Be concentrations in detrital and aragonite material from Lake Lisan laminated sediments were compared to those measured in modern dust, terra rossa soil (aeolian in origin), loess from the Negev Desert, flood suspended load and waters along a rain-flood development pathway (the transition from rain to incipient runoff and fully developed floods). 10Be concentrations decreased throughout the flood development profile, from 8.2 × 10 3 atoms g − 1 in the runoff down to ~ 1 × 10 3 atoms g − 1 in Dead Sea brine due to fast removal of 10Be by the soil and dust particles. Thus, most of the 10Be in the lake is contained within the detrital sediments that collect the 10Be transported by particles from the surrounding terrain (e.g. desert dust with 1.6 ± 0.8 × 10 8 atoms g − 1 and terra rossa soil-material with up to 12.5 ± 0.5 × 10 8 atoms g − 1 ). The high-stand periods of Lake Lisan were characterized by annual deposition of silty-detritus sediments reflecting rapid transfer of desert dust to the lake by floods. Indeed, the bulk sediments of Lake Lisan (in which 10Be is associated mainly with silty-detritus) display 10Be concentrations similar to those of desert dust. This demonstrates that 10Be variations were modulated by climate (i.e., particle transport). Significant positive 10Be peaks (up to 1.6 × 10 8 atoms g − 1 ) appear during intervals of geomagnetic anomalies in Lake Lisan stratigraphy and in the global record (i.e. during the Laschamp geomagnetic event at ~ 41 ka BP). This indicates that 10Be atmospheric production signal is superimposed on the climatic 10Be variations. We conclude that after “de-trending” of the climatic signal, Lake Lisan sediments may be used as an archive for atmospheric 10Be production.

Exposure age dating and Equilibrium Line Altitude reconstruction of an Egesen moraine in the Maritime Alps, Italy

Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present‐day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas.

In-phase anomalies in Beryllium-10 production and palaeomagnetic field behaviour during the Iceland Basin geomagnetic excursion

Increases in the production rate of cosmogenic radionuclides associated with geomagnetic excursions have been used as global tie-points for correlation between records of past climate from marine and terrestrial archives. We have investigated the relative timing of variations in 10Be production rate and the corresponding palaeomagnetic signal during one of the largest Pleistocene excursions, the Iceland Basin (IB) event (ca. 190 kyr), as recorded in two marine sediment cores (ODP Sites 1063 and 983) with high sedimentation rates. Variations in 10Be production rate during the excursion were estimated by use of 230Th xs normalized 10Be deposition rates and authigenic 10Be/ 9Be. Resulting 10Be production rates are compared with high-resolution records of geomagnetic field behaviour acquired from the same discrete samples. We find no evidence for a significant lock-in depth of the palaeomagnetic signal in these high sedimentation-rate cores. Apparent lock-in depths in other cores may sometimes be the result of lower sample resolution. Our results also indicate that the period of increased 10Be production during the IB excursion lasted longer and, most likely, started earlier than the corresponding palaeomagnetic anomaly, in accordance with previous observations that polarity transitions occur after periods of reduced geomagnetic field intensity prior to the transition. The lack of evidence in this study for a significant palaeomagnetic lock-in depth suggests that there is no systematic offset between the 10Be signal and palaeomagnetic anomalies associated with excursions and reversals, with significance for the global correlation of climate records from different archives.

Production of the cosmogenic isotopes 3H, 7Be, 10Be, and 36Cl in the Earth's atmosphere by solar and galactic cosmic rays

In a follow‐up study to the earlier work of Webber and Higbie (2003) on 10Be production in the Earth's atmosphere by cosmic rays, we have calculated the atmospheric production of the cosmogenic isotopes 3H, 7Be, 10Be, and 36Cl using the FLUKA Monte Carlo code. This new calculation of atmospheric yields of these isotopes is based on 107 vertically incident protons at each of 24 logarithmically spaced energies from 10 MeV to 10 GeV, 102 times the number used in the earlier calculation, along with the latest cross sections. This permits a study of the production due to solar cosmic rays as well as galactic cosmic rays at lower energies where isotope production is a very sensitive function of energy. Solar cosmic ray spectra are reevaluated for all of the major events occurring since 1956. In terms of yearly production of 10Be, only the February 1956 solar event makes a major contribution. For 36Cl these yearly SCR production contributions are 2–5 times larger depending on the solar cosmic ray energy spectra. We have determined the yearly production of 10Be, 36Cl, and other cosmogenic isotopes above 65° geomagnetic latitude for the time period 1940–2006 covering six solar 11‐year (a) cycles. The average peak‐to‐peak 11‐a amplitude of this yearly production is 1.77. The effects of latitudinal mixing alter these direct polar production values considerably, giving an average peak‐to‐peak 11‐a amplitude of 1.48 for the global average production.

Sensitivity and response of beryllium‐10 in marine sediments to rapid production changes (geomagnetic events): A box model study

The response and the sensitivity of the marine beryllium‐10 flux to abrupt production changes (e.g., caused by a geomagnetic event) are investigated by using a simple box model. The effect of mixing processes in the water column on the 10Be flux is simulated, and the influence of bioturbation on the sedimentary record is studied. While the effect of the oceanic residence time is found to be small, bioturbation can drastically change the shape and the amplitude of the modeled 10Be peak. The simulations indicate that 10Be production peaks persisting for more than 1500 years are recorded well in deep‐sea sediments if bioturbation‐induced integration times are small (tbio ≤ 1000 years), while sediment cores with tbio ≥ 1000 years are found to be not well suited for stratigraphic purposes. The results further show that the sedimentary 10Be peak lags initial signal. This time lag is almost independent of the event duration (for tbio ≤ 1000 years), ranging between about 400 and 600 years. Therefore the model results support the idea that marine 10Be peaks corresponding to geomagnetic events can be used as a global time marker to match marine, terrestrial, and ice core chronologies on the millennial and (if the time lag of (500 ± 100) years is considered) the submillennial timescale.

Attenuation of cosmogenic 10Be production in the first 20 cm below a rock surface

Cosmogenic 10Be has been measured in short drill cores taken from a glacially polished cliff surface. The high-resolution concentration depth profile is compared to theoretical profiles of various attenuation lengths and different shapes near the surface. Preliminary modeling results shows that long apparent attenuation lengths and perhaps a non-decreasing or “flat” section right below the surface are best suited to bring experiment and theory into agreement.

Modeling production and climate‐related impacts on 10Be concentration in ice cores

The connection between the production of the cosmogenic isotope 10Be and changes in heliomagnetic activity makes ice core 10Be an attractive proxy for studying changes in solar output. However, interpreting 10Be ice core records on centennial timescales is complicated by potential climate‐related deposition changes that could obscure the 10Be production signal. By using the Goddard Institute for Space Studies ModelE general circulation model to selectively vary climate and production functions, we model 10Be flux at key ice‐coring sites. We vary geomagnetic field strength and the solar activity modulation parameter (ϕ), CO2, sea surface temperatures, and volcanic aerosols to assess impacts on 10Be. Specifically, we find significant latitudinal differences in the response of 10Be fluxes to changes in the production function. In the climate experiments the 10Be deposition changes simulated over ice sheets in both hemispheres are comparable to those seen in the production experiments. This altered deposition combined with changes of snow accumulation results in significant climate‐related 10Be concentration variation in both Greenland and Antarctica. Over the Holocene our results suggest that the 10Be response to climate change should not be neglected when inferring production changes.

High-resolution records of 10Be production rates during the Iceland Basin excursion

High-resolution records of 10Be production rates during the Iceland Basin excursion

Authigenic 10Be/ 9Be signature of the Laschamp excursion: A tool for global synchronisation of paleoclimatic archives

Authigenic 10Be and 9Be isotope concentrations have been measured in marine sediments deposited between 10 and 60 ka BP in the western equatorial Pacific and their ratio compared to the geomagnetic relative paleointensity (RPI) record obtained from the same core [C.L. Blanchet, N. Thouveny, T. de Garidel-Thoron, New evidences of geomagnetic moment lows between 30 and 45 ka BP from a sedimentary sequence of the west equatorial Pacific, Quat. Sci Rev. (in press)]. Over the studied time interval, dated by radiocarbon and oxygen isotope stratigraphy, three periods of reduced RPI occurring at ∼ 32, 37 and 45 ka, according to the constructed age model, are concomitant with three significant increases in atmospheric 10Be production. Since the most prominent 10Be/ 9Be peak necessarily results from the weakest geomagnetic moment event, i.e. that associated with the Laschamp excursion, we assign to this cosmogenic nuclide event the age of the Laschamp excursion (i.e. 40.4 ± 2.0 ka BP) [H. Guillou, B.S. Singer, C. Laj, C. Kissel, S. Scaillet, B.R. Jicha, On the age of the Laschamp geomagnetic excursion, Earth Planet. Sci. Lett. 227 (2004) 331–343]. Cosmogenic nuclide production peaks provide critical complementary evidence for the identification of geomagnetic dipole lows linked to excursions and constitute accurate markers for global intercorrelation of paleoclimatic archives.

Cosmogenic-nuclide and varve chronologies for the deglaciation of southern New England

We report new cosmogenic-nuclide exposure ages from the Ledyard and Old Saybrook Moraines in eastern Connecticut, summarize previously published exposure ages from elsewhere in southern New England, and compare the resulting deglaciation chronology with that derived from the New England varve chronology. The geomorphic context of southern New England moraine boulders indicates that postdepositional disturbance of boulders, and consequent scatter in boulder exposure ages, should be negligible. Exposure ages of these boulders reinforce this conclusion: the scatter among boulder ages from each moraine is no more than that expected from the measurement uncertainty of the ages. We therefore conclude that geologic uncertainties in the exposure histories of the boulders are relatively unimportant, and that the precision of the exposure-age chronology for deglaciation of southern New England is limited only by the measurement uncertainty of each exposure age and the number of exposure ages. However, exposure ages for deglaciation are nominally at least 1700 yr younger than deglaciation ages inferred from the New England varve chronology and its associated calibration to the absolute calendar year time scale, which is a significant discrepancy relative to the internal precision of each chronology. This discrepancy is similar in size to the uncertainties in the two independently determined parameters that link the two chronologies to the absolute calendar year time scale, that is, the 10Be production rate and the varve year–calendar year offset. Taking into account the uncertainty in these two parameters, the two chronologies essentially agree, and present the opportunity to more accurately determine these parameters by enforcing internal consistency between the two chronologies. The combined deglaciation chronology that results from this exercise indicates that southeastern Connecticut was deglaciated 18,500–19,000 yr BP. It suggests that the varve year–calendar year offset has been overestimated by several hundred years and that the local 10Be production rate has been overestimated by a few percent, and it is consistent with: (a) independent measurements of the varve year–calendar year offset; (b) independent measurements of the 10Be production rate; (c) relevant limiting radiocarbon ages; and (d) the present understanding of the most likely relationship between the exposure age of major moraines and North Atlantic climate changes. The internal consistency of the two chronologies could be further improved by additional exposure dating of ice-marginal landforms that have direct stratigraphic links to the varve chronology. This, in turn, would also result in improved estimates of both the varve year–calendar year offset and cosmogenic-nuclide production rates.

In situ 10Be exposure ages from southeastern Norway: implications for the geometry of the Weichselian Scandinavian ice sheet

As an initial attempt to constrain the geometry and history of the southern part of the Scandinavian ice sheet, in situ 10Be concentrations in bedrock samples have been measured from four sites in southeastern Norway. Among our results are a number of pre-Last Glacial Maximum (LGM) exposure ages. Bedrock outcrops in high elevation blockfields typically give surface exposure ages older than 20 10Be ka, whereas glacially moulded bedrock surfaces at lower elevations yield surface exposure ages younger than 15 10Be ka. These results clearly indicate the preservation of surfaces and landforms predating the LGM. Most ice-sheet models predict a thick ice mass in southeastern Norway at the LGM. Pre-LGM 10Be ages either contradict the models, supporting geomorphological reconstructions of a thin LGM ice sheet, or indicate preservation of previously exposed surfaces beneath cold-based ice. In the latter case, models of 10Be production incorporating regional glacial chronology and periodic burial suggest that the surfaces with the highest 10Be concentrations may have existed for more than one million years.

In situ cosmogenic 10Be and 21Ne in sanidine and in situ cosmogenic 3He in Fe–Ti-oxide minerals

We report concentrations of in situ cosmogenic 10Be and 21Ne from coexisting quartz and sanidine separates and of cosmogenic 3He in coexisting Fe–Ti-oxide minerals from ignimbritic successions of northern Chile (Oxaya and Lauca ignimbrites). New mineral-isotope pairs such as sanidine and Fe–Ti-oxide minerals are helpful in quantitative geomorphology for geological settings where the lithology lacks the commonly used minerals quartz, pyroxene or olivine. Production rates in sanidine and Fe–Ti-oxide minerals were determined by normalizing nuclide concentrations to established production rates in quartz. The experimentally determined production rates are compared to model production rates calculated with new cross-sections for 3He, 21Ne, and 10Be production from the individual target elements. The mean experimental 21Ne production rate for five sanidine samples is 30.4 ± 3.7 atoms g − 1 yr − 1 (30.4 ± 5.4 atoms g − 1 yr − 1 including the uncertainty of the 21Ne production rate in quartz, P 21Ne qtz). This is in excellent agreement with the modelled value of 28.3 atoms g − 1 yr − 1 , which has an estimated uncertainty of 20%. The 21Ne production rate in sanidine is thus about 50% higher than that in quartz. The cosmogenic neon in sanidine is entirely released in low temperature steps (400–600 °C) and no signs of an interfering nucleogenic neon component were observed. This is in stark contrast to quartz and makes sanidine an attractive mineral for terrestrial cosmogenic neon studies. 3He diffuses out of the sanidine structure. Preliminary results also indicate that sanidine is well suited for 10Be studies. The mean experimental 10Be production rate from two sanidine samples is 4.45 ± 0.38 atoms g − 1 yr − 1 (4.45 ± 0.42 atoms g − 1 yr − 1 including uncertainty of P 10Be qtz), very close to the modelled value of 4.55 atoms g − 1 yr − 1 , which has an estimated uncertainty of 20%. We emphasize that 10Be and 21Ne production in sanidine is composition dependent. Therefore, major element analyses should be carried out and production rates calculated on a sample by sample basis. Fe–Ti-oxide minerals retain 3He quantitatively. Experimentally derived production rates are in excellent agreement with new values derived from physical modelling. The mean experimental 3He production rate for five Fe–Ti-oxide minerals samples is 120 ± 11 atoms g − 1 yr − 1 (120 ± 12 atoms g − 1 yr − 1 including the uncertainties of P 21Ne qtz), compared to a mean modelled value of 124 atoms g − 1 yr − 1 , which has an estimated uncertainty of 20%. The variable chemical and structural composition of the solid solution lines of Fe–Ti-oxide minerals has little effect on the total 3He production rate. Cosmogenic 21Ne is not produced in significant quantities in Fe–Ti-oxide minerals due to the absence of suitable target elements.

Use of in situ-produced 10Be in carbonate-rich environments: A first attempt

We have determined the production rate of in situ-produced 10Be in calcite through measurements of 10Be and 36Cl concentrations in the same calcite samples and of 10Be concentrations in depth profiles of flint from the same erosional surface. This yields a 10Be production rate in calcite of 37.9 ± 6.0 at/g/yr at sea level and high latitude, approximately sixfold higher than production in the coexisting flint. We propose that this higher rate of production may be due to high production cross sections for C spallation by cosmic rays with energies below 50 MeV. These results also open the possibility of dating burial events in carbonate-rich environments by differential radioactive decay of 10Be and 36Cl.

Solar Activity Record from Archeomagnetic Data

Each of the available solar activity (SA) proxy data (historical notes, radio nuclides 14C and 10Be production) are contaminated by their specific noise factors. So, any additional proxy with its independent noise factors will essentially increase the accuracy of composite SA restorations. It is proposed here that archaeomagnetic measurements 95% confidence interval (α95) may serve as new proxy for the SA estimation in the past. This proxy is compared with other available proxies during the years 1500–2000.

New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado

New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. 10Be data sets from the three areas were scaled to a single 10Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average 10Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this 10Be production rate yields ages comparable to those calculated with a commonly used 36Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ∼16.8 36Cl ka (Cosmogenic ages in this paper are labeled 10Be or 36Cl ka or just ka when both 10Be or 36Cl ages are being discussed; radiocarbon ages are labeled 14C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (±1 σ) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 10Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 36Cl ka at Hogback Mountain, Colorado.

Geomagnetic effects on time-integrated cosmogenic nuclide production with emphasis on in situ 14C and 10Be

Production of cosmogenic nuclides (CNs) in geologic material is a function of the cosmic-ray flux at the Earth's surface, which in turn is a function of the intensity and orientation of the Earth's geomagnetic field. Temporal variations in the intensity of the geomagnetic field and the position of the geomagnetic dipole axis (i.e., polar wander) must be considered when calculating production rates that are integrated through time. We have developed a model, based in part on protocols set forth by Desilets and Zreda [Earth Planet. Sci. Lett. 206 (2003) 21–42], that accounts for these variations in an effort to systematically determine their impact on time-integrated production of short-lived (in situ 14C; t1/2=5.73 ka) and long-lived (in situ 10Be; t1/2=1.5 Ma) CNs. Our modeling results show that for samples exposed for the last 3 ka, integrated in situ 14C and 10Be production rates that account for temporal variations in the intensity of the Earth's geomagnetic field are up to ∼13% lower than modern rates at the same location [modern rates are referenced to the 1945.0 Definitive Geomagnetic Reference Field (DGRF)]. In contrast, intensity-corrected 10Be rates are up to ∼30% higher than modern for samples exposed for >25–30 ka. Intensity variations have little effect (<5%) on integrated CN production for samples exposed for the last 15–20 ka, regardless of site location or nuclide used.Our modeling results also show that the impact of polar wander on integrated CN production is secondary compared to intensity variations. Accounting for polar wander is critical, however, when determining modern production rates at midlatitudes (30–40°) because of the current offset between the geomagnetic and geographic poles. At sea level, integrated in situ 14C production rates that account for both intensity variations and polar wander range from 27% higher to 24% lower than modern rates at the same location, and integrated in situ 10Be rates range from 48% higher to 26% lower than modern. Differences between integrated and modern rates increase significantly at higher altitudes. Based on these results, we recommend correcting the modern production rate (referenced to the 1945.0 DGRF or another specific geomagnetic reference field) at site latitudes <60° for variations in the intensity of the Earth's geomagnetic field during exposure and for polar wander over the last 10 ka.

Solar activity record from archaeomagnetic data

Each of the available solar activity (SA) proxy data (historical notes, radio nuclides 14C and 10Be production) are contaminated by their specific noise factors. So, any additional proxy with its independent noise factors will essentially increase the accuracy of composite SA restorations. It is proposed here that archaeomagnetic measurements 95% confidence interval (α95) may serve as new proxy for the SA estimation in the past. This proxy is compared with other available proxies during the years 1500–2000.

A re-evaluation of the 0–10 ka 10Be production rate for exposure dating obtained from the Köfels (Austria) landslide

The sea level, high latitude 10Be production rate for exposure dating obtained from the giant 9.8 ka landslide of Köfels (Austria) has been calculated based on a re-assessment of the contribution of the muonic cosmic ray component. The 0–10 ka production rate value is 5.44±0.19 10Be atoms/yg quartz.

Cosmogenic 10Be and 26Al dating of erratic boulders in the southern coastal area of Lake Baikal, Siberia

Cosmogenic 10Be and 26Al dating of three erratic boulders in the southern coastal area of Lake Baikal was performed using accelerator mass spectrometry (AMS) at MALT (MicroAnalysis Laboratory, Tandem accelerator) of the University of Tokyo. We examined the accuracy of our 10Be AMS measurements and the differences in scaling factors for the 10Be and 26Al production rates. The measured 10Be and 26Al ages are 15–13 and 17–11.5 kyr, respectively. The 10Be ages suggest that release of the erratic boulders from a melting glacier occurred during the Bølling/Allerød warm period, when the land and lacustrine environments of the Baikal region changed dramatically.

Exposure dating of underwater rocks: potential application to studies of land bridges during the Ice Ages

10Be concentrations for four underwater rock samples from the Tsugaru Strait, Japan were obtained. Most of the 10Be concentrations of these samples are higher than the expected steady state concentration at the relevant underground depth, implying that most samples have been pre-exposed during the last ice age. The model calculation of 10Be production using recent rates for underground production and parameters of sea level change, uplift rate and erosion rate of this study could be an essential tool for exposure dating applications for both underwater and marine terrace samples.