10Be Production Research Articles

Cosmogenic 10Be production rate calibrated against 3He in the high Tropical Andes (3800–4900 m, 20–22° S)

Many geomorphologic applications, notably glacier chronologies, require improvements in both the precision and the accuracy of the cosmogenic dating tool. Of particular importance is the need to better constrain the spatial variability of the cosmogenic nuclides production rates at high elevation and low latitudes. One strategy that can be adopted for this is to couple absolute calibrations, from independently dated surfaces, with cross-calibration studies, performed by measuring several cosmogenic nuclides in the same rock.In the present study, we report the highest-elevation (>4800 m) cross-calibration published to date, comprising measurements of cosmogenic 3He and 10Be in cogenetic pyroxene and quartz. The samples were collected from six dacitic moraine boulders, exposed from 32 to 65 ka at 4820 m on the flanks of the Uturuncu volcano (22° S, 67° W), Southern Lipez (Bolivia). The samples yield a remarkably tight cluster of 3He–10Be production ratios, with a weighted mean of 33.3±0.9(1σ). This production ratio is undistinguishable, within uncertainties, from the 3He–10Be production ratio of 32.3±0.9 determined in the same mineral pair at low elevation (1333 m) by Amidon et al. (2009). These results agree at the 1σ level and suggest that any hypothetical increase of the 3He–10Be production ratio in pyroxene and quartz is likely to be lower than 5% over this elevation range (1000–5000 m). Moreover, the production ratio is almost insensitive to the Li content of the pyroxene (20 to 50 ppm Li), suggesting that the cosmogenic thermal neutron production of 3He is very low in this setting.The high-elevation 3He–10Be production ratio is used in combination with a local determination of the 3He production rate in the high Central Altiplano (3800 m) (Blard et al., 2013) to establish a local 10Be production rate of 30.0±1.4 atg−1yr−1 at 3800 m and 20° S. After scaling to sea-level high latitude with the time-dependent Lal/Stone model, this yields a 10Be production rate in quartz of 3.63±0.17 atg−1yr−1. Importantly, this rate can be used for high-precision geomorphologic dating, for example for determining glacial chronologies (1σ<4%) through 10Be dating of moraines in the high Tropical Andes. Any inaccuracy attached to the scaling model is canceled out when the calibration site is located close to the dated object.The same experiment was also undertaken in pyroxene and plagioclase from two andesitic boulders from the Tunupa volcano moraines, exposed at 3800 m and 4200 m. A 3He–10Be production ratio of 35.9±1.3(1σ) is obtained for this mineral pair, indicating that the 10Be production rate in plagioclase is about 8% lower than in quartz.

Phase of solar activity affects response of solar proxy 10Be

The solar proxy 10Be, measured in natural archives, has previously been assumed to lag solar activity by 1–2 yr. This reflects its residence time in the stratosphere where its main source lies. This study, based on a 30-yr global model simulation of the atmospheric transport of 10Be, shows that the stratospheric fraction of production varies significantly with the phase of solar activity. This leads to a lag between production change and deposition response of ca. 1 yr during the decreasing phase of solar activity but nearly no lag when solar activity increases. No lag is found for 7Be. The fraction of 10Be production in the stratosphere varies from ca. 65% to 69% between solar minimum (ϕ=400 MV) and maximum (ϕ=1200 MV), being highest during low solar activity when production is highest. When solar activity starts to decrease and production rate increase, the change is largest in polar stratosphere where residence time is long. This leads to a delayed response in 10Be deposition. When production rate decreases, the relative production change is larger in the troposphere, leading to a quicker deposition response. The difference between phases is larger in southern hemisphere. The form of reconstructed 11-yr cycles based on high-resolution 10Be records could therefore be biased if no correction is applied.

A 10Be production‐rate calibration for the Arctic

ABSTRACTWe present a Baffin Bay 10Be production‐rate calibration derived from glacial deposits in western Greenland and Baffin Island, and test our results against published 10Be calibration datasets to develop an Arctic 10Be production rate. Our calibration comprises: (i) 10Be measurements from moraine boulders linked to a 14C‐dated moraine at Jakobshavn Isfjord in western Greenland, (ii) an independent and previously published 10Be production rate at Jakobshavn Isfjord and (iii) re‐measured 10Be concentrations from a Baffin Island calibration site that is included in the north‐eastern North America dataset. Combined, we calculate a sea‐level/high‐latitude 10Be production rate for the Baffin Bay region of 3.96 ± 0.07 atoms g−1 a−1 (Lal/Stone scaling model). After testing the Baffin Bay rate against calibration sites in Norway and north‐eastern North America, we calculate a more conservative Arctic production rate of 3.96 ± 0.15 atoms g−1 a−1. The Baffin Bay and Arctic 10Be production rates are indistinguishable from the north‐eastern North America 10Be production rate (3.91 ± 0.19 atoms g−1 a−1) and yield overall uncertainties of &lt;2–3.7% (1σ). These production rates reduce systematic uncertainties in 10Be‐based chronologies of ice‐margin change and allow 10Be‐based chronologies to be more confidently compared with high‐resolution climate records, such as those from Greenland ice cores.

Constraints on 10Be and 41Ca distribution in the early solar system from 26Al and 10Be studies of Efremovka CAIs

Three refractory coarse grained CAIs from the Efremovka CV3 chondrite, one (E65) previously shown to have formed with live 41Ca, were studied by ion microprobe for their 26Al–26Mg and 10Be–10B systematic in order to better understand the origin of 10Be. The high precision Al–Mg data and the inferred 26Al/27Al values attest that the precursors of the three CAIs evolved in the solar nebula over a period of few hundred thousand years before last melting–crystallization events. The initial 10Be/9Be ratios and δ10B values defined by the 10Be isochrons for the three Efremovka CAIs are similar within errors. The CAI 10Be abundance in published data underscores the large range for initial 10Be/9Be ratios. This is contrary to the relatively small range of 26Al/27Al variations in CAIs around the canonical ratio. Two models that could explain the origin of this large 10Be/9Be range are assessed from the collateral variations predicted for the initial δ10B values: (i) closed system decay of 10Be from a “canonical” 10Be/9Be ratio and (ii) formation of CAIs from a mixture of solid precursors and nebula gas irradiated during up to a few hundred thousand years. The second scenario is shown to be the most consistent with the data. This shows that the major fraction of 10Be in CAIs was produced by irradiation of refractory grains, while contributions of galactic cosmic rays trapping and early solar wind irradiation are less dominant. The case for 10Be production by solar cosmic rays irradiation of solid refractory precursors poses a conundrum for 41Ca because the latter is easily produced by irradiation and should be more abundant than what is observed in CAIs. 10Be production by irradiation from solar energetic particles requires high 41Ca abundance in early solar system, however, this is not observed in CAIs.

Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric 10Be overproduction: Contribution of authigenic 10Be/9Be ratios in west equatorial Pacific sediments

Authigenic 10Be/9Be ratios were measured along a sediment core collected in the west equatorial Pacific in order to reconstruct cosmogenic 10Be production variations near the equator, where the geomagnetic modulation is maximum. From 60 to 20 ka, the single significant 10Be production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the Laschamp excursion. No significant 10Be overproduction signature is recorded at the age of the Mono Lake excursion (∼34 ka). A compilation of authigenic 10Be/9Be records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged 10Be flux record of Greenland ice cores. Their remarkable similarity demonstrates that 10Be production is globally modulated by geomagnetic dipole variations and redistributed by atmosphere dynamics. After calibration using absolute values of the virtual dipole moment drawn from paleomagnetic database, the authigenic 10Be/9Be stack allows reconstructing the geomagnetic dipole moment variations over the 20–50 ka time interval. Between 48 and 41 ka, the dipole moment collapsed at a rate of −1.5 × 1022 A m2 kyr−1, which will be an interesting criterion for the assessment of the loss rate of the historical field and the comparison of dipole moment loss prior to excursions and reversals. After a 2 kyr duration of the minimum dipole moment (∼1 × 1022 A m2), a slow increase started at 39 ka, progressively reaching 5 × 1022 A m2 at 20 ka. The absence of a significant dipole moment drop at 34 ka, the age of the Mono lake excursion, suggests that the duration and amplitude of the dipole weakening cannot be compared with that of the Laschamp. This study provides a reliable basis to model the production of radiocarbon and in situ cosmogenic nuclides and to improve the calibration of these dating methods.

A regional cosmogenic 10Be production rate calibration using two 12 kyr radiocarbon-dated rock avalanches at 69° N, Norway

A regional cosmogenic 10Be production rate calibration using two 12 kyr radiocarbon-dated rock avalanches at 69° N, Norway

Towards a 10Be production rate for Scotland

Towards a 10Be production rate for Scotland

Trimlines, blockfields, mountain-top erratics and the vertical dimensions of the last British–Irish Ice Sheet in NW Scotland

Periglacial trimlines separating glacially eroded lower slopes from blockfield-covered plateaus on British and Irish mountains have been interpreted either (1) in terms of representing the maximum altitude of the last ice sheet during the Last Glacial Maximum (LGM), or (2) as a thermal boundary separating wet-based ice at pressure melting point from cold-based ice on summit plateaus. We test these competing hypotheses through 10Be exposure dating of high-level erratic boulders above trimlines on five mountains in NW Scotland. Nine out of 14 erratics yielded post-LGM exposure ages ranging from 14.0 ± 0.7 ka to 16.5 ± 0.9 ka or from 14.9 ± 0.9 ka to 17.6 ± 1.1 ka, depending on the 10Be production rate employed in exposure age calculation. These ages refute hypothesis (1) as they imply that the last ice sheet overtopped the mountains. Preservation of apparently intact blockfields on the summits implies cold-based ice cover, supporting hypothesis (2). As altitudinally consistent high-level trimlines extend from our sampled sites across much of NW Scotland and the Hebrides, our conclusions apply to all trimlines in this broader area, and probably to all high-level trimlines elsewhere in the British Isles. Preservation of blockfields under cold-based ice is consistent with blockfield evolution on plateaus throughout much or all of the Quaternary. Averaged exposure ages of ∼15–16 ka for plateau-top erratics implies nunatak emergence from the downwasting ice sheet prior to a regional readvance of the ice margin (the Wester Ross Readvance) and before rapid warming at ∼14.7 ka at the onset of the Lateglacial Interstade, but after the timing of ice-sheet thinning as retrodicted by recent proxy climate-driven thermo-mechanical coupled models. Our findings provide an additional constraint on the future development of such models by implying that high-level trimlines represent the altitude of a former transition zone between ice at pressure-melting point and ice below pressure melting point.

Calibration of the in situ cosmogenic 14C production rate in New Zealand's Southern Alps

AbstractIn situ cosmogenic 14C (in situ 14C) analysis from quartz‐bearing rocks is a novel isotopic tool useful for quantifying recent surface exposure histories (up to ∼25 ka). It is particularly powerful when combined with longer‐lived cosmogenic isotopes such as 10Be. Recent advances in the extraction of in situ 14C from quartz now permit the routine application of this method. However, only a few experiments to calibrate the production rate of in situ 14C in quartz have been published to date. Here, we present a new in situ 14C production rate estimate derived from a well‐dated debris flow deposit in the Southern Alps, New Zealand, previously used to calibrate 10Be production rates. For example, based on a geomagnetic implementation of the Lal/Stone scaling scheme we derive a spallogenic production rate of 11.4 ± 0.9 atoms 14C (g quartz)−1 a−1 and a 14C/10Be spallogenic production rate ratio of 3.0 ± 0.2. The results are comparable with production rates from previous calibrations in the northern hemisphere. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Long-term shoreline retreat rates on Whidbey Island, Washington, USA

Long-term retreat rates of Puget Sound's unconsolidated sediment shorelines have been difficult to quantify, and little systematic research has been completed to constrain retreat in this area. We put forward a new application of cosmogenic 10Be exposure dating to assess long-term shoreline retreat on Whidbey Island, WA by dating lag boulders exposed on the shore platform as the shoreline erodes. Production of 10Be in shoreline boulders is modulated by both tidal submergence and topographic shielding from the retreating bluff. By modeling the combined effect of these variables on 10Be production, the timing of exposure can be determined and used to calculate long-term (103–104yr) bluff retreat rates. In rare cases, retreat rates are underestimated due to inherited 10Be. Within the study area, average retreat rates ranged between 0 and 8cmyr−1. Our results demonstrate the utility of cosmogenic nuclides for determining long-term shoreline retreat rates in areas with thick sediment cover, where large numbers of samples can be collected, and where the pre-depositional history of the boulders is uncomplicated.

Linking ice sheet and lake sediment archives of 10Be, 1468–1980 CE

As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric 10Be production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of 10Be in varved lake sediments.Varves were sampled over an interval covering the period 1468–2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual 10Be deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment 10Be deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity.Sediment 10Be concentrations range 2.1–17.6×108atomsg−1. The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1×108atomsg−1. The deposition rates range 0.5–3.9×106atomscm−2year−1, with an average of 1.8×106atomscm−2year−1 (0.057atomscm−2s−1). We note higher 10Be deposition during the Spörer (∼1415–1535 CE) and Maunder (∼1645–1715 CE) solar minima, and also at the onset of the Dalton (∼1790–1830 CE) minimum. Equally high 10Be values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment 10Be data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 10Be flux around 1500–1750 CE.

10Be in lacustrine sediments—A record of solar activity?

Concentrations and fluxes of cosmogenic 10Be in three varved lake sediments covering the last 100 years were determined to investigate their suitability to record past solar activity. The 10Be signal in lake sediments is composed of a component reflecting the radionuclide production in the atmosphere and a component related to the subsequent transport into the sediment. In order to separate these two components we applied singular-spectrum analysis (SSA). The extracted patterns in concentrations and depositional fluxes were compared to 10Be records from polar ice cores and to the solar modulation potential derived from neutron monitor data. In the transport component we discovered the existence of a long-term trend in the 10Be concentrations, which can be attributed to the redox cycle of both lakes. In the production component we found a similar pattern as in the NGrip ice core. A cross-correlation analysis yielded a significant negative correlation between the 10Be production component and the solar modulation potential. 10Be lags the production on average by 1.5 years which corresponds to the expected transport time from the atmosphere to the Earth's surface. Hence, we conclude that varved lake sediments are potentially suitable to study the solar activity of the past. However, one should be aware that various mechanisms may mask the 10Be signal in the sediment.

Chronology of glaciation and deglaciation during the Loch Lomond (Younger Dryas) Stade in the Scottish Highlands: implications of recalibrated 10Be exposure ages

Considerable uncertainty surrounds the timing of glacier advance and retreat during the Younger Dryas or Loch Lomond Stade (LLS) in the Scottish Highlands. Some studies favour ice advance until near the end of the stade (c. 11.7 ka), whereas others support the culmination of glacier advance in mid‐stade (c. 12.6–12.4 ka). Most published 10 Be exposure ages reported for boulders on moraines or deglacial sites post‐date the end of the LLS, and thus appear to favour the former view, but recalibration of 33 10 Be ages using a locally derived 10 Be production rate and assuming rock surface erosion rates of zero to 1 mm ka−1 produces exposure ages 130–980 years older than those originally reported. The recalibrated ages are filtered to exclude anomalous data, and then employed to generate aggregate probability density distributions for the timing of moraine deposition and deglaciation. The results suggest that the most probable age for the timing of the deposition of the sampled outermost moraines lies in the interval 12.4–12.1 ka or earlier. Deglacial ages obtained for sites inside Loch Lomond Stadial glacier limits imply that glaciers at some or all of the sampled sites were retreating prior to 12.1 ka. Use of aggregated data does not exclude the possibility of asynchronous glacier behaviour at different sites, but confirms that some glaciers reached their maximum limits and began to retreat several centuries before the rapid warming that terminated the LLS at 11.7–11.6 ka, consistent with the retrodictions of recent numerical modelling experiments and with geomorphological evidence for gradual oscillatory ice‐margin retreat under stadial conditions.

Centennial to millennial geomagnetic field variations

Reconstructions of the geomagnetic field in the past represent a useful tool not only to investigate the geodynamo process, but also to estimate the effect of geomagnetic shielding for any studies on cosmogenic radionuclides and galactic cosmic rays. A number of new millennial-scale geomagnetic field reconstructions have been published over the last years, based on improved global archeo- and paleomagnetic data compilations. Here we review several spherical harmonic models and compare their dipole field predictions to reconstructions based on virtual axial dipole moments and virtual geomagnetic poles. Dipole intensity estimates from cosmogenic radionuclide production records, with suitable filtering to minimise the solar influence, have also been included in the comparison to provide independent information about variations in the strength of the geomagnetic field. However, due to differences among geomagnetic models and between 14C and 10Be production records this comparison is fairly inconclusive with respect to multi-centennial variations. Different geomagnetic dipole tilt reconstructions agree well for much of the Holocene, but dipole moment estimates still differ substantially. Recent spherical harmonic models for the past 3 and 10 kyrs have improved considerably compared to earlier versions. Nevertheless at present we recommend to test if any interpretation depends on the choice of model.

Constraining Holocene 10Be production rates in Greenland

AbstractThe absence of a production rate calibration experiment on Greenland has limited the ability to link 10Be exposure dating chronologies of ice‐margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbræ, western Greenland, to investigate 10Be production rates. The radiocarbon chronology is inconsistent with the 10Be age calculations based on the current globally averaged 10Be production rate calibration data set, but is consistent with the 10Be production rate calibration data set from north‐eastern North America, which includes a calibration site nearby on north‐eastern Baffin Island. Based on the best‐dated feature available from the Jakobshavn Isbræ forefield, we derive a 10Be production rate value of 3.98 ± 0.24 atoms g a−1, using the ‘St’ scaling scheme, which overlaps with recently published reference 10Be production rates. We suggest that these 10Be production rate data, or the very similar data from north‐eastern North America, are used on Greenland. Copyright © 2011 John Wiley &amp; Sons, Ltd.

The Laschamp geomagnetic dipole low expressed as a cosmogenic 10Be atmospheric overproduction at ~ 41 ka

Authigenic 10Be/ 9Be ratio measurements were performed at high resolution along a Portuguese Margin deep-sea core (37°48 N; 10°09 W) spanning the 20–50 ka time interval, in order to reconstruct variations in atmospheric cosmogenic 10Be production rates and derive the related geomagnetic dipole moment modulation. A complementary approach consisting in 230Th xs-normalized 10Be deposition rate determination on selected samples confirmed the reliability of the authigenic 10Be/ 9Be record. This study constitutes the first successful comparison of the two widely-used normalization techniques of 10Be concentrations. For both methods, the presented results herein evidence a factor of ~ 2 cosmogenic nuclide overproduction linked to a minimum dipole moment associated with the Laschamp Excursion. The latter is stratigraphically constrained beneath Heinrich Event 4. Its age is estimated at ~ 41 ka on the basis of direct correlation between the series of rapid paleoclimatic events recorded in the Portuguese Margin sediments and in the Greenland ice sheet, and is confirmed by calibrated radiocarbon dating carried out on the same sediments. The remarkable agreement between the authigenic 10Be/ 9Be and the Greenland Ice cores 10Be deposition rate records attests to their global significance. This new authigenic 10Be/ 9Be record has been combined with that previously obtained at the same site to produce a stacked record that is calibrated using absolute values of Virtual Dipole Moment determined on lava flows. This provides a reconstruction of dipole geomagnetic moment variations over the 20–50 ka interval, independent from paleomagnetically-constrained methods, that documents the Laschamp dipole low but fails to express any dipole low related to the Mono Lake Excursion. This high resolution record responds to the necessity of supplementing the knowledge of the atmospheric Δ 14C variations in the 30–45 ka interval during which the 14C calibration curve suffers from a lack of accurate data, and during which a discrepancy of about 5500 yr between the 14C and U–Th ages is due to the Laschamp geomagnetic dipole low. Such new high resolution datasets from records obtained from different latitudes will be required to make significant advances in understanding the causes of atmospheric Δ 14C variations.

Did large ice caps persist on low ground in north‐west Scotland during the Lateglacial Interstade?

AbstractRecent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived 10Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley &amp; Sons, Ltd.

10Be Production in the Atmosphere by Galactic Cosmic Rays

Galactic cosmic ray nuclei and energetic protons produced in solar flares and accelerated by coronal mass ejections are the main sources of high-energy particles of extraterrestrial origin in near-Earth space and inside the Earth’s atmosphere. The intensity of galactic cosmic rays inside the heliosphere is strongly influenced by the modulation of the interstellar source particles on their way through interplanetary space. Among others, this modulation depends on the activity of the Sun, and the resulting intensity of the energetic particles in the atmosphere is an indicator of the solar activity. Therefore, rare isotopes found in historical archives and produced by spallation reactions of primary and secondary hadrons of cosmic origin in the atmosphere, so-called cosmogenic nuclides, can be used to reconstruct the solar activity in the past. The production rate of 10Be, one of the cosmogenic nuclides most adequate to study the solar activity, is presented showing its variations with geographic latitude and altitude and the dependence on different production cross-sections present in literature. In addition, estimates for altitude integrated production rates of 10Be at different locations since the early nineteen sixties are shown.

Volcanic and solar activity, and atmospheric circulation influences on cosmogenic 10Be fallout at Vostok and Concordia (Antarctica) over the last 60 years

The cosmogenic nuclide beryllium-10 ( 10Be), recovered from ice cores, is often used to study solar activity on long timescales. However, the 10Be signal is also influenced by factors other than the Sun. To identify and quantify various contributions to the 10Be signal, two Antarctic snow records from the Vostok and Concordia sites spanning the last 60 years were studied at a sub-annual resolution. Three factors that contribute to the 10Be signal were identified. First, a significant period of approximately 11 yr that can be associated with the modulation of 10Be production by solar activity was detected in both records. The solar imprint constitutes 20–35% of the variance within the total signal. The 11-yr 10Be snow component was attenuated by a factor of ∼0.5 and was delayed by ∼1.4 yr compared to the 10Be production expected within the polar atmosphere. The result could be interpreted as the composite response of a stratospheric 10Be reservoir with an 11-yr modulation that was attenuated and delayed (with respect to 10Be polar production) and to a tropospheric 10Be reservoir with an 11-yr modulation that was not attenuated or delayed. Then, peaks in 10Be concentrations that were ∼66% and ∼35% higher than the average concentration were observed during the stratospheric volcanic eruptions of Agung (in 1963) and Pinatubo (in 1991), respectively. In light of these new results, published 10Be ice core records could be reinterpreted because spikes in 10Be concentration appear at the time of several stratospheric events. The data indicate that stratospheric volcanic eruptions can impact 10Be transport and deposition as a result of the roles played by the sedimentation of sulfate aerosols and the formation and rapid settling of polar stratospheric clouds (PSC). Also, an interannual variability of ∼4 yr was determined in both 10Be records, corresponding to ∼26% of the variance within the signal at Vostok. As with species of marine origin (sodium), this 4-yr variability is interpreted as a tropospheric modulation. The 4-yr variability could be associated with atmospheric circulation associated with the coupled Southern Ocean ocean–atmosphere system. The results presented here, from sites within the high Antarctic plateau, open new possibilities for ice core dating over the last few centuries and for the reconstruction of past solar activity in relation to climate.

Late glacial and holocene 10Be production rates for western Norway

AbstractWe present a new regional calibration of the 10Be production rate from two well‐dated surfaces in southern Norway: a rock avalanche with 14C‐dated wood and a precisely dated Younger Dryas moraine. Calculated 10Be production rates are 4.26 ± 0.13 and 4.65 ± 0.14 at g−1 a−1 for the Lal/Stone and Lifton scaling models, respectively. Our regional production rate for southern Norway is 5% lower than the canonical global 10Be production rate with lower uncertainties. Our 10Be production rate agrees with regional 10Be production rates from north‐eastern North America and New Zealand. The 10Be production rate estimate presented here can be used to improve the precision and accuracy of exposure‐dated ice‐marginal features, as well as other surfaces, in northern Europe. Copyright © 2011 John Wiley &amp; Sons, Ltd.