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... The average time resolution of these three records are 850 years (400 years over the 46-36 ka time interval) for core MD95-2042 (limited to 60-27.4 ka), 600 years (500 years over the 48-28 ka time interval) for core MD04-2811 (limited to 51-20 ka) and 1000 years for core MD05-2930. We recalculated all published Be ratio results based on original 10 Be and 9 Be data following Simon et al. (2016b) (see results in the supporting material, Tables S1-S4). ...
... New authigenic Be isotopes analyses were carried out at the CEREGE National Cosmogenic Nuclides Laboratory (LN2C, France) on 44 samples according to the chemical procedure established by Bourlès et al. (1989) and revised by Simon et al. (2016b). Authigenic 10 Be and its stable isotope 9 Be were extracted from 1 g dry samples by soaking them in a 20 ml leaching solution (0.04 M hydroxylamine (NH 2 OH-HCl) and 25% acetic acid) at 95 ± 5 • C for 7 h. ...
... The Be ratio varies from 4.3 to 12.5 × 10 −8 with an average value and standard deviation of 7.5 ± 1.7 × 10 −8 (Fig. 2D). A systematic offset of nearly 10% between the "old" 10 Be and 9 Be concentrations from Ménabréaz et al. (2012) and our new data is observed ( Fig. 2B-C) and explained by different leaching durations between the two studies, since all other steps of the original method proposed by Bourlès et al. (1989) are nearly similar (Simon et al., 2016b). Most importantly, these offsets are canceled out when using the Be ratio ( Fig. 2D) emphasizing the need to use the ratio between the cosmogenic radionuclide ( 10 Be) and the authigenic fraction of its stable isotope ( 9 Be) for robust interpretations of past 10 Be production variations, rather than comparing variations of 10 Be-leachate concentrations or raw 10 Be-fluxes ( 10 Be leachate concentrations × sediment density × sedimentation rate) that are methods dependent. ...
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Documenting accurately amplitude and rhythms of geomagnetic variations is a prerequisite to understand the mechanisms triggering geomagnetic excursions and reversals. We present new authigenic 10Be/9Be ratio (Be ratio) results covering the 60–20 ka time interval from equatorial core MD05-2920. The most significant Be ratio peak is located 18 cm above the main relative paleointensity (RPI) minimum recorded in this sequence. These are interpreted as two independent recordings of the geomagnetic dipole moment (GDM) decrease linked to the Laschamp excursion dated at ca 41 ka. The stratigraphic offset is assignable to post-depositional magnetization lock-in processes resulting in time delay of 1.6 ka. The Be ratio and RPI records show comparable asymmetric behavior before and after the dipole low. The Be ratio record is combined with three other series to construct a global record of 10Be paleoproduction variations. This compilation demonstrates the strong coherence of low and mid latitudes data sets and its comparison with 10Be-flux records from polar regions fully supports the hypothesis of a global atmospheric 10Be production doubling during the Laschamp. The Be ratio stack is converted in terms of GDM using both a theoretical model and a reconstruction of GDM values using absolute paleointensities measured on lava flows. Both methods provide similar results. The dipole moment record derived from this approach (BeDM20–60) shows the following characteristics: high field values (>11 × 1022 Am2) prior to a sharp two-steps dipole decrease until reaching minimum values (1.8 ± 0.7 × 1022 Am2) between 41.6 and 40.9 ka at the time of the Laschamp excursion. The GDM partly recovers up to values of ∼6.3 × 1022 Am2, and oscillates in this range, without showing any sharp decreases that could be associated with excursions reported within the 38–20 ka time interval (e.g. the Mono Lake excursion).
... The most recognizable such stratigraphic marker in the NW Labrador Sea is the detrital carbonate-rich Heinrich iceberg-rafted layers (Andrews and Tedesco, 1992;Hesse and Khodabakhsh, 1998;Rashid et al., 2003). In contrast to the H-layers, thin dolomite layers are found in the Baffin Bay Basin which is commonly termed as the Baffin Bay detrital carbonate (BBDC) layers (Aksu, 1981;Aksu and Piper, 1987;Simon et al., 2016;Jennings et al., 2018). ...
... BBDC6 in the MTD has a high chlorite/kaolinite ratio (Fig. 8). The high a*, dolomite (%) and chlorite/kaolinite ratio are characteristic of carbonate-rich facies from Lancaster Sound (Aksu and Piper, 1987), but Greenland ice sources also contribute to the BBDC events (Simon et al., 2014(Simon et al., , 2016Jackson et al., 2017). The supply of sediment from Baffin Bay during the maximum ice advances of the BBDC events demonstrates that the hypothesis of grounded ice in Davis Strait (Hughes et al., 1977;Hulbe et al., 2004;Jennings et al., 2018) is untenable. ...
... Seven 14 C-AMS dates either on the depth-horizons or bounding depths provide ages for the BBDC events 1e3 at 13.42 ka, 21.3 ka and 26.7 ka (Fig. 10). Using three cores from the SW Baffin Slope and the Baffin Bay basin, Jackson et al. (2017) and Simon et al. (2014Simon et al. ( , 2016 defined the BBDC events using XRF derived Ca/Sr ratio and XRD carbonates (%), respectively. However, the duration of these events is longer compared to the BBDC events on the SE Baffin Slope at site Hu97-07. ...
Article
The paleoceanography and sediment dynamics of the northernmost Labrador Sea provides critical records of glacial history, glacially-dominated sedimentation, and paleocirculation. A reference core at 938 m on the SE Baffin Slope was investigated with new oxygen isotope stratigraphy, X-ray fluorescence geochemistry, and 18 14 C-AMS dates and correlated to 14 regional deep-water cores. The reference core provides a paleoceanographic and sediment source record over the last 40 ka, overlying a 3-m-thick blocky mass-transport deposit over MIS 5 autochthonous sediment. Detrital carbonate-rich sediment layers H0-H4, based on bulk geochemistry, were derived principally from Hudson Strait. Shortly after H2 and H3, the shelf-crossing Cumberland Sound ice stream supplied dark brown ice-proximal stratified sediments. Minor supply of carbonate-rich sediment from Baffin Bay allows chronologic integration of the Baffin Bay and Labrador Sea detrital carbonate records and implies an open seaway through Davis Strait. The counterparts of H3, H4, and (?)H5 events in the deep Labrador basin are 4e10 m thick units of thin-bedded carbonate-rich mud turbidites from glacigenic debris flows on the Hudson Strait slope. The behavior of the Hudson Strait ice stream changed through the last glacial cycle. In H1 and H2, the ice stream retreated back across the shelf but did not deglaciate Hudson Bay; in H3eH5 it remained at the shelf break long enough to supply thick turbidites, and subsequent retreat after H4 and H5 deglaciated Hudson Bay. The maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was not synchronous.
... The authigenic beryllium isotope analyses were carried out on 103 samples, with variable resolution (from 10 to 280 cm), at the CEREGE National Cosmogenic Nuclides Laboratory (France) according to the chemical procedure established by Bourlès et al. (1989) and summarized by Simon et al. (2016b). The natural authigenic 9 Be concentrations were measured using a graphite-furnace Atomic Absorption Spectrophotometer (AAS) with a double beam correction (Thermo Scientific ICE 3400 ® ). ...
... This specific interval is arguably associated with eruption and post-eruption Be scavenging condition changes and 10 Be dilution by the rapid tephra deposition, not directly related with atmospheric 10 Be production changes. Moreover, the coarse grain size depicted by relatively high sand percentages in this interval (Fig. 2E) likely results in lower scavenging efficiency of dissolved 10 Be (Simon et al., 2016b). Above this interval, the 10 Be concentrations vary around an average of 0.84 ± 0.20 × 10 8 at/g (phases 4 ...
... The authigenic 10 Be/ 9 Be ratios vary between 0.04 and 0.59 × 10 −8 with an average value of 0.29 ± 0.13 × 10 −8 (Fig. 2H). Such low average 10 Be/ 9 Be ratios (<1 × 10 −8 ) correspond to typical values for environments experiencing high terrigenous inputs (e.g. Brown et al., 1992;Simon et al., 2016b). The 10 Be/ 9 Be ratio curve mimics the 10 Be variation mainly characterized by a major enhancement interval (phase 3). ...
Article
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Geomagnetic dipole moment (GDM) lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide Beryllium-10 (10Be) production. Hence, the reconstruction of atmospheric 10Be production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach, independent from paleomagnetic measurements, to decipher past GDM fluctuations. This is particularly important in the Montalbano Jonico succession (South Italy) since it is candidate to host the Global Stratotype Section and Point of the Middle Pleistocene Stage but where the magnetostratigraphic positioning of the Matuyama–Brunhes boundary (MBB) has not been available up to now. This study presents (1) original authigenic 10Be cosmogenic nuclide and 9Be stable isotope results, and (2) new high-resolution benthic oxygen isotope record covering termination IX and Marine Isotope Stage (MIS) 19. A robust chronological framework is established on the basis of (i) our oxygen isotope stratigraphy, using the strong analogies between MIS 1 and MIS 19c in terms of orbital forcing and CO2 level, and (ii) one precise 40Ar/39Ar date obtained in the tephra layer V4. The authigenic 10 Be/9 Be ratio record marks the atmospheric 10 Be overproduction linked to the dipole low accompanying the MBB transition, with a characteristic twofold increase of the 10Be production at the end of MIS 19c and early MIS 19b. This signature is similar to those described in both marine and ice core records. The detailed chronostratigraphy constrained by a radiometrically- dated tephra layer (773.9 ± 1.3 ka) within the MBB interval, makes it possible to discuss the structure and to assess the timing of the 10Be-production changes, and thus the MBB geomagnetic variations, with an unprecedented accuracy for a marine archive (sedimentation rates ∼80 cm/ka). These new cosmogenic nuclide production signatures provide the only missing constraint required for retaining the Montalbano Jonico succession as a global-scale correlation reference section for the Early–Middle Pleistocene boundary.
... Turbid meltwater plumes released from the ice front produce plumites, which are finer grained than the turbidites as the sand is dropped near the ice front and the silt and clay continue offshore in suspension (Hesse et al., 1997;Lucci and Rebesco, 2007). Depending on sea surface conditions such as perennial sea ice and/or ice shelves, icebergs would also deliver sediment to the slope as they melted during their transit in Baffin Bay (Andrews et al., 1998Jennings et al., 2014;Simon et al., 2012Simon et al., , 2014Simon et al., , 2016Sheldon et al., 2016). ...
... This assumed basal age results in a large uncertainty in the modeled age of the base of the core (24 to 28 cal ka BP). Given this basal age, we might expect to record Baffin Bay Detrital Carbonate (BBDC) event BBDC3 that is found in central Baffin Bay from c. 23.5 to 25 cal ka BP (Simon et al., 2016). A single data point with 20% NBB source at 21.5 cal ka BP may represent BBDC2 (21 cal ka BP; Simon et al., 2016) although it is not associated with a coarse clast-rich interval as would be expected if it represented a BBDC event (Andrews et al., 1998;Simon et al., 2012;Jackson et al., 2017) (Fig. 3). ...
... Given this basal age, we might expect to record Baffin Bay Detrital Carbonate (BBDC) event BBDC3 that is found in central Baffin Bay from c. 23.5 to 25 cal ka BP (Simon et al., 2016). A single data point with 20% NBB source at 21.5 cal ka BP may represent BBDC2 (21 cal ka BP; Simon et al., 2016) although it is not associated with a coarse clast-rich interval as would be expected if it represented a BBDC event (Andrews et al., 1998;Simon et al., 2012;Jackson et al., 2017) (Fig. 3). The lack of an interval of high NBB and IRD below 467 cm (16.2 cal ka BP) in 12PC indicates that BBDC2 and BBDC3 were not recovered in 12PC. ...
... An average 2-cm sam- pling interval is attained within the MBT interval in each core. The samples have been treated according to the chemical proce- dure established by Bourlès et al. (1989) and revised by Simon et al. (2016b). Authigenic 10 Be and its stable isotope 9 Be were extracted from ∼1 g dry samples by soaking them in a 20 ml leaching solution (0.04 M hydroxylamine (NH 2 OH-HCl) and 25% ...
... 9 Be concentration maxima coincide with glacial δ 18 O values, which suggests that 9 Be delivery at the location is influenced by denudation rates and clas- tic inputs (e.g. Simon et al., 2016b) and/or hydrographic changes (water flow speed and northern source water; Kleiven et al., 2011). In core MD90-0949, on the contrary, 9 Be maxima occur during in- terglacial MIS 19, while in nearby MD90-0961 core no particular 9 Be trend is observed during MIS 19, which suggests different 9 Be oceanic pathways for these neighboring cores situated at differ- ent water depths (Table 1). ...
... The global production rate of atmospheric 10 Be changes calculated using this function and the Be-ratio stack increases two-fold from the base to the peak of the 10 Be enhancement (Fig. 8). The periods that surround the main increase interval have average 10 Be pro- duction rates similar to those measured in year 1980 by Monaghan et al. (1986) or simulated for modern periods (see box in Fig. 8 or Table 4 in Simon et al., 2016b). ...
Article
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New high-resolution authigenic 10Be/9Be ratio (Be-ratio) records covering the last geomagnetic reversal, i.e. the Matuyama–Brunhes transition (MBT), have been obtained and set on a time scale using benthic δ18O (Cibicides wuellerstorfi) records. The geographic distribution of the four studied sites allows global comparison between the North Atlantic, Indian and Pacific Oceans. All Be-ratio records contain a two-fold increase triggered by the geomagnetic dipole moment (GDM) collapse associated with the MBT. The stratigraphic position of the Be-ratio spike, relative to marine isotope stages, allows establishment of a robust astrochronological framework for the MBT, anchoring its age between 778 and 766 ka (average mid-peaks at 772 ka), which is consistent with all other available 10Be-proxy records from marine, ice and loess archives. The global 10Be atmospheric production doubling represents an increase of more than 300 atoms m−2 s−1 that is compatible with the increased magnitude of atmospheric 10Be production obtained by simulations between the present GDM and a null-GDM. The minimum 10Be-derived GDM average computed for the 776–771 ka interval is 1.7±0.4×1022 Am2, in agreement with model simulations and absolute paleointensities of transitional lava flows.
... When delivered to continental margins via riverine transport, the dissolved 10 Be load is scavenged from the water column with a particular affinity for aluminosilicates (Frank et al., 2000;Sharma et al., 1987) and biogenic opal (Chase et al., 2002;Lal et al., 2006). Due to their sensitivity to changes in atmospheric production, particle flux, and bioproductivity, 10 Be concentrations have been the focus of numerous geophysical and ocean geochemical studies for their flexible application as a proxy of geomagnetic field strength in ice cores and marine sediments (Aldahan & Possnert, 2003;Christl et al., 2010;Raisbeck et al., 2006;Steig et al., 1996;Yiou et al., 1997), sea ice extent and ice shelf coverage (Frank et al., 2008;Yokoyama et al., 2016), and freshwater discharge from melting ice (Simon et al., 2016). When normalized to its stable isotope 9 Be, the ratio is proposed as a faithful recorder of deep ocean circulation patterns (von Blanckenburg et al., 1996) and continental sedimentation to deep marine basins on coarse timescales (von Blanckenburg et al., 2015;von Blanckenburg & Bouchez, 2014;Willenbring & von Blanckenburg, 2010b). ...
... It was important to sample sediments proximal to the ice sheet to document ice sheet/terrestrial contributions before that signal was overprinted after exchange with well-mixed water masses, which instead reflect a deep marine signal (Wittmann et al., 2017). Indeed, while global, deep marine 10 Be/ 9 Be records fluctuate negligibly throughout glacial-interglacial transitions (von Blanckenburg et al., 2015;Willenbring & von Blanckenburg, 2010b), records closer to glaciated margins taken at finer sampling resolutions indicate a sensitive response in 10 Be/ 9 Be to ice mass changes (Eisenhauer et al., 1994;Simon et al., 2016). ...
... ( 10 Be/ 9 Be) reac follows the same pattern as [ 9 Be] reac and [ 10 Be] reac in alternating sediment intervals and ranges from 5.97 ± 0.94 to 50.58 ± 0.69 × 10 À9 . This range is slightly lower than the globally averaged deep water 10 Be/ 9 Be dissolved in seawater (von Blanckenburg & Bouchez, 2014) and adsorbed to authigenic minerals (von Blanckenburg et al., 2015, and references therein), but in accordance with regional (Sjunneskog et al., 2007) and high-latitude records (Aldahan et al., 1997;Frank et al., 1997Frank et al., , 2008Simon et al., 2016) from authigenic minerals. ...
Article
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Along glaciated margins, ratios of meteoric cosmogenic beryllium-10, ¹⁰Be, normalized to its stable isotope, ⁹Be, reflect an environmental signal, driven ultimately by climatic change. We explore the application of this isotopic pair as a proxy for East Antarctic Ice Sheet dynamics. We analyze ¹⁰Be/⁹Be in middle Pliocene glaciomarine sediments offshore the Wilkes Land Region (Integrated Ocean Drilling Program (IODP) Site U1361A) and examine our new record alongside existing biochemical/geochemical records (Ba/Al, opal %wt, εNd, and ⁸⁷Sr/⁸⁶Sr). ¹⁰Be/⁹Be ratios reach local maxima during pulsed, mild warming events and are strongly correlated with existing records that indicate concurrent ice sheet retraction and increased bioproductivity. We suggest climate change as the primary driver of the ¹⁰Be/⁹Be record near glaciated margins, whereby increased warming drives ice sheet retraction, discharging freshwaters and diluting the open ocean ¹⁰Be/⁹Be signal recorded in authigenic minerals.
... 10 Be deposition rate has also been directly estimated from measurements in precipitation samples (Graham et al., 2003;Heikkilä et al., 2008a;Maejima et al., 2005;Monaghan et al., 1986;Somayajulu et al., 1984). Significant efforts have also been made to build the temporal variation in 10 Be depositional flux from various geological proxies such as ice cores (Finkel and Nishiizumi, 1997;Muscheler et al., 2005;Yiou et al., 1997) and sediment archives (Carcaillet et al., 2004b;Christl et al., 2010;Frank et al., 1997;Simon et al., 2016a;Valet et al., 2014). As per the current understanding, 10 Be depositional flux can vary between 0.06 and 3.8 × 10 6 atoms/cm 2 / year spatially (Heikkilä and Smith, 2013;Heikkilä and von Blanckenburg, 2015), and it can be almost twice the present value during the events of geomagnetic excursions and reversals Ménabréaz et al., 2011;Simon et al., 2020). ...
... Six such samples covering the time range between 43 ka to present and nine high-resolution samples at each one cm interval between 84 and 94 cm (centered at 41 ka) were taken for leaching with a weak acid solution. Nearly 1.5 g of crushed and homogenized sediment sample was treated with 0.04 M hydroxylamine hydrochloride (NH 2 OH.HCl) in 25% acetic acid solution (~20 ml/g) in a sonification bath at 85°C for 6 h (Bourles et al., 1989;Jena et al., 2021;Simon et al., 2016aSimon et al., , 2016b. The leachate solution represents the authigenic fraction, which has a composition very similar to the chemical constituents of seawater with fractions from exchangeable ions, carbonates, and Fe\ \Mn oxyhydroxides (McHargue et al., 2000(McHargue et al., , 2011. ...
... In earlies studies, for the extraction of authigenic phase, both weak (e.g., Acetic acid) (Carcaillet et al., 2004a;Simon et al., 2016a) and strong (e.g., Hydrochloric acid (HCl)) (Brown et al., 1985;Henken-Mellies et al., 1990) leaching agents have been used. Though leaching with a weak acid (acetic acid) may fail to extract 100% of the authigenic fraction, strong acid (hydrochloric acid) has a capability to attack the non-authigenic (mineral) fraction as well (Bourles et al., 1989). ...
Article
The advent of the Accelerator Mass Spectrometer (AMS) enhanced the application of meteoric ¹⁰Be (half-life of 1.39 Ma) as a tracer for understanding earth surface processes on million-year time scales. However, for the majority of applications, an adequate understanding of the ¹⁰Be depositional flux is a prerequisite. A number of efforts have been made to understand both spatial and temporal variation of ¹⁰Be depositional flux. Yet, due to the limited globally distributed dataset and modulation of the ¹⁰Be signal by local processes, a significant offset is observed between model-derived and measured deposition rates of ¹⁰Be. In this study, an attempt has been made to determine the ¹⁰Be depositional flux from a marine sediment core from the central Indian Ocean chronologically constrained with the AMS radiocarbon dating and ¹⁰Be concentration measured with AMS. The ¹⁰Be depositional flux estimates using weak leaching method are found to be nearly 45% lower compared to the strong leaching method. The calculated ¹⁰Be depositional flux during the Holocene varies between 9.63 and 13.01 × 10⁵ atoms/cm²/yr, which is 2-28% lower compared to the modeled depositional flux for the region. The difference observed in ¹⁰Be depositional flux could be due to local processes (such as boundary scavenging, changing rate of sediment deposition at the location) affecting ¹⁰Be deposition into the sediment column or offset associated with the model estimations. The changes in ¹⁰Be depositional flux and the ¹⁰Be/⁹Be ratio have been reconstructed up to 43 ka. An increase in the ¹⁰Be/⁹Be ratio during 28 to 43 ka is observed due to the lower geomagnetic field intensity during the period. A high-resolution ¹⁰Be/⁹Be ratio reconstruction shows a peak at 41.2 ka, which can be attributed to the Laschamp event.
... The effect of scavenging efficiency variations can be eliminated by normalizing 10 Be with the stable 9 Be isotope that is released by weathering rocks (Measures and Edmond, 1983;von Blanckenburg et al., 2012) and uptaken by the same particles (Sharma et al., 1987). The isotopic ratio 10 Be/ 9 Be obtained from the measurement of reactive Be selectively extracted from the authigenic rim is therefore identical to that of the dissolved isotopes Bourl es et al., 1989a;Anderson et al., 1990;McHargue and Damon, 1991;Simon et al., 2016bSimon et al., , 2018a. Even so, the 10 Be/ 9 Be ratio is not a globally homogeneous proxy of cosmogenic 10 Be production, due to the different distribution of 10 Be and 9 Be sources, which make the two isotopes undergo different transport paths (von von Blanckenburg et al., 2012). ...
... Samples of $1 g dry sediment were processed for Be isotope analyses following the chemical procedure described in Simon et al. (2016b). The leaching technique of Bourl es et al. (1989a) allows extracting both isotopes in the phase that corresponds to the equilibrated authigenic fraction of soluble 10 Be and 9 Be. ...
... Approximately 70% and 40% of authigenic 10 Be and 9 Be, respectively, are carried by iron and manganese oxyhydroxides, and the rest is attributed to exchangeable and carbonated fractions (Bourl es et al., 1989b). Because both isotopes have identical chemical properties, 10 Be/ 9 Be obtained by this technique is supposedly insensitive to downcore lithological changes (Henken-Meillies et al., 1990;Simon et al., 2016b). The natural authigenic 9 Be concentration was measured using a graphite-furnace atomic absorption spectrophotometer (AAS) with double-beam correction. ...
Article
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Reconstructions of the global production rate of the cosmogenic isotope 10Be from sedimentary records of authigenic 10Be/9Be ratios have been successfully used to obtain independent estimates of geomagnetic dipole moment variations caused by field excursions or reversals. In this study, we assess the reliability of 10Be/9Be as a proxy for the cosmogenic 10Be production rate by evaluating two potential biasing sources represented by sediment composition and climatic modulation. For this purpose, we compare five high-resolution 10Be/9Be records of the Matuyama-Brunhes (M-B) field reversal from sediment cores of the Indian, West Pacific, and North Atlantic oceans. Significant increase of 10Be/9Be ratios at 774 ka is explained in terms of the dominant control of geomagnetic modulation during the M-B reversal. Results do not support the existence of a direct proportionality between measured sedimentary 10Be/9Be ratio and cosmogenic 10Be production rate, as shown by 10Be/9Be records that offset relative to each other during and outside the M-B reversal. Residual differences between offset-corrected rescaled records do not appear to be related to an incomplete correction of variable sediment scavenging efficiencies by 9Be normalization. Instead, these differences can be explained by a common climatic modulation model, assuming a linear relation between 10Be/9Be and the global 10Be production rate with site- and time-dependent additive and multiplicative coefficients. These coefficients are linear functions of a single global climate proxy identified with the benthic O record. Additive coefficients are almost constant in time and can represent up to 60% of the average 10Be/9Be value during periods of stable field polarity. Multiplicative coefficients are also site-specific, with mean values representing the bulk scavenging efficiency of the site, and variations about this mean expressing a multiplicative climatic modulation of the 10Be production rate. The amplitude of this modulation amounts to 10–15% of the maximum variations recorded during the M-B reversal and is sufficiently large to mask minor variations of the dipole moment during stable polarity periods. Reconstructions of the geomagnetic dipole intensity can benefit from the information about climatic modulation effects gained with our modelling approach. Best suited sites for magnetic field reconstructions should be characterized by minimal Be-recycling contributions from ancient 10Be reservoirs and minimal climatic modulation, as far as it can be determined from relative comparisons with other records. These conditions are most likely encountered in open basins at sites (1) with 2.8 km water depth, (2) 200 km offshore, and (3) located underneath a large current system extending over regions with minimum terrigenous inputs. Scaling all records with respect to a chosen reference enables to produce 10Be/9Be stacks with reduced noise and short-term local environmental effects. Differences between stacks obtained in this manner highlight global climatic effects that need to be considered when generating calibrated reconstructions of the geomagnetic dipole moment.
... However, 10 Be scavenging from the atmosphere follows complex pathways that may affect the mode and tempo of the cosmogenic fallout (e.g., Field et al., 2006;Monaghan et al., 1986;Willenbring and von Blanckenburg, 2010a;Raisbeck et al., 2006). In the case of marine sedimentary environments, several additional variables may also contribute to the 10 Be conveyance and deposition, ranging from ocean circulation patterns to the local depositional style and setting (e.g., Mangini et al., 1984;Bourl es et al., 1989;Kusakabe et al., 1990Kusakabe et al., , 1991Brown et al., 1992;Measures et al., 1996;von Blanckenburg et al., 1996;Willenbring and Von Blanckenburg, 2010b;von Blanckenburg and Bouchez, 2014;Simon et al., 2016b;Capraro et al., 2018). Dynamics within the catchment area, such as the episodic mobilization of continental reservoirs, can promote massive 10 Be fluxes to the basins, where 10 Beerich particles may be involved in intricate depositional processes before and after their settling (e.g. ...
... In fact, the tight correlation between the measured 10 Be and calculated records (Fig. 11) proves that the 10 Be peak found at VdM and MJ does not provide an independent and unbiased depiction of the period of cosmogenic 10 Be overproduction and fallout that is expected to have occurred globally at about the Matuyama-Brunhes boundary (e.g., Simon et al., 2018a,Simon et al., 2018b, and references within). Our data confirm that, in marginal marine settings, the terrestrial 10 Be input can be large enough to completely overshadow the cosmogenic flux ( Brown et al., 1988;You et al., 1988;Simon et al., 2016b). It is worth stressing that, limited to the available Mediterranean records, intervals of higher ...
... Therefore, Baffin Bay, located between Baffin Island and Greenland, forms a unique setting capturing sediments related to the pulses of ice-sheet margins on the surrounding continental shelves (e.g. Simon et al. 2012Simon et al. , 2014Simon et al. , 2016Brouard & Lajeunesse 2017;Jenner et al. 2018). Recent studies have suggested that the LIS margin extended on the northeastern Baffin Island shelf during the Last Glacial Maximum (LGM) and reached the shelf edge (Fig. 1A, B; Li et al. 2011;Brouard & Lajeunesse 2017;Jenner et al. 2018). ...
... These results attest to the presence of detrital carbonate probably associated with BBDC events (Fig. 6B; e.g. Balsam et al. 1999;Hodell et al. 2008;Channell et al. 2012;Winsor et al. 2012;Simon et al. 2014Simon et al. , 2016Jackson et al. 2017). LF7 tops the core from 65 to 0, but also from 129 to 117 cm. ...
Article
Three sediment cores recovered on the lower slope of the continental shelf in western Baffin Bay (Arctic Canada) as well as swath bathymetry and subbottom profiler data collected on the shelf and slope of the region were analysed to investigate whether the Laurentide Ice Sheet (LIS) reached the shelf edge offshore Home Bay during the Last Glacial Maximum (LGM). Physical, sedimentological and palaeomagnetic analyses of the cores were also used to constrain the chronostratigraphy of upper sedimentary facies of the Home Bay trough‐mouth fan (TMF). Seven lithofacies were identified in the cores and reveal that the sediments recorded a genuine geomagnetic signal and that the cores span the last 40 ka. In the Home Bay Trough, sets of elongated ridges are discernible on swath bathymetry imagery and are interpreted as mega‐scale glacial lineations (MSGLs) resulting from an ice stream eroding the trough and delivering glacigenic sediments to the TMF. The geomorphology of the TMF, combined with the sedimentary records and the chronostratigraphy, indicates that a series of debris flows and turbidity currents were generated between 35 and 15 ka BP. These results indicate that the LIS margin extended near the shelf edge during the LGM and allow us to propose a new maximum extent of the LIS during the Last Glacial episode.
... Therefore, Baffin Bay, located between Baffin Island and Greenland, forms a unique setting capturing sediments related to the pulses of ice-sheet margins on the surrounding continental shelves (e.g. Simon et al. 2012Simon et al. , 2014Simon et al. , 2016Brouard & Lajeunesse 2017;Jenner et al. 2018). Recent studies have suggested that the LIS margin extended on the northeastern Baffin Island shelf during the Last Glacial Maximum (LGM) and reached the shelf edge (Fig. 1A, B; Li et al. 2011;Brouard & Lajeunesse 2017;Jenner et al. 2018). ...
... These results attest to the presence of detrital carbonate probably associated with BBDC events (Fig. 6B; e.g. Balsam et al. 1999;Hodell et al. 2008;Channell et al. 2012;Winsor et al. 2012;Simon et al. 2014Simon et al. , 2016Jackson et al. 2017). LF7 tops the core from 65 to 0, but also from 129 to 117 cm. ...
Article
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Three sediment cores recovered on the lower slope of the continental shelf in western Baffin Bay (Arctic Canada) as well as swath bathymetry and subbottom profiler data collected on the shelf and slope of the region were analysed to investigate whether the Laurentide Ice Sheet (LIS) reached the shelf edge offshore Home Bay during the Last Glacial Maximum (LGM). Physical, sedimentological and palaeomagnetic analyses of the cores were also used to constrain the chronostratigraphy of upper sedimentary facies of the Home Bay trough‐mouth fan (TMF). Seven lithofacies were identified in the cores and reveal that the sediments recorded a genuine geomagnetic signal and that the cores span the last 40 ka. In the Home Bay Trough, sets of elongated ridges are discernible on swath bathymetry imagery and are interpreted as mega‐scale glacial lineations (MSGLs) resulting from an ice stream eroding the trough and delivering glacigenic sediments to the TMF. The geomorphology of the TMF, combined with the sedimentary records and the chronostratigraphy, indicates that a series of debris flows and turbidity currents were generated between 35 and 15 ka BP. These results indicate that the LIS margin extended near the shelf edge during the LGM and allow us to propose a new maximum extent of the LIS during the Last Glacial episode.
... Changes in the gradient of this relationship above or below one is driven by an additional input of 9 Be or 10 Be, respectively 22,37 . The relative 10 Be vs. relative 9 Be relationship of sediments from Baffin Bay and offshore Wilkes Land are defined by a gradient less than one (Fig. 3b) controlled by the additional flux of meltwater-derived 10 Be from nearby ice sheets 36,37 . This leads to higher 10 Be/ 9 Be ratios during periods of intense glacial discharge such as Heinrich events 36 and Pliocene interglacials 37 . ...
... The relative 10 Be vs. relative 9 Be relationship of sediments from Baffin Bay and offshore Wilkes Land are defined by a gradient less than one (Fig. 3b) controlled by the additional flux of meltwater-derived 10 Be from nearby ice sheets 36,37 . This leads to higher 10 Be/ 9 Be ratios during periods of intense glacial discharge such as Heinrich events 36 and Pliocene interglacials 37 . Sediments from KC-15 to KC-17 display a similar relationship to Baffin Bay and offshore Wilkes Land (Fig. 3b) indicating an additional input of meltwater-derived 10 Be to Ferrero Bay may be contributing to the increase in 10 Be/ 9 Be ratios from~9.8 ...
Article
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The primary Antarctic contribution to modern sea-level rise is glacial discharge from the Amundsen Sea sector of the West Antarctic Ice Sheet. The main processes responsible for ice mass loss include: (1) ocean-driven melting of ice shelves by upwelling of warm water onto the continental shelf; and (2) atmospheric-driven surface melting of glaciers along the Antarctic coast. Understanding the relative influence of these processes on glacial stability is imperative to predicting sea-level rise. Employing a beryllium isotope-based reconstruction of ice-shelf history, we demonstrate that glaciers flowing into the Amundsen Sea Embayment underwent melting and retreat between 9 and 6 thousand years ago. Despite warm ocean water influence, this melting event was mainly forced by atmospheric circulation changes over continental West Antarctica, linked via a Rossby wave train to tropical Pacific Ocean warming. This millennial-scale glacial history may be used to validate contemporary ice-sheet models and improve sea-level projections. Ice loss from the Amundsen Sea sector of West Antarctica is rapidly accelerating. Here, the authors reveal that this region also underwent thinning and retreat from 9 to 6 thousand years ago, due to atmospheric connections with a warming tropical Pacific.
... Scherer et al. (1998) was able to determine the timing of the West Antarctic Ice Sheet collapse in the Pleistocene, suggesting higher concentrations of meteoric 10 Be indicated an open marine environment. Subsequently, changes in the depositional environment of 10 Be, such as open marine, sub-ice-shelf, or subglacial environments, have been interpreted to cause variations in the sedimentary 10 Be record (Sjunneskog et al., 2007, Simon et al., 2016, White et al., 2019. Lower accumulation of meteoric 10 Be occurs in areas with higher annual sea ice concentration of areas covered by ice shelves, as opposed to open marine environments which accumulate relatively high concentrations of meteoric 10 Be. ...
... The variation in 10 Be values obtained may correspond to changes in meltwater output. However, as 10 Be concentration may vary depending on influences from sub-ice-shelf ocean currents, basal ice-shelf melt, and calving icebergs (Simon et al., 2016, White et al., 2019, it is necessary to perform more analyses on core U1357A, such as 9 Be, to assess the cause of fluctuations in sedimentary 10 Be. As ocean currents, such as Modified Circumpolar Deep Water, are one of the major transportation pathways of 10 Be, 10 Be/ 9 Be ratios of the authigenic phase of marine sediments are needed to more accurately assess the depositional environment of the 10 Be increases at~9.8 ka,~6.3 ...
Article
Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (10Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric 10Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric 10Be events to be derived from the deposition of 10Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric 10Be concentration at~4 ka may correspond to changes in climate patterns at this time.
... A total of 90 new levels were measured in the upper Ideale and Ciaranfi Master sections to improve and complete the authigenic 10 Be/ 9 Be ratio record of the Ideale section presented in Simon et al. (2017). The analyses were carried out at the CEREGE National Cosmogenic Nuclides Laboratory (LN 2 C, France) following the same method used in Simon et al. (2017) and fully reviewed in Simon et al. (2016). The 9 Be concentrations were measured using a graphite-furnace Atomic Absorption Spectrophotometer (AAS) with a double beam correction (Thermo Scientific ICE 3400 ® ). ...
... Namely, the two largest authigenic 10 Be/ 9 Be ratio increase intervals observed between 19a-2 and 19a-3 and at the transition toward MIS 18 (Fig. 5) correspond to two significant 9 Be-lows (not observed in the 10 Be signal) associated with periods of mineralogical changes and coarser grain size fraction supply . The influence of such grain size and mineralogical changes on Be-budget is averaged out when using the ratio between both Be isotopes, but the 9 Be load during these two stadial episodes is acting as the primary controlling parameter on the authigenic 10 Be/ 9 Be ratio signature (Simon et al., 2016). This observation precludes straightforward geomagnetic interpretations of the authigenic 10 Be/ 9 Be ratio at these levels, contrarily to the MIS 20e19b interval (see Simon et al., 2017 for details), but provides hint on the denudation rate and terrigenous input variations. ...
... The authigenic beryllium isotopes analyses were carried out at the CEREGE 'Cosmogenic Nuclides National Laboratory' (LN2C, Aix-en-Provence in France). A total of 14 subsamples were pretreated according to the chemical procedure established by Bourlès et al. (1989) and revised by Simon et al. (2016a). ...
... How the Earth's magnetic field intensity changes is a critical question for understanding the past, the present, and the future of geodynamo regimes (Hulot et al., 2010). Due to the relatively short periods of direct observation, geological investigations of sediments and lavas can provide information on long-term variations of the dipole field (e.g., Cai et al., 2017;Channell et al., 2009;Guyodo & Valet, 1999;Simon et al., 2016a;Tauxe, 1993;Valet et al., 2005). Specifically, the absolute, but scattered, paleointensity reconstructed from lava records can be used to model virtual axial dipole moment (e.g., Cai et al., 2017), while relative paleointensity reconstructed from sedimentary records can produce long-term and continuous global stacks to significantly extend our understanding of changes in the Earth's magnetic field intensity (e.g., Channell et al., 2016). ...
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The Clarion and Clipperton Fracture Zones in the Eastern Pacific are well known as a manganese nodule belt, that developed since the late Oligocene. The slow growth rate of these marine ferromanganese nodules implies that they have potentially recorded long‐term environmental changes. To produce environmental records from these nodules, their chronology needs to be established first. In order to achieve this objective, many dating methods have been applied; however, due to relatively low‐resolution temporal constraint, high‐resolution environmental signals recorded in marine ferromanganese nodules have not been well documented yet. In this paper, we present a geochronological study based jointly on magnetic scanning and analyses of the authigenic beryllium isotopes (authigenic 10Be/9Be) and the cobalt (Co) flux of a marine ferromanganese nodule. Results lead to the following observations: (1) the growth of the studied nodule resulted from a combination of hydrogenetic and diagenetic processes, and (2) a total of 24 magnetozones are recognized for the studied nodule. Correlation to the geomagnetic polarity timescale suggests that chrons from C3n.2r to C1n were recorded in the nodule, implying that the growth of this nodule initiated ~4.70 Ma, which agrees well with the authigenic 10Be/9Be and Co chronometers. Furthermore, a consistent pattern of broad paleomagnetic field variations was observed between the nodule's magnetic signal and the ocean‐floor magnetic fields of the South Atlantic, confirming the validity of our growth model. Overall, our study highlights the potential of marine ferromanganese nodules from the Eastern Pacific as recorders of changes in Earth's magnetic field.
... Though the systematics of 10 Be met in soils have been mostly studied in the midlatitudes, 10 Be met data from high latitudes also show long-term transport of the isotope to depth (Ebert et al., 2012). High latitude flux of 10 Be met to marine sediment has been measured in glaciomarine settings near Greenland and Antarctica, though its relationship to terrestrial soil concentrations is complicated by the scavenging of 10 Be met from ocean water (Simon et al., 2016;Sjunneskog et al., 2007;Yokoyama et al., 2016). ...
... If the regions of erosion and deposition are equal in area, the background sedimentation rate is equivalent to 50 m$Ma À1 of subglacial erosion (though the channeling of ice into distinct outlets implies that the true value is lower). Analysis of authigenic 10 Be/ 9 Be in a sediment core from the center of Baffin Bay suggests slightly higher erosion rates for the entire region, with background rates near 80 m$Ma À1 that approximately double during Heinrich events (Simon et al., 2016). Rates of sediment deposition in the near shelf of central East Greenland are similar to those measured in West Greenland, though deposition rates in fjords are an order of magnitude higher (Andrews et al., 1994). ...
Article
In order to test whether sediment emerging from presently glaciated areas of Greenland was exposed near or at Earth's surface during previous interglacial periods, we measured the rare isotope ¹⁰Be contained in grain coatings of sediment collected at five ice marginal sites. Such grain coatings contain meteoric ¹⁰Be (¹⁰Bemet), which forms in the atmosphere and is deposited onto Earth's surface. Samples include sediment entrained in ice, glaciofluvial sediment collected at the ice margin, and subglacial sediment extracted during hot water drilling in the ablation zone. Due to burial by ice, contemporary subglacial sediment could only have acquired substantial ¹⁰Bemet concentrations during periods in the past when the Greenland Ice Sheet was less extensive than present. The highest measured ¹⁰Bemet concentrations are comparable to those found in well-developed, long-exposed soils, suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods. Ice-bound sediment has significantly higher ¹⁰Bemet concentrations than glaciofluvial sediment, suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures. Northern Greenland sites where ice and sediment are supplied from the ice sheet's central main dome have significantly higher ¹⁰Bemet concentrations than sites in southern Greenland, indicating greater preglacial or interglacial landscape preservation in central Greenland than in the south. Because southern Greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure, we suggest that ¹⁰Bemet measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length.
... Our new data for [ 10 Be] reac , [ 9 Be] reac , and ( 10 Be/ 9 Be) reac show that in this nearcoastal setting, measured ( 10 Be/ 9 Be) reac of authigenic phases contained in marine surface sediments have not reached open ocean values relative to their terrestrial source. That marginal sites show lower 10 Be/ 9 Be than their adjacent open ocean counterparts has been observed in the Baffin Bay [Simon et al., 2016a] and at sites surrounding Papua New Guinea [Ménabréaz et al., 2012;Ménabréaz et al., 2014], and from a Mediterranean marginal site [Simon et al., 2017] (for summary of this published data, see Table S2). ...
... There, 10 Be/ 9 Be ratios will record ocean-basin wide weathering and denudation fluxes [Willenbring and von Blanckenburg, 2010a;von Blanckenburg et al., 2015] and global changes in cosmic ray production as modulated by magnetic field strength [Christl et al., 2003;Carcaillet et al., 2004;Knudsen et al., 2008;Simon et al., 2016b]. between open ocean ratios and meltwater discharge [Simon et al., 2016a]. These marginal sites are probably best-suited to decipher the hitherto elusive boundary exchange and the processes that contribute to it today, and back though time. ...
Article
At an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic 10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the marine authigenic phase in surface sediments along a coast-perpendicular transect, and compared to samples from their riverine source. We find evidence for growth of authigenic rims through co-precipitation, not via reversible adsorption, that incorporate an open ocean 10Be/9Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10Be/9Be signatures. Together with increasing 10Be/9Be ratios, particulate-bound Fe concentrations increase, which we attribute to release of Fe-rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleo-denudation flux reconstructions are: in coast-proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater, whereas sites beneath well-mixed seawater will preserve global flux signatures.
... The 10 Be concentrations measured in marine sediments do not only depend on atmospheric 10 Be production rates but also on environmental conditions that affect the chemical and granulometric composition of sediments (Bourlès et al., 1989;Robinson et al., 1995). Absolute 10 Be concentrations of marine sediments are inversely proportional to carbonate content (Henken-Mellies et al., 1990) and proportional to the surface of the settling particles (Simon et al., 2016a). Thus, total 10 Be concentration must be corrected for environmental effects by normalizing the 10 Be concentration to the concentration of the stable 9 Be isotope associated with continental erosion. ...
... Samples of ∼1 g of dry sediment were processed for Be isotope analyses following the chemical procedure described by Bourlès et al. (1989) and revisited by Simon et al. (2016a). Both cosmogenic 10 Be and stable 9 Be isotopes have different sources, but their soluble form is homogenized in the water column before being scavenged and deposited by sinking particles. ...
Article
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We studied four marine sediment records of the Matuyama-Brunhes geomagnetic reversal from four sites located in the Indian, Atlantic and western Pacific oceans. The results combine paleomagnetic, cosmogenic nuclide beryllium (10 Be) and oxygen isotope analyses that were performed on the same samples in order to avoid any stratigraphic bias. The three records from the equatorial Indian Ocean and North Atlantic Ocean did not reveal any offset between the authigenic 10 Be/ 9 Be ratio (Be-ratio) peak and the interval of low relative paleointensity (RPI) that characterizes the reversal. The lower and upper limits of transitional directions are also concomitant with the increased atmospheric 10 Be production that accompanied the geomagnetic dipole intensity decrease. In contrast, the record from western equatorial Pacific Ocean sediments was found 18 cm below the Be-ratio changes as a result of late magnetization acquisition. At all four sites, maximum 10 Be production occurred at the same period soon after the maximum of Marine Isotope Stage 19 (MIS 19) and, therefore, indicates its synchronous worldwide character. Such features are effectively observed from the Be-ratio signals and their relationship with the magnetic transition interval, which further confirms the synchronous character of the transition. Taking all dating uncertainties (1.6 ka between sites and 5 ka for the age model) into consideration, our records suggest a mean reversal age of 772.4 ± 6.6 ka. The age of the transition in the Atlantic Ocean record is closer to 774 ka but this difference is within the limit of significance.
... The exchangeable-10 Be concentrations measured in the sediments, or authigenic 10 Be (i.e. the fraction dissolved or chemically precipitated and adsorbed onto settling particles) do not only reflect atmospheric production at the time of their deposition but also depend on oceanic transport processes and detrital inputs from surrounding continents [Bourlès et al., 1989; Christl et al., 2010; Simon et al., 2016]. The normalization of authigenic 10 Be concentration is necessary to correct for such sedimentary imprints and compare 10 Be records with geomagnetic variability. ...
... Chemistry blank ratios range from 10 -14 to 10 -15 , i.e. at least 3 orders of magnitude lower than the sample 10 Be/ 9 Be ratios. The authigenic 10 Be/ 9 Be ratios are calculated from 9 Be-AAS and 10 Be-AMS concentration measurements transformed in atoms [Simon et al., 2016]. Associated uncertainties (2σ) are derived from the propagation of both uncertainties and vary around 4.3%, 4.7% and 5.6% in cores MD05-2920, -2930 and MD90-0961, respectively (see Tables S3, S4 and S5). ...
Article
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Authigenic 10 Be/ 9 Be ratios from three equatorial ocean cores are stacked and averaged  The 10 Be cosmogenic nuclide overproduction episodes are systematically associated with Geomagnetic Dipole Lows  The 10 Be signatures of the Brunhes/Matuyama transition and Brunhes geomagnetic excursions yield distinct rates and durations Abstract Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (10 Be) production rates. Authigenic 10 Be/ 9 Be ratios (proxy of atmospheric 10 Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10 Be/ 9 Be ratio results obtained from cores MD05-2920 and core MD05-2930 collected in the West Equatorial Pacific Ocean. Be ratios from cores MD05-2920,-2930 and MD90-0961 have been stacked and averaged. Variations of the authigenic 10 Be/ 9 Be ratio are analyzed and compared with the geomagnetic dipole lows series reported from global RPI stacks. The largest 10 Be overproduction episodes are related to dipole field collapses (below a threshold of 2 x 10 22 Am 2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion and the Iceland Basin event (190 ka). Other significant 10 Be production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated using absolute dipole moment values drawn from the Geomagia and Pint paleointensity values databases. The 10 Be derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.
... Samples for beryllium isotope analysis were taken from core sections N1-A and N1-B ( Fig. 2A) on one side of the trench left by paleomagnetic cube sampling at corresponding depth intervals. A total of 45 samples were analysed at CEREGE National Cosmogenic Nuclides Laboratory following the method established by Bourlès et al. (1989) and revised by Simon et al. (2016b). Authigenic 10 Be and its stable isotope 9 Be were extracted from ~1 g dry sample by soaking the samples in 20 ml of leaching solution (0.04 M hydroxylamine (NH2OH-HCl) and 25% acetic acid) at 95 ± 5 • C for 7 h. ...
... Such large-scale concentration variations indicate large changes of Be inputs into the lake controlled by transport and deposition processes, but not associated with 10 Be production rates (e.g. Simon et al., 2016b). The fact that both 9 Be and 10 Be concentrations vary similarly (correlation coefficient r = 0.97; Sup. ...
Article
Lake sediment archives covering several glacial cycles are scarce in the Southern Hemisphere and they are challenging to date. Here we present the chronostratigraphy of the oldest continuous lake sediment archive in Tasmania, Australia; a 5.5 m and 270 ka (Marine Isotope Stage 8) sediment core from Lake Selina. We employ radiometric dating (radiocarbon and optically stimulated luminescence) and relative dating (geomagnetic and climate comparisons). Bayesian modeling of the radiometric ages reaches back to 80 ka (1.7 m) and relative dating using a dynamic programing algorithm allows dating of the full sequence. Elemental data, magnetic properties and beryllium isotopes from Lake Selina reveal a close fit to Antarctic ice core climate proxies. Weaker correlation during the Last Glacial Period (MIS 2–4) is attributed to additional local factors impacting Lake Selina proxies at a time of climate changes and human arrival into Tasmania. Over that period, full vector paleomagnetic records and authigenic ¹⁰Be/⁹Be ratios are combined to identify the Laschamp geomagnetic excursion for the first time in Australia and constrain the chronology. The multi-method approach provides two preferred age models, indiscernible within their uncertainties, which allows the use of a geomagnetic dipole-independent (full archive) or a climate-independent (111 ka to present) age model.
... Sample processing and isotopic measurements were carried out at the Xi'an Accelerator Mass Spectrometry Center (Xi'an-AMS Center), Institute of Earth Environment, Chinese Academy of Sciences. A total of seven sediment samples was pretreated according to the protocol proposed by Bourlès et al. (1989) and updated by Simon et al. (2016). Sample 10 Be/ 9 Be ratios were calibrated against ICN-01-5-1 material, using a certified ratio of 2.709 × 10 −11 (Nishiizumi et al., 2007). ...
Article
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The Mariana Trench is the deepest part of Earth's surface, with a maximum depth of close to 11,000 m in the Challenger Deep. Great progress has been made in studying the trench in the past years; however, several basic issues regarding the sedimentology and geochronology of the abyssal surficial sediments in the trench remain unclear. In this study, two gravity cores of Plio-Pleistocene sediments were retrieved from the southern slope of the Mariana Trench. They were used for an integrated investigation of magnetostratigraphy, authigenic ¹⁰Be/⁹Be dating, and element manganese content. The principal results are as follows. (1) Ten magnetozones are recognized for Core A25, which can be correlated to the geomagnetic polarity time scale from Chrons C1n to C3r. (2) The paleomagnetic and ¹⁰Be/⁹Be-based ages agree well for both of the two cores, yielding a continuous depositional hiatus since the middle Pleistocene (0.63–0.74 Ma). (3) The sediment accumulation rates prior to ~1.3 Ma are 35–83 cm/Myr and then increased substantially to 167–200 cm/Myr. Based on these results, a sedimentary transition at ~1.3–1.2 Ma is confirmed, which can be potentially correlated to climatic, oceanic, and tectonic changes in the Mid-Pleistocene transition. In addition, an elemental Mn proxy is derived to reflect changes in bottom-water ventilation, which is consistent with Lower Circumpolar Deep Water and North Atlantic Deep Water on glacial-interglacial time scales. We conclude that the sedimentary record of the Mariana Trench provides a unique window for investigating the integrated effects of long-term climatic, oceanic, and tectonic processes.
... However, the data herein do not indicate conclusively when the NOW formed. and conflicts with previous reconstructionsThe deglaciation of core site 014 recordsa late phase of the retreat of northern Baffin Bay ice streams, which began after Heinrich Event 1 as inferred from the timing of Baffin Bay Detrital Carbonate (BBDC) events(Simon et al. 2016;Jackson et al. 2017;Jennings et al. 2017a). BBDC1 (c. ...
Article
Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.
... Two BBDC events have been previously identified during the last deglaciation (Aksu and Piper, 1987;Andrews et al., 1998;Hiscott et al., 1989;Simon et al., 2014Simon et al., , 2012. Magnetostratigraphic dating of these records has been recently used to suggest that these events were not in phase with the North Atlantic Heinrich Events (Simon et al., , 2012 but much uncertainty exists in such a paleomagnetic-based chronology, demonstrated by its recent revision (Simon et al., 2016). This uncertainty derives from the ambiguity in tuning noisy curves to a target curve that, in itself, includes dating uncertainty. ...
Article
The chronology of deglacial meltwater pulses from the Laurentide Ice Sheet is well documented. However , the deglacial history of the North American-Arctic (north-eastern Laurentide and Innuitian) and western Greenland ice sheets draining into the Labrador Sea via Baffin Bay is less well constrained. Here we present new high-resolution, radiocarbon-dated records from the central Baffin Bay spanning ~17 to 10 kyr BP and documenting the full deglacial history of Baffin Bay. Sedimentological and geochemical data confirm the presence of two periods of enhanced detrital carbonate delivery, termed Baffin Bay Detrital Carbonate Events (BBDCs). These events are dated to ~14.2e13.7 kyr BP and ~12.7e11 kyr BP. They are synchronous across Baffin Bay and their mineralogical signature indicates a common source of detrital carbonate from northern Baffin Bay. The first event, BBDC 1, postdates Heinrich Event 1 and the second event, BBDC 0, predates the recently revised timing of Heinrich Event 0. The onset of the BBDC events appears not to be systematically linked to Greenland temperature change as they occur during both interstadial and stadial periods. This indicates that deglaciation of North American-Arctic and western Greenland ice sheets with the associated iceberg and meltwater discharge were decoupled from the dominant North Atlantic climate mode, where iceberg discharge events from the Laurentide Ice Sheet occurred during stadial periods.
... non-open ocean sites). [Carcaillet et al., 2004;Ménabréaz et al., 2014;Simon et al., 2016a;Simon et al., 2016b] Table S3 contains major elemental data for reactive ("reac") fractions (summed am-ox and x-ox leached fractions) and data for silicate residuals (post-leach "min" fraction). We observe an increase in the concentrations of the reactive fraction of most major elements from the terrestrial to the marine realm, summarized in the red bold row in Table S3. ...
... Care was taken to ensure the beryllium isotopes sampling depths correspond to the paleomagnetic sample depths. A total of 45 samples were analysed following the method established by Bourlès et al. [17] and revised by Simon et al. [18] at CEREGE National Cosmogenic Nuclides Laboratory (France) . Authigenic 10 Be and its stable isotope 9 Be were extracted from ∼1 g dry sample by soaking the samples in 20 ml of leaching solution at 95 ± 5 °C for 7 h. ...
Article
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This Data in Brief paper comprises dataset obtained for sediment cores collected from Lake Selina, located in the West Coast Range of Tasmania, Australia. Datasets include radiocarbon and optically stimulated luminescence age estimates, elemental composition, beryllium isotopes, magnetic properties and the paleomagnetic record measured on the cores assigned as TAS1402 (Location: Tasmania, Year: 2014, Site number: 02). The multi-proxy dataset was used to develop a chronostratigraphy for the 5.5 m and 270,000 year old record. See Lisé-Pronovost et al. (2021) (doi.org/10.1016/j.quageo.2021.101152) for interpretation and discussion. The data presented in this study serve as an archive for future studies focusing on Earth system dynamics and the timeline and linkages of environmental changes across Tasmania, the Southern Hemisphere and at a global scale.
... p<0.01) might point to a reduced affinity of 10 Be for Ca (Figs. 2 and 3). A similar behavior was detected in studies about 10 Be scavenging from the marine realm (Aldahan and Possnert, 1998;Chase et al., 2002, Simon et al., 2016. (Muscheler et al., 2016). ...
Article
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Time-scale uncertainties between paleoclimate reconstructions often inhibit studying the exact timing, spatial expression and driving mechanisms of climate variations. Detecting and aligning the globally common cosmogenic radionuclide production signal via a curve fitting method provides a tool for the quasi-continuous synchronization of paleoclimate archives. In this study, we apply this approach to synchronize ¹⁰Be records from varved sediments of Lakes Tiefer See and Czechowskie covering the Maunder-, Homeric- and 5500 a BP grand solar minima with ¹⁴C production rates inferred from the IntCal13 calibration curve. Our analyses indicate best fits with ¹⁴C production rates when the ¹⁰Be records from Lake Tiefer See were shifted for 8 (−12/+4) (Maunder Minimum), 31 (−16/+12) (Homeric Minimum) and 86 (−22/+18) years (5500 a BP grand solar minimum) towards the past. The best fit between the Lake Czechowskie ¹⁰Be record for the 5500 a BP grand solar minimum and ¹⁴C production was obtained when the ¹⁰Be time-series was shifted 29 (−8/+7) years towards present. No significant fits were detected between the Lake Czechowskie ¹⁰Be records for the Maunder- and Homeric Minima and ¹⁴C production, likely due intensified in-lake sediment resuspension since about 2800 a BP, transporting old ¹⁰Be to the coring location. Our results provide a proof of concept for facilitating ¹⁰Be in varved lake sediments as novel synchronization tool required for investigating leads and lags of proxy responses to climate variability. However, they also point to some limitations of ¹⁰Be in these archives mainly connected to in-lake sediment resuspension processes.
... The authigenic beryllium isotope analyses were carried out at the CEREGE National Cosmogenic Nuclides Laboratory (LN 2 C, France). A total of 250 samples selected with an average 7-cm (∼6 ka) resolution were collected from the paleomagnetic cubes and treated according to the chemical procedure established by Bourlès et al. (1989) and summarized by Simon et al. (2016b). The MBT, Jaramillo and Olduvai boundaries and Cobb Mountain events were scrutinized with higher sampling resolution (∼2 ka). ...
Article
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Long-term variations of the geomagnetic dipole moment (GDM) during periods of stable polarity and in transitional states (reversals and excursions) provide key information for understanding the geodynamo regime. Following several studies dealing with the Brunhes chron and the Matuyama-Brunhes transition, this study presents a new authigenic 10Be/9 Be ratio (Be-ratio) record obtained from the MD97-2143 core (western Pacific Ocean). This new Be-ratio series yields a record of GDM variations covering the early Brunhes and mid to late Matuyama time period (i.e. 700-2140 ka), independently from the relative paleointensity (RPI) record obtained from the same core, that can be compared with available RPI records and stacks. Stratigraphic offsets measured between the Be-ratio peaks and the corresponding RPI minima reach 2 to 14 cm. They can be assigned to (post-) detrital remanent magnetization (pDRM) effects leading to magnetization locking-in delays varying from 2 to 12 ka in the studied core. 10 Be overproduction episodes triggered by geomagnetic dipole moment lows (GDL) linked to polarity reversals and excursions confirm the global control exerted by the GDM on cosmogenic radionuclides production. A dipole moment reconstruction derived from the Beryllium-10 (BeDiMo) was compiled and calibrated using absolute paleointensity data. This independent record complements the available paleomagnetic RPI records, permitting 1) to overcome the pDRM lock-in offsets induced below the mixing layer, 2) to confront and increase the robustness and precision of GDM reconstructions and, 3) to better constrain the chronology of geomagnetic field instabilities during the mid to late Matuyama chron. Our new 10Be derived inventory is fully compatible with the GDL series linked to geomagnetic polarity reversals and events (Matuyama-Brunhes transition, Jaramillo and Olduvai subchron boundaries, Cobb Mountain, Réunion) and it strengthens the occurrence of several excursions (Kamikatsura, Santa Rosa, Punaruu, Bjorn, Gilsa, Gardar) that were until now reported from only sparse locations.
... We may reasonably assume that the deposition of cosmogenic 10 Be in ice caps and loess deposits results from the instantaneous "freezing" of the atmospheric signal, although 10 Be deposition is known to respond to numerous environmental and climatic factors, such as the regional precipitation rates and regimes (e.g., McHargue & Damon, 1991;Raisbeck et al., 2006). When dealing with marine terrigenous successions, further levels of uncertainty should be added in order to account for the much more complex arrangement of the marine sedimentary system (e.g., Brown et al., 1987Brown et al., , 1988Yiou et al., 1988;Simon et al., 2017). ...
Article
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The ¹⁰Be/⁹Be ratio is acknowledged as an effective tool for establishing the stratigraphic position of paleomagnetic excur-sions. Still, our data suggest that, in particular depositional settings, the interplay between climate, sedimentation and oceanography may jeopardize a realistic depiction of the natural ¹⁰Be/⁹Be record. © 2010 AIQUA - Associazione Italiana per lo Studio del Quaternario e EMMEVI - Servizio Congressi SPA.
... Because 10 Be and its stable isotope counterpart 9 Be have independent origins, their ratio (i.e. authigenic 10 Be/ 9 Be ratio) can be use to estimate denudation rates or freshwater inputs changes (Simon et al., 2016a). Because 10 Be decays (T 1/2 =1.39 Ma), it can be used to radiometrically date Mio-Plio-Pleistocene sedimentary archives (Simon et al., 2020a). ...
Conference Paper
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Ethiopia is a mountainous country known for its distinct topography ranging from alpine environment to desert-like conditions along the rift valley. Topoclimate, orographic rains on windward slopes and leeward rain shadow control rainfall variability in tropical mountains (Van den Hende et al., 2021). Such variability has a substantial societal impact. For instance, they can cause differences in susceptibility to geohazards and wealth of rain-fed agriculture farmers among the windward and leeward sides of the mountain. However, due to lack of detailed scientific knowledge, a one-size-fits-all approach has so far been used, without considering the inter-event rainfall variability. This study aims at characterizing and understanding the spatio-temporal characteristics of the summer rain climatology over the Ethiopian highlands using regional climate model ALARO-0 at 4 km resolution. Multiple determining factors are explored including: wind (windward or leeward), rain (wet or dry day) categories, and elevation. These are used to categorize the diurnal cycles of different meteorological variables including wind, temperature, humidity, and rainfall frequency and intensity. Ethiopia's summer rain exhibits a clear diurnal and semi-diurnal pattern with the highest rainfall during the afternoon hours 1100 - 1800 EAT and the minimum values identified in the morning hours 0200 - 0900 EAT. During these peak hours, the mountain peaks receive up to 1.5mm per hr for as long as seven hours a day, while lowlands receive little to no rainfall at most of the time. Besides, windward events are found to have an extended spatial and diurnal range of rainfall with respect to the shorter duration on leeward events. The predominant afternoon maximum rainfall, as well as the prevalence of windward over leeward events and high orographic rainfall suggest terrain-induced ascent owing to thermal rather than wind-induced forcing (Kirshbaum et al., 2018). Moreover, the ALARO-0 model is found to reproduce well rainfall extremes. The recurrent flood hazard in lowland settlements such as Dire Dawa and Awash (Erena et al., 2018), an area of little or no rain, comes after heavy rainfall in the Ahmar mountains. Similarly, flash flood in catchment headwaters and hydrological deficit in the flood-plains (Negash et al., 2020), show higher rainfall with increasing elevation; where highland farmers mainly depend on rainfed agriculture while lowlanders could not harvest almost any crop unless supplemented by spate irrigation. This suggests the need for an alternative approach replacing the one-size-fits-all management approach with a site-specific approach taking into account topoclimatic differences.
... Red arrows illustrate the relatively warm and salty water of the west Greenland current, whereas the blue arrows represent colder Arctic waters. et al. 1989;O Cofaigh et al. 2003;Simon et al. 2014Simon et al. , 2016. High sedimentation rates are typically found on highlatitude continental shelves and slopes and generally vary between 40 and 140 cm ka À1 for northern Baffin Bay (e.g. ...
Article
The northeastern Baffin Bay continental margin, which experiences high sediment accumulation rates, is an excellent location to study Holocene sedimentary variations. However, it is often difficult to obtain reliable chronologies of the sediment archives using traditional methods (δ¹⁸O and radiocarbon) due to specific oceanographic conditions (e.g. corrosive bottom waters). Here we propose a chronostratigraphy of three cores collected on the northwestern Greenland margin (AMD14‐204, AMD14‐210 and AMD14‐Kane2B) based on a combination of radiocarbon dating and palaeomagnetic records. Geophysical properties of discrete samples were used to verify the reliability of the palaeomagnetic records. Palaeomagnetic analyses indicate a strong and stable natural remanent magnetization carried by low coercivity ferrimagnetic minerals (magnetite) in the pseudo‐single domain grain size range. Correlation of the full palaeomagnetic vector (inclination, declination, and relative palaeointensity) was used to establish a reliable chronostratigraphical framework for two of the cores (AMD14‐204 and AMD14‐210) and to propose an original palaeomagnetic record for the previously ¹⁴C‐dated core AMD14‐Kane2B that covers most of the Holocene. Overall, this new chronostratigraphy allowed improvement of the timing of the main palaeoenvironmental changes that occurred in this area during the Holocene.
... The chemical purification procedures for our seawater samples were slightly modified from a method developed by Bourlès et al. (1989) and summarized by Simon et al. (2016) for marine sediments, and are described here. The co-precipitate was dissolved in 3 mL 10.2 M HCl, loaded onto a column packed with 15 mL Dowex® 1 × 8 (100-200 mesh) anion exchange resin, rinsed with 20 mL MilliQ® water, and conditioned with 20 mL 10.2 M HCl. ...
Article
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The cosmogenic radionuclide ¹⁰Be and its stable isotope ⁹Be can be used as a tracer for water mass mixing, but such applications are rare in both open oceans and marginal seas. Here we report distributions of dissolved ⁹Be and ¹⁰Be concentrations of the seawater in the surface and water columns along a section from shelf to deep basin in the northern South China Sea (SCS). The concentrations of ⁹Be and ¹⁰Be in surface waters range between 8.8–43.6 pmol/kg and 118–576 atoms/g, respectively. The ⁹Be in the northern SCS is dominantly sourced from river waters, while ¹⁰Be has a prominent input from the western Pacific, resulting in the highest ¹⁰Be/⁹Be ratio of 10.9 × 10⁻⁸ closest to the Luzon Strait. Along the depth section, the ⁹Be concentrations decrease southward while ¹⁰Be concentrations increase with the maximum value of 1,237 atoms/g occurring at 2,843 m depth of Station A10. The ¹⁰Be/⁹Be ratios are interpreted with consideration of water mixing and boundary scavenging, which reveal evidence of a branch of the intruding Kuroshio Current (>7.7 × 10⁻⁸) in subsurface water and a deep cyclonic current (>8.9 × 10⁻⁸). A box model yields a sedimentation flux of ¹⁰Be around 1,167 atoms/m²/s, that is, 4.6 times of the atmospheric deposition flux, pointing to active boundary scavenging of ¹⁰Be. The residence time of ¹⁰Be in the deep water is estimated to be longer than 79 years in the northern SCS. The beryllium isotopes as a water mass tracer will find wide applications in basins where the endmembers are sufficiently differentiated.
... 2) In most samples we only measured meteoric 10 Be in reactive fractions where the majority of 10 Be is contained. However, a small fraction of 10 Be can be contained in the silicate residual "min" fraction after chemical leaching (Simon et al., 2016;Wittmann et al., 2012). This observation may be explained by non-quantitative extraction of reactive 10 Be in oxyhydroxides by the leaching procedure or 10 Be contribution of secondary clay minerals that can not be decomposed by the leaching procedure. ...
Article
The cosmogenic meteoric 10 Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10 Be depositional flux to Earth's surface. Previous efforts on obtaining 10 Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10 Be records, and determining the inventory of soil profiles of known age. Here, we derive 10 Be depositional fluxes from Holocene river terrace 10 Be inventories across the Taiwan mountain belt. We measured 10 Be and 9 Be concentrations from three terrace profiles, with 14 C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m. Based on 10 Be inventories of our river terraces, the calculated long-term 10 Be depositional fluxes vary from 0.32 to 0.49 Â 10 6 at/cm 2 /yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66e0.88 Â 10 6 at/cm 2 /yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10 Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10 Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10 Be fluxes.
... Be isotope analysis was performed at the CEREGE National Cosmogenic Nuclides Laboratory (LN2C) according to the chemical procedure set-up by Bourl� es et al. (1989) and an updated separation procedure (e.g. Simon et al., 2016;� Sujan et al., 2016). The authigenic 10 Be concentrations were determined using the spiked 10 Be/ 9 Be ratios normalized to the NIST 4325 Standard Reference Material (2.79 � 0.03 � 10 11 ; Nishiizumi et al., 2007), measured at the French AMS national facility ASTER, and decay-corrected using the 10 Be half-life of 1.387 � 0.012 Ma (Chmeleff et al., 2010;Korschinek et al., 2010). ...
Article
A 601 m long sedimentary sequence was drilled in Lake Acigöl, located in the lakes region of SW Anatolia, near the Denizli travertine from which the oldest hominin of Turkey was unearthed. Among all dating methods applied to the sedimentary sequence, paleomagnetism, through the recognition of geomagnetic chrons, was the most successful and led to a quasi linear age model, with the 601 m long sedimentary record covering the last 2.3 Ma. An attempt to use the atmospherically deposited 10Be as a dating method was not very successful but provides interesting clues on this new method. Long-term lake level changes are depicted through lithological variations, in particular the carbonates and evaporites abundance. This change could be influenced by both long term cooling during the last 2 Ma and tectonic activity, which may in particular be responsible for a maximum water depth at around 1.8 Ma. Despite active tectonic influence, the sedimentary facies description and the magnetic susceptibility record (cleaned from tephra intervals) show that climate fluctuations (i.e., glacial-interglacial alternations) are likely recorded in the sedimentary succession, with warm periods marked by enhanced carbonate precipitation and cold and dry periods characterized by more detrital input linked to reduced vegetation cover and consequently more erosion in the catchment area. Preliminary pollen data, used to interpret magnetic susceptibility fluctuations, show that an average dry and open landscape prevailed around Acigöl lake during the whole record.
... The BeO was mixed with Nb powder in a 1:2 ratio, respectively, and pressed in aluminium cathode before being taken for measurement with AMS. A detailed schematic for the Be chemistry and column procedure is shown in Fig. 2. The sample processing procedure followed is modified from Corbett et al. (2016), Simon et al. (2016), and Von Blanckenburg et al. (1996). ...
Article
The first measurement of meteoric beryllium-10 (¹⁰Be) using Accelerator Mass Spectrometer (AMS) is reported from PRL-AURiS (Physical Research Laboratory-Accelerator Unit for Radioisotope Studies). Strategically, the meteoric ¹⁰Be dating method can date events as old as 10 Myr, and its accuracy while dating marine sediment cores has been well tested with magnetic methods. An attempt is made for a comparative study between radiocarbon (¹⁴C) and meteoric ¹⁰Be dating methods from a 6 m long sediment core collected from the equatorial Indian Ocean. The core was dated using both radiocarbon and meteoric ¹⁰Be and results showed remarkable similarity for both methods in terms of the sedimentation rate. A continuous age offset observed within 50 kyr could be due to a continuous influx of sediment with low ¹⁰Be content and that may have caused the meteoric ¹⁰Be ages to be younger. The sedimentation rate calculated by changing the ¹⁰Be depositional flux rate from 1.5 to 2.5 × 10⁻² atoms.cm⁻².s⁻¹ shows large variation, indicating the choice of appropriate ¹⁰Be depositional flux rate for the region. Additionally, being the first meteoric beryllium-10 measurements using AURiS, we have also discussed and reported the laboratory protocols and efficiency based on repeat standard and blank measurements.
... Fourteen samples from the COL17-2 and COL17-3 cores ( Fig. 2) have been prepared for 10 Be and 9 Be measurements following the method of Bourlès et al. (1989) revised by Simon et al. (2016aSimon et al. ( , 2016b. Authigenic 10 Be and its stable isotope 9 Be were extracted from ∼1 g dry samples by soaking them in a 20 ml leaching solution (0.04 M hydroxylamine (NH 2 OH-HCl) and 25% acetic acid) at 95±5°C for 7h. ...
Article
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We present a new 52 m composite record (COL17c) composed of five sedimentary sequences retrieved from the Colônia basin (Southeastern Brazil). The COL17c record is composed of two main sub-units deposited under different regimes: a peatland above ∼14 m and lacustrine sediments below. Sedimentary description and core scanning (MSCL and XRF) are first used to align individual cores in order to produce a nearly continuous composite record. We then established an original chronological framework based on radiocarbon, paleomagnetic, optically stimulated luminescence (OSL), post-infrared infrared stimulated luminescence at elevated temperature (pIRIR290°C) and authigenic ¹⁰Be/⁹Be dating. We describe the protocols used for each technique and discuss the positive and negative results, as well as their implications for proxy interpretation. In spite of negative results of some techniques, mainly due to the absence of adequate sample material, the multi-proxy approach used is essential to maximize the chances of obtaining a satisfactory age model for this unique continental sedimentary sequence. All valid chronological proxies, comprising three AMS ¹⁴C ages, one pIRIR290°C age, two paleomagnetic constraints and eight authigenic ¹⁰Be/⁹Be datum, are integrated within a Bayesian age-depth modeling to produce a 1.5 ± 0.1 Ma chronology for the whole COL17c sequence. This age model represents the first long-term chronological estimate of sediments deposition in the Colônia basin. The record allows to refine the age of the Colônia basin formation between 5.3 and 11.2 Ma, much older than previously estimated from short sedimentary cores.
... In addition, the study of late Quaternary sediments from the Baffin Bay have provided important information to distinguish (i) variations in the provenance of detrital particles Sheldon et al., 2016;Simon, 2013;Simon et al., 2014Simon et al., , 2016, (ii) climate and atmospheric changes in source regions and surrounding land masses (e.g., Thomas et al., 2016), and (iii) variations in sediment propagation and ocean current trajectories (e.g., Georgiadis et al., 2018;Jennings et al., 2017;Simon, 2013). In this regard, the present study proposes new mineralogical and geochemical data from three marine sediment cores recovered from the Upernavik cross-shelf trough (AMD14-204), Melville Bay cross-shelf trough (AMD14-210), and Kane Basin (AMD14-Kane2B). ...
Article
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The mineralogical and geochemical compositions of three sediment cores from the northwestern Greenland continental margin (AMD14‐204, AMD14‐210) and Kane Basin (AMD14‐Kane2B) were investigated using quantitative X-ray diffraction (qXRD) and X-ray fluorescence (ED-XRF) in order to document the impact of ice-ocean interactions on the sediment provenance and transport pathways during the Holocene. Unmixing of the sediment composition and ratios such as quartz/clays and K/Fe indicate that detrital sediments in cores from the northwest Greenland margin are derived mainly from Prøven granite and reworked Archean gneiss, whereas sediments from Kane Basin are derived mainly from detrital carbonate (Ellesmere Island) and Proterozoic gneiss (Humboldt Glacier). Mineralogical and geochemical signatures also reveal that changes in detrital sediment provenance and transport in the region are strongly interconnected to regional ice stream dynamics, especially during the early Holocene with strong meltwater discharge from the Greenland Ice Sheet associated with the end of deglaciation. With the establishment of milder conditions during the mid-Holocene and reduced glacial activity once ice sheets retreated inland, sediment inputs via ocean currents became more effective. Thus, detrital proxies in core AMD14‐204, located in the Upernavik cross-shelf trough, support the hypothesis of an intensification of the West Greenland Current influence after 7.7 cal ka BP, which eventually affected the regional sediment dynamic by a greater contribution from basalt to the sediment supply. Finally, our results suggest that the interactions between climate, glacial dynamics and surface ocean circulation, controlled the paleoenvironmental changes observed in the three cores.
... When precipitated into the authigenic phase of marine sediment, consisting of Fe-Mn-oxyhydroxides, biogenic opal, and neo-formed clay, the 10 Be/ 9 Be ratio of the overlying water column is preserved (Bourlès et al., 1989;Kusakabe & Ku, 1984;. This ratio has been applied as a silicateweathering proxy at a global ocean-basin scale (Rugenstein et al., 2019;von Blanckenburg et al., 2015;von Blanckenburg & Bouchez, 2014;Willenbring & von Blanckenburg, 2010), to reconstruct past events of ice melting at a regional scale (Simon, Thouveny, Bourles, Nuttin, et al., 2016;Valletta et al., 2018) and to constrain the chronology of marine sediment archives (Bourlès et al., 1989), growth rates of manganese crusts (Segl et al., 1984), and 10 Be-production changes resulting from variations of Earth's magnetic field (e.g., Carcaillet et al., 2004;Christl et al., 2003;Knudsen et al., 2008;Ménabréaz et al., 2012Ménabréaz et al., , 2014Simon, Thouveny, Bourlès, Valet, et al., 2016;Simon et al., 2018). When seawater Be is incorporated into neo-formed authigenic clays during marine diagenesis, and these clays are added to the clay-sized detrital sediments, an increase in the 10 Be/ 9 Be ratio after their deposition in the ocean will result. ...
Article
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Plain Language Summary Clay minerals can form on land by the chemical breakdown of rock‐forming minerals, but clays can also form in the ocean. When clay formation takes place in the ocean, CO2 is released. To date, there is no method that can easily measure the amount of clay minerals formed in the ocean. We used two isotopes of the same element, beryllium (Be), with the atomic mass of 9 and 10 to test whether this isotope system can be used to measure marine clay formation. The abundance of these isotopes differs majorly on land and in the ocean. We measured beryllium isotopes in river sediment and ocean‐bottom sediment offshore the Chile coast and compared the ratios of the isotopes (¹⁰Be/⁹Be). The ratio is four times higher in ocean sediment, when compared to river sediment. We interpret this increase to be due to the formation of clay minerals in the ocean, which include the high ¹⁰Be/⁹Be ratio during their formation. We conclude that the beryllium‐isotope system can be used to measure the formation of even very small amounts (less than 2%) of marine clay minerals. This is important, as the clay‐forming chemical reactions release CO2 which has a long‐term effect on global climate.
... The different source of both nuclides potentially results in high variability of initial ratios with geographical position, mainly related to (1) variable lithology of source rocks, (2) variable intensity of chemical weathering over time (Willenbring and von Blanckenburg, 2010), (3) changes in the production of 10 Be with latitude (Dunai, 2010), (4) changes of sedimentary environment proximity during deposition, because the authigenic phase forms continuously growing rims around particles in a water column, which exhibit different 10 Be/ 9 Be ratio depending on the distance of a terrestrial source of 9 Be (e.g., river deltas; Wittmann et al., 2017) and (5) mixing of waters with various origin (e.g., melting of glaciers, hydrothermal feeders) (Simon et al., 2016). Despite the complexity of the mentioned effects, the initial ratios for alluvial and lacustrine environments were determined for the Danube Basin using recent/Holocene samples (Šujan et al., 2016). ...
Article
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We present new age constraints for the late Miocene Volkovce Formation of Slovakia, alluvial facies that accumulated adjacent to Lake Pannon. Facies analysis and authigenic 10Be/9Be dating was undertaken at the Bernolákovo and Triblavina localities while the latter outcrop also yielded additional small mammal and mollusk assemblages as well as remains of flora. The results of seven radiometric dating ages yielded a weighted mean age of 9.65 ± 0.61 Ma for the Triblavina outcrop and 8.85 ± 0.32 Ma for the Bernolákovo outcrop. The small mammal assemblage at the Triblavina outcrop is indicative of the lowermost MN11 zone, which in the Western European standard definition suggests an age of <8.9 Ma. The ~0.1 Ma inconsistency between absolute dating and biostratigraphic dating at Bernolákovo outcrop might be explained either by the variation of initial 10Be/9Be ratio in the depositional environment or/and by diachronous development of the mammal faunas across the Europe. The mollusk assemblage at this outcrop indicates the paleoenvironment of freshwater lakes was affected by distant stream with evidence for a nearby riparian forests; it may be roughly correlated with Papp's lithostratigraphic units G and H defined for the Pannonian stage in the Vienna Basin. Our results provide a detailed insight to the late Miocene stratigraphy and terrestrial environments alongside the Lake Pannon shoreline.
... The settling and scavenging rate in the water column can cause the LCO, as well as blocking of the atmospheric 10 Be supply by the presence of sea ice, partial dissolution of the detrital terrigenous particles, reworking or redistribution of the marine sediments (Frank et al., 1995;von Blanckenburg et al., 1996;Frank et al., 2002;Sjunneskog et al., 2007;Frank et al., 2009;von Blanckenburg and Bouchez, 2014). Combined 10 Be/ 9 Be ratios and 10 Be concentrations can be used to correct for the offsets caused by different sedimentation rates, particle sizes, sediment storage, and water mass mixing (Eisenhauer et al., 1994;Simon et al., 2016;Valletta et al., 2018). ...
Article
This study documents spatial variations in authigenic 9Be and 10Be concentrations and 10Be/9Be ratios in different glacial settings in the Weddell and Ross seas, Antarctica. Weddell Sea surface sediments have the lowest 10Be and highest 9Be concentrations, and most depleted 10Be/9Be ratios, as compared with other regions, indicating 9Be enrichment from the recently collapsed Larsen Ice Shelf (LIS) B and reduction of 10Be supply due to blockage by the un-deglaciated LIS C. Local 10Be deposition varies across the open marine Ross Sea, which is more affected by seasonal sea ice persistence than ocean currents. Higher 10Be/9Be ratios in the western Ross Sea and higher 10Be concentrations in the eastern Ross Sea correlate with higher sea ice concentrations and changes, and vice versa in the central Ross Sea. The higher sea ice concentration not only blocks atmospheric 10Be and dust deposition during the frozen season, but increases the dust flux and supply of Be isotopes during the sea ice melting season. Thus, the spatial distribution of Be isotopes in surface sediments of the Antarctic oceans can be used as a proxy for sea ice dynamics and sedimentary environments.
... The cosmogenic radionuclide 10 Be found in natural archives is commonly used as a proxy of cosmic-ray flux (e.g. [1]), a tracer of environmental/sedimentological processes [2][3][4][5][6][7], and a chronometer for geological/paleoclimatological evolution (e.g. [8][9][10][11]). ...
Article
To explore the possibility of using ground ice archives for studies of the cosmogenic radionuclide ¹⁰Be, we analyzed the beryllium isotopes in ice wedges exposed in the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel and the Barrow Permafrost Tunnel in Alaska. We determined the concentrations of ¹⁰Be and ⁹Be in samples pretreated following two procedures: acidification before (procedure A) and after (procedure B) removal of particles. The ¹⁰Be and ⁹Be concentrations spanned wide ranges. Concentrations in procedure A samples were higher than those in procedure B samples. The ¹⁰Be/⁹Be ratios fell within a narrow range, and values from CRREL (about 8.5 × 10⁻⁹) and Barrow (about 7 × 10⁻⁹) were of the same order of magnitude. Further studies are needed to validate our findings and assess the feasibility of using the ¹⁰Be/⁹Be ratio of syngenetic ice wedges for reconstruction of ¹⁰Be variations due to cosmogenic and environmental changes, and radiometric dating of ice-wedge sequences that contain very old (beyond 1 Ma) ice.
Article
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The depocenters of epicontinental basins usually comprise relatively continuous depositional records, and these can be used in the determination of sediment routing and paleogeographic changes via a set of various geophysical, sedimentological, biostratigraphic and geochronological approaches. Although the margins of such basins will have a major role as constraints for that sediment routing, their depositional records are typically scarce and incomplete, posing a common challenge in terms of gaining information about them. The present study focuses on the upper Miocene succession present in the Malé Karpaty Mts., a pre-Cenozoic horst dividing the Vienna and Danube basins (Central Europe). The data gained by facies analysis, biostratigraphy, shallow seismic survey, authigenic 10Be/9Be dating and correlation of archival borehole profiles reveals, that the succession under consideration represents a record of the Lake Pannon transgression, which appeared in the study area at ~10.9–10.6 Ma. The subaerially exposed granitic massif and Middle Miocene successions sourced a shoal water delta, which intercalated with wave-induced dunes and open lacustrine muds in brackish sublittoral to marginal littoral environments. The granitic massif was probably also exposed later, during the regression of Lake Pannon at ~10.2–10.0 Ma, as a result of the progradation of the paleo-Danube delta from the Vienna Basin southeastwards. The depositional record of the regressive sequence was documented and dated in well-cores from the nearby Danube Basin margin. The documented scenario of transgression preceding the overall regression of the paleo-Danube delta system by a relatively short period is characteristic of several other localities across the Pannonian Basin System, and may imply that the progradation of depositional system caused a base-level rise on account of sediment loading-induced subsidence.
Thesis
The direction and strength of geomagnetic field had been evolving continuously in the past. One of the few means of obtaining continuous reconstructions of this evolution relies on sedimentary records. The latter are therefore important for understanding the geodynamo and the underlying evolution of the Earth’s interior, as well as providing an important dating tool through magnetostratigraphy. Sedimentary records of geomagnetic field variations rely on two main recording mechanisms: the alignment of magnetic particles, which underlies continuous records of relative paleointensity (RPI), and the archivation of cosmogenic isotopes, in particular ¹⁰Be, whose production by cosmic ray spallation is modulated by the screening action of the dipole component of the Earth’s field. Previous studies reported similarities as well as significant differences between RPI and cosmogenic ¹⁰Be (expressed as ¹⁰Be/⁹Be) records. While a perfect match of the two records is not expected due to environmental contaminations present in both records, the similar changes during the periods characterised by significant decrease of the dipole moment are suggested owning to global field strength control of ¹⁰Be production and attenuation of non-dipolar features in RPI records measured within the sediments with the low sedimentation rates (<10 cm/ka). The aim of the present work was to improve our present knowledge on the field recording mechanisms of marine sediments, in particular: The environmental factors responsible for ¹⁰Be transport and removal from the water column, and the effect of source distributions on ⁹Be supply. The effect of post-depositional processes, in particular sediment mixing, on ¹⁰Be and RPI records. The mechanism by which a post-depositional magnetization is acquired near the bottom of the surface mixed layer. The causes of a systematic lag between ¹⁰Be and RPI records, and the environmental factors affecting RPI. In order to disentangle the environmental and magnetic contribution in sedimentary ¹⁰Be/9Be records, we analysed five records, covering the last geomagnetic reversal. Different recording characteristics at the five sites have been described in terms of additive and multiplicative climatic modulations, which depend essentially on water depth, location along large oceanic current systems, and distance to the coast. Simple criteria have been derived for the identification of most suited sites yielding minimal environmental contaminations. A new bioturbation model has been developed to explain sedimentary NRM in bioturbated sediment. This model includes a newly discovered phenomenon of size segregation in the surface mixed layer (SML), analogous to the well-known Brazil nut effect. Size segregation is responsible for the longer permanence of larger particles in the SML, up to the limit case of ferromanganese nodules and has important implications for sediment dating with benthic foraminifera. Calibration of the bioturbation model with microtektite profiles from two Indian Ocean cores enabled to reproduce the correct degree of delay between ¹⁰Be and RPI records, as well the environmental dependence of RPI in two cores from the North Atlantic and the Equatorial Pacific Oceans. The results obtained in this work can aid in developing integrated approaches for the correction of climatic contaminations in ¹⁰Be and RPI records. Furthermore, the predictive power of the bioturbation-based model for NRM acquisition can be used to design new laboratory experiments for the simulation of specific magnetic recording mechanisms. We have demonstrated the Brazilian-nut effect on the microtektite particles, that consists in size-dependent fragments segregation. The results of this research have significant importance not only for the sediment mixing response characterisation and reconstruction of affected by bioturbation processes records (e.g. ¹⁰Be /⁹Be),..
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Timescale uncertainties between paleoclimate reconstructions often inhibit studying the exact timing, spatial expression and driving mechanisms of climate variations. Detecting and aligning the globally common cosmogenic radionuclide production signal via a curve fitting method provides a tool for the quasi-continuous synchronization of paleoclimate archives. In this study, we apply this approach to synchronize ¹⁰Be records from varved sediments of Tiefer See and Lake Czechowskie covering the Maunder, Homeric and 5500 a BP grand solar minima with ¹⁴C production rates inferred from the IntCal13 calibration curve. Our analyses indicate best fits with ¹⁴C production rates when the ¹⁰Be records from Tiefer See were shifted for 8 (−12∕ + 4) (Maunder Minimum), 31 (−16∕ + 12) (Homeric Minimum) and 86 (−22∕ + 18) years (5500 a BP grand solar minimum) towards the past. The best fit between the Lake Czechowskie ¹⁰Be record for the 5500 a BP grand solar minimum and ¹⁴C production was obtained when the ¹⁰Be time series was shifted 29 (−8∕ + 7) years towards present. No significant fits were detected between the Lake Czechowskie ¹⁰Be records for the Maunder and Homeric minima and ¹⁴C production, likely due to intensified in-lake sediment resuspension since about 2800 a BP, transporting old ¹⁰Be to the coring location. Our results provide a proof of concept for facilitating ¹⁰Be in varved lake sediments as a novel synchronization tool required for investigating leads and lags of proxy responses to climate variability. However, they also point to some limitations of ¹⁰Be in these archives, mainly connected to in-lake sediment resuspension processes.
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The ratio of cosmogenic 10Be and its stable isotope 9Be has been used as a proxy of long-term continental weathering fluxes and denudation rates, but transport processes of these isotopes from river water to estuarine water and seawater, as well as interference of potential anthropogenic source of 9Be on natural 10Be/9Be around populated estuaries are not well constrained. Here, we present results of 10Be and 9Be concentrations of dissolved and reactive particulate phase in the Pearl River Estuary (PRE) and its eight major outlets. The concentrations of Cu, Cd, and Pb are also measured, allowing us to assess their contamination levels and anthropogenic source together with 9Be by the geo-accumulation index (Igeo–reac) and enrichment factor (EF). A wide distribution pattern of dissolved 10Be (137–1,194 at/gwater) and 9Be (0.781–8.31 × 10–12 g/gwater) among these outlets is observed. The distribution coefficients (Kd) of both isotopes between sediment and water are in the order of 105, and on average only 5% of 10Be exists as dissolved form. Compared with total meteoric 10Be deposited on the river basin, 23% of the meteoric 10Be is retained while 38% of 10Be finally escape the estuary and is transported into coastal seawater. Despite the high contamination levels of Cu and Cd, the lower Igeo–reac and EF values of 9Be indicate that 9Be is hardly polluted by anthropogenic source. Thus, the 10Be/9Be in the PRE area is mainly associated with natural processes instead of human activities.
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Recent work has confirmed that grounded ice reached the shelf break in central West Greenland during the Last Glacial Maximum (LGM). Here we use a combination of marine sediment-core data, including glacimarine lithofacies and IRD proxy records, and geomorphological and acoustic facies evidence to examine the nature of and controls on the retreat of a major outlet of the western sector of the Greenland Ice Sheet (GrIS) across the shelf. Retreat of this outlet, which contained the ancestral Jakobshavns Isbræ ice stream, from the outer shelf in Disko Trough was rapid and progressed predominantly through iceberg calving, however, minor pauses in retreat (tens of years) occurred on the middle shelf at a trough narrowing forming subtle grounding-zone wedges. By 12.1 cal kyr BP ice had retreated to a basalt escarpment and shallow banks on the inner continental shelf, where it was pinned and stabilised for at least 100 years. During this time the ice margin appears to have formed a calving bay over the trough and melting became an important mechanism of ice-mass loss. Fine-grained sediments (muds) were deposited alternately with IRD-rich sediments (diamictons) forming a characteristic deglacial lithofacies that may be related to seasonal climatic cycles. High influxes of subglacial meltwater, emanating from the nearby ice margins, deposited muddy sediments during the warmer summer months whereas winters were dominated by iceberg calving leading to the deposition of the diamictons. This is the first example of this glacimarine lithofacies from a continental-shelf setting and we suggest that the calving-bay configuration of the ice margin, plus the switching between calving and melting as ablation mechanisms, facilitated its deposition by channelling meltwater and icebergs through the inner trough. The occurrence of a major stillstand on the inner shelf in Disko Trough demonstrates that the ice-dynamical response to local topography was a crucial control on the behaviour of a major outlet in this sector of the GrIS during retreat.
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This paper presents a comprehensive review and synthesis of ice streams in the Laurentide Ice Sheet (LIS) based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed. The inventory includes 117 ice streams, which have been identified based on a variety of evidence including their bedform imprint, large-scale geomorphology/topography, till properties, and ice rafted debris in ocean sediment records. Despite uncertainty in identifying ice streams in hard bedrock areas, it is unlikely that any major ice streams have been missed. During the Last Glacial Maximum, Laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets. Large ice streams had extensive onset zones and were fed by multiple tributaries and, where ice drained through regions of high relief, the spacing of ice streams shows a degree of spatial self-organisation which has hitherto not been recognised. Topography exerted a primary control on the location of ice streams, but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock, and where networks of ice streams switched direction repeatedly and probably over short time scales. As the ice sheet retreated onto its low relief interior, several ice streams show no correspondence with topography or underlying geology, perhaps facilitated by localised build-up of pressurised subglacial meltwater. They differed from most other ice stream tracks in having much lower length-to-width ratios and have no modern analogues. There have been very few attempts to date the initiation and cessation of ice streams, but it is clear that ice streams switched on and off during deglaciation, rather than maintaining the same trajectory as the ice margin retreated. We provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30% of the margin was drained by ice streams at the LGM (similar to that for present day Antarctic ice sheets), but this decreases to 15% and 12% at 12 cal ka BP and 10 cal ka BP, respectively. The extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate, or internal ice dynamical feedbacks unrelated to climate (or both) is largely unknown and represents a key area for future work to address.
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The polar ice cores, in addition to improving our understanding of the climate, give access to beryllium-10 (10Be) fallout, an isotope of cosmogenic origin created by the interaction of Galactic Cosmic Rays with the upper atmosphere. Its production rate depends on the intensity of the primary cosmic rays, which are modulated by solar activity and the Earth’s magnetic field. 10Be therefore provides information on these two parameters. It has allowed, among others, the improvement of ice cores chronologies thanks to absolute stratigraphic markers linked to remarkable events of the geomagnetic field as the Laschamp excursion or the Brunhes-Matuyama reversal. EPICA Dome C (75° 06' S, 123° 21' E) is a 3270 m ice core drilled in East Antarctica. It offers a complete climate record over the last 800 000 years (kyr BP). In the framework of the PhD, 2200 10Be samples were measured between 2384 m (269 kyr BP) and 2627 m (355 kyr BP) deep. This continuous sequence provides, on the one hand, the opportunity to study the solar activity during the interglacial period of the Marine Isotope Stage (MIS) 9.3, where the resolution reaches ≥20 years. Our results contrast with those during the Holocene, with the noted absence of the de Vries cycle (210 years) in our 10Be profile. On the other hand, this sequence allowed us to verify that the classical estimate of snow accumulation obtained by the dating models of ice cores is correct to within 20% during the succession of glacial – interglacial cycles. These measurements were combined with those previously performed under the responsibility of Grant Raisbeck (publication in preparation). This allows to dispose of a continuous and detailed profile (resolution: 20 to 250 years) between 200 and 800 kyr BP on the EPICA Dome C ice core. The observed 10Be flux variations compare well with changes in the intensity of the geomagnetic field recorded in marine sediments. From this observation, it is possible to propose a synchronization of these profiles in order to place them on a common age scale. The observed phase shifts between the rise of temperature in Antarctica (increase of dD at EDC) and the rise of global sea level (decrease of marine d18O from marine sediments) do not exceed 3200, except at the Termination VII. The low resolution of the d18O records from marine sediments makes it difficult to analyze the phase shifts. The obtained results encourage to analyze more recent periods around Termination II, including the Blake and Iceland Basin geomagnetic excursions. Indeed, this would allow to constrain more strongly the synchronization between the paleomagnetic signal in marine sediments and the 10Be flux at EDC.
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Context. Abreu et al. (2012, A&A.; 548, A88) have recently compared the periodicities in a 14C - 10Be proxy record of solar variability during the Holocene and found a strong similarity with the periodicities predicted on the basis of a model of the time-dependent torque exerted by the planets on the sun's tachocline. If verified, this effect would represent a dramatic advance not only in the basic understanding of the Sun's variable activity, but also in the potential influence of this variability on the Earth's climate. Cameron and Schussler (2013, A&A.; 557, A83) have seriously criticized the statistical treatment used by Abreu et al. to test the significance of the coincidences between the periodicities of their model with the Holocene proxy record. Aims: If the Abreu et al. hypothesis is correct, it should be possible to find the same periodicities in the records of cosmogenic nuclides at earlier times. Methods: We present here a high-resolution record of 10Be in the EPICA Dome C (EDC) ice core from Antarctica during the Marine Interglacial Stage 9.3 (MIS 9.3), 325-336 kyr ago, and investigate its spectral properties. Results: We find very limited similarity with the periodicities seen in the proxy record of solar variability during the Holocene, or with that of the model of Abreu et al. Conclusions: We find no support for the hypothesis of a planetary influence on solar activity, and raise the question of whether the centennial periodicities of solar activity observed during the Holocene are representative of solar activity variability in general.
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Sea-floor landforms and acoustic-stratigraphic records allow interpretation of the past form and flow of a westward-draining ice stream of the Greenland Ice Sheet, Rink Isbrae. The Late Pliocene–Pleistocene glacial package is several hundred metres thick and down-laps onto an upper Miocene horizon. Several acoustic facies are mapped from sub-bottom profiler records of the 400 km-long Uummannaq fjord-shelf-slope system. An acoustically stratified facies covers much of the fjord and trough floor, interpreted as glacimarine sediment from rain-out of fine-grained debris in turbid meltwater. Beneath this facies is a semi-transparent deformation-till unit, which includes buried streamlined landforms. Landform distribution in the Uummannaq system is used to reconstruct past ice extent and flow directions. The presence of streamlined landforms (mega-scale glacial lineations, drumlins, crag-and-tails) shows that an ice stream advanced through the fjord system to fill Uummannaq Trough, reaching the shelf edge at the Last Glacial Maximum. Beyond the trough there is a major fan built mainly of glacigenic debris flows. Turbidity-current channels were not observed on Uummannaq Fan, contrasting with well-developed channels on Disko Fan, 300 km to the south. Ice retreat had begun by 14.8 cal. ka ago. Grounding-zone wedges (GZW) in Uummannaq Trough imply that retreat was episodic, punctuated by several still-stands. Ice retreat between GZWs may have been relatively rapid. There is little sedimentary evidence for still-stands in the inner fjords, except for a major moraine ridge marking a Little Ice Age maximum position. On the shallow banks either side of Uummannaq Trough, iceberg ploughing has reworked any morphological evidence of earlier ice-sheet activity.
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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 m 2 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.
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Precise relationships between high-frequency ice sheet dynamics and late Quaternary climate variability are still poorly understood, notably with regard to their relative timing and causal mechanisms. Baffin Bay is of particular interest in this regard due to the influence of ice streaming activities from the north-eastern Laurentide, southern Innuitian and western Greenland ice margins on its sedimentary regimes during glacial times. Here we document such ice margin dynamics using a sedimentological analysis performed on a piston core from central Baffin Bay and spanning the last 115 ka. Lithofacies analysis and mineralogical assemblages are used to reconstruct sediment sources (using the SedUnMix program) and depositional mechanisms. Coarse detrital carbonate (DC, dolomite-rich) layers are attributed either to north-eastern Laurentide and Innuitian ice stream surges or to pervasive ice rafted debris delivery processes at distinct periods. Out-of-phase fine-grained glaciomarine sediments with a mineralogical signature from western Greenland, linked to Uummannaq ice streaming activity, are interbedded with the coarse DC layers. The new results suggest that during the last glacial cycle, the north-eastern Laurentide and southern Innuitian ice streams were sensitive to high-frequency climate fluctuations, such as the Dansgaard–Oeschger events, while the western Greenland margins were more sensitive to large-scale climatic/oceanic reorganizations, such as relative sea-level changes and/or advection of warmer Atlantic waters into the bay.
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Based on quantitative X-ray diffraction mineralogical analysis of cores HU2008029-0006/0008 (857-m water depth) located south of the Davis Strait sill, we seek answers to two questions: (i) the temporal correlation of NW Labrador Shelf Sea Heinrich (H-) and Baffin Bay detrital carbonate (BBDC) events, and (ii) the provenance of the sediments? A sediment-unmixing model (SedUnMix) is used to determine provenance variations. Although 12 radiocarbon dates were obtained there were many age reversals and we favour a depth/age model for HU2008029-0008PC based on correlations to well-dated neighbouring cores north and south of Davis Strait. We find no correlation between H- and BBDC events except for H-0, which appears to be a broadly synchronous event along the NE Canadian margin and is correlative with an episode of major moraine building along this flank of the Laurentide Ice Sheet. Unmixing of the sediment composition based on six potential glacial source regions indicates that the bulk of the sediment in 0008PC is derived from glacial erosion of West Greenland, but is punctuated by intervals when dolomite-rich sediments, derived from outcrops north of Baffin Bay, dominate the composition. Estimated dates on these BBDC events are ∼13, 25 and 30–38 cal ka BP.
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The late Quaternary Baffin Bay sediments provide exclusive records of Greenland, Innuitian and Laurentide ice sheet margin activities, as well as information about the Arctic and northern Atlantic ocean linkages through the Canadian Arctic Archipelago. Because of specific oceanographic conditions, foraminiferal δ18O-stratigraphies and radiocarbon ages fail to provide reliable chronologies. Here we propose an original chronostratigraphy spanning the last glacial cycle based on high-resolution paleomagnetic investigations on a 741-cm long core (HU2008-029-016PC) raised from the deep central Baffin Bay, near ODP site 645. Two major difficulties were encountered: (1) the high-frequency occurrence of rapidly deposited layers related to short ice sheet margin events (e.g., ice surges), and (2) the magnetic grain size variability. Physical and magnetic mineralogical properties were used to screen out unreliable magnetic sediment layers. The obtained relative paleointensity (RPI) proxy matches reference paleomagnetic stacks and regional records. Moreover, the resulting record depicts two major excursions which were assigned to the Laschamp and the Norwegian-Greenland-Sea events. It has thus been possible to derive a robust 115ka chronology for the cored sequence. We concluded that even under such a dynamic sedimentary regime, magnetic properties of the sediments can provide a reliable chronostratigraphy, together with information on sedimentary processes.
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We present a 5.3-Myr stack (the "LR04" stack) of benthic δ 18 O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm. This is the first benthic δ 18 O stack comprised of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene. We also present a new LR04 age model for the Plio-Pleistocene derived from tuning the δ 18 O stack to a simple ice model based on June 21 insolation at 65 • N. Stacked sedimentation rates provide additional age model constraints to prevent overtuning. Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 5.3 Myr and in the precession band for more than half of the record. The LR04 stack contains significantly more variance in benthic δ 18 O than previously published stacks of the late Pleistocene as the result of higher resolution records, a better alignment technique, and a greater percentage of records from the Atlantic. Finally, the relative phases of the stack's 41-and 23-kyr components suggest that the precession component of δ 18 O from 2.7–1.6 Ma is primarily a deep-water temperature signal and that the phase of δ 18 O precession response changed suddenly at 1.6 Ma.
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The reliability of paleomagnetic records as proxies of the geomagnetic field intensity is still a matter of controversy since volcanic materials hardly provide continuous records, and marine sediments are suspected to carry a remanence biased by post-depositional realignments and/or by overprints. Such long standing debate emphasizes the need for the development of methods independent from paleomagnetism to decipher geomagnetic intensity variations. High resolution measurements of authigenic 10Be/9Be along with a detailed sedimentary record of directional and relative paleointensity variations evidence, over the 0.6-1.3 Ma time interval, frequent and recurrent excursions or short events in the late Matuyama and the early Brunhes epochs, among which two Brunhes-Matuyama reversal precursors and an intra-Jaramillo excursion. The results of this study confirm the idea of a highly unstable geomagnetic field as suggested by paleomagnetic evidences.
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The upper 200 m of the sediments recovered during IODP Leg 302, the Arctic Coring Expedition (ACEX), to the Lomonosov Ridge in the central Arctic Ocean consist almost exclusively of detrital material. The scarcity of biostratigraphic markers severely complicates the establishment of a reliable chronostratigraphic framework for these sediments, which contain the first continuous record of the Neogene environmental and climatic evolution of the Arctic region. Here we present profiles of cosmogenic 10Be together with the seawater-derived fraction of stable 9Be obtained from the ACEX cores. The down-core decrease of 10Be/9Be provides an average sedimentation rate of 14.5 +/- 1 m/Ma for the uppermost 151 m of the ACEX record and allows the establishment of a chronostratigraphy for the past 12.3 Ma. The age-corrected 10Be concentrations and 10Be/9Be ratios suggest the existence of an essentially continuous sea ice cover over the past 12.3 Ma.
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10Be concentrations in an ice core at Taylor Dome, Antarctica show greater variation over the last 75 years than similar 10Be time-series from Greenland. Like the Greenland records, the new Antarctic data exhibit a strong periodicity which follows expected changes in the production rate of 10Be over the 11-year solar cycle. Noting that the amplitude of production-rate variation is both latitude and altitude dependent, we estimate the relative contribution of 10Be from different atmospheric reservoirs. The calculations yield a relatively small (
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10Be measured in a Greenland Ice Core Project (GRIP) snow pit (1986–1990) with a seasonal resolution is compared with the ECHAM5–HAM GCM run. The mean modeled 10Be concentration in ice (1.0·104 atoms/g) agrees well with the measured value (1.2·104 atoms/g). The measured 10Be deposition flux (88 atoms/m2/s) also agrees well with the modeled flux (69 atoms/m2/s) and the measured precipitation rate (0.67 mm/day) agrees with the modeled rate (0.61 mm/day). The mean surface temperature of −31°C estimated from δ18O is lower than the temperature measured at a near-by weather station (−29°C) and the modeled temperature (−26°C). During the 5-year period the concentrations and deposition fluxes, both measured and modeled, show a decreasing trend consistent with the increase in the solar activity. The variability of the measured and modeled concentrations and deposition fluxes is very similar suggesting that the variability is linked to a variability in production rather than the local meteorology.