Browsing by Author "Enge, TG"
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- ItemThe distribution and fractionation of beryllium isotopes in various reactive phases of Antarctic marine sediments(Australian Nuclear Science and Technology Organisation, 2021-11) Jeromson, MR; Fujioka, T; Fink, D; Post, A; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DABeryllium isotopes, ¹⁰ Be and ⁹ Be, in Antarctic marine sediments are increasingly being applied as paleoenvironmental proxies and indicators of past ice shelf extent. The evidence base for interpreting meteoric-¹⁰ Be concentrations and ¹⁰ Be/⁹ Be ratios has largely been derived from examining their spatial distribution in modern depositional environments, or by correlation with other proxies in paleo-records, such as diatom abundance. Meteoric-¹⁰ Be is geochemically adsorbed onto sediment grains in the reactive phase during transport from the atmosphere to deposition on the seafloor. Unlike meteoric-¹⁰ Be, ⁹ Be is both available within the reactive phase after crustal weathering and native within mineral lattice in significant quantities. The complexity in fixing and preserving the Be isotopes onto grain surfaces leads to uncertainties in selecting the chemistry methods to consistently extract the reactive phases of ¹⁰ Be and ⁹ Be in different sediments. This gap in understanding the physical behaviour and geochemical forms of reactive Be in Antarctic sediments limits their utility in reconstruction of paleoenvironmental conditions. We conducted a sequential leach procedure on three homogenised sediment grab samples from the front of the Amery Ice Shelf that span a range of water masses. Using different chemical reagents, from very weak to very strong, five phases of Be isotope signatures were extracted sequentially, including : i) water soluble, ii) amorphous oxides leached by 0.5M HCl, iii) crystalline oxides leached by 1M NH₂ OH-HCl in 1M HCl, iv) organic leached by 0.01M HNO₃ and H₂ O₂ , and v) mineral/residual phase dissolved by HF– with the water through to organic leach making the reactive phase. We found that the amorphous and crystalline oxide phases contained the largest fraction of ¹⁰ Be, about 90% of total ¹⁰ Be, with the remaining 10% being in the mineral/residual phase. For ⁹ Be, the oxide phases contained only 10-30%, the majority of ⁹ Be being in the residual phase. The water-soluble and organic chemical treatments were inefficient in extracting any significant reactive Be. This distribution has been observed in other deep marine and continental riverine sediments. However, the proportional distribution of the two isotopes between the amorphous and crystalline oxides differed for our Antarctic sediments compared to those other studies. While reactive ⁹ Be was close to equally split across the two oxide phases, 80% of reactive ¹⁰ Be was located within the amorphous phase, with the remainder within the crystalline oxide phase. The difference in fractionation provides evidence for different sources of each isotope and different processes affecting their deposition. ⁹ Be is sourced primarily from the Earth’s crust and is likely segregated into the different fractions during the process of subglacial chemical weathering. Open water ¹⁰ Be is processed in the water column, where interaction with biogeochemical processes likely segregates it into the more labile phases. These findings inform decisions regarding the selection of procedures for efficient and reproducible extraction of meteoric-¹⁰ Be, and for understanding the processes that drive the source and distribution of different isotopes around ice shelf systems. © The Authors
- ItemExtracting 10Be and 9Be from Antarctic marine sediments – a comparison of different extraction techniques(Australian Nuclear Science and Technology Organisation, 2021-11-17) Jeromson, MR; Fujioka, T; Fink, D; Post, AL; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DAApplication of meteoric-¹⁰ Be (M¹⁰ Be) in sediments and soils from diverse geomorphic settings has been active for many decades. In some cases, M¹⁰ Be is normalized by the reactive ⁹ Be from the same sediment sample. Given the complexities in geochemical pathways that M¹⁰ Be is incorporated in the reactive mineral phase of such sediments, very different Be isotope chemistry extraction techniques have been developed. Measurement of M¹⁰ Be and the reactive phase of ⁹ Be in coastal Antarctic marine sediments has increasingly become promising as a paleo-proxy for the presence (or absence) of past ice shelves, and/or subglacial meltwater discharge from grounded outlet glaciers draining the ice sheet. However, published works select different methods to chemically leach Be isotopes from the reactive phase of Antarctic marine sediment and few studies have quantitively compared the efficacy of different leaching recipes. This is problematic because comparisons of ¹⁰ Be/⁹ Be ratios across different Antarctic sites assumes the same chemical fractionation of Be isotopes regardless of the leaching method. We examined three large-volume sediment grabs from near the Amery Ice Shelf front in East Antarctica that represent a range of grainsize and environmental conditions. For Be extraction, homogenised materials from each of the three samples were treated with four different leaching procedures, 1–3 targeting the reactive phase: 1) 6M HCl; 2) 0.5M HCl followed by 1M hydroxylamine hydrochloride in 1M HCl; 3) 0.04M hydroxylamine hydrochloride in 25% acetic acid solution 4) a total extraction dissolving in HF, HNO₃ , and HClO₄ . We also selected one grab to assess the effect of grainsize within the following fractions: <38 um, 38–63 um, 63–90 um, 90–125 um, and >125 um. Each fraction was leached with 6M HCl for 24 hours at room temperature. We found that both the 6M HCl and the 1M hydroxylamine procedures leached the same amount of ¹⁰ Be as the total extraction, while the 0.04M hydroxylamine treatment leached only two thirds. Interestingly, the 6M HCl and the 0.04M hydroxylamine procedures leached the same relative proportion of ⁹ Be to ¹⁰ Be, and thus gave the same ¹⁰ Be/⁹ Be ratio, while the 1M hydroxylamine procedure leached relatively more ⁹ Be in relation to ¹⁰ Be, resulting in a lower ¹⁰ Be/⁹ Be than the other two methods. As shown in previous studies, our results indicate that Be-isotope concentrations varied inversely with grainsize, in our case increasing 4- fold from coarsest to finest fractions, critically showing that the ¹⁰ Be/⁹ Be ratio remained constant across all grainsizes. Hence, grainsize can be normalised by applying the reactive ¹⁰ Be/⁹ Be ratio. We conclude that differences in leaching procedures, can lead to significant variations in efficiencies in extracting Be isotopes from the reactive phase of sediment, whereas the ¹⁰ Be/⁹ Be ratio appears to remain the same. This study highlights the importance of careful method selection and its consistent application to allow for comparison between studies and more robust interpretation.