Tona Sanchez-Palacios

Theme: T-5: Advances in sample preparation Type of presentation: Poster-Plus Presentation Application of meteoric-¹ Be (M¹ Be) in sediments and soils from diverse geomorphic settings has been active for many decades. In some cases, M¹ Be is normalized by the reactive Be from the same sediment sample. Given the complexities in geochemical pathways that M¹ Be is incorporated in the reactive mineral phase of such sediments, very different Be isotope chemistry extraction techniques have been developed. Measurement of M¹ Be and the reactive phase of 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 sub-glacial 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 ¹ Be/ 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, HNO , and HClO. 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 ¹ 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 Be to ¹ Be, and thus gave the same ¹ Be/ Be ratio, while the 1M hydroxylamine procedure leached relatively more Be in relation to ¹ Be, resulting in a lower ¹ Be/ 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 ¹ Be/ Be ratio remained constant across all grainsizes. Hence, grainsize can be normalised by applying the reactive ¹ Be/ 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 ¹ Be/ 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.