Beryllium-isotope signatures in ice sheet proximal marine sediments

Abstract

Meteoric-10Be has become a popular proxy for assessing glacial environments and processes around Antarctica, such as meltwater discharge or ice shelf environments. Despite applications in recent paleostudies, little testing of the mechanisms driving the deposition of Be-isotopes into marine sediments has been conducted. We used chemical leach procedures to sequentially or partially extract 10Be and 9Be from bulk sediments to assess the possible sources and depositional processes affecting them. Additionally, we leached the reactive phase of five different grainsize splits to determine whether 10Be/9Be ratios normalise for grainsize effects acting upon the 10Be concentration. Reactive Be-isotopes are primarily situated in the oxide phases of sediments, with the amorphous oxide (Am-Ox) phases consisting of much higher 10Be/9Be ratios (∼7–10 × 10−8) than the crystalline oxides (∼1–3 × 10−8; X-Ox), indicating that the Am-Ox phase better represents authigenic oxide production and a circumpolar deep water source, which is contrary to most of the current literature. Published leach procedures targeting the reactive phase of sediment consist of ratios in between the Am-Ox and X-Ox phases (∼3–7 × 10−8), indicating that they target both phases to some degree. The fractionation of Be-isotopes in Antarctic sediment samples shows that circumpolar deep water is the primary source of 10Be, and that the “reactive” signatures from different leach steps targeting the reactive phase are not the same.