(Table 1) The 10Be and 9Be isotope record of IODP EXP202 composite Site

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.

在 IODP 第 302 航次，北极钻探考察（ACEX）于中央北极洋的隆斯沃斯海脊所采集的沉积物上层 200 米几乎完全由碎屑物质构成。生物地层学标记的稀缺性极大地增加了构建这些沉积物可靠年代地层框架的难度，这些沉积物中包含了北极地区新生代环境与气候演化的首个连续记录。在本研究中，我们展示了从 ACEX 核心样本中获取的宇宙成因 10Be 以及海水衍生的稳定 9Be 的剖面。10Be/9Be 比值在核部下移中的降低，为 ACEX 记录最上层 151 米的平均沉积速率提供了 14.5 ± 1 米/百万年的数据，并允许建立过去 12.3 百万年的年代地层。年龄校正后的 10Be 浓度和 10Be/9Be 比率表明，在过去 12.3 百万年内，北极地区基本保持了连续的海冰覆盖。