Geochemical data derived from an absolutely dated shell-based chronology for the Irish Sea

The identification in various proxy records of periods of rapid (decadal scale) climate change over recent millennia, together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric CO2, highlights the importance of a detailed understanding, at high spatial and temporal resolutions, of forcings and feedbacks within the system. Such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree-rings for the terrestrial environment and by corals for the tropical marine environment. Here we present the first annually resolved, multi-centennial (489-year), absolutely dated, shell-based marine master chronology. The chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long-lived bivalve mollusc Arctica islandica, collected from sites to the south and west of the Isle of Man in the Irish Sea. The strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree-ring chronologies. Analysis of the 14C signal in the shells shows no trend in the marine radiocarbon reservoir correction (DR), although it may be more variable before ~1750. The d13C signal shows a very significant (R**2 = 0.456, p < 0.0001) trend due to the 13C Suess effect.

对各类代用气候记录（proxy records）中近千年来十年尺度快速气候变化时段的识别，以及反馈机制可能放大气候系统对大气二氧化碳浓度升高响应的可能性，凸显了以高空间、时间分辨率深入解析气候系统内部强迫与反馈过程的重要性。此前此类认知始终存在局限，原因在于温带海洋环境缺乏类似陆地环境树轮、热带海洋环境珊瑚所提供的绝对定年标尺。本文首次构建了一套年分辨率、长达489年的数百年尺度绝对定年的基于壳体的海洋主年代序列（shell-based marine master chronology）。该年代序列通过对采自爱尔兰海马恩岛（Isle of Man）南部及西部海域的长寿双壳软体动物冰岛北极蛤（Arctica islandica）多个个体的壳体年生长增量宽度开展去趋势处理与平均运算后构建得到。该年代序列所表征的共同环境信号强度，可与树轮年代序列的同类统计结果相媲美。对壳体中碳14（14C）信号的分析显示，海洋放射性碳储层校正（marine radiocarbon reservoir correction, DR）无显著长期趋势，但在约1750年之前其波动幅度可能更大。受碳同位素δ13C（d13C）修斯效应（Suess effect）影响，该δ13C信号呈现出极为显著的变化趋势（决定系数R²=0.456，p<0.0001）。