High-resolution precipitation records for the past millennia from Tibetan ice cores analyzed by LA-ICP-MS

Net accumulation records derived from alpine ice cores provide the most direct measurement of past precipitation. However, quantitative reconstruction of accumulation for past millennia remains challenging due to the difficulty in identifying annual layers in the deeper sections of ice cores. In this study, we propose a quantitative method to reconstruct annual accumulation from alpine ice cores for past millennia, using as an example an ice core drilled at the Chongce ice cap in the northwestern Tibetan Plateau (TP). First, we used laser ablation inductively coupled plasma mass spectrometry (LAICP-MS) technology to develop ultra-high-resolution trace element records in three sections of the ice core and identified annual layers in each section based on seasonality of these elements. Second, based on nine 14C ages determined for this ice core, we applied a two-parameter flow model to established the thinning parameter of this ice core. Finally, we converted the thickness of annual layers in the three sample sections to past accumulation rates based on the thinning parameter derived from the ice flow model. Our results show that the mean annual accumulation rates for the three sample sections are 109 mm yr−1 (2511–2541 years BP), 74 mm yr−1 (1682–1697 years BP), and 68 mm yr−1 (781–789 years BP), respectively. For comparison, the Holocene mean precipitation is 103 mm yr−1. This method has the potential to reconstruct continuous high-resolution precipitation records covering millennia or even longer time periods.

高山冰芯的净积累记录，是定量反演过去降水信息最直接的手段。然而，由于难以识别冰芯深部的年层，千年尺度的积累量定量重建仍颇具挑战。本研究提出了一种可用于千年尺度高山冰芯年积累量定量重建的方法，并以青藏高原西北部崇测冰帽（Tibetan Plateau, TP）钻取的冰芯作为研究案例。首先，本研究采用激光剥蚀电感耦合等离子体质谱法（laser ablation inductively coupled plasma mass spectrometry, LAICP-MS）技术，对该冰芯的三个段次开展超高分辨率微量元素记录分析，并基于这些元素的季节变化特征识别各段次的年层。其次，基于该冰芯的9个14C测年数据，本研究采用双参数流动模型确定了该冰芯的变薄参数。最后，基于冰流模型得到的变薄参数，将三个样段的年层厚度转换为过去的积累速率。研究结果显示，三个样段的年均积累速率分别为109毫米/年（距今2511~2541年）、74毫米/年（距今1682~1697年）以及68毫米/年（距今781~789年）。作为对比，全新世的平均降水为103毫米/年。该方法具备重建覆盖千年乃至更长时间尺度的连续高分辨率降水记录的潜力。