Dating the Initiation of Polar Ice Sheet Formation

大冰原是地球上最好的气候档案之一，但目前还没有可靠的方法来确定这些冰原最后一次开始形成的时间。这些信息对于验证气候模型和利用保存在接近冰底的化石材料（如古代DNA）的其他研究非常重要。虽然冰本身可能无法确定年代，但原则上，在最初的冰形成过程中加入的任何矿物颗粒都可以使用发光技术来确定年代。在该项目的过程中，将开发一种新的发光法来确定极地冰盖最后一次开始形成的时间。首先，将在冰芯材料上测试最近研究的单个沙粒长石发光信号的适用性。为了确定单个颗粒内部放射性钾（40K）的储能率，将使用扫描电子显微镜（SEM）和激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）对单个颗粒进行分析。此外，一种新的基于激光的光谱系统（目前正在开发中，用于自动分析颗粒中的K/Na比率）将在项目的第二阶段进行测试。根据发光数据和有关内剂量率的信息，可以推导出冰形成的年龄估计。该项目将为全球气候模型提供以前无法获得的输入和验证数据，并为基底冰的化石记录提供一个时间框架。

Major ice sheets are one of the best climate archives on Earth, but there are at present no reliable methods for determining when these ice sheets last began to form. Such information is of great importance to verifying climate models and to other studies which make use of fossil material preserved close to the bottom of the ice (e.g., ancient DNA). Although the ice itself may not be datable, any mineral grains incorporated during initial ice build up can, in principle, be dated using luminescence techniques.In the course of the project a new luminescence method for dating the last time polar ice sheets began to form will be developed. Firstly, the suitability of recently-investigated luminescence signals from individual sand-sized grains of feldspar will be tested on ice core material. To determine the rate of energy storage from internal radioactive potassium (40K) of the individual grains both scanning electron microscopy (SEM) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) will be applied on the individual grains. Additionally, a new laser based spectrometry system (now under development to automatically analyse K/Na ratios in the grains) will be tested in the second phase on the project. Based on the luminescence data and the information on the internal dose rate, age estimates for the ice formation can be derived. The project will provide previously unavailable input and verification data to global climate models, and a chronological framework for the fossil record in basal ice.