IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores
IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores
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DOI：
10.5194/gmd-8-1473-2015
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发表时间：
2014-10
影响因子：
5.1
通讯作者：
F. Parrenin;L. Bazin;E. Capron;A. Landais;B. Lemieux-Dudon;V. Masson‐Delmotte
中科院分区：
文献类型：
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作者：
F. Parrenin;L. Bazin;E. Capron;A. Landais;B. Lemieux-Dudon;V. Masson‐Delmotte
极地冰芯提供了过去环境条件的特殊档案。冰芯的测年和年龄尺度不确定性的估计对于解释它们所包含的气候和环境记录至关重要。然而，这是一个复杂的问题，涉及不同的方法。在这里，我们提出了IceChrono 1，一个新的概率模型，集成了各种来源的年代信息，以产生一个共同的和优化的年表几个冰芯，以及它的不确定性。IceChrono 1基于三个量的反演：表面累积率、气泡锁定深度（LID）和变薄函数。纳入模型的年代学信息包括沉积过程模型（雪的积累、雪致密化成冰和空气捕获、冰流）、冰和空气定年层位、具有已知持续时间的冰和空气深度间隔、Δ深度观测（冰和空气中记录的同步事件之间的深度变化）以及冰芯之间的空气和冰地层联系。最优化被配制成一个最小二乘问题，这意味着所有的概率密度被假定为高斯。它是数值求解使用Levenberg-Marquardt算法和数值评估模型的雅可比矩阵。IceChrono采用的方法类似于Datice模型，该模型最近用于为四个南极冰芯和一个格陵兰冰芯制作AICC 2012（南极冰芯年表）。IceChrono 1从数学、数值和编程的角度对Datice进行了改进和简化。IceChrono 1的能力在类似于AICC 2012测年实验的案例研究中得到了证明。在几个世纪内，我们发现结果与Datice的结果相似，这证实了IceChrono 1和Datice代码。我们还测试了新的功能，相对于原始版本的Datice：观测冰间隔与已知的持续时间，相关的观测，观测空气间隔与已知的持续时间和观测混合冰-空气地层链接。IceChrono 1在通用公共许可证v3开源许可证下免费提供。
Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg–Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice–air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.