Flexible paleoclimate age-depth models using an autoregressive gamma process
Flexible paleoclimate age-depth models using an autoregressive gamma process
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DOI：
10.1214/11-ba618
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发表时间：
2011-09
影响因子：
4.4
通讯作者：
M. Blaauw;J. Christen
中科院分区：
文献类型：
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作者：
M. Blaauw;J. Christen
放射性碳测年法通常用于古生态学，以建立湖泊和泥炭沉积物的年代学，旨在推断一个将沉积物深度与其年龄联系起来的模型。本文提出了一种新的年代学建立方法（称为“培根法”）。我们的方法是基于控制核心积累率使用伽马Au-回归半参数模型与任意数量的细分沿着沉积物。使用关于积累率的先验知识是至关重要的，并且通常使用信息先验。由于目前许多沉积物岩心分析，使用不同的数据集和先验分布，一个强大的（自适应）MCMC是非常有用的。我们使用t步（Christen和Fox，2010年），一种自调整，鲁棒的MCMC采样算法，在许多情况下都能很好地工作。也解决了使用最近的方法，认为放射性碳数据的学生t模型。这里介绍了两个例子，泥炭核心和核心从一个湖，我们的结果与其他方法进行了比较。过去的气候和环境可以从海洋或湖泊沉积物，冰盖和泥炭沼泽等沉积物中重建。在垂直沉积剖面（岩芯）中，在一定深度范围内对微体化石、宏体化石、同位素和其他变量的测量可作为这些深度的沉积物沉积时气候和环境条件的替代估计或“替代”。在这些深度和它们的年龄之间建立可靠的关系是至关重要的。水深-深度关系用于研究气候/环境代用指标沿着沉积物深度的演变，从而研究随时间的演变（例如，Lowe和步行者1997）。以各种方式构造深度模型。对于含有有机质的沉积物深度，年龄小于c。5万年前，放射性碳测年法通常用于建立年龄深度模型。岩芯被分成薄片，其中一些是放射性碳年代测定。对放射性碳数据进行曲线拟合和插值，以获得每个岩心深度的年龄估计。要考虑的第一个限制是，年龄应随深度单调增加，因为沉积物不可能在时间上向后积累（导致混合或反转沉积物的异常事件在大多数情况下在地层学中是明显的，因此此类岩心被排除在进一步分析之外）。此外，岩心可能有缺失的部分，导致年龄深度模型中的部分为∞。
Radiocarbon dating is routinely used in paleoecology to build chronolo- gies of lake and peat sediments, aiming at inferring a model that would relate the sediment depth with its age. We present a new approach for chronology building (called \Bacon") that has received enthusiastic attention by paleoecologists. Our methodology is based on controlling core accumulation rates using a gamma au- toregressive semiparametric model with an arbitrary number of subdivisions along the sediment. Using prior knowledge about accumulation rates is crucial and in- formative priors are routinely used. Since many sediment cores are currently ana- lyzed, using difierent data sets and prior distributions, a robust (adaptive) MCMC is very useful. We use the t-walk (Christen and Fox, 2010), a self adjusting, robust MCMC sampling algorithm, that works acceptably well in many situations. Out- liers are also addressed using a recent approach that considers a Student-t model for radiocarbon data. Two examples are presented here, that of a peat core and a core from a lake, and our results are compared with other approaches. Past climates and environments can be reconstructed from deposits such as ocean or lake sediments, ice sheets and peat bogs. Within a vertical sediment proflle (core), mea- surements of microfossils, macrofossils, isotopes and other variables at a range of depths serve as proxy estimates or \proxies" of climate and environmental conditions when the sediment of those depths was deposited. It is crucial to establish reliable relationships between these depths and their ages. Age-depth relationships are used to study the evolution of climate/environmental proxies along sediment depth and therefore through time (e.g., Lowe and Walker 1997). Age-depth models are constructed in various ways. For sediment depths containing organic matter, and for ages younger than c. 50,000 years, radiocarbon dating is often used to create an age-depth model. Cores are divided into slices and some of these are radiocarbon dated. A curve is fltted to the radiocarbon data and interpolated to obtain an age estimate for every depth of the core. The flrst restriction to be considered is that age should be increasing monotonically with depth, because sediment can never have accumulated backwards in time (extraordinary events leading to mixed or reversed sediments are, most of the time, noticeable in the stratigraphy and therefore such cores are ruled out from further analyses). Moreover, cores may have missing sections, leading to ∞at parts in the age depth models.