Integrating plant wax abundance and isotopes for paleo-vegetation and paleoclimate reconstructions: a multi-source mixing model using a Bayesian framework
Integrating plant wax abundance and isotopes for paleo-vegetation and paleoclimate reconstructions: a multi-source mixing model using a Bayesian framework
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DOI：
10.5194/cp-18-2181-2022
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发表时间：
2022-09
影响因子：
4.3
通讯作者：
Deming Yang;G. Bowen
中科院分区：
文献类型：
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作者：
Deming Yang;G. Bowen
抽象的。植物蜡、正构烷烃链长分布和同位素已成为现代生态系统重建过去植被和气候的代用指标。然而，大多数古代用指标关注浓度或同位素，而两者都携带关于混合源的补充信息。我们提出了一个多源混合模型的贝叶斯框架，同时评估链长分布和同位素。该模型由包括用户定义的源组及其相关的正构烷烃浓度和δ 13 C的参数分布的先验组成。混合过程涉及新定义的混合分数，如分数叶质量贡献（FLMC），可用于植被重建。马尔可夫链蒙特卡罗是用来产生样本的后验分布的这些参数的条件下，这两种数据类型。我们提出了三个案例研究，从不同的设置。第一种是青海湖表层沉积物中的n-C27、n-C29和n-C31烷烃。该模型提供了更具体的解释，从水生来源的正构烷烃输入比传统的Paq代理。第二个涉及n-C29，n-C31，和n-C33烷烃在喀麦隆，西非的湖泊表层沉积物。该模型产生混合分数的森林C3，稀树草原C3，C4植物，提供更多的信息相比，传统的两端成员混合制度的优势生物群系。第三个耦合的植被源模型的氢同位素模型组件，使用生物群落特定的表观分馏因子（εa），以估计平均年降水量的δ 2 H。通过利用四种正构烷烃链的链长分布、δ 13 C和δ 2 H数据，该模型产生了具有相对较小的不确定性限度的降水δ 2 H估计值。新的框架显示了对古数据解释的承诺，但可以通过包括与植物中正构烷烃周转、运输和整合到沉积档案中相关的过程来进一步改进。未来对现代植物和集水系统的研究对于开发校准数据集至关重要，这些数据集可以提高框架的强度和实用性。
Abstract. Plant wax n-alkane chain length distribution and isotopes have been studied in modern ecosystems as proxies to reconstruct vegetation and climate of the past. However, most paleo-proxies focus on either concentrations or isotopes, whereas both carry complementary information on the mixing sources. We propose a multi-source mixing model in a Bayesian framework that evaluates both chain length distributions and isotopes simultaneously. The model consists of priors that include user-defined source groups and their associated parametric distributions of n-alkane concentration and δ13C. The mixing process involves newly defined mixing fractions such as fractional leaf mass contribution (FLMC) that can be used in vegetation reconstruction. Markov Chain Monte Carlo is used to generate samples from the posterior distribution of these parameters conditioned on both data types. We present three case studies from distinct settings. The first involves n-C27, n-C29, and n-C31 alkanes in lake surface sediments of Lake Qinghai, China. The model provides more specific interpretations on the n-alkane input from aquatic sources than the conventional Paq proxy. The second involves n-C29, n-C31, and n-C33 alkanes in lake surface sediments in Cameroon, western Africa. The model produces mixing fractions of forest C3, savanna C3, and C4 plants, offering additional information on the dominant biomes compared to the traditional two-end-member mixing regime. The third couples the vegetation source model to a hydrogen isotope model component, using biome-specific apparent fractionation factors (εa) to estimate the δ2H of mean annual precipitation. By leveraging chain length distribution, δ13C, and δ2H data of four n-alkane chains, the model produces estimated precipitation δ2H with relatively small uncertainty limits. The new framework shows promise for interpretation of paleo-data but could be further improved by including processes associated with n-alkane turnover in plants, transport, and integration into sedimentary archives. Future studies on modern plants and catchment systems will be critical to develop calibration datasets that advance the strength and utility of the framework.