Forward and inverse modeling of Black spruce tree ring series: applications to paleohydrology and paleoclimatology

NSERC DG的长期目标是在温带和北方地区等严重缺乏过去水文波动知识的地区进行基于树木年轮的水文气候重建。这些重建将提供一个更准确的基线，可以与最近的变化进行比较，并将为这些研究不足的地区的长期水文气候变化的起源提供新的线索。为了实现这一目标，我们将提出一种新的代理模型融合方法，专门设计用于克服树木年代学家在远离环境压力的地区生长时遇到的困难。 在过去的几十年里，树年代学对理解长期的水文气候变化做出了巨大贡献。然而，在温度和降水都控制增长率的地区，这导致了模棱两可的结果。气候重建的基本方法要求在空间分辨率和气候敏感性之间进行权衡，并倾向于将对温度敏感(仅限于纬度/高度树线)或对降水敏感(仅限于半干旱地区)的森林作为过去气候的代替品。然而，完善我们对过去不稳定因素的理解，将迫使年轮科学家从对我们了解全球变化贡献较小的地区提取强大的水文气候信号。事实上，这类区域的典型特征是复杂、多变量和时变(不同)的代理气候关系，这些关系是生产基于树轮的重建的主要障碍。 这种新的重建方法将在北美东北部的S北方针叶林中实施，这代表了一个典型的地区，在那里，树木-年轮-气候关系盛行。该办法将基于两个相辅相成的方面。首先，气候信号提取将依赖于多个指标(树木年轮宽度、碳和氧稳定同位素)，以加强对温度和降水信号的分析。其次，将使用基于过程的建模来评估指标和气候之间的关系，该模型建立在一个庞大的多指标测量网络上，该网络整合了与从树木年轮推断过去气候相关的所有时间尺度：年内、年际、十年、千年。这项研究计划将在NENA中产生关于长期水文气候变化和持续性的关键信息，这将有助于完善我们预测(和适应)未来变化的能力。该计划将依赖于国家和国际层面强大而活跃的合作网络，并将为受训人员提供一个极好的机会，让他们参与代表古气候学前沿的研究计划。

The long-term objective of this NSERC DG is to produce hydro-climatic, tree-ring-based reconstructions in regions, such as the temperate and the boreal zones, where knowledge on past hydro-fluctuations is critically lacking. These reconstructions will provide a more accurate baseline to which recent changes can be compared and will cast a new light on the origin of long-term hydro-climatic variability in these understudied regions. To achieve this, we will propose a novel proxy-model fusion approach, specifically designed to overcome the difficulties encountered by dendrochronologists in regions where trees grow far from environmentally stressful conditions. In the past few decades, dendrochronology has greatly contributed to the understanding of long-term hydro-climatic changes. However, it led to equivocal results in regions where both temperature and precipitation control growth rates. The basic approach to climate reconstruction dictates a trade off between spatial resolution and climate-sensitivity, and favours the inclusion of either temperature-sensitive (restricted to latitudinal / altitudinal tree lines) or precipitation-sensitive (restricted to semi-arid regions) forest stands as proxies for past climates. However, refining our understanding of past instabilities will force tree ring scientists to extract robust hydro-climatic signals from regions that have contributed less to our understanding of global changes. Indeed, such regions are typically characterized by complex, multivariate and time-varying (divergent) proxy-climate relationships that represent major obstacles to the production of tree-ring-based reconstructions. The novel reconstruction approach will be implemented in North-Eastern North-America (NENA)’s boreal forest which represents an archetypal example of a region where ambiguous tree-ring-to-climate relationships prevail. The approach will be based on two complementary aspects. First, climatic signal extraction will rely on multiple proxies (tree ring widths, carbon and oxygen stable isotopes) in order to strengthen the analysis of both temperature and precipitation signals. Second, relationships between proxies and climate will be assessed using process-based modeling anchored to a vast network of multi-proxy measurements that integrate all temporal scales relevant to infer past climates from tree rings: infra-annual, inter-annual, decadal, millennial. This research program will generate crucial information on long-term hydro-climate variability and persistence in NENA, which will help refine our capacity to predict (and adapt to) future changes. The program will rely on a strong and active network of collaborations at the national and international levels and will represent an excellent opportunity for trainees to be involved in a research initiative that represents the cutting edge of paleoclimatology.