Patterns of Variability in Alaskan Salmon Populations and Their Ecosystems During the Last Five Centuries

了解长时间尺度上生物变异的原因和表现仍然是生态系统生态学的一个关键和难以实现的目标。在东北太平洋，大气-海洋耦合的长期变化似乎在上个世纪将生物生产组织成一系列不同的年代际机制。例如，阿拉斯加海流鲑鱼捕获量的三倍变化与年代际气候变化一致。尽管鱼类种群动态具有巨大的时间变异性，但我们对控制这一巨大而重要的生态系统中生物生产力的长期气候驱动因素的理解却很薄弱。一个关键假设提出，东北太平洋生物变化的主要驱动因素涉及泛太平洋、双年代际和五十年代际气候振荡的相互作用。在20世纪之前，东北太平洋阿拉斯加海流区域的生物生产力的历史记录尚未建立；它们的缺失是理解该生态系统中生物生产力的时间组织的主要障碍。在这里，研究人员建议量化阿拉斯加海流中红鲑鱼种群在过去500年中年代际变化的基本模式和幅度，以提高我们对东北太平洋时间组织的关键来源的理解。这些科学家将利用古生态学来描述东北太平洋阿拉斯加洋流区域生物变异的长期模式。具体来说，他们将通过追踪一种天然地球化学示踪剂（15N）的变化来推断红鲑（Oncorhynchus nerka）种群的历史变化，这种示踪剂在产卵湖的沉积物中积累，与鲑鱼密度成比例。沉积序列的高分辨率定年将通过沉积物的详细放射性同位素分析和确定已知年龄的火山灰层来完成。现有的35至100年的鲑鱼种群动态、气候条件和湖泊产量的历史记录将使他们能够校准地球化学和生物标记的沉积年代学。他们还将使用碳稳定同位素和沉积物中的藻类色素化石来量化鲑鱼来源的营养物质对湖泊生产力的影响。他们将使用光谱分析和时域时间序列模型来量化鱼类产量历史变化的频率、持续时间和幅度，以及这些变化与古气候条件的独立代用物之间的关系。然后，他们将应用从沉积和其他现有的古气候记录中发展出来的时间序列模型来预测下个世纪东北太平洋生物生产力的未来变化。这种对新数据和现有数据的综合将为东北太平洋阿拉斯加洋流区域生物生产力的长期变化提供高分辨率、具体的描述。他们将测试这样一个假设，即该海洋区域内的生物生产力与与双年代际和五年期气候振荡相关的年代际气候制度同步。这些数据将为研究整个东北太平洋生物生产力与气候波动的时空耦合提供所需的信息。特别是，我们的工作将提供所需的数据，以检验东北太平洋阿拉斯加和加利福尼亚洋流域的生物生产力对年代际气候强迫的同步响应（但非相位）的假设。综合海洋条件、气候条件和生物生产力的历史和古指标，将把最近一个世纪的生态系统动态置于一个比目前所能得到的时间长得多的时间范围内。这些知识将为使管理适应与东北太平洋沿海海洋、淡水和河岸生态系统有关的时间尺度提供科学基础。

Understanding the causes and manifestations of biological variability over long time scales remains a critical and elusive goal for ecosystem ecology. In the Northeast Pacific, long-term variation in atmosphere-ocean coupling appears to have organized biological production into a series of distinct interdecadal regimes during the last century. For instance, up to three-fold changes in salmon fishery catches in the Alaska Current were coindicent with shifts between interdecadal climate regimes. Despite this enormous temporal variability in fish population dynamics, we have only a weak understanding of the long-term climatic drivers that control biological productivity in this vast and important ecosystem. A key hypothesis proposes that the main drivers of biological change in the Northeast Pacific involve the interactive effects of pan-Pacific, bi-decadal and penta-decadal climate oscillations. Historical records of biological productivity prior to the 20th century have not been established for the Alaskan Current domain of the Northeast Pacific; their absence represents a major impediment towards understanding the temporal organization of biological productivity in this ecosystem. Here, the investigators propose to quantify the fundamental modes and magnitude of interdecadal variability in sockeye salmon populations of the Alaska Current during the last 500 years, to improve our understanding of the critical sources of temporal organization in the Northeast Pacific. These scientists will use paleoecology to characterize the long-term patterns of biological variability in the Alaskan Current domain of the Northeast Pacific. Specifically, they will infer historical changes in populations of sockeye salmon (Oncorhynchus nerka) by tracking variation of a natural geochemical tracer (15N) that accumulates in the sediments of spawning lakes in proportion to salmon density. High resolution dating of sedimentary sequences will be accomplished through detailed radio-isotope analyses of sediments and by identifying volcanic ash layers with known ages. Existing 35-to-100 year long historical records of salmon population dynamics, climatic conditions, and lake production will enable them to calibrate sedimentary chronologies of geochemical and biological markers. They will also use carbon stable isotopes and fossil algal pigments from sediments to quantify the impact of salmon-derived nutrients on lake productivity. They will use spectral analysis and temporal domain time-series models to quantify the frequency, duration, and magnitude of historical shifts in fish production, and how these relate to independent proxies of paleoclimatic conditions. They will then apply the time-series models developed from sedimentary and other existing paleoclimate records to forecast future changes in the biological productivity of the Northeast Pacific for the next century. This synthesis of new and existing data will provide a high-resolution, concrete description of the long-term variability in the biological productivity of the Alaska Current domain of the Northeast Pacific. They will test the hypothesis that the biological productivity within this oceanic domain has been synchronized by inter-decadal climate regimes associated with bidecadal and pentadecadal climate oscillations. These data will provide the information needed to investigate the spatial and temporal coupling of biological productivity to climate oscillations throughout the Northeast Pacific. In particular, our work will provide the data needed to test the hypothesis that biological productivity in the Alaska and California current domains of the Northeast Pacific respond synchronously, but out of phase, to interdecadal climatic forcing. The synthesis of historical- and paleo-indicators of oceanic conditions, climatic conditions, and biological productivity will place the recent century of ecosystem dynamics in a substantially longer temporal context than is currently available. This knowledge will provide a scientific basis for adapting management to the time scales relevant to the coastal marine, freshwater and riparian ecosystems of the Northeast Pacific.