High Resolution Time-Series of California Climate Over the Last 12,000 Years: Testing the North Atlantic and North Pacific Linkage

加利福尼亚的仪器气候数据和历史记录记录了许多严重的年度和多年干旱事件。这样的记录只能追溯到200年前或更短的时间。史前气候的古环境重建表明，史前时期发生了更为严重和更长时间的多年代际干旱。不幸的是，这些古记录往往是零碎的，不足以提供过去12000年干旱强度、持续时间和频率的清晰连续记录。采用校准集方法，该研究将统计评估当前气温和降水、湖泊水温、盐度和深度的差异如何反映在湖泊水的当代元素化学和碳氧同位素组成中，以及湖泊沉积物中发现的chironomids（蠓幼虫）、cladocera（甲壳类动物）、硅藻（单细胞藻类）、花粉和气孔中。来自内华达山脉至少50个小湖泊的地表沉积物和水样将被收集和分析。这些湖泊将被选择提供不同海拔的站点网络，显示空气和水的温度、深度、盐度和蒸发平衡的差异。如果发现气候和湖泊条件与地球化学和生物指标之间存在统计上显著的关系，则将这种关系以数学传递函数的形式量化。然后，新开发的传递函数将可用于地球化学记录和包含在过去12,000年湖泊岩心沉积物中的化石生物组合。这些湖芯的气候、湖泊温度、深度和盐度的变化可以为这一敏感地区的重大干旱提供长期和连续的记录。加州人口众多，农业基础庞大，气候普遍半干旱，季节性降水强烈，对干旱的影响极为敏感。尽管20世纪的年度干旱和多年干旱造成了严重的经济问题，但在过去2000年的一些化石记录中，更严重的几十年干旱将对该州的自然生态系统、农业和社会产生灾难性影响。目前还没有关于过去气候的适当连续记录来评估这种干旱在长时间尺度上的绝对规模、确切持续时间和潜在频率。如果没有这些资料，就很难确定这种大规模干旱事件的原因，并评估未来发生这种事件的可能性。这项拟议的研究将评估内华达山脉小湖泊的地球化学、微观植物群和微观动物群是否对温度、盐度和湖泊深度的差异敏感，以及湖泊沉积物中这些生物的地球化学含量和残留物是否可以用来重建加州长期的气候和干旱历史。拟议的研究结果将对气候学家、水文学家、古生物学家、生物学家、生物地理学家和水资源管理者具有重要意义。

Numerous episodes of severe annual and multi-annual drought have been recorded in instrumental climate data and historical records from California. Such records extend back only 200 years or less. Paleoenvironmental reconstructions of prehistoric climate indicate that even more severe and longer multi-decadal droughts have occurred in the prehistoric period. Unfortunately, these paleo records are often fragmentary and are not sufficient to provide a clear and continuous record of drought intensity, duration and frequency over the past 12,000 years. Using a calibration-set approach, the proposed research will statistically assess how current differences in air temperature and precipitation, lake water temperature, salinity, and depth are reflected in the contemporary elemental chemistry and carbon and oxygen isotopic composition of lake waters, and the chironomids (midge fly larva), cladocera (crustacean), diatoms (unicellular algae), pollen and stomates found in lake sediments. Surficial sediment and water samples from at least 50 small lakes in the Sierra Nevada will be collected and analyzed. The lakes will be chosen to provide a network of sites at different elevations displaying differences in air and water temperatures, depth, salinity and evaporative balance. If statistically significant relationships are found between climate and lake conditions and the geochemical and biological proxies, the relations will be quantified in the form of mathematical transfer functions. The newly developed transfer functions will then be available for application to geochemical records and fossil biological assemblages contained within the sediments of lake cores that span the last 12,000 years. The changes in climate, lake temperature, depth and salinity from such lake cores can provide long and continuous records of major droughts in this sensitive region. Due to its large population, massive agricultural base and generally semi-arid climate with strongly seasonal precipitation, California is extremely sensitive to the impact of droughts. Although annual and multi-year droughts of the 20th Century have caused significant economic problems, the more severe multi-decadal droughts evident in some fossil records from the past 2000 years would have a catastrophic impact upon natural ecosystems, agriculture and society in the state. Appropriate continuous records of past climate do not yet exist to appraise the absolute magnitude, exact duration and potential frequency of such droughts over long time scales. Without such information it is difficult to determine the causes of such large scale episodes of aridity and assess the probability of such an event in the future. The proposed research will assess if the geochemistry, microscopic flora and microscopic fauna of small lakes in the Sierra Nevada are sensitive to differences in temperature, salinity and lake depth, and if the geochemical content and remains of such organisms from lake sediments can be used to reconstruct long histories of climate and drought in California. The results of the proposed research will be of importance to climatologists, hydrologists, paleontologists, biologists, biogeographers and water resource managers.