Pedothem carbonates reveal anomalous North American atmospheric circulation 70,000–55,000 years ago
Pedothem carbonates reveal anomalous North American atmospheric circulation 70,000–55,000 years ago
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Pedothem碳酸盐揭示了70,000-55,000年前北美大气环流的异常
DOI：
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发表时间：
2016
影响因子：
11.1
通讯作者：
R. Amundson
中科院分区：
文献类型：
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作者：
Erik J. Oerter;W. Sharp;J. Oster;A. Ebeling;J. Valley;R. Kozdon;I. Orland;J. Hellstrom;J. Woodhead;J. Hergt;O. Chadwick;R. Amundson
意义我们第一次表明，据我们所知，成壤（土壤）碳酸盐矿物积累可以保存连续的古气候记录，竞争对手的时间分辨率广泛使用的档案，如洞穴或湖泊沉积物。通过对氧、碳和铀同位素的微量分析以及铀系定年，我们发现了北美内陆大气环流在7万至5.5万年前发生明显变化的证据，这一发现突出了大型大陆冰盖对大气环流的影响。也许最重要的是，这项工作表明，在世界各地的干旱和半干旱地区常见的土壤层是大陆景观古气候信息的丰富档案。在过去的两个冰期周期中，我们对北美气候条件的理解，以及由此产生的强迫因素，在一定程度上受到缺乏长期的、日期明确的、连续的古气候记录的限制。在这里，我们提出了第一个，据我们所知，连续的，千年分辨率的古气候代理记录来自毫米厚的成壤碳酸盐岩碎屑涂层（pedothems），这是广泛分布在半干旱到干旱地区的世界各地。我们的新的多同位素pedothem记录从风河流域在怀俄明州证实了以前假设的时期，从70，000年到55，000年前，墨西哥湾的水分向北输送到大陆内部，根据离子探针和铀同位素测定的氧和碳同位素和激光烧蚀电感耦合等离子体质谱法测定的U-Th年代。这种明显的纬向水汽输送，与70，000~55，000年前太平洋水汽通过西风向北美内陆的纬向输送形成鲜明对比，可能是海洋同位素第4阶段期间北美冰盖上方形成的持续反气旋造成的。我们的结论是，土壤层，使用微分析技术进行分析时，可以提供高分辨率的古气候记录，可能会打开新的途径，了解过去的陆地气候的地区，古气候记录，否则无法获得。当土壤层古气候记录与现有记录相结合时，它们将增加对古气候条件的基于土壤的观点。
Significance We show for the first time, to our knowledge, that pedogenic (soil) carbonate mineral accumulations can preserve continuous paleoclimate records that rival the temporal resolution of widely used archives, such as speleothems or lake sediments. Using microanalysis of oxygen, carbon, and uranium isotopes coupled with uranium series dating, we find evidence for a distinct shift in atmospheric circulation in North America’s interior from 70,000 to 55,000 years ago, a finding that highlights the influence of large continental ice sheets on atmospheric circulation. Perhaps most significantly, this work shows that pedothems, which are common in arid and semiarid regions around the world, are a rich archive of paleoclimate information for continental landscapes. Our understanding of climatic conditions, and therefore forcing factors, in North America during the past two glacial cycles is limited in part by the scarcity of long, well-dated, continuous paleoclimate records. Here, we present the first, to our knowledge, continuous, millennial-resolution paleoclimate proxy record derived from millimeter-thick pedogenic carbonate clast coatings (pedothems), which are widely distributed in semiarid to arid regions worldwide. Our new multiisotope pedothem record from the Wind River Basin in Wyoming confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and U-Th dating by laser ablation inductively coupled plasma mass spectrometry. This pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the North American interior by westerly winds before and after 70,000–55,000 years ago, may have resulted from a persistent anticyclone developed above the North American ice sheet during Marine Isotope Stage 4. We conclude that pedothems, when analyzed using microanalytical techniques, can provide high-resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available. When pedothem paleoclimate records are combined with existing records they will add complimentary soil-based perspectives on paleoclimate conditions.