ESH: COLLABORATIVE RESEARCH: Climatic Variations During the Last Glaciation in Southwestern Alaska

9809330HuWe建议对阿拉斯加南部Arolik湖保存的晚第四纪环境变化史进行研究，以获得具有百年尺度分辨率的古气候记录。我们已经从湖中获得了两个连续的6到8米长的岩心，其中一个至少可以追溯到22000年前（214c ka）。现在，我们建议带着地球物理设备返回湖泊，以获得更详细的水深图和地下地层剖面，将这些和新的岩心放入整个盆地的地层背景中，确定指示湖泊水位波动的特征，并在盆地内确定可能获得更长的记录（60 ka）的地点进行额外的取心。我们还将在Arolik湖西北26公里处的第二个湖（Nimgun湖）测量海底地层，以确定延伸到最后一个全冰期的岩心目标。所有岩心都将进行基本物理参数的处理，并选择最有希望的岩心进行集中的互补物理（粒度、体积密度、磁化率）、生化（有机碳、生物成因二氧化硅）和生态（花粉、硅藻）代用气候指标的研究，以及地质年代学（AMS 14C和温度年代学）的研究。目标是获得代用气候指标的百年尺度分辨率。这些分析将由具有从湖泊中获取沉积物岩心和声学地层数据经验的工作人员（Kaufman, Werner）和来自阿拉斯加西南部的花粉（Hu）、硅藻（Smol）和芦苇（Riehle）分析专家共同努力。这些结果将有助于白令陆桥的PALE研究人员先前和正在进行的工作，他们的目标是提供高分辨率的古气候记录，以与气候模型模拟以及冰川冰和海洋沉积物的记录进行比较。Arolik湖具有记录古环境变化的良好位置。除其他因素外，湖泊的沉积学应反映区域冰川活动的变化。它的位置与来自威斯康辛州晚期冲刷平原的风成沉积物源的距离最佳：近到足以传递信号，但又不至于近到淹没湖泊沉积物。在威斯康辛州晚期，宁根湖是由一个小的环状冰川形成的。这两个湖都在我们对晚更新世冰川波动的范围和时间进行了广泛研究的区域内，之前在邻近低地的研究为第四纪古环境变化提供了一个独立的框架，我们正在开发一种用于精确的盆地内和盆地间地层对比的地层地层学。湖泊被早期威斯康星时代（~110 -60 ka）的冰碛筑坝。由于湖泊沉积物在数万年的时间里不断积累，而且往往可以确定年代，因此它们提供了大陆过去气候变化的最佳自然档案之一。从阿拉斯加西南部回溯到整个冰期的气候变化的连续记录尚未获得，但对于评估在北大西洋地区的海洋和冰芯中已知的快速气候振荡是否也影响到北美西北部的大陆地区很重要。评估快速气候变化是否在这些区域之间同步发生，或者时空模式是否随机，甚至是反相位，对于理解控制气候振荡的机制至关重要。在阿拉斯加西南部发展这种对全冰期的认识是很重要的，因为去冰期记录（15-10 ka）可能受到广泛大陆架淹没引起的区域气候效应的影响。全冰期气候的记录也将用于全球环流模式模拟的大气环流的一个基本特征的数据模式比较：冰川反气旋。在18ka，模拟的反气旋产生了强烈的南风，使阿拉斯加变暖，特别是在冬季。在阿拉斯加北部和加拿大西部的古植被记录中，所谓的“悬湖热事件”可追溯到~22-20 ka，这是白令陆桥东部全冰期变暖的一个候选事件。在Arolik湖的岩心中，植物大化石丰度的增加代表了这一区间。我们将通过评估化石（花粉、植物大化石和硅藻）证据和冰川波动的物理证据来评估这种变暖归因于全球气候模式模拟的冰川反气旋的假设，这些证据表明冬季气温升高和降雪增加（因此湖冰减少），以及冰川波动。

9809330HuWe propose to study the history of late Quaternary environmental change preserved in Arolik Lake, southern Alaska, to obtain a paleoclimate record with centennial-scale resolution. We already have two continuous 6-to-8m-long cores from the lake, including one that extends back at least 22,000 yr (22 14C ka). Now we propose to return to the lake armed with geophysical equipment for obtaining more detailed bathymetric charts and subsurface stratigraphic profiles to place these and new cores into a basin-wide stratigraphic context, to identify features indicative of lake-level fluctuations, and to locate sites within the basin for additional coring where a longer record (60 ka) might be obtainable. We will also measure the sub-bottom stratigraphy at a second lake (Nimgun Lake), 26 km northwest of Arolik Lake, to locate targets for cores extending into the last full-glacial period. All cores will be processed for basic physical parameters and the most promising core will be selected for concentrated study of complementary physical (grain size, bulk density, magnetic susceptibility), biochemical (organic carbon, biogenic silica), and ecological (pollen, diatoms) proxy climate indicators, and for geochronology (AMS 14C and tephrochronology). The goal is to obtain centennial-scale resolution for the proxy-climate indicators. The analyses will be a collaborative effort by workers with experience in obtaining sediment cores and acoustic-stratigraphic data from lakes (Kaufman, Werner), and by experts in the analysis of pollen (Hu), diatoms (Smol), and tephra (Riehle) from southwestern Alaska. The results will contribute to previous and on-going work by PALE researchers in Beringia whose goal is to provide highly resolved records of paleoclimate to compare with climate model simulations and with records from glacier ice and marine sediment.Arolik Lake is in a good position to record paleoenvironmental changes. Among other factors, the sedimentology of the lake should reflect changes in the regional glacial activity. It is situated at the optimal distance from a source of eolian sediment derived from a late Wisconsin outwash plain: close enough to deliver a signal, but not so close as to overwhelm the lake deposits. Nimgun Lake was fed distally by a small cirque glacier during the late Wisconsin. Both lakes are within the area where we have conducted extensive research into the extent and timing of late Pleistocene glacier fluctuations, where previous studies in the adjacent lowlands provide an independent framework of Quaternary paleoenvironmental change, and where we are developing a tephrostratigraphy for precise intra-and inter-basinal stratigraphic correlation's. The lakes are dammed by moraines of early Wisconsin age (~110 -60 ka).Because lake sediments accumulate continuously over tens of thousands of years and are often dateable, they afford one of the best natural archives of past climate variability on the continents. A continuous record of climate change extending back through the full-glacial period has not yet been obtained from southwestern Alaska, but is important for assessing whether the rapid climate oscillations known in marine and ice cores from North Atlantic region also affected continental regions of northwestern North America. Assessing whether rapid climate changes occurred synchronously between these regions, or whether the spatial and temporal patterns are random, or even anti-phase, is fundamental to understanding the mechanisms that control climate oscillations. Developing this understanding for the full-glacial period is important in southwestern Alaska because deglacial records (15-10 ka) are potentially influenced by regional-climatic effects resulting from the submergence of extensive continental shelf.The record of full-glacial climate will also be used in a data-model comparison of a fundamental feature of atmospheric circulation simulated by global circulation models: The glacial anticyclone. At 18 ka, the simulated anticyclone generates strong southerly flow that warms Alaska, especially during the winter. A candidate for full-glacial warming in eastern Beringia is the so-called "Hanging Lake thermal event" dated in paleovegetation records in northern Alaska and western Canada at ~22-20 ka. This interval is represented in the core from Arolik Lake by increased plant macrofossil abundance. We will evaluate the hypothesis that this warming is attributable to the glacial anticyclone as simulated by global climate models by assessing the fossil (pollen, plant macrofossils, and diatoms) evidence for higher winter temperatures and increased snowfall (and therefore for reduced lake ice), and the physical evidence for glacier fluctuations.