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

我们建议研究阿拉斯加南部阿罗里克湖晚第四纪环境变化的历史，以获得百年尺度的古气候记录。我们已经有两个连续的6到8米长的湖心，其中一个延伸到至少22,000年前(22 14C Ka)。现在，我们建议带着地球物理设备返回湖中，以获得更详细的水深图和地下地层剖面，将这些岩心和新岩心置于盆地范围的地层学背景下，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记录(60ka)的额外取心地点。我们还将测量位于阿罗利克湖西北26公里处的第二个湖(尼姆贡湖)的海底地层，以确定延伸到最后一个全冰期的岩芯的目标。将对所有岩心进行基本物理参数处理，最有希望的岩心将被选择用于补充物理(颗粒大小、体积密度、磁化率)、生化(有机碳、生物硅)和生态(花粉、硅藻)替代气候指标的集中研究，以及地质年代学(AMS14C和岩石年代学)。其目标是为替代气候指标获得百年尺度的分辨率。这些分析将由在从湖泊(考夫曼，沃纳)获得沉积物岩心和声波地层数据方面有经验的工作人员以及来自阿拉斯加西南部的花粉(HU)、硅藻(SmoL)和特弗拉(Riehle)分析专家共同努力。这些结果将有助于贝林贾PALE研究人员之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。阿罗利克湖处于记录古环境变化的良好位置。在其他因素中，湖泊的沉积学应该反映出区域冰川活动的变化。它距离来自威斯康星州晚期冲刷平原的风尘沉淀源的距离是最佳的：距离足够近，足以传递信号，但又不至于淹没湖泊沉积物。在威斯康星州晚期，尼姆贡湖是由一个小的环形冰川向远端输送的。这两个湖泊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，以前对邻近低地的研究提供了第四纪古环境变化的独立框架，我们正在开发盆地内和盆地间精确的盆地内和盆地间地层对比的冰盖地层学。这两个湖泊被威斯康星州早期(约110-60ka)的冰雹筑坝。由于湖泊沉积物在数万年内持续积累，而且通常是可测年的，它们为大陆过去的气候变化提供了最好的自然档案之一。阿拉斯加西南部尚未获得整个冰川时期气候变化的连续记录，但这对于评估北大西洋地区海洋和冰芯已知的快速气候振荡是否也影响到北美西北部大陆地区很重要。评估这些地区之间的快速气候变化是否同步发生，或者空间和时间模式是否是随机的，甚至是反相的，这是理解控制气候振荡的机制的基础。在阿拉斯加西南部发展这种对全冰期的理解是很重要的，因为去冰期记录(15-10ka)可能受到广泛大陆架淹没引起的区域气候效应的影响。全冰期气候记录也将用于全球环流模型模拟的大气环流基本特征的数据模型比较：冰川反气旋。在18ka，模拟的反气旋产生强烈的南风气流，使阿拉斯加变暖，特别是在冬天。贝林贾东部冰川变暖的候选者是阿拉斯加北部和加拿大西部古植被记录中所说的“悬湖热事件”，其年代约为22-20ka。在阿罗里克湖的岩心中，这一间隔表现为植物大型化石丰度的增加。我们将通过评估化石(花粉、植物大型化石和硅藻)证据表明冬季气温升高和降雪量增加(从而减少湖冰)以及冰川波动的物理证据来评估全球气候模式模拟的冰川反气旋导致气候变暖的假设。

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.