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

ESH：合作研究：阿拉斯加西南部末次冰期期间的气候变化

• 批准号: 9808593
• 负责人: Darrell Kaufman
• 金额: $ 10.07万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-10-01 至 2001-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9808593&HistoricalAwards=false
• 关键词: ESH; COLLABORATIVE; RESEARCH; Climatic; Variations

9808593KaufmanWe 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.

9808593 Kaufman我们建议研究阿拉斯加南部Arolik湖保存的晚第四纪环境变化历史，以获得百年尺度分辨率的古气候记录。 我们已经有两个连续的6至8米长的核心从湖，其中一个延伸到至少22,000年（22 14 C ka）。 现在，我们建议返回到湖武装的地球物理设备，获得更详细的测深图和地下地层剖面，将这些和新的核心到一个盆地范围内的地层背景下，以确定功能指示湖平面波动，并定位在盆地内的额外取芯的地方可能会获得更长的记录（60万年）。 我们还将测量第二个湖（Nimgun湖）的底层地层，Arolik湖西北26公里，以确定延伸到最后一个完整冰期的岩心目标。 将对所有岩芯进行基本物理参数处理，并将选择最有希望的岩芯集中研究补充物理（粒度、体积密度、磁化率）、生物化学（有机碳、生物硅）和生态（花粉、硅藻）代用气候指标，并进行地质年代学（AMS 14 C和火山灰年代学）。 目标是获得代用气候指标的百年尺度分辨率。 这些分析将是具有从湖泊（考夫曼、维尔纳）获得沉积物岩心和声学地层数据经验的工作人员以及分析阿拉斯加西南部花粉（Hu）、硅藻（Smol）和火山灰（Riehle）的专家的共同努力。 这些结果将有助于PALE研究人员在Beringia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湖处于记录古环境变化的有利位置。 除其他因素外，湖泊的沉积学应反映区域冰川活动的变化。 它与来自威斯康星州晚期冰水平原的风成沉积物源的距离最佳：近到足以传递信号，但又不至于太近以至于淹没湖泊沉积物。 在威斯康星州晚期，尼姆贡湖的远端由一个小冰斗冰川补给。 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，在邻近低地的先前研究提供了第四纪古环境变化的独立框架，并且我们正在开发一种火山灰地层学，用于精确的盆地内和盆地间地层对比。 这些湖泊由威斯康星州早期（~110 - 60 ka）的冰碛物形成，由于湖泊沉积物在数万年内不断积累，而且通常可以确定年代，它们提供了大陆上过去气候变化的最好的自然档案之一。 阿拉斯加西南部尚未获得贯穿整个冰期的气候变化的连续记录，但对于评估北大西洋地区海洋和冰芯中已知的快速气候振荡是否也影响了北美西北部的大陆地区非常重要。 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，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对整个冰期的这种理解是很重要的，因为冰消记录（15-10 ka）可能受到大面积大陆架淹没所产生的区域气候效应的影响。整个冰期气候的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18 ka，模拟的反气旋产生强烈的偏南气流，温暖阿拉斯加，特别是在冬季。 东白令加冰川变暖的一个候选者是阿拉斯加北方和加拿大西部古植被记录中的所谓“悬湖热事件”，时间约为22-20 ka。 这段时间在Arolik湖的岩芯中表现为植物宏体化石丰度的增加。 我们将通过评估冬季气温升高和降雪量增加（因此湖冰减少）的化石（花粉、植物宏化石和硅藻）证据以及冰川波动的物理证据，评估这种变暖归因于全球气候模型模拟的冰川反气旋的假设。