Collaborative Research: Nonlinearities in the Arctic climate system during the Holocene

合作研究：全新世北极气候系统的非线性

• 批准号: 0909354
• 负责人: Raymond Bradley
• 金额: $ 20.91万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0909354&HistoricalAwards=false
• 关键词: Collaborative; Research; Nonlinearities; Arctic; climate

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Abstract Rapid changes in the arctic climate system that occurred in the relatively recent past can be compared with the output of climate models to improve the understanding of the processes responsible for nonlinear system change. This study focuses on the transition between the Holocene thermal maximum (HTM) and the onset of Neoglaciation, and on the step-like changes that occurred subsequently during the late Holocene. The millennial-scale cooling trend that followed the HTM coincides with the decrease in Northern Hemisphere summer insolation driven by slow changes in Earth?s orbit. Despite the nearly linear forcing, the transition from the HTM to the Little Ice Age (1500-1900 AD) was neither gradual nor uniform. To understand how feedbacks and perturbations result in rapid changes, a geographically distributed network of proxy climate records will be used to study the spatial and temporal patterns of change, and to quantify the magnitude of change during these transitions. The researchers of this collaborative project will use lacustrine sediments to produce 13 new high-resolution proxy climate records of the past 8000 years. The study sites form two focus regions (eastern Beringia and the NW Atlantic) that generally coincide with the nodes of the surface temperature expression of the Arctic Oscillation (AO). This effort will nearly double the number of high-resolution lacustrine records that extend through the last two millennia, and will generate some of the first high resolution records that capture the HTM. During the HTM, summer sea-ice cover over the Arctic Ocean was likely the smallest of the present interglacial period; certainly it was less extensive than at any time in the past 100 years, and therefore affords an opportunity to investigate a period of warmth similar to what is projected during the coming century. This study focuses on lakes because lakes are the most widely distributed sources of proxy climate records that consistently extend through the post-glacial interval. Because climate change is amplified in the Arctic, the climate signal preserved in arctic lake sediments should be stronger than elsewhere. The proxy records generated in this project will use conventional and newly emerging techniques to document the spatio-temporal patterns of abrupt environmental changes, and to derive quantitative estimates of past summer temperature and hydroclimate variables. Most lakes have been cored previously and show potential for generating high-quality proxy records. Five of the lakes contain laminated sediment with annually resolved records; others have high sedimentation rates (0.5 mm yr-1) for sub-decadal resolution across the climate transitions. Confidence in the paleoclimate reconstructions will be bolstered by a multi-proxy approach, and by replicate lake records in each of the focus regions that will be used to distinguish basin-scale thresholds from regional-scale climate shifts. This project builds on on-going climate-modeling experiments that use NCAR?s Climate System Model (CCSM3) to study the sensitivities of the arctic system to volcanism and solar variability. A new data-model comparison proposed for this study will test whether the most prominent changes in the arctic system during the past 8 ka, as reconstructed from the proxy records, can be explained by a plausible combination of system-component conditions coincident with prolonged volcanism. The experiments, conducted with NCAR collaborators, will focus on the elements of the Arctic system (e.g., AO and extent of sea ice) that participate in abrupt transitions, and that might elicit nonlinear changes in the future.

该奖项根据 2009 年《美国复苏和再投资法案》（公法 111-5）提供资金。摘要 最近发生的北极气候系统的快速变化可以与气候模型的输出进行比较，以提高对非线性系统变化过程的理解。这项研究的重点是全新世最热期（HTM）和新冰川作用开始之间的过渡，以及随后在全新世晚期发生的阶梯式变化。 HTM之后的千禧年规模的降温趋势与地球轨道缓慢变化导致的北半球夏季日照减少同时发生。尽管强迫几乎是线性的，但从 HTM 到小冰河时代（公元 1500-1900 年）的过渡既不是渐进的，也不是均匀的。为了了解反馈和扰动如何导致快速变化，将使用代理气候记录的地理分布网络来研究变化的空间和时间模式，并量化这些转变期间变化的幅度。该合作项目的研究人员将利用湖泊沉积物生成过去 8000 年的 13 个新的高分辨率代理气候记录。研究地点形成两个重点区域（白令陆桥东部和大西洋西北部），通常与北极涛动（AO）表面温度表达的节点重合。这项工作将使过去两千年的高分辨率湖泊记录数量增加近一倍，并将生成一些捕捉 HTM 的第一批高分辨率记录。在HTM期间，北冰洋上空的夏季海冰覆盖范围可能是目前间冰期中最小的。当然，它的范围比过去 100 年来的任何时候都要小，因此提供了一个机会来研究类似于下个世纪预计的温暖时期。这项研究的重点是湖泊，因为湖泊是代理气候记录分布最广泛的来源，一直延伸到后冰期间隔。由于气候变化在北极被放大，因此北极湖泊沉积物中保存的气候信号应该比其他地方更强。该项目生成的代理记录将使用传统和新兴技术来记录环境突变的时空模式，并得出过去夏季温度和水文气候变量的定量估计。大多数湖泊之前都已取芯，并显示出生成高质量代理记录的潜力。其中五个湖泊含有层状沉积物，每年都有记录；其他沉积物则具有较高的沉积率（0.5 mm yr-1），可在整个气候转变过程中实现亚十年分辨率。多代理方法和每个重点区域的湖泊记录复制将增强对古气候重建的信心，这些记录将用于区分盆地规模的阈值和区域规模的气候变化。该项目建立在正在进行的气候建模实验的基础上，这些实验使用 NCAR 的气候系统模型 (CCSM3) 来研究北极系统对火山活动和太阳变化的敏感性。本研究提出的新数据模型比较将测试根据代理记录重建的过去 8 ka 期间北极系统最显着的变化是否可以通过与长期火山活动相一致的系统组成条件的合理组合来解释。这些实验是与 NCAR 合作者一起进行的，重点关注北极系统中参与突然转变并可能在未来引发非线性变化的要素（例如，AO 和海冰范围）。