Seasonality of Abrupt Climate Change over Greenland: Direct Tests for the Younger Dryas and 8.2 ka event using Paleolimnology

格陵兰岛气候突变的季节性：利用古湖沼学对新仙女木期和 8.2ka 事件进行直接测试

• 批准号: 2002515
• 负责人: Yarrow Axford
• 金额: $ 64.06万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2002515&HistoricalAwards=false
• 关键词: Seasonality; Abrupt; Climate; Change; over

The Younger Dryas (YD) is the best documented example of abrupt climate change in Earth’s history, yet fundamental traits of the YD remain enigmatic. Greenland sat at the epicenter of YD climate change, with intense cooling registered in ice cores, but nevertheless the Greenland Ice Sheet retreated during the YD. An influential hypothesis suggests that North Atlantic abrupt climate changes were characterized by extreme seasonality, with mild summers that explain counterintuitive YD glacier retreat. Resolving seasonality is crucial to understanding the impacts of past and future climate change on all aspects of the Arctic system – including the ice sheet, because summer temperatures drive surface melt. This study will directly assess seasonality of the YD on Greenland for the first time by developing quantitative summer and winter temperature reconstructions. This study will also assess seasonality of the major cold snap over Greenland 8,200 years ago. Intriguingly, despite being shorter and smaller in annual magnitude than the YD, that event drove glacier advances around Greenland.This research will clarify how abrupt climate change affects the Arctic/subarctic North Atlantic region, especially Greenland and its ice sheet. By resolving seasonality of air temperatures during the YD, when the ice sheet retreated despite evidence for extremely cold (annual) air temperatures, this study will also clarify the competing roles of precipitation and ocean temperatures in driving past ice sheet behavior – with implications for projections of future ice sheet mass loss. This study will test whether the Holocene 8.2 ka event was essentially a mini YD, or fundamentally different. The latter could make the YD a poor analog for future abrupt climate change, which would unfold in an interglacial world. The 8.2 ka event has been described as an ideal target for testing climate models, but the quantitative reconstructions of associated terrestrial climate changes needed to optimize such tests are rare.Another major contribution of this work is calibration and advancement of season-specific methods for reconstructing arctic climate. Such methods are needed to address questions about seasonality on diverse Quaternary timescales, providing essential tests for climate models. The proposed work will also enable more sophisticated interpretations of stable isotope records and paleotemperature reconstructions from the Greenland ice cores by providing direct comparisons. This may yield new insights from those iconic records, once seasonality of the climate changes they capture is clarified.This project will utilize classic sites that preserve rare, readily dateable YD lake sediment records. Multiple calibrated, season-specific proxies in sediment cores – including insect and pollen assemblages, terrestrial leaf wax δ2H, and aquatic insect δ18O – will test and complement one another and provide new comparisons to annually integrated records from ice cores. This work will build upon the research team’s experience calibrating and applying these proxies in Greenland. A new calibration study will verify the seasonality of leaf wax δ2H in a range of Greenland climates.The possibility of future abrupt climate change is a major societal concern. As evidence accumulates for recent and ongoing changes in North Atlantic Ocean circulation, past abrupt changes in the subpolar North Atlantic are increasingly relevant to the future. This project will train two Ph.D. students and at least six undergraduates. In addition to conducting research during the academic year, students will participate in mentored summer research institutes to build research and communication skills. To share science beyond academia and hone outreach skills, students will conduct outreach (a) in Greenland near the study site, and (b) in a Chicago area high school serving a diverse population of 3200 students, in partnership with teachers who participated in the PI’s 2018 climate science workshop for high school teachers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

新仙女木期（YD）是地球历史上气候突变的最有记录的例子，但格陵兰岛的基本特征仍然是神秘的，它位于YD气候变化的中心，冰芯出现强烈变冷，但格陵兰岛仍然是一个谜。一个有影响力的假设表明，北大西洋气候突变的特点是极端的季节性，温和的夏季解释了违反直觉的 YD 冰川退缩对于理解冰川退缩至关重要。过去和未来的气候变化对北极系统各个方面的影响——包括冰盖，因为夏季温度驱动地表融化，这项研究将通过定量夏季和冬季温度重建，首次直接评估格陵兰岛YD的季节性。这项研究还将评估 8,200 年前格陵兰岛主要寒流的季节性，尽管该事件比 YD 更短且年强度更小，但该事件推动了格陵兰岛周围的冰川前进。这项研究将阐明气候突变如何影响。北极/亚北极北大西洋地区，特别是格陵兰岛及其冰盖，通过解决 YD 期间气温的季节性问题，尽管有证据表明（年度）气温极冷，但冰盖却消退了，这项研究还将阐明北极/亚北极地区的气温季节性。降水和海洋温度对过去冰盖行为的影响——对未来冰盖质量损失的预测有影响。这项研究将测试全新世 8.2 ka 事件是否本质上是一个迷你 YD，或者是否会从根本上使 YD 变得很差。 8.2 ka事件被描述为测试气候模型的理想定量目标，但优化此类测试所需的相关陆地气候变化的重建很少见。这项工作的贡献是校准和改进重建北极气候的特定季节方法。这些方法需要解决不同第四纪时间尺度上的季节性问题，为气候模型提供必要的测试。通过提供直接比较，对格陵兰冰芯的稳定同位素记录和古温度重建进行分析，一旦它们捕获的气候变化的季节性得到澄清，这可能会从这些标志性记录中产生新的见解。该项目将利用保存稀有且易于确定年代的经典遗址。 YD 湖沉积物记录。沉积物核心中的多个校准的、特定季节的代理——包括昆虫和花粉组合、陆地叶蜡 δ2H 和水生昆虫δ18O – 将相互测试和补充，并与冰芯的年度综合记录进行新的比较。这项工作将建立在研究团队在格陵兰岛校准和应用这些替代值的经验的基础上，一项新的校准研究将验证叶蜡 δ2H 的季节性。随着北大西洋环流最近和持续变化的证据不断积累，未来气候突变的可能性越来越与北大西洋副极地的变化相关。该项目将培训两名博士生和至少六名本科生，除了在学年期间进行研究外，学生还将参加受指导的暑期研究机构，以培养学术界以外的科学知识和交流技能。为了提高外展技能，学生将与参加 PI 2018 年高中气候科学研讨会的教师合作，在 (a) 研究地点附近的格陵兰岛，以及 (b) 在为 3200 名学生提供服务的芝加哥地区高中进行外展活动。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Arctic chironomid training set from Canada, Greenland, Iceland and Svalbard for estimating paleotemperatures (2022)

来自加拿大、格陵兰岛、冰岛和斯瓦尔巴群岛的北极摇蚊训练集，用于估算古气温（2022 年）

• DOI: 10.18739/a27h1dn9q
• 发表时间: 2022
• 期刊: NSF Arctic Data Center
• 作者: Medeiros, Andrew;Axford, Yarrow;Chipman, Melissa;Francis, Donna;Hamerlik, Ladislav;Langdon, Peter;Schellinger, Grace;Puleo, Peter;Steigleder, Regan;Walker, Ian
• 通讯作者: Walker, Ian

Chironomid species counts and chironomid-inferred summer temperatures, Lake N14, Greenland (early Holocene and late glacial) (2022)

摇蚊物种计数和摇蚊推断的夏季温度，格陵兰岛 N14 湖（全新世早期和冰川晚期）（2022 年）

• DOI: 10.18739/a2qb9v69x
• 发表时间: 2022
• 期刊: NSF Arctic Data Center
• 作者: Axford, Yarrow;Medeiros, Andrew;Puleo, Peter;Schellinger, Grace;Steigleder, Regan;Woodroffe, Sarah
• 通讯作者: Woodroffe, Sarah

Direct evidence for thinning and retreat of the southernmost Greenland ice sheet during the Younger Dryas

• DOI: 10.1016/j.quascirev.2021.107105
• 发表时间: 2021-09
• 期刊: Quaternary Science Reviews
• 影响因子: 4
• 作者: A. Carlson;A. Reyes;Emily Gusterson;Y. Axford;K. Wilcken;D. Rood

Younger Dryas and early Holocene climate in south Greenland inferred from oxygen isotopes of chironomids, aquatic Moss, and Moss cellulose

• DOI: 10.1016/j.quascirev.2022.107810
• 发表时间: 2022-11
• 期刊: Quaternary Science Reviews
• 影响因子: 4
• 作者: P. Puleo;A. Masterson;A. Medeiros;G. Schellinger;Regan Steigleder;S. Woodroffe;M. Osburn;Y. Axford

A continental-scale chironomid training set for reconstructing Arctic temperatures

• DOI: 10.1016/j.quascirev.2022.107728
• 发表时间: 2022-10
• 期刊: Quaternary Science Reviews
• 影响因子: 4
• 作者: A. Medeiros;M. Chipman;D. Francis;L. Hamerlík;P. Langdon;P. Puleo;G. Schellinger;Regan Steigleder;I. Walker;S. Woodroffe;Y. Axford