Collaborative Research: P2C2: Reconstructing Holocene Climate Change in the Southern Hemisphere from Southern Alps Mountain Glaciers and Tree Rings

气候科学的一个主要目标是在过去气候系统自然变化的背景下评估当前的行星变暖，例如众所周知的小冰河时代和黑暗时代的寒冷时期，中世纪和罗马的温暖时期，以及大约8,000至10,000年前全新世早期记录的一些地区比现在温暖的条件。这些过去的气候异常现象在北半球得到了最好的记录。因此，尚不清楚它们是否构成大气热收支的全球波动，或者是否具有区域性。这个问题对于理解自然气候变化的潜在驱动因素，以及确定工业时代的变暖是否已经超过过去一万年记录的气候变化的范围具有根本意义。该项目基于新西兰南阿尔卑斯山的冰川和对温度敏感的树木，建立了全新世气候变化的记录——新西兰南阿尔卑斯山位于地球与北大西洋地区的另一侧。山地冰川是地球上数十年或更长时间尺度上最敏感的气候记录器之一。全球范围内山地冰川的退缩是全球变暖的一个标志性例证。冰川地貌提供了过去冰川范围的物理证据，这项工作将在这些地貌上采用最先进的宇宙成因测年技术，以建立记录观测期间和之前冰川变化的精确年代表。这项工作结合了对温度敏感的南岛物种的树木年表，提供了年度时间尺度上气候波动的连续记录。总而言之，冰川范围和树木生长的年表将用于开发南阿尔卑斯山过去温度变化的综合记录，以便与北半球的同等记录进行比较。由此产生的温度重建还将为评估美国国家海洋和大气管理局地球物理流体动力学实验室开发的一套全球气候和地球系统模型提供关键指标，其中一些模型目前正被国家气象局用于天气预报。这项努力将为下一代科学家和科学记者提供实地教育经验。古气候研究的一个目标是了解全新世自然气候变化的模式和驱动因素。轨道、百年和较短频率的自然气候变化记录为模拟由于大气二氧化碳增加的影响而导致的持续和未来变暖提供了一个背景框架。在持续变暖之前，北大西洋地区最近的主要自然气候变化是罗马温暖期（~公元前250年至~公元400年）、黑暗时代寒冷期（~公元450年至~公元950年）、中世纪温暖期（~公元950年至~公元1150年）和小冰河期（~公元1150年）至公元 1850 年）。这些全新世晚期的温度变化由欧洲阿尔卑斯山冰川长度变化的高分辨率记录以及独立的、每年解析的基于树木年轮的区域夏季温度重建记录下来。此外，欧洲冰川在全新世早期监测到一段冰面积减少的时期，同时林线海拔较高。这两项观测都表明夏季比今天温暖。但目前尚不清楚这些气候特征是全球性的还是区域性的。因此，根本机制仍不确定。这项工作将通过开发精确的 10Be 表面暴露年代学来解决这个问题，这些冰碛是在新西兰南阿尔卑斯山全新世期间由冰川形成的，位于地球与欧洲阿尔卑斯山的另一侧。研究人员还将通过 14C 测年最近消融的有机遗迹来制定全新世冰退缩的年代学。研究人员采用经过良好校准的冰川学模型将这些冰碛年表转换为过去两千年冰川衍生的温度记录。拟议的冰川年代学将与根据南岛银松年轮宽度得出的过去 2000 年区域夏季温度的独立和补充记录进行综合。冰川和树木年轮记录将用作调查 GFDL ESM2M 工业化前气候模拟结果的基准。在这种冰川、树突和建模方法的基础上，这项工作的目标是确定全新世气候变化是否是全球性的，从而提高对潜在驱动因素和自然气候变化范围的理解，以应对持续的全球变暖。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。

A major objective of climate science is to evaluate ongoing planetary warming within the context of past natural variations of the climate system, such as the well-known Little Ice Age and Dark Ages cold periods, and Medieval and Roman warm periods, as well as warmer-than-present conditions in some regions registered during the early Holocene, about 8,000 to 10,000 years ago. These past climatic anomalies are best documented from the Northern Hemisphere; thus, it is not clear whether they constituted global fluctuations in the atmospheric heat budget or if they were regional in nature. This question has fundamental implications for understanding the underlying drivers of natural climate variability, and for determining whether industrial-age warming has yet exceeded the envelope of climate variability registered over the past 10,000 years. This project establishes the record of Holocene climate variations, based on glaciers and temperature-sensitive trees, in the Southern Alps of New Zealand - on the opposite side of the planet from the North Atlantic region. Mountain glaciers are among Earth's most sensitive climate recorders on timescales of decades and longer. Worldwide recession of mountain glaciers is an iconic illustration of global warming. Glacial landforms afford physical evidence of past glacier extent, and this effort will employ state-of-the-art cosmogenic dating techniques on those landforms to establish precise and accurate chronologies of glacier changes during and prior to the period of recorded observations. This work incorporates tree-ring chronologies of temperature-sensitive South Island species that afford continuous records of climatic fluctuations on annual timescales. Altogether, chronologies of glacier extent and tree growth will be used to develop a comprehensive record of past temperature variation in the Southern Alps for comparison to equivalent records in the Northern Hemisphere. The resultant temperature reconstruction will also provide a key metric for evaluating a suite of global climate and earth-system models developed by the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory, some of which are now being used for weather forecasting by the National Weather Service. This effort will afford field-based educational experiences for the next generation of scientists and science journalists. A goal of paleoclimate research is to understand patterns and drivers of natural climate variations during the Holocene. Documentation of natural climate variability on orbital, centennial, and shorter frequencies provides a contextual framework for modeling ongoing and future warming due to the effects of increasing atmospheric CO2. The most recent major natural climatic variations in the North Atlantic regime prior to the ongoing warming were those of the Roman Warm Period (~250 B.C. to ~A.D. 400), Dark Ages Cold Period (~A.D. 450 to ~A.D. 950), Medieval Warm Period (~A.D. 950 to ~A.D. 1150) and the Little Ice Age (~A.D. 1150 to ~A.D. 1850). These late-Holocene temperature variations are documented by highly resolved records of glacier-length variation in the European Alps, as well as independent, annually resolved tree-ring-based regional summer temperature reconstructions. In addition, European glaciers monitored a period of reduced ice extent during the early Holocene at the same time as tree-line altitudes were higher. Both observations signify summers that were warmer than those of today. But it is not yet clear whether these climate signatures were global or regional in scope; thus, the underlying mechanisms remain uncertain. This work will address this problem by developing a precise 10Be surface-exposure chronology of moraines constructed by glaciers during the Holocene in the Southern Alps of New Zealand - on the opposite side of the planet from the European Alps. The researchers will also develop chronology of Holocene ice retraction by 14C dating recently deglaciated organic remains. Investigators employ a well-calibrated glaciological model to convert these moraine chronologies into a glacier-derived record of temperature over the past two millennia. The proposed glacier chronology will be synthesized with an independent and complementary record of regional summer temperatures for the past 2000 years derived from South Island silver pine ring widths. The glacier and tree-ring records will be used as benchmarks to investigate results from the GFDL ESM2M preindustrial climate simulations. On the basis of this glacier, dendro, and modeling approach, the goal of this work is to determine whether Holocene climate variations were global or not, and therefore improve understanding of underlying drivers and the scope of natural climate variability in light of ongoing planetary warming.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.