Collaborative Research: P2C2--2000 Years of Variability in the Southern Annular Mode from Tree Rings and Ice

该项目旨在利用澳大利亚塔斯马尼亚州南部亚高山山脊上的比利松树(卷柏)的新数据，结合两个高分辨率的东南极冰芯，重建过去2000年来南环状模式(SAM)的行为。这一点很重要，因为SAM不仅影响南半球气候，还影响碳和热量吸收以及南极冰川融化。SAM是南半球中高纬度气候变化的主导模式，它影响西风的强度和位置，从而影响海洋和大陆的降水和温度异常。SAM控制着南半球西风带的强度和位置，因此将多个大陆和海洋的大范围气候异常联系在一起。这些亚极地风还调节了南大洋对热量和碳的吸收，并影响了冰冻圈。虽然北半球气候动力学的研究受益于每年确定的气候指标的强大网络，但南半球在共同时代的古气候数据要有限得多，特别是在印度洋地区，这是全球气候数据最稀少的区域。最近在比利松树上发现的亚化石木材为产生数千年来区域温度和海平面气压的重建提供了新的机会--这是中纬度SAM的关键指标。这个树木站点网络建立在另一个来自南极东部冰层的高分辨率气候记录的新兴网络之上，并与之相辅相成。以南半球印度洋部分为中心的新的环境重建将有助于解决太平洋部分现有SAM重建中的重大不确定性，并使人们能够在人类改变大气之前评估南半球气候的内部动力和自然强迫的作用。此外，新的数据和重建有助于识别和量化与代理类型、位置和季节性有关的不确定性，以及这些因素对关于SAM趋势的时间和出现的推断的影响。新的环境和气候重建也有助于探索是什么驱动了这一动态特征的可变性。这些新的重建可能会将南极半岛现有的SAM重建延长至少1000年。利用数据模式比较技术，可以更好地了解南方涛动的长期可变性及其与印度洋和ENSO动力学的联系，以及与外部强迫机制(如臭氧消耗、温室气体)的联系。该项目加强了美国和澳大利亚科学家之间以及古气候学科(树轮和冰芯)之间的国际合作。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project aims to use new data from King Billy pine trees (Athrotaxis selaginella) located on subalpine ridges in southern Tasmania, Australia, in combination with two high-resolution East Antarctic ice cores, to reconstruct the behavior of the Southern Annular Mode (SAM) over the last 2,000 years. This is important because the SAM influences not only Southern Hemisphere climate but also carbon and heat uptake and Antarctic ice melt.The SAM is the leading mode of climate variability in the middle to high latitudes of the Southern Hemisphere, where it affects the strength and position of the westerly winds and, therefore, precipitation and temperature anomalies across oceans and continents. The SAM controls the strength and position of the Southern Hemisphere westerlies, and therefore links large-scale climate anomalies across multiple continents and oceans. These subpolar winds also modulate the uptake of heat and carbon by the Southern Ocean and affect the cryosphere.While investigations of Northern Hemisphere climate dynamics have benefitted from a robust network of annually resolved climate proxies, the Southern Hemisphere has far more limited paleoclimate data during the Common Era, particularly in the Indian Ocean sector, the most climate data-sparse region globally. The recently discovered sub-fossil wood from King Billy pine trees provides a new opportunity for generating multi-millennial reconstructions of regional temperature and sea level pressure - key indicators of the SAM at mid-latitudes. This network of tree sites builds on and complements another emerging network of high-resolution climate records from east Antarctic ice. A new environmental reconstruction, centered on the Indian Ocean sector of the Southern Hemisphere, will help address significant uncertainties in existing SAM reconstructions from the Pacific sector and allow an assessment of the role of internal dynamics and natural forcing of Southern Hemisphere climate prior to human modifications of the atmosphere. Further, new data and reconstructions help make possible identification and quantification of uncertainty related to proxy type, location, and seasonality, and the influence of these on inferences about the timing and emergence of trends in the SAM. New environmental and climatological reconstructions also help explore what drives variability in this dynamical feature. These new reconstructions may extend existing reconstructions of SAM from the Antarctic Peninsula by at least 1,000 years. Greater understanding of the long-term variability of SAM and its links to Indian Ocean and ENSO dynamics, as well as to external forcing mechanisms (e.g ozone depletion, greenhouse gases) using data-model comparison techniques is possible. This project strengthens international collaborations between American and Australian scientists as well as across paleoclimate disciplines (tree rings and ice cores).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.