Pliocene tree-ring width and isotopic composition: Deciphering Arctic climate variability in a past analog greenhouse world

高纬度地区对全球气候变化的极端敏感性是研究温室条件下古代北极生态系统的刺激因素。随着越来越多的研究，包括政府间气候变化专门委员会(IPCC)的最新报告，强调上新世气候是未来变暖的类比，需要这一时期的准确替代记录是至关重要的。整个北极存在许多跨越上新世(260万-500万年前)的极地森林遗址，这为利用树木年轮以年际分辨率研究上新世提供了机会。该奖项旨在解决理解北极气候的这一关键时期的需要，以洞察气候系统和变化范围，因为它存在于早期的“温室世界”中。此外，该奖项还将涉及与整个上新世北极气候演变有关的问题，以及众所周知的现代气候变异性模式是否正在运作，甚至可能暗示整个上新世气候变化的机制。 在目标1中，气候信息将从上新世北极化石木材的生长参数和同位素比率中获得。这些数据将用于限制对温度和相对湿度的估计，并探讨年际和年代际气候振荡是否是上新世气候的一个重要组成部分。上新世为验证全球气候模型(GCM)对高纬度变暖的预测提供了一个理想的“试验台”，因为这是最后一个气温像21世纪初预测的那样温暖的时期。对上新世变暖的经验估计和模型估计之间的差异突出了古植物学数据对气候模型开发和测试的重要性。 在目标2中，我将使用所代表的地点和时间段的多样性来研究上新世气候是如何从早到晚上新世演变的。这将提供机会来研究随着气候冷却接近冰川开始，高纬度地区的年际和季节变化是如何变化的。这些高分辨率的记录可以洞察季节性、生态系统和水文循环在这段全球气候变化期间是如何变化的。 第四纪以前的高分辨率气候记录是出了名的稀缺，因此该项目的学术价值在于该奖项将导致详细的上新世气候重建。这项研究产生的北极上新世温度和相对湿度的经验估计有助于气候模型的验证。这项研究将生成额外的气候替代数据时间序列，用于评估气候振荡(即北极涛动、北大西洋涛动)在地质时间尺度上的行为变化。 这项研究的更广泛影响将是提供每年解析的数据集，这些数据集将为研究北极气候系统在普遍变暖的世界中的运作提供基线。这可能有助于重建上新世海冰(北极气候系统的一个重要组成部分)。这些数据将使进一步研究上新世冷却机制成为可能。该项目还将补充目前正在进行的关于北极生态系统对过去温暖时段的反应的研究。

The extreme sensitivity of high latitudes to global climate changes is the stimulus for the study of ancient Arctic ecosystems under greenhouse conditions. With an increasing number of studies, including the most recent Intergovernmental Panel on Climate Change (IPCC) report, highlighting Pliocene climate as an analogue for future warmth, the need for accurate proxy records for this period is crucial. The presence of numerous polar forest sites throughout the Arctic spanning the Pliocene (2.6-5 million years ago) provides the opportunity to study the Pliocene with interannual resolution, through the use of tree-rings. This award addresses the need to understand this critical period of Arctic climate to provide insight into the climate system and the range of variability as it existed in an earlier ‘greenhouse world’. Additionally this award will address questions relating to the evolution of Arctic climate throughout the Pliocene, whether well-known modern modes of climate variability were in operation and perhaps even hint at mechanisms of climate change throughout the Pliocene. In Objective 1, climatic information will be derived from the growth parameters and isotopic ratios of Pliocene Arctic fossil wood. These data will be used to constrain estimates of temperature and relative humidity and also to explore whether inter-annual and inter-decadal climatic oscillations were an important component of Pliocene climate. The Pliocene provides an ideal ‘testbed’ for validating global climate model (GCM) predictions of high-latitude warming, given that this is the last period when temperatures were as warm as those predicted for around the turn of the 21st Century. The discrepancy between empirical and model estimates of Pliocene warming highlights the importance of paleobotanical data to the development and testing of climate models. In Objective 2, I will use the diversity of sites and time periods represented to investigate how Pliocene climates have evolved from the early through the mid-late Pliocene. This will afford the opportunity to examine how inter-annual and seasonal variability changed at high latitudes as climate cooled approaching the onset of glaciation. The high resolution records may provide insight into how seasonality, ecosystems and the hydrologic cycle changed through this period of global climate change. Pre-Quaternary high-resolution climate records are notoriously scarce, thus the intellectual merit of this project rests in the detailed Pliocene climatic reconstructions that will result from this award. Empirical estimates of Pliocene temperature and relative humidity for the Arctic generated by this study are beneficial for the validation of climate models. This study will generate additional time series of climate proxy data for evaluating changes in the behavior of climate oscillations (i.e. Arctic Oscillation, North Atlantic Oscillation) over geologic time scales. The broader impacts of this study will be in providing annually resolved data sets that will provide a baseline for studies of the operation of the Arctic climate system in a generally warmer world. This may contribute to reconstructions of Pliocene sea ice (an important constituent of the Arctic Climate system). These data will permit further investigations into the mechanisms of Pliocene cooling. This project will also complement research currently being conducted on the response of Arctic ecosystems to past warm intervals.