Collaborative Research: Quantifying the Ocean's Responses to Solar Forcing: Multidecadel Century-scale Variability of North Atlantic SSTs Over Recent Millenia

该项目的目的是开发北大西洋表面温度变化的第一个详细的日历日期记录，以调查过去3000年来海洋对几十年至百年时间尺度上的自然太阳强迫的反应。尽管有可靠的SST替代物和具有必要高沉积速率的采样点，但过去数千年来，没有直接或基本上根据海洋观测重建北大西洋盆地规模的SST场。这几乎完全是由于在海洋沉积物中缺乏适当的年龄测定控制。该合作项目由哥伦比亚大学拉蒙特-多尔蒂地球天文台和科罗拉多大学博尔德分校的一个团队共同开展，开发了一种所谓的放射性碳“摆动匹配”测年方法的新海洋应用，在这种方法中，可以获得可靠的日历年龄估计，而不需要假设当地海相储集层年龄的大小和过去的变异性，这是测年不确定性的主要来源。由于该方法客观地将岩心下部海洋沉积物的放射性碳变化映射到树轮中的全新世晚期放射性碳校准，其中还包含主要受太阳开放磁通量变化控制的初始大气放射性碳活动(在这里的时间尺度上)的记录，因此它提供了同一沉积物中SST和太阳替代变异性的直接比较。研究人员利用8个具有盆地范围分布的高累积速率沉积物岩心来捕捉当今大西洋温度变化的主要模式(NAO和AMO)的空间表达。每个岩心的年表以AMS放射性碳测年(名义分辨率为40年)为基础，并使用为该项目开发的自动摆动匹配算法客观地分配日历年龄。SST重建将基于有孔虫的氧同位素地层学和镁/钙比值，这为过去的钙化温度提供了可靠的估计。这些数据将提供必要的观测，以检验任何可能的全盆地海温模式对太阳强迫的响应，以及这种响应是否具有与北大西洋涛动(NAO)、大西洋年代际涛动(AMO)或其他先前模拟的响应相同的特征。更广泛的影响：这项工作直接解决了根据需要确定自然气候变异性的需要，以便区分对自然和人为强迫因素的持续反应，并改进预测模型。尽管海洋区域在空间上和在许多情况下在能量上占主导地位，但目前在海洋上缺乏这种特征。该项目还将支持哥伦比亚大学博士生的教育和研究培训。

The purpose of this project is to develop the first detailed, calendrically-dated records of North Atlantic Sea Surface Temperature (SST) variability in order to investigate the ocean's response to natural solar forcing at multi-decadal to century time scales over the last 3000 years. Despite the availability of reliable SST proxies and of sampling sites with the necessary high deposition rates, there exist no reconstructions of the North Atlantic basin-scale SST field over past millennia based directly or substantially on ocean observations. This is due almost entirely to the lack of adequate age-dating control in marine sediments. This collaborative project, undertaken by a team from both Columbia University's Lamont-Doherty Earth Observatory and the University of Colorado, Boulder, develops a new marine application of the so-called radiocarbon "wiggle-match" dating method in which reliable calendar age estimates are obtained free of assumptions regarding the size and past variability of the local marine reservoir age, which is the principle source of dating uncertainty. Because the method objectively maps down-core marine sediment radiocarbon variations to the late Holocene radiocarbon calibration in tree-rings, which also contains a record of initial atmospheric radiocarbon activity controlled (at the timescale of interest here) largely by variations in the Sun's open magnetic flux, it provides for direct comparison of SST and solar proxy variability in the same sediments. The researchers makes use of eight high-accumulation rate sediment cores with a basin-wide distribution selected to capture the spatial expression of the leading modes of Atlantic temperature variability today (the NAO and AMO). Chronologies for each core are based on AMS radiocarbon dating (at a nominal resolution of 40 years) with calendar ages assigned objectively using an automated wiggle-match algorithm developed for this project. SST reconstructions will be based on foraminiferal oxygen isotope stratigraphy and Mg/Ca, which provide a reliable estimate of past calcification temperature. Together these data will provide the observations necessary to test for any possible basin-wide SST pattern response to solar forcing and whether this response has features in common with the North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO) or with other previously simulated responses. Broader Impacts: This work directly addresses the need to characterize natural climate variability as needed in order to separate ongoing responses to natural and anthropogenic forcing agents and to improve predictive models. Such characterization is presently lacking over the oceans although ocean regions are spatially and, in many instances, energetically dominant. The project will also support education and research training for a PhD student at Columbia University.